cd /home/daytona/workspace/attachments/1545b85c-3615-43f5-8dee-2b4f7923fad8/ && …

python3 -c " import pdfplumber with pdfplumber.open('/home/daytona/workspace/att…

mkdir -p /home/daytona/workspace/csir-net-notes && echo "Directory ready"

~/csir-net-notes/CSIR_NET_LifeScience_Notes_Part1.md

# CSIR-NET LIFE SCIENCE - COMPREHENSIVE QUICK NOTES
### Entrance Exam Oriented | Conceptual + Factual + Theoretical
---

# UNIT 1: STRUCTURE AND FUNCTION OF BIOMOLECULES

## A. CHEMICAL BONDS IN BIOMOLECULES

| Bond Type | Strength | Example |
|-----------|----------|---------|
| Covalent | Strongest (~350 kJ/mol) | C-C, C-H in organic molecules |
| Hydrogen bond | Weak (12-30 kJ/mol) | DNA base pairs, protein secondary structure |
| Ionic/Electrostatic | Moderate | Salt bridges in proteins |
| Van der Waals | Weakest (<5 kJ/mol) | Non-polar interactions, packing |
| Hydrophobic | Entropic | Protein folding core |

**Key Points:**
- Hydrogen bonds in DNA: A=T (2 H-bonds), G≡C (3 H-bonds)
- Van der Waals forces are distance-dependent (strongest at optimal distance)
- Hydrophobic interactions drive protein folding (entropy-driven)

---

## B. BIOMOLECULES

### CARBOHYDRATES
- **Monosaccharides:** D-glucose (aldohexose), D-fructose (ketohexose), D-ribose (aldopentose)
- **Glycosidic bonds:** α-1,4 (starch/glycogen), β-1,4 (cellulose - NOT digestible by humans)
- **Reducing sugars:** Free anomeric C (glucose, maltose, lactose) - positive Benedict's test
- **Non-reducing:** Sucrose (no free anomeric C)
- **Starch:** Amylose (α-1,4 linear) + Amylopectin (α-1,4 with α-1,6 branches every 24-30 residues)
- **Glycogen:** Like amylopectin but branches every 8-12 residues (more branched = faster mobilization)
- **Chitin:** β-1,4 N-acetylglucosamine (fungal cell wall, insect exoskeleton)

### LIPIDS
- **Fatty acids:** Saturated (no double bonds) vs Unsaturated (double bonds = lower melting point)
- **Phospholipids:** Amphipathic - form bilayer (hydrophilic head + hydrophobic tail)
- **Cholesterol:** Stabilizes membrane fluidity; present in animal membranes only
- **Sphingolipids:** Ceramide backbone; important in cell signaling
- **Waxes:** Ester of long-chain FA + long-chain alcohol
- **Prostaglandins:** Derived from arachidonic acid (C20 PUFA); local hormones

### PROTEINS
- **Amino acids:** 20 standard; all L-form (except Glycine - achiral)
- **Essential AAs (HILLMVTPF):** His, Ile, Leu, Lys, Met, Val, Thr, Phe, Trp (+Arg conditionally)
- **Peptide bond:** Planar, partial double bond character, trans configuration (180°)
- **Isoelectric point (pI):** pH at which protein has zero net charge
- **Protein levels:**
  - 1° = AA sequence (primary structure)
  - 2° = α-helix, β-sheet (H-bonds between backbone)
  - 3° = Overall 3D fold (all non-covalent forces + disulfide bonds)
  - 4° = Multi-subunit assembly

### NUCLEIC ACIDS
- **DNA:** Deoxyribose sugar, Thymine (not Uracil), Double stranded, antiparallel
- **RNA:** Ribose sugar, Uracil, usually single-stranded
- **Purines:** Adenine, Guanine (double ring)
- **Pyrimidines:** Cytosine, Thymine, Uracil (single ring)
- **3'-5' phosphodiester bond** connects nucleotides
- **B-DNA:** Right-handed, 10 bp/turn, most common physiological form
- **A-DNA:** Right-handed, 11 bp/turn, shorter & wider, found in dehydrated conditions/RNA:DNA hybrid
- **Z-DNA:** Left-handed, 12 bp/turn, found at high salt concentration

### VITAMINS
| Vitamin | Coenzyme Form | Function |
|---------|--------------|---------|
| B1 (Thiamine) | TPP | Pyruvate decarboxylation |
| B2 (Riboflavin) | FAD, FMN | Electron carrier in oxidation |
| B3 (Niacin) | NAD+, NADP+ | Redox reactions |
| B5 (Pantothenic acid) | CoA | Acyl group transfer |
| B6 (Pyridoxine) | PLP | Transamination |
| B7 (Biotin) | Biotin-enzyme | Carboxylation reactions |
| B9 (Folic acid) | THF | One-carbon transfers, DNA synthesis |
| B12 (Cobalamin) | Adenosylcobalamin | Isomerization, methylation |
| C (Ascorbic acid) | - | Antioxidant, collagen synthesis |

---

## C. STABILIZING INTERACTIONS

- **Van der Waals:** Induced dipole-dipole; important for packing in protein core
- **Electrostatic:** Salt bridges between oppositely charged R-groups (Lys/Arg vs Asp/Glu)
- **Hydrogen bonds:** N-H...O or O-H...N; backbone H-bonds define 2° structure
- **Hydrophobic:** Non-polar residues bury away from water; major force in protein folding
- **Disulfide bonds:** Covalent; between Cys residues; important for extracellular proteins

---

## D. BIOPHYSICAL CHEMISTRY

### pH and Buffers
- **Henderson-Hasselbalch:** pH = pKa + log([A⁻]/[HA])
- **Best buffer range:** pH = pKa ± 1
- **Biological buffers:** Bicarbonate (blood, pKa=6.1), Phosphate (intracellular, pKa=7.2), Histidine (protein, pKa=6.0)

### Reaction Kinetics
- **First order:** Rate = k[A]; t½ = 0.693/k
- **Second order:** Rate = k[A][B]
- **Zero order:** Rate = k (enzyme saturated)

### Thermodynamics
- **ΔG = ΔH - TΔS** (Gibbs free energy)
- **Spontaneous:** ΔG < 0 (exergonic)
- **ΔG° = -RT ln Keq**
- **Coupled reactions:** Unfavorable reaction driven by favorable one (e.g., ATP hydrolysis)

### Colligative Properties
- Depend on NUMBER of solute particles, not identity
- **Osmotic pressure (π) = iMRT**
- Boiling point elevation, freezing point depression, vapor pressure lowering

---

## E. BIOENERGETICS & METABOLISM

### Glycolysis (Cytoplasm)
- **Glucose → 2 Pyruvate + 2 ATP (net) + 2 NADH**
- Key enzymes: Hexokinase, PFK-1 (rate-limiting), Pyruvate kinase
- **PFK-1 regulation:** Activated by AMP, ADP, fructose-2,6-bisphosphate; inhibited by ATP, citrate
- **Substrate-level phosphorylation** at steps 7 (PGK) and 10 (Pyruvate kinase)

### TCA Cycle (Mitochondrial matrix)
- **Acetyl-CoA + 3NAD⁺ + FAD + GDP → 3NADH + FADH₂ + GTP + 2CO₂**
- Key enzymes: Citrate synthase, Isocitrate DH (rate-limiting), α-ketoglutarate DH
- Regulated by: ATP/ADP ratio, NADH/NAD+ ratio, calcium

### Oxidative Phosphorylation (Inner mitochondrial membrane)
- **Complex I (NADH DH):** NADH → ubiquinone; pumps 4H+
- **Complex II (Succinate DH):** FADH₂ → ubiquinone; does NOT pump H+
- **Complex III (Cytochrome bc1):** Ubiquinol → cytochrome c; pumps 4H+
- **Complex IV (Cytochrome oxidase):** Cyt c → O₂; pumps 2H+
- **ATP synthase (Complex V):** 3H+ per ATP synthesized
- **Total yield:** ~30-32 ATP per glucose (modern estimates)

### Electron Carriers (in order)
NADH → FMN → Fe-S → CoQ → Cyt b → Cyt c1 → Cyt c → Cyt a → Cyt a3 → O₂

---

## F. ENZYMES AND ENZYME KINETICS

### Michaelis-Menten Kinetics
- **v = Vmax[S] / (Km + [S])**
- **Km** = substrate concentration at ½ Vmax (measure of affinity; lower Km = higher affinity)
- **Vmax** = maximum velocity (when enzyme is saturated)
- **kcat** = turnover number (catalytic rate constant)
- **kcat/Km** = catalytic efficiency (specificity constant)

### Types of Enzyme Inhibition
| Type | Effect on Km | Effect on Vmax | Example |
|------|-------------|---------------|---------|
| Competitive | Increases | No change | Statins inhibit HMG-CoA reductase |
| Non-competitive | No change | Decreases | Heavy metals |
| Uncompetitive | Decreases | Decreases | |
| Mixed | Changes | Decreases | |

### Allosteric Regulation
- **Activators:** Shift curve left (lower K0.5)
- **Inhibitors:** Shift curve right (higher K0.5)
- **Cooperativity:** Sigmoidal kinetics; Hill coefficient (n > 1 = positive cooperativity)
- Examples: Hemoglobin (n=2.8), ATCase

### Isozymes
- Same reaction, different structural forms
- Example: LDH (5 isozymes of H and M subunits); CK-MB for cardiac diagnosis

---

## G. PROTEIN CONFORMATION

### Ramachandran Plot
- **φ (phi):** Rotation around N-Cα bond
- **ψ (psi):** Rotation around Cα-C bond
- Allowed regions: α-helix (φ ≈ -60°, ψ ≈ -45°), β-sheet (φ ≈ -120°, ψ ≈ +120°)
- Proline: Restricted φ angle (cyclic side chain); often found in turns
- Glycine: Occupies all regions (smallest side chain)

### Secondary Structures
- **α-helix:** 3.6 residues/turn, pitch = 5.4Å, H-bonds between i and i+4 residues, right-handed
- **β-sheet:** Parallel (same direction) or antiparallel (opposite direction); antiparallel more stable
- **β-turn:** 4 residues; Gly and Pro common; reverses chain direction
- **Collagen triple helix:** 3 chains wound together; Gly-X-Y repeat (X=Pro, Y=Hyp)

### Protein Domains, Motifs & Folds
- **Domain:** Independently folding unit with distinct function
- **Motif:** Short structural pattern (helix-turn-helix, zinc finger, leucine zipper)
- **Fold:** Overall topological arrangement (TIM barrel, Rossman fold)

---

## H. NUCLEIC ACID CONFORMATION

| Feature | A-DNA | B-DNA | Z-DNA |
|---------|-------|-------|-------|
| Helix sense | Right | Right | Left |
| bp/turn | 11 | 10 | 12 |
| Rise/bp | 2.6Å | 3.4Å | 3.7Å |
| Diameter | 23Å | 20Å | 18Å |
| Conditions | Low water/RNA:DNA | Physiological | High salt, CG repeats |

### RNA Structures
- **rRNA:** 3 types in prokaryotes (23S, 16S, 5S); 4 types in eukaryotes (28S, 18S, 5.8S, 5S)
- **tRNA:** Cloverleaf secondary structure, L-shaped 3D; 3'-CCA terminus; anticodon loop
- **mRNA:** 5'-cap (7-methylguanosine) + 3'-poly-A tail in eukaryotes
- **snRNA:** Splicing (in spliceosome)
- **miRNA/siRNA:** Gene silencing

---

## I. STABILITY OF PROTEINS AND NUCLEIC ACIDS

- **Tm (melting temperature):** Higher G-C content → higher Tm (3 H-bonds vs 2)
- **Hyperchromic effect:** Increase in UV absorbance at 260nm upon DNA denaturation
- **Protein denaturation:** Heat, extreme pH, urea, guanidinium chloride - disrupts non-covalent bonds
- **Chaperones:** Hsp70, Hsp90, GroEL/GroES - assist protein folding, prevent aggregation

---

## J. METABOLISM QUICK SUMMARY

### Carbohydrate Metabolism
- **Glycogenesis:** Glucose → Glycogen (liver & muscle); UDP-glucose is activated form
- **Glycogenolysis:** Glycogen → Glucose-1-P; glycogen phosphorylase (requires pyridoxal phosphate)
- **Gluconeogenesis:** Non-carbohydrate sources → Glucose; occurs in liver/kidney
  - Substrates: Pyruvate, Lactate, Glycerol, Glucogenic AAs
  - Bypasses 3 irreversible glycolytic steps (Pyruvate carboxylase, PEPCK, F-1,6-BPase, G-6-Pase)
- **Pentose Phosphate Pathway:** Produces NADPH (for biosynthesis) and Ribose-5-P (for nucleotides)

### Lipid Metabolism
- **β-oxidation:** FA → Acetyl-CoA; occurs in mitochondria; generates NADH + FADH₂
- **Fatty acid synthesis:** Acetyl-CoA → FA; occurs in cytoplasm; requires NADPH; 2C added per cycle
- **FAS enzyme:** Multienzyme complex; malonyl-CoA is activated form
- **Ketone bodies:** Acetoacetate, β-hydroxybutyrate, acetone; made in liver during starvation

### Amino Acid Metabolism
- **Transamination:** AA + α-ketoglutarate ↔ Keto acid + Glutamate (ALT, AST)
- **Urea cycle:** Ornithine → Citrulline → Argininosuccinate → Arginine → Urea + Ornithine
  - Location: Mitochondria (carbamoyl phosphate synthesis) + Cytoplasm
- **Glucogenic AAs:** Form pyruvate or TCA intermediates → glucose
- **Ketogenic AAs:** Form acetyl-CoA or acetoacetyl-CoA → ketone bodies (Lys, Leu only purely ketogenic)

---

# UNIT 2: CELLULAR ORGANIZATION

## A. CELL WALL AND MEMBRANES

### Prokaryotic Cell Wall
- **Gram +ve:** Thick peptidoglycan (20-80 nm), teichoic acids, no outer membrane
- **Gram -ve:** Thin peptidoglycan (2-7 nm), outer membrane with LPS (lipopolysaccharide), periplasmic space
- **Peptidoglycan:** N-acetylglucosamine (NAG) + N-acetylmuramic acid (NAM) with β-1,4 bonds; cross-linked by peptide bridges
- **Lysozyme:** Cleaves β-1,4 bond between NAG and NAM → cell lysis
- **Penicillin:** Inhibits transpeptidase (cross-linking enzyme)
- **Archaeal cell wall:** Pseudopeptidoglycan or S-layer (NO NAM)

### Plasma Membrane
- **Fluid Mosaic Model (Singer & Nicholson, 1972)**
- **Lipid bilayer:** Phospholipids + cholesterol + glycolipids
- **Membrane proteins:**
  - Integral (transmembrane): span the bilayer
  - Peripheral: attached to surface
  - Lipid-anchored: GPI-anchored (outer leaflet), myristoylated/palmitoylated (inner leaflet)
- **Membrane fluidity** increases with: unsaturated FA, shorter FA chains, higher temperature, lower cholesterol
- **Lipid rafts:** Microdomains rich in cholesterol and sphingolipids; important for signaling

### Transport Across Membranes
| Type | Energy | Direction | Example |
|------|--------|-----------|---------|
| Simple diffusion | None | Conc. gradient | O₂, CO₂, ethanol |
| Facilitated diffusion | None | Conc. gradient | GLUT transporters, aquaporins |
| Active transport (primary) | ATP | Against gradient | Na+/K+ ATPase |
| Active transport (secondary) | Ion gradient | Against gradient | Na+/glucose symport |
| Endocytosis | ATP | Into cell | Receptor-mediated, phagocytosis |

- **Na+/K+ ATPase:** Pumps 3 Na+ out, 2 K+ in per ATP; electrogenic
- **Aquaporins:** Water channels; AQP2 regulated by ADH (vasopressin) in kidney

---

## B. INTRACELLULAR ORGANELLES

### Nucleus
- **Nuclear envelope:** Double membrane with nuclear pore complexes (~120 nm; ~500 per nucleus)
- **Nucleolus:** rRNA synthesis and ribosome assembly; disappears during mitosis
- **Lamins:** Intermediate filaments forming nuclear lamina (structural support)
- **Chromatin:** DNA + histone proteins; 30nm fiber → loops → higher-order structure

### Mitochondria
- **Double membrane:** Inner (cristae) + outer
- **Matrix:** TCA cycle, β-oxidation, mtDNA
- **Inner membrane:** Oxidative phosphorylation, ATP synthase
- **Origin:** Endosymbiosis of α-proteobacterium
- **mtDNA:** Circular, 16.6 kb in humans, 37 genes; maternal inheritance
- **Mitochondrial ribosome:** 55S (28S + 39S) in mammals

### Golgi Apparatus
- **Cis:** Receives vesicles from ER
- **Trans:** Sorts and dispatches proteins
- **Functions:** Glycosylation, sulfation, phosphorylation, sorting, secretory pathway
- **Mannose-6-phosphate signal:** Directs proteins to lysosomes

### Endoplasmic Reticulum
- **Rough ER:** Ribosomes attached; protein synthesis and N-linked glycosylation
- **Smooth ER:** No ribosomes; lipid synthesis, drug detoxification, Ca²+ storage
- **Signal hypothesis (Blobel):** Signal sequence (N-terminal hydrophobic) → SRP → translocation to ER

### Lysosomes
- **pH ~5** (maintained by vacuolar H+ ATPase)
- **Contain:** Hydrolytic enzymes (proteases, lipases, nucleases, glycosidases)
- **I-cell disease:** M6P missing → lysosomal enzymes secreted instead of targeted

### Peroxisomes
- **Functions:** β-oxidation of very-long-chain FA, H₂O₂ generation and breakdown (catalase)
- **No DNA**; proteins imported post-translationally (PTS1/PTS2 signals)
- **Zellweger syndrome:** Peroxisome biogenesis defect

### Chloroplasts
- **Double membrane** + thylakoid membrane system
- **Stroma:** Dark reactions (Calvin cycle), chloroplast DNA
- **Thylakoid:** Light reactions, ETC, ATP synthase
- **Origin:** Endosymbiosis of cyanobacterium

### Cytoskeleton
| Component | Subunit | Function |
|-----------|---------|---------|
| Microfilaments (actin) | G-actin (42 kDa) | Cell shape, motility, cytokinesis |
| Intermediate filaments | Various (keratin, vimentin, lamin) | Structural support |
| Microtubules | α-β tubulin dimers | Cell division, vesicle transport, cilia/flagella |

- **Microtubule polarity:** (+) end = fast growing; (-) end = anchored at MTOC/centrosome
- **Motor proteins:** Kinesin (+ end directed), Dynein (- end directed)
- **Colchicine/Vinblastine:** Inhibit tubulin polymerization (used in cancer treatment)
- **Taxol:** Stabilizes microtubules (prevents depolymerization)

---

## C. GENES AND CHROMOSOMES

### Chromatin Organization
- **Nucleosome:** 147 bp DNA wrapped around histone octamer (2×H2A, H2B, H3, H4) + H1 linker
- **Histone modifications:**
  - H3K4me3: Active transcription
  - H3K27me3: Repression (Polycomb)
  - H3K9me3: Heterochromatin
  - H3K9ac / H3K27ac: Active enhancers/promoters
- **Euchromatin:** Loosely packed, transcriptionally active
- **Heterochromatin:** Densely packed, transcriptionally silent
  - Constitutive: Always condensed (centromeres, telomeres)
  - Facultative: Can be either (Barr body = inactive X chromosome)

### DNA Types
- **Unique (single copy):** Most protein-coding genes
- **Moderately repetitive:** Histone genes, rRNA genes, tRNA genes
- **Highly repetitive:** Satellite DNA (centromeres, telomeres); NOT transcribed
- **Tandem repeats:** VNTR, STR (microsatellites) - used in DNA fingerprinting

### Transposons
- **Class I (Retrotransposons):** Copy-and-paste via RNA intermediate; Ty elements (yeast), LINEs, SINEs
- **Class II (DNA transposons):** Cut-and-paste; encode transposase; Tc/mariner elements
- **Discovered by:** Barbara McClintock (maize, Nobel 1983)

### Operon (Prokaryotes)
- **Lac operon (inducible):** lacI (repressor) → binds operator; inducer (allolactose) removes repressor
- **Trp operon (repressible):** Trp (co-repressor) + aporepressor → binds operator; attenuation
- **Catabolite repression:** CAP-cAMP activates transcription when glucose is absent

---

## D. CELL DIVISION AND CELL CYCLE

### Cell Cycle Phases
| Phase | Duration | Events |
|-------|----------|--------|
| G1 | Variable | Growth, preparation for S phase |
| S | ~8 hrs | DNA replication |
| G2 | ~4 hrs | Growth, prepare for mitosis |
| M | ~1 hr | Mitosis |
| G0 | Variable | Quiescent state |

### Cyclins and CDKs
| Complex | Phase | Function |
|---------|-------|---------|
| Cyclin D/CDK4,6 | G1 | Phosphorylate Rb → release E2F |
| Cyclin E/CDK2 | G1/S | S phase entry |
| Cyclin A/CDK2 | S | DNA replication |
| Cyclin B/CDK1 | M | MPF, mitosis entry |

### Checkpoints
- **G1/S checkpoint:** DNA damage check; p53 → p21 → inhibits CDK2
- **G2/M checkpoint:** DNA damage check before mitosis
- **Spindle checkpoint (SAC):** All chromosomes attached to spindle before anaphase
- **Rb (Retinoblastoma protein):** Tumor suppressor; when hypophosphorylated = transcriptional repressor; phosphorylation by Cyclin D/CDK4 releases E2F

### Mitosis Stages
- **Prophase:** Chromosome condensation; spindle formation
- **Prometaphase:** Nuclear envelope breakdown; kinetochore-microtubule attachment
- **Metaphase:** Chromosomes at metaphase plate
- **Anaphase:** Sister chromatid separation (cohesins cleaved by separase)
- **Telophase:** Nuclear envelope reformation; chromosome decondensation
- **Cytokinesis:** Cleavage furrow (actin-myosin ring) in animals; cell plate in plants

### Apoptosis
- **Intrinsic pathway:** Mitochondrial; Bax/Bak → cytochrome c release → Apaf-1 → caspase-9 → effector caspases (3,6,7)
- **Extrinsic pathway:** Death receptors (Fas/TNFR) → FADD → caspase-8 → effector caspases
- **Anti-apoptotic:** Bcl-2, Bcl-XL (inhibit Bax/Bak)
- **Pro-apoptotic:** Bax, Bak, BH3-only proteins (Bid, Bad, PUMA, NOXA)
- **Caspases:** Cysteine proteases; cleave after Asp residues

### Autophagy
- Self-digestion via lysosome; survival mechanism during starvation
- **Macroautophagy:** Phagophore → autophagosome → autolysosome
- **mTOR inhibition** → autophagy activation
- Key proteins: Atg1-Atg18, Beclin-1

---

## E. MICROBIAL PHYSIOLOGY

### Bacterial Growth Kinetics
- **Lag phase → Log/Exponential phase → Stationary phase → Death phase**
- **Generation time (doubling time) = ln2/μ = 0.693/μ** (μ = specific growth rate)
- **Monod equation:** μ = μmax × [S]/(Ks + [S]) (analogous to Michaelis-Menten)

### Antimicrobial Resistance (AMR)
- **Mechanisms:**
  1. Drug inactivation (β-lactamase hydrolyzes penicillin ring)
  2. Target modification (altered PBP in MRSA)
  3. Efflux pumps (pump drug out)
  4. Reduced permeability (porin loss in Gram -ve)
  5. Bypass pathway (alternative enzyme)
- **Horizontal gene transfer (HGT):** Transformation, Conjugation, Transduction
- **Integrons:** Gene cassette capture systems; important for multi-drug resistance

---

# UNIT 3: FUNDAMENTAL PROCESSES

## A. DNA REPLICATION

### Key Concepts
- **Semiconservative replication** (proved by Meselson-Stahl experiment, 1958)
- **Origin of replication:** oriC in E. coli (AT-rich 245 bp); ARS in yeast; many origins in eukaryotes
- **Direction:** Bidirectional from origin

### Enzymes in Replication
| Enzyme | Function |
|--------|---------|
| Helicase (DnaB in E. coli) | Unwinds DNA at replication fork |
| SSB (Single Strand Binding Protein) | Stabilizes ssDNA |
| Primase | Synthesizes RNA primer (needed for DNA Pol) |
| DNA Pol III (E. coli) | Main replicative polymerase; 5'→3' synthesis; 3'→5' exonuclease |
| DNA Pol I (E. coli) | Removes RNA primer; fills gap |
| DNA Ligase | Joins Okazaki fragments |
| Topoisomerase I | Relaxes positive supercoils (nicks one strand) |
| Topoisomerase II (Gyrase) | Relieves positive supercoils ahead of fork (nicks both strands) |

- **Leading strand:** Continuous synthesis (5'→3')
- **Lagging strand:** Discontinuous (Okazaki fragments, ~1-2 kb in prokaryotes, 100-200 bp in eukaryotes)
- **Telomerase:** Reverse transcriptase; adds TTAGGG repeats to chromosomal ends; uses RNA template

### DNA Repair Mechanisms
| Mechanism | Type of Damage | Key Proteins |
|-----------|---------------|-------------|
| Base Excision Repair (BER) | Small lesions (uracil, 8-oxoG) | DNA glycosylase, APE1, Pol β |
| Nucleotide Excision Repair (NER) | Bulky lesions (UV thymine dimers) | XP proteins (XPA-XPG) |
| Mismatch Repair (MMR) | Replication errors | MutS, MutL, MutH (prokaryotes); MSH, MLH (eukaryotes) |
| Double Strand Break (DSB) Repair | DSBs | NHEJ (Ku70/Ku80), HR (RAD51, BRCA1/2) |
| Direct reversal | O⁶-methylguanine, CPDs | Photolyase (CPDs), MGMT |

- **Xeroderma pigmentosum:** NER defect; UV sensitivity; skin cancer
- **HNPCC (Lynch syndrome):** MMR defect; colorectal cancer
- **BRCA1/BRCA2:** Homologous recombination; breast/ovarian cancer

### Recombination
- **Homologous recombination:** Holliday junction intermediate; RecA (prokaryotes), Rad51 (eukaryotes)
- **Site-specific recombination:** λ integrase (Int); Cre-lox (bacteriophage P1); FLP-FRT (yeast)
- **V(D)J recombination:** RAG1/RAG2; generates antibody diversity

---

## B. TRANSCRIPTION

### Prokaryotic Transcription
- **RNA Polymerase:** Core enzyme (α₂ββ'ω) + σ factor = Holoenzyme
- **σ70:** Housekeeping genes (recognizes -10 and -35 elements)
- **Other σ factors:** σ54 (nitrogen metabolism), σ32 (heat shock), σ28 (flagella)
- **Steps:** Promoter binding → Open complex → Elongation → Termination
- **Termination:**
  - Intrinsic (Rho-independent): GC-rich hairpin + poly-U
  - Rho-dependent: Rho ATPase-helicase unwinds RNA:DNA

### Eukaryotic Transcription
| RNA Pol | Transcribes | Location |
|---------|------------|---------|
| RNA Pol I | rRNA (28S, 18S, 5.8S) | Nucleolus |
| RNA Pol II | mRNA, snRNA, miRNA | Nucleoplasm |
| RNA Pol III | tRNA, 5S rRNA, snRNA | Nucleoplasm |

- **CTD (C-terminal domain) of RNA Pol II:** Phosphorylated during elongation; platform for RNA processing machinery
- **TATA box:** -25 to -30 region; recognized by TBP (TATA-binding protein)
- **Transcription factors:** TFIIA, TFIIB, TFIID (TBP), TFIIE, TFIIF, TFIIH (PIC formation)
- **Enhancers:** Can act at distance; orientation and position independent; looping model

### RNA Processing
- **5' Capping:** 7-methylguanosine; added co-transcriptionally; protects from exonuclease; needed for translation
- **3' Polyadenylation:** AAUAAA signal → cleavage 10-30 nt downstream → poly-A polymerase adds ~200 A's
- **Splicing:** Spliceosome (snRNPs: U1, U2, U4, U5, U6); branch point A attacks 5' splice site; lariat intermediate
- **Alternative splicing:** One gene → multiple proteins; exon skipping, intron retention, etc.
- **RNA editing:** A-to-I (ADAR enzyme) or C-to-U editing; changes protein sequence (e.g., ApoB)

### Non-coding RNAs
- **miRNA:** ~22 nt; processed by Drosha (nucleus) + Dicer (cytoplasm); RISC complex; silences mRNA
- **siRNA:** ~21-23 nt; exogenous dsRNA; Dicer processing; RISC; mRNA cleavage
- **lncRNA:** >200 nt; diverse functions (chromatin regulation, imprinting, X-inactivation)
- **Xist RNA:** Long ncRNA; coats X chromosome; required for X inactivation
- **Riboswitches:** mRNA elements that change conformation on binding metabolite → control expression

---

## C. PROTEIN SYNTHESIS

### Ribosome Structure
| Feature | Prokaryotes | Eukaryotes |
|---------|------------|-----------|
| Size | 70S | 80S |
| Small subunit | 30S (16S rRNA + 21 proteins) | 40S (18S rRNA + ~33 proteins) |
| Large subunit | 50S (23S + 5S + 31 proteins) | 60S (28S + 5.8S + 5S + ~49 proteins) |

### Translation Steps
1. **Initiation:** mRNA + Met-tRNAiMet + ribosome assembly; Shine-Dalgarno (prokaryotes) / Kozak sequence (eukaryotes)
2. **Elongation:** Aminoacyl-tRNA → A site; Peptide bond formation (peptidyl transferase = 23S rRNA = ribozyme); Translocation (EF-G/EF2)
3. **Termination:** Stop codons (UAA, UAG, UGA); Release factors (RF1, RF2 in prokaryotes; eRF1 in eukaryotes)

### Genetic Code
- **Degenerate (redundant):** 64 codons → 20 AAs + 3 stop codons
- **Universal** (with exceptions: mitochondria, ciliates)
- **Wobble hypothesis (Crick):** 3rd codon position allows non-Watson-Crick pairing
- **Start codon:** AUG (Met/fMet)
- **Stop codons:** UAA (ochre), UAG (amber), UGA (opal/umber)

### Translational Inhibitors
| Antibiotic | Target | Mechanism |
|-----------|--------|---------|
| Streptomycin | 30S | Misreading of mRNA |
| Tetracycline | 30S | Blocks aminoacyl-tRNA binding |
| Chloramphenicol | 50S | Inhibits peptidyl transferase |
| Erythromycin | 50S | Blocks translocation |
| Puromycin | Both | Mimics aminoacyl-tRNA; premature chain release |
| Cycloheximide | 80S (eukaryotic) | Blocks translocation |
| Diphtheria toxin | EF-2 (eukaryotic) | ADP-ribosylates EF-2 |

### Post-translational Modifications
- Phosphorylation (Ser, Thr, Tyr) - signaling
- Glycosylation (N-linked at Asn; O-linked at Ser/Thr)
- Ubiquitination - proteasomal degradation
- Acetylation (Lys) - chromatin regulation
- Methylation (Lys, Arg) - chromatin regulation
- Sumoylation - protein localization

### Protein Degradation
- **Ubiquitin-Proteasome System:** E1 (activating) → E2 (conjugating) → E3 (ligase) → polyubiquitin chain → 26S proteasome
- **PEST sequences:** Rich in Pro, Glu, Ser, Thr → short-lived proteins
- **N-end rule:** N-terminal residue determines half-life

---

## D. GENE EXPRESSION REGULATION

### Epigenetic Regulation
- **DNA methylation:** CpG dinucleotides; 5-methylcytosine; gene silencing; maintained by DNMT1 (maintenance) and DNMT3a/3b (de novo)
- **Histone modification:**
  - Writers: HAT (acetylation), HMT (methylation), kinases (phosphorylation)
  - Erasers: HDAC (deacetylation), demethylases
  - Readers: Bromodomain (acetyl), Chromodomain (methyl)
- **Chromatin remodeling:** SWI/SNF complex; uses ATP to reposition nucleosomes
- **PRC1/PRC2 (Polycomb):** H3K27me3; gene repression; developmental gene silencing
- **Trithorax/MLL complex:** H3K4me3; gene activation; antagonizes Polycomb

### Imprinting
- Monoallelic expression based on parent-of-origin
- **Igf2:** Paternal expression; maternal silenced (H19 acts as insulator)
- **H19:** Maternal expression; paternal silenced
- **Prader-Willi syndrome:** Deletion of paternal 15q11-13
- **Angelman syndrome:** Deletion of maternal 15q11-13

### RNAi (RNA interference)
- **Discovered by:** Fire and Mello (Nobel Prize 2006)
- dsRNA → Dicer → siRNA → RISC (AGO2 = Slicer) → mRNA degradation
- **Applications:** Gene knockdown, therapeutics

---

# UNIT 4: CELL COMMUNICATION AND CELL SIGNALING

## A. CELL SIGNALING

### Types of Signaling
- **Autocrine:** Cell signals to itself (growth factors in cancer)
- **Paracrine:** Local signaling to nearby cells (neurotransmitters, growth factors)
- **Endocrine:** Long-distance via blood (hormones)
- **Juxtacrine:** Direct cell-cell contact (Notch-Delta)

### Receptor Types
| Receptor Type | Location | Example |
|--------------|---------|---------|
| Intracellular | Cytoplasm/nucleus | Steroid hormones, thyroid hormone |
| Ion channel-linked | Membrane | Acetylcholine receptor (nAChR) |
| G-protein coupled (GPCR) | Membrane | β-adrenergic receptor |
| Enzyme-linked | Membrane | RTKs (EGFR, PDGFR) |
| JAK-STAT | Membrane | Cytokine receptors |

### G-Protein Coupled Receptors (GPCRs)
- 7-transmembrane (7-TM) receptors
- **Gs (stimulatory):** Activates adenylate cyclase → ↑ cAMP → PKA activation
- **Gi (inhibitory):** Inhibits adenylate cyclase → ↓ cAMP
- **Gq:** Activates PLC → IP3 + DAG
  - IP3 → Ca²+ release from ER
  - DAG + Ca²+ → PKC activation
- **G12/13:** Activates Rho GTPases → actin cytoskeleton

### Second Messengers
| Messenger | Source | Effector |
|----------|--------|---------|
| cAMP | ATP (adenylate cyclase) | PKA |
| cGMP | GTP (guanylate cyclase) | PKG, PDE |
| IP3 | PIP2 (PLC) | IP3R → Ca²+ |
| DAG | PIP2 (PLC) | PKC |
| Ca²+ | ER/extracellular | Calmodulin → CaM-kinase |
| Arachidonic acid | Membrane phospholipids | Prostaglandins |

### RTK (Receptor Tyrosine Kinase) Signaling
- Ligand binding → receptor dimerization → trans-autophosphorylation
- **RAS/MAPK pathway:** RTK → Grb2/SOS → RAS (GDP→GTP) → Raf → MEK → ERK → transcription
- **PI3K/AKT pathway:** RTK → PI3K → PIP3 → PDK1 → AKT → mTOR, GSK3β, FOXO
- **RAS:** Small GTPase; oncogene when mutated (KRAS most common cancer mutation)
- **GTPase-activating proteins (GAPs):** Stimulate RAS GTPase activity (inactivate RAS)
- **Guanine nucleotide exchange factors (GEFs):** Exchange GDP for GTP (activate RAS)

### Bacterial Two-Component Systems
- **Sensor histidine kinase + Response regulator**
- Stimulus → Autophosphorylation of His → Phosphotransfer to Asp of response regulator → Changed gene expression
- Example: EnvZ/OmpR (osmolality), PhoQ/PhoP (Mg²+ sensing, virulence)

### Plant Light Signaling
- **Phytochromes (PHY):** Red/far-red light receptors (Pr ↔ Pfr)
  - Pr (660nm) ↔ Pfr (730nm); Pfr = active form
  - Functions: Seed germination, shade avoidance, flowering
- **Cryptochromes (CRY):** Blue/UV-A light; circadian rhythm, flowering, photomorphogenesis
- **Phototropins (PHOT):** Blue light; phototropism, chloroplast movement, stomatal opening

### Bacterial Chemotaxis
- **Two-component system:** CheA kinase + CheY response regulator
- Attractant → ↓ CheA activity → ↓ CheY-P → smooth swimming (counterclockwise flagella)
- Repellent → ↑ CheA activity → ↑ CheY-P → tumbling (clockwise flagella)
- **Adaptation:** CheR (methylates receptor, resets sensitivity), CheB (demethylates)

### Quorum Sensing
- Bacteria monitor population density via autoinducers
- **AHL (acyl-homoserine lactone):** Gram-negative bacteria (LuxI/LuxR in V. fischeri)
- **CSP/AIP:** Gram-positive bacteria
- **AI-2:** Interspecies communication (LuxS enzyme)
- Controls: Biofilm formation, virulence, sporulation, bioluminescence

---

## B. CELLULAR COMMUNICATION

### Cell Adhesion Molecules
| Type | Ca²+-dependent | Example | Function |
|------|---------------|---------|---------|
| Cadherins | Yes | E-cadherin (epithelial), N-cadherin (neural) | Homophilic, cell-cell |
| Integrins | No | α5β1 (fibronectin receptor) | Cell-ECM |
| Selectins | Yes | L, E, P-selectin | Rolling adhesion (leukocyte extravasation) |
| IgCAMs | No | NCAM, ICAM | Homophilic/heterophilic |

### Gap Junctions
- **Connexins** form hemichannels; 2 hemichannels = gap junction
- Allow passage of small molecules (<1 kDa): ions, cAMP, IP3
- Closed by: acidification, Ca²+ rise, voltage
- **Plasmodesmata** in plants = functional equivalent

### Extracellular Matrix (ECM)
- **Collagen:** Most abundant protein; fibrillar (type I, II, III) or non-fibrillar (type IV - basement membrane)
- **Fibronectin:** Contains RGD motif; links ECM to integrins
- **Laminin:** Basement membrane; cross-shaped; binds integrins, heparan sulfate
- **Proteoglycans:** Core protein + glycosaminoglycans (heparan sulfate, chondroitin sulfate)
- **Hyaluronic acid:** Large GAG; no protein core; highly hydrated

### Neurotransmission
- **Ionotropic receptors:** Ligand-gated ion channels (fast; ms); nAChR, NMDA, AMPA, GABA-A
- **Metabotropic receptors:** GPCRs (slow; seconds); mAChR, mGluR, GABA-B
- **Acetylcholine (ACh):** Neuromuscular junction; degraded by AChE
- **Dopamine:** Reward pathway; Parkinson's (loss of dopaminergic neurons)
- **Serotonin (5-HT):** Mood; depression; SSRIs
- **GABA:** Main inhibitory neurotransmitter; benzodiazepines enhance GABA-A

### Haematopoiesis
- **HSC (Hematopoietic Stem Cell)** in bone marrow → all blood cells
- **Transcription factors:** GATA-1 (erythroid/megakaryocyte), PU.1 (myeloid/lymphoid), GATA-2 (early progenitors)
- **Growth factors:** EPO (erythropoiesis), TPO (megakaryopoiesis), G-CSF, M-CSF, SCF (c-Kit ligand)

---

## C. IMMUNE SYSTEM

### Innate Immunity
- **First line:** Physical barriers (skin, mucus), antimicrobial peptides
- **Second line:** Phagocytes (neutrophils, macrophages, DCs), NK cells, complement
- **Pattern Recognition Receptors (PRRs):**
  - TLRs (Toll-like receptors): Recognize PAMPs (LPS, flagellin, CpG DNA, dsRNA)
  - NLRs: Intracellular; inflammasome
  - RIG-I/MDA5: Cytoplasmic RNA sensors
- **Complement system:**
  - Classical pathway: Antibody-antigen complex activates C1
  - Lectin pathway: MBL binds mannose on pathogens
  - Alternative pathway: Spontaneous C3 hydrolysis
  - All converge at C3 convertase → C3b (opsonin) → C5-9 (MAC/lysis)
- **Interferons (IFN):** Type I (IFN-α/β) = viral infection; Type II (IFN-γ) = macrophage activation

### Adaptive Immunity

#### Antibodies
- **Structure:** 2 heavy chains + 2 light chains; Fab (variable) + Fc (constant)
- **Classes (Isotypes):**
  | Isotype | Location/Function |
  |---------|----------------|
  | IgG | Blood; most abundant; secondary response; crosses placenta |
  | IgM | Pentamer; first antibody produced; good agglutinator; activates complement |
  | IgA | Dimer; mucosal surfaces; breast milk |
  | IgE | Mast cells; allergy; anti-helminth |
  | IgD | B cell surface; naïve B cells |
- **Antibody diversity mechanisms:** V(D)J recombination, junctional diversity (TdT), somatic hypermutation, class switching

#### MHC Molecules
| Feature | MHC I | MHC II |
|---------|-------|--------|
| Structure | α chain + β₂-microglobulin | α + β chains |
| Expression | All nucleated cells | APCs (DC, macrophage, B cell) |
| Presents to | CD8+ T cells (CTL) | CD4+ T cells (helper) |
| Peptide source | Cytoplasmic proteins (endogenous) | Endocytosed proteins (exogenous) |
| HLA genes | HLA-A, B, C | HLA-DP, DQ, DR |

#### T Cell Activation
- **Two signals required:** TCR+MHC (signal 1) + co-stimulation CD28-B7 (signal 2)
- Without signal 2 = anergy
- **T helper subsets:**
  - Th1: IFN-γ; cell-mediated immunity; intracellular pathogens
  - Th2: IL-4, IL-5, IL-13; humoral immunity; helminths; allergy
  - Th17: IL-17; extracellular bacteria/fungi; autoimmunity
  - Treg: Foxp3+; IL-10, TGF-β; suppress immunity

#### Hypersensitivity Reactions (Gell & Coombs)
| Type | Mediator | Example |
|------|---------|---------|
| Type I (Immediate) | IgE/Mast cells | Allergy, anaphylaxis |
| Type II (Cytotoxic) | IgG/IgM + complement | Hemolytic anemia, Graves disease |
| Type III (Immune complex) | IgG complexes | SLE, serum sickness |
| Type IV (Delayed/Cell-mediated) | T cells (24-72h) | TB skin test, contact dermatitis |

---

## D. HOST-PATHOGEN INTERACTION

### Bacterial Entry Mechanisms
- **Salmonella:** Type III secretion system (T3SS) injects effectors → macropinocytosis
- **Listeria:** Internalin A/B → E-cadherin/Met → endocytosis → ActA for actin-based motility
- **Yersinia:** Type III SS; injects YopE (RhoGAP), YopH (PTPase) to prevent phagocytosis

### Viral Entry
- **Attachment:** Viral surface protein + host receptor (e.g., HIV gp120+CD4+CCR5/CXCR4)
- **Endocytosis** or **direct fusion** (HIV, Herpes)
- **Influenza:** HA binds sialic acid; NA cleaves to release new virions
- **SARS-CoV-2:** Spike protein + ACE2; TMPRSS2 primes spike

### Virus-induced Cell Transformation
- **Oncogenic viruses:**
  - HPV: E6 (degrades p53), E7 (inactivates Rb) → cervical cancer
  - HBV/HCV → hepatocellular carcinoma
  - EBV → Burkitt's lymphoma, nasopharyngeal carcinoma
  - HTLV-1 → Adult T cell leukemia (Tax protein activates NF-κB)
  - HHV-8 (KSHV) → Kaposi's sarcoma

---

## E. CANCER

### Hallmarks of Cancer (Hanahan & Weinberg)
1. Sustaining proliferative signaling
2. Evading growth suppressors
3. Resisting cell death
4. Enabling replicative immortality
5. Inducing angiogenesis
6. Activating invasion and metastasis
7. Reprogramming energy metabolism
8. Evading immune destruction
9. Tumor-promoting inflammation
10. Genome instability and mutation

### Key Oncogenes and Tumor Suppressor Genes
| Gene | Type | Cancer Association |
|------|------|-------------------|
| RAS (KRAS, NRAS, HRAS) | Oncogene | Pancreatic, colorectal, lung |
| MYC | Oncogene | Many cancers; amplification |
| HER2/ERBB2 | Oncogene | Breast cancer; Trastuzumab target |
| BCL2 | Oncogene | B-cell lymphoma; t(14;18) |
| TP53 | TSG | ~50% of all cancers |
| RB1 | TSG | Retinoblastoma; other cancers |
| BRCA1/2 | TSG | Breast, ovarian cancer |
| APC | TSG | Colorectal cancer; Wnt pathway |
| PTEN | TSG | Multiple cancers; PI3K pathway |

### Metastasis Steps
1. Local invasion
2. Intravasation into blood/lymph
3. Survival in circulation
4. Extravasation at distant site
5. Micrometastasis formation
6. Colonization
- **EMT (Epithelial-Mesenchymal Transition):** Loss of E-cadherin; gain of vimentin/N-cadherin
- **Organ tropism:** "Seed and soil" hypothesis (Paget)

~/csir-net-notes/CSIR_NET_LifeScience_Notes_Part2.md

# CSIR-NET LIFE SCIENCE NOTES - PART 2
### Units 5-8: Developmental Biology | Plant Physiology | Animal Physiology | Inheritance Biology

---

# UNIT 5: DEVELOPMENTAL BIOLOGY

## A. BASIC CONCEPTS OF DEVELOPMENT

### Key Terms
- **Totipotency:** Ability to form complete organism (fertilized egg, early blastomeres)
- **Pluripotency:** Can form all 3 germ layers but NOT extraembryonic tissues (inner cell mass, ESCs)
- **Multipotency:** Limited to specific lineages (HSCs → blood cells only)
- **Commitment:** Restriction of developmental potential (reversible → irreversible)
- **Specification:** Cell fate restricted; can still change if transplanted (labile state)
- **Determination:** Cell fate fixed irreversibly; cell develops autonomously
- **Competence:** Ability of cell to respond to inductive signal
- **Induction:** One tissue directs differentiation of another
- **Morphogenetic gradient:** Graded concentration of morphogen specifies positional identity

### Morphogens
- Act in concentration-dependent manner
- Examples: Bicoid (anterior head in Drosophila), Activin (mesoderm patterning), Shh (dorsal-ventral axis), BMP4 (ventral, neural inhibitor)
- **French flag model (Wolpert):** Different threshold concentrations specify different cell fates

### Genomic Equivalence
- All cells of an organism contain same genome
- Proved by: **Nuclear transplantation (Briggs & King, 1952; Gurdon, 1962)**
- **Cytoplasmic determinants:** mRNAs and proteins localized in oocyte specify cell fate

### Imprinting
- Differential expression based on parental origin of chromosome
- **PWS (Prader-Willi):** Paternal 15q11-13 deletion or maternal UPD
- **AS (Angelman):** Maternal 15q11-13 deletion or paternal UPD

### Stem Cells
- **ESC (Embryonic Stem Cells):** From ICM; pluripotent; Oct4, Nanog, Sox2
- **iPSC (Induced Pluripotent Stem Cells):** Yamanaka factors: Oct4, Sox2, Klf4, c-Myc (Nobel 2012)
- **Adult stem cells:** Tissue-specific; self-renew + differentiate
- **Niche:** Microenvironment maintaining stemness

---

## B. GAMETOGENESIS, FERTILIZATION, AND EARLY DEVELOPMENT

### Spermatogenesis
- Spermatogonia (mitosis) → Primary spermatocyte (Meiosis I) → Secondary spermatocytes → Spermatids (Meiosis II) → Spermatozoa (spermiogenesis)
- Takes ~74 days in humans; occurs in seminiferous tubules
- **Sertoli cells:** Nurse cells; blood-testis barrier; FSH sensitive
- **Leydig cells:** Testosterone production; LH sensitive

### Oogenesis
- Oocyte arrested in **Prophase I** at birth (dictyotene stage)
- Meiosis I completed just before ovulation
- Meiosis II completed only upon fertilization
- **Primary oocyte:** Diploid; arrested in Prophase I
- **Ovulation:** Secondary oocyte released; arrested in Metaphase II

### Fertilization (Animals)
- **Acrosome reaction:** Zona pellucida proteins (ZP3) trigger; releases hydrolytic enzymes
- **Cortical reaction:** Ca²+ wave; cortical granule exocytosis → polyspermy block
- **Sperm-egg fusion:** Bindin (sea urchin), IZUMO1 (sperm) + JUNO (egg) in mammals

### Cleavage Patterns
| Type | Yolk distribution | Example |
|------|-----------------|---------|
| Holoblastic | Isolecithal (uniform) | Sea urchin, mammals |
| Holoblastic | Mesolecithal | Frog (unequal cleavage) |
| Meroblastic (discoidal) | Telolecithal | Birds, reptiles |
| Meroblastic (superficial) | Centrolecithal | Insects |

### Gastrulation
- **Sea urchin:** Vegetal plate invaginates → archenteron; mesenchyme migrates
- **Frog:** Blastopore forms at vegetal-animal boundary; bottle cells; yolk plug
- **Chick:** Primitive streak formation; Hensen's node = organizer
- **Embryonic induction:** Spemann organizer (dorsal lip of blastopore in amphibia) → induces neural plate; Chordin and Noggin (BMP antagonists) from organizer

### Germ Layers
- **Ectoderm:** Epidermis, nervous system, neural crest
- **Mesoderm:** Muscle, bone, kidney, gonads, cardiovascular system, connective tissue
- **Endoderm:** Gut epithelium, liver, pancreas, lungs

---

## C. MORPHOGENESIS IN ANIMALS

### Drosophila Development (key model)
**Anterior-posterior axis:**
- **Bicoid mRNA:** Localized at anterior; gradient specifies head/thorax
- **Nanos mRNA:** Localized at posterior; specifies abdomen
- **Hunchback:** Activated by Bicoid; suppressed by Nanos in posterior

**Segmentation gene hierarchy:**
1. Maternal genes (Bicoid, Nanos, Torso)
2. Gap genes (Hunchback, Krüppel, Knirps, Giant)
3. Pair-rule genes (Even-skipped, Fushi tarazu) - 7 stripes
4. Segment polarity genes (Engrailed, Wingless/Wnt)
5. Homeotic (Hox) genes - determine segment identity

**Dorso-ventral axis:**
- **Dorsal (NF-κB homolog):** Nuclear in ventral cells → specifies mesoderm/neuroectoderm
- **Toll receptor:** Activated in ventral cells; nuclear Dorsal gradient
- **Sog (short gastrulation):** Dpp/BMP antagonist; promotes neural fate ventrally

### Hox Genes
- **Homeodomain transcription factors:** 60 AA DNA-binding domain
- **Colinearity:** Gene order on chromosome corresponds to anterior-posterior expression pattern
- **Mammals:** 4 Hox clusters (HoxA, B, C, D) on 4 chromosomes; 39 genes
- **Anterior transformation:** Loss of Hox gene → anterior identity
- **Posterior transformation (homeotic):** Gain of function in anterior segment

### Caenorhabditis elegans (Vulva formation)
- **Cell lineage invariant:** All 959 somatic cells mapped
- **Anchor cell (AC) → LIN-3 (EGF) → LIN-7/LIN-23 → P6.p cell = vulva**
- **Lateral inhibition (Notch):** P6.p signals via LIN-12 to prevent P5.p and P7.p from becoming primary VPC

### Eye Lens Induction
- **Primary induction (Spemann):** Optic vesicle → overlying ectoderm → lens placode → lens
- **Pax6:** Master regulator; "eyeless" in Drosophila; can induce ectopic eyes anywhere on body

### Limb Development
- **Zone of Polarizing Activity (ZPA):** Posterior mesenchyme; Shh expression → specifies posterior
- **AER (Apical Ectodermal Ridge):** FGF4/8/10; required for proximo-distal outgrowth
- **Progress zone model** vs. **Early specification model**
- **Limb regeneration:** Blastema formation; newts/salamanders can regenerate limbs

---

## D. PLANT DEVELOPMENT

### Meristems
- **SAM (Shoot Apical Meristem):** CLV3 (stem cell identity) → CLV1/CLV2 receptor → restricts WUS; WUS maintains stem cells
- **RAM (Root Apical Meristem):** Quiescent center (QC) maintains stem cells; columella cells; root cap
- **Columella:** Sedimentation of amyloplasts → gravitropism

### Phyllotaxy
- Arrangement of leaves on stem
- **Fibonacci spiral:** Golden angle (137.5°); optimal packing
- Controlled by auxin (PIN proteins) at SAM periphery

### Floral Transition (Flowering)
- **Photoperiodism:** Plants use night length to determine season
  - Long-day plants (LDP): Flower when dark < critical night length (e.g., Arabidopsis, wheat)
  - Short-day plants (SDP): Flower when dark > critical night length (e.g., Chrysanthemum, soybean)
  - Day-neutral: Insensitive to photoperiod (tomato)
- **CO (CONSTANS):** Stabilized in long days (LDP) → activates FT (Florigen)
- **FT (FLOWERING LOCUS T):** "Florigen"; mobile signal from leaf → SAM via phloem

### ABC Model of Floral Development
| Gene Class | Where expressed | Organ formed |
|-----------|----------------|-------------|
| A only | Sepal |
| A + B | Petal |
| B + C | Stamen |
| C only | Carpel |
| A antagonizes C |

- **A genes:** AP1, AP2
- **B genes:** AP3, PI
- **C gene:** AG (AGAMOUS)
- **D genes (ovule):** STK, SHP1, SHP2
- **E genes (all whorls):** SEP1-SEP4 (sepallata)

---

## E. PROGRAMMED CELL DEATH AND AGING

### Apoptosis in Development
- **Digit formation:** Interdigital webbing removed by apoptosis; BMP4 promotes; FGF inhibits
- **C. elegans:** 131 cells die during development; ced-3 (caspase), ced-4 (Apaf-1), ced-9 (Bcl-2)
- **EGL-1** (BH3-only) → inhibits CED-9 → CED-4 free → activates CED-3

### Senescence
- **Replicative senescence:** Telomere shortening → p53/Rb activation → cell cycle arrest
- **Oncogene-induced senescence:** Ras activation → p16/p21 → senescence (tumor suppressor)
- **SASP (Senescence Associated Secretory Phenotype):** Pro-inflammatory cytokines from senescent cells

### Plant Senescence
- Chlorophyll breakdown → yellowing (carotenoids remain)
- **SAG (Senescence-Associated Genes):** SAG12 (Cys protease), SAG113 (PP2C)
- Ethylene and ABA promote; cytokinin delays senescence

---

# UNIT 6: SYSTEM PHYSIOLOGY - PLANT

## A. PHOTOSYNTHESIS

### Light Reactions (Thylakoid membrane)
- **PSI (Photosystem I):** Absorbs 700nm (P700); produces NADPH; cyclic and non-cyclic
- **PSII (Photosystem II):** Absorbs 680nm (P680); water splitting (oxygen evolution); Z-scheme
- **Electron flow (non-cyclic):** H₂O → PSII → PQ → Cyt b6f → PC → PSI → Fd → NADPH
- **Cyclic electron flow:** PSI → Fd → Cyt b6f → PC → PSI; generates only ATP (no NADPH)
- **Light-harvesting complexes:** LHCII (PSII) and LHCI (PSI); contain chlorophyll a, b + carotenoids
- **OEC (Oxygen Evolving Complex):** Mn₄CaO₅ cluster; Kok cycle (S0-S4 states)
- **Photophosphorylation:** Chemiosmosis; CFo-CF1 ATP synthase

### Calvin Cycle (C3 - Dark reactions, Stroma)
- **Phase 1 (Carbon fixation):** CO₂ + RuBP → 2× 3-PGA (RuBisCO)
- **Phase 2 (Reduction):** 3-PGA → G3P (using ATP + NADPH)
- **Phase 3 (Regeneration):** G3P → RuBP (using ATP)
- **Net:** 3CO₂ + 9ATP + 6NADPH → 1 G3P
- **RuBisCO:** Most abundant enzyme on Earth; can also fix O₂ (oxygenase activity → photorespiration)

### C4 Photosynthesis
- Spatial separation of CO₂ fixation
- **Mesophyll cell:** PEP + CO₂ → Oxaloacetate (PEP carboxylase; HIGH affinity for CO₂)
- **Bundle sheath cell:** Malate/aspartate decarboxylated → CO₂ → Calvin cycle
- **Kranz anatomy:** Bundle sheath cells surround vascular bundle
- **Advantage:** Concentrates CO₂ around RuBisCO; reduces photorespiration; efficient at high temp
- Examples: Maize, sugarcane, sorghum

### CAM (Crassulacean Acid Metabolism)
- Temporal separation of CO₂ fixation
- **Night:** Stomata open; CO₂ fixed by PEP carboxylase → malate stored in vacuole
- **Day:** Stomata closed; malate released → decarboxylated → CO₂ to Calvin cycle
- **Advantage:** Minimizes water loss; adapted to arid environments
- Examples: Cacti, pineapple, succulents

### Photoprotection
- **Non-photochemical quenching (NPQ):** Excess energy dissipated as heat
- **PsbS protein:** Lumen pH sensor; triggers qE (energy-dependent quenching)
- **Zeaxanthin:** Formed from violaxanthin by VDE; direct quencher
- **Photorespiration:** RuBisCO oxygenase activity; O₂ fixes to RuBP → 2-phosphoglycolate → glycolate → processed in peroxisome and mitochondria; wasteful (CO₂ released)

---

## B. RESPIRATION AND PHOTORESPIRATION

### Plant Mitochondrial ETC
- Similar to animal but has **Alternative Oxidase (AOX)**
- AOX: Accepts electrons from ubiquinol → reduces O₂ to H₂O; no H+ pumping (energy wasted as heat)
- **Thermogenic plants:** (Arum lily, skunk cabbage) - AOX generates heat for volatilizing scent compounds
- **External NADH DH:** Can oxidize cytoplasmic NADH without going through Complex I

### Photorespiration
- RuBisCO + O₂ → 2-phosphoglycolate + 3-PGA
- **2-phosphoglycolate → glycolate (chloroplast) → glyoxylate (peroxisome) → glycine (peroxisome) → serine (mitochondria, releases CO₂) → glycerate → 3-PGA (chloroplast)**
- Involves chloroplast, peroxisome, and mitochondria
- Wasteful: Consumes ATP/NADPH; releases CO₂; no net carbon gain

---

## C. NITROGEN METABOLISM

### Nitrate Assimilation
- Nitrate → Nitrite (Nitrate Reductase; cytoplasm; requires NADH; Mo-containing)
- Nitrite → Ammonium (Nitrite Reductase; chloroplast/plastid; requires Fd)
- **NH₄+ → Glutamate:** GS/GOGAT cycle (primary assimilation)
  - Glutamine Synthetase (GS): NH₄+ + Glutamate + ATP → Glutamine
  - Glutamate Synthase (GOGAT): Glutamine + α-KG → 2 Glutamate

### Biological Nitrogen Fixation
- **N₂ → NH₃** (Nitrogenase enzyme)
- **Nitrogenase complex:** Dinitrogenase (MoFe protein) + Dinitrogenase reductase (Fe protein)
- Requires: 16 ATP, 8 e⁻, 8 H+ per N₂
- **O₂ sensitive!** Protected by: Leghemoglobin (in nodules), heterocysts (cyanobacteria)
- **Rhizobium-Legume symbiosis:**
  - Nod factors (LCOs) produced by Rhizobium → root hair curling → nodule development
  - **Leghemoglobin:** Maintains low O₂ for nitrogenase; pink color of nodules

---

## D. PLANT HORMONES

| Hormone | Synthesis | Transport | Key Functions |
|---------|----------|----------|--------------|
| Auxin (IAA) | Young leaves, stem apex | Polar (PAT via PIN proteins) | Cell elongation, apical dominance, tropisms, root initiation |
| Cytokinin | Roots (mainly) | Via xylem | Cell division, shoot growth, delay senescence, stomatal opening |
| Gibberellin (GA) | Young tissues, seeds | Via phloem/xylem | Stem elongation, germination, fruit development, bolting |
| Abscisic Acid (ABA) | Stressed tissues | Via phloem/xylem | Stomatal closure, dormancy, stress response, seed maturation |
| Ethylene (C₂H₄) | Ripening fruits, stressed tissue | Gas (diffusion) | Fruit ripening, leaf abscission, stress response, senescence |
| Brassinosteroids | Ubiquitous | Short-range | Cell expansion, photomorphogenesis, stress tolerance |
| Jasmonates (JA) | Many tissues | Local + systemic | Defense against herbivores/pathogens, fertility |
| Salicylic acid (SA) | Leaves | Systemic | SAR (Systemic Acquired Resistance), defense vs. pathogens |
| Strigolactones | Roots | Upward | Inhibit branching, mycorrhizal signaling, parasitic plant germination |

### Auxin Signaling
- **Receptor:** TIR1 (F-box protein in SCF E3 ligase complex)
- Auxin → binds TIR1 → AUX/IAA proteins ubiquitinated and degraded → ARF (transcription factor) activated

### ABA Signaling (Stomatal closure)
- ABA → PYR/RCAR receptors → inhibit PP2C (phosphatases) → SnRK2 kinases active → SLAC1 (anion channel) opens → K+ efflux → stomatal closure

### Gibberellin Signaling
- GA → GID1 receptor → DELLA proteins ubiquitinated and degraded → GA-responsive genes expressed
- **DELLA proteins:** Repressors of GA responses; dwarf plants when constitutively active

---

## E. SENSORY PHOTOBIOLOGY

### Phytochromes
- **Chromophore:** Phytochromobilin (linear tetrapyrrole)
- **Pr form (660nm):** Inactive; accumulates in dark
- **Pfr form (730nm):** Active form → nuclear translocation → COP1/SPA inhibited → HY5 (transcription factor) active
- **5 phytochromes in Arabidopsis:** PhyA (low fluence, far-red), PhyB (high irradiance, red)
- **Functions:** Seed germination, de-etiolation, shade avoidance, flowering

### Cryptochromes
- **Flavoprotein:** FAD chromophore
- **Blue/UV-A light:** CRY1 (steady-state growth inhibition), CRY2 (flowering, circadian)
- **Mechanism:** Blue light → CRY dimerization → COP1 inhibition → HY5 stability

### Circadian Clock (Plants)
- **Central oscillator:** TOC1 and CCA1/LHY (mutual repression)
- **TOC1:** Evening-expressed; represses CCA1/LHY
- **CCA1/LHY:** Morning-expressed; represses TOC1
- ~24h period; temperature-compensated

---

## F. SOLUTE TRANSPORT

### Water Transport
- **Osmosis:** Water moves from low solute (high water potential) to high solute (low water potential)
- **Water potential (Ψ) = Ψs (solute) + Ψp (pressure)**
- **Transpiration-cohesion-tension theory (Dixon & Joly):** Tension in xylem pulls water column
- **Aquaporins (TIP, PIP):** Facilitate water movement across tonoplast and PM

### Phloem Transport (Pressure-flow hypothesis - Münch)
- **Source:** Loading of sucrose (mesophyll → phloem by sucrose transporters or plasmodesmata symplastic)
- **Sink:** Unloading at roots, fruits, seeds
- **Turgor pressure difference** drives flow

### Mineral Nutrition
- **Essential macronutrients:** N, P, K, Ca, Mg, S
- **Micronutrients:** Fe, Mn, Zn, Cu, Mo, B, Cl, Ni
- **Deficiency symptoms:**
  - N (nitrate): Chlorosis (older leaves first; mobile)
  - Fe: Interveinal chlorosis (young leaves; immobile)
  - Mg: Interveinal chlorosis (older leaves; mobile; part of chlorophyll)
  - K: Marginal leaf scorch

---

## G. SECONDARY METABOLITES

| Class | Biosynthetic pathway | Examples | Function |
|-------|-------------------|---------|---------|
| Terpenoids | MVA or MEP pathway | Sterols, rubber, taxol, menthol | Defense, pollinator attraction |
| Phenolics / Phenylpropanoids | Shikimic acid + Phe | Lignin, flavonoids, tannins | Defense, structural, UV protection |
| Alkaloids | Amino acid derived | Morphine, caffeine, nicotine, quinine | Defense |
| Glucosinolates | Tyr/Trp/Met | Sinigrin, glucoraphanin | Defense (crucifer family) |

- **Lignin:** Phenylpropanoid polymer; structural support; disease resistance; NOT digestible

---

## H. STRESS PHYSIOLOGY

### Abiotic Stress Responses
- **Drought/Osmotic:** ABA → stomatal closure; LEA proteins (late embryogenesis abundant); osmoprotectants (proline, glycine betaine)
- **Heat stress:** HSPs (Hsp70, Hsp90, sHSPs); HSF (heat shock factor) transcription
- **Cold/Chilling:** Membrane rigidification; cold-induced fatty acid desaturation; cold acclimation
- **Salt stress:** Na+ toxicity; SOS pathway (SOS3-SOS2 kinase → SOS1 Na+/H+ antiporter)
- **Heavy metal:** Phytochelatins, metallothioneins; vacuolar sequestration

### Biotic Stress (Plant Immunity)
- **PTI (PAMP-triggered immunity):** PRRs (FLS2, EFR) recognize PAMPs → ROS burst, callose deposition
- **ETI (Effector-triggered immunity):** NBS-LRR proteins (R genes) recognize effectors → hypersensitive response (HR), cell death at infection site
- **SAR (Systemic Acquired Resistance):** Salicylic acid (SA) → NPR1 → PR genes (PR1, PR2, PR5)
- **ISR (Induced Systemic Resistance):** Rhizobacteria-induced; jasmonate/ethylene dependent

---

# UNIT 7: SYSTEM PHYSIOLOGY - ANIMAL

## A. BLOOD AND CIRCULATION

### Blood Composition
- **Plasma (55%):** Water, proteins (albumin, globulins, fibrinogen), ions, nutrients
- **Formed elements (45%):**
  - RBCs (Erythrocytes): 4.5-5.5 million/µL; no nucleus; 120 day lifespan; HbA (α₂β₂)
  - WBCs (Leukocytes): 4,500-11,000/µL; 5 types
  - Platelets (Thrombocytes): 150,000-400,000/µL; derived from megakaryocytes

### Hemoglobin
- **Structure:** Tetramer α₂β₂; heme group (Fe²+); cooperative O₂ binding (T↔R state)
- **Bohr effect:** ↑CO₂/↑H+ → shifts O₂ dissociation curve right → more O₂ released at tissues
- **2,3-BPG:** Stabilizes T state; decreases O₂ affinity (shifts curve right); high altitude adaptation
- **Fetal Hb (HbF):** α₂γ₂; higher O₂ affinity than HbA (less 2,3-BPG binding); replaced by HbA at 6 months
- **Sickle cell anemia:** HbS; E6V mutation (Glu→Val at β-chain position 6); polymerizes when deoxygenated

### Blood Groups
- **ABO system:** IA (A antigen), IB (B antigen), i (no antigen); IA and IB codominant over i
- **Rh system:** D antigen most important; Rh+ / Rh-
- **Hemolytic disease of newborn:** Rh- mother, Rh+ fetus → anti-D antibodies → second pregnancy risk

### Hemostasis
1. Vascular spasm
2. Platelet plug formation (GP1b-von Willebrand factor; GPIIb/IIIa-fibrinogen)
3. Coagulation cascade:
   - **Extrinsic (tissue factor/TF):** TF + VIIa → Xa
   - **Intrinsic (contact):** XII → XI → IX → X
   - **Common pathway:** Xa + Va → Prothrombin → Thrombin → Fibrinogen → Fibrin
- **Vitamin K:** Required for factors II, VII, IX, X, Protein C, Protein S (γ-carboxylation)

---

## B. CARDIOVASCULAR SYSTEM

### Cardiac Cycle
- **Systole:** Contraction; ventricular pressure > aortic → semilunar valves open
- **Diastole:** Relaxation; AV valves open; filling
- **Heart sounds:** S1 (AV valve closure), S2 (semilunar valve closure)
- **ECG:**
  - P wave: Atrial depolarization
  - QRS complex: Ventricular depolarization
  - T wave: Ventricular repolarization
  - PR interval: AV node delay (0.12-0.20 s)
  - QT interval: Ventricular action potential duration

### Cardiac Action Potential
- **Pacemaker cells (SA node):** Slow depolarization (If current = funny current; HCN channels); no resting potential
- **Ventricular cardiomyocytes:** Fast Na+ (phase 0) → rapid repolarization (phase 1; K+) → plateau (phase 2; Ca²+) → repolarization (phase 3; K+)

### Blood Pressure Regulation
- **Short-term:** Baroreceptor reflex (carotid sinus, aortic arch) → NTS → medullary cardiovascular centers
- **Long-term:** RAAS (Renin-Angiotensin-Aldosterone System); ANP/BNP

---

## C. RESPIRATORY SYSTEM

### Gas Exchange
- **Fick's law:** Rate of diffusion ∝ (Area × ΔP × solubility) / (thickness × MW^0.5)
- **O₂ transport:** 97% as HbO₂; 3% dissolved
- **CO₂ transport:** 70% as bicarbonate; 23% as carbaminoHb; 7% dissolved
- **CO₂ + H₂O ↔ H₂CO₃ ↔ H+ + HCO₃⁻** (carbonic anhydrase in RBCs)
- **Chloride shift:** HCO₃⁻ exchanges for Cl⁻ across RBC membrane

### Control of Respiration
- **Central chemoreceptors (medulla):** Respond to CO₂/H+; main driver of ventilation
- **Peripheral chemoreceptors (carotid + aortic bodies):** Respond to ↓O₂, ↑CO₂, ↑H+
- **Hering-Breuer reflex:** Lung stretch → inhibits inspiration (prevents overinflation)

---

## D. NERVOUS SYSTEM

### Neuron Action Potential
- **Resting potential:** -70mV (due to K+ equilibrium and Na+/K+ pump)
- **Depolarization:** Na+ channels open → inward Na+ current
- **Repolarization:** K+ channels open → outward K+ current; Na+ channels inactivate
- **Refractory period:** Absolute (no AP possible); Relative (only strong stimulus)
- **Conduction velocity:** Increases with axon diameter; myelin sheath (saltatory conduction via Nodes of Ranvier)

### Synapse
- **Electrical synapse (gap junction):** Fast, bidirectional
- **Chemical synapse:** Unidirectional; Ca²+-triggered vesicle fusion (SNARE proteins); exocytosis
- **SNARE proteins:** v-SNARE (synaptobrevin) + t-SNARE (SNAP25 + syntaxin) → membrane fusion
- **EPSPs and IPSPs:** Summation (temporal + spatial) determines firing

### Brain Organization
- **Cerebral cortex:** Frontal (executive, motor), Parietal (somatosensory), Temporal (hearing, language), Occipital (vision)
- **Limbic system:** Amygdala (emotion), Hippocampus (memory formation)
- **Cerebellum:** Motor coordination, balance
- **Brainstem:** Autonomic functions (medulla), relay (pons), arousal (reticular formation)

---

## E. EXCRETORY SYSTEM

### Kidney Function
- **Nephron:** Functional unit; ~1 million per kidney
- **Glomerular filtration:** 180 L/day; molecular weight cutoff ~70 kDa; **GFR** ~120 mL/min
- **Proximal tubule:** Reabsorption of 67% Na+, glucose (completely), amino acids; PCT
- **Loop of Henle:** Countercurrent multiplier; establishes medullary osmotic gradient
  - Descending: Water permeable; Na+ impermeable
  - Ascending: Na+ reabsorption (active); water impermeable
- **Distal tubule:** Fine Na+ and K+ regulation; regulated by Aldosterone
- **Collecting duct:** Water reabsorption regulated by ADH (vasopressin); urea recycling

### Hormonal Regulation of Kidney
- **ADH (Vasopressin):** AQP2 insertion in collecting duct → ↑ water reabsorption → ↑ urine concentration
- **Aldosterone:** Na+ reabsorption, K+ secretion in DCT/collecting duct; from adrenal cortex
- **ANP (Atrial Natriuretic Peptide):** ↑ Na+ excretion; ↓ BP; released from atria with ↑ blood volume
- **RAAS:** Renin (kidney) → Angiotensinogen (liver) → Ang I → ACE (lung) → Ang II → aldosterone + vasoconstriction

---

## G. THERMOREGULATION

- **Endotherms (homeotherms):** Generate own heat (birds, mammals); maintain constant Tb
- **Ectotherms (poikilotherms):** Gain heat from environment (reptiles, fish)
- **Hypothalamus:** Thermoregulatory center; set point ~37°C in humans
- **Heat loss:** Radiation, conduction, convection, evaporation (sweating is most effective at high temp)
- **Counter-current heat exchange:** Rete mirabile in extremities; conserves heat
- **Fever:** IL-1, IL-6, TNF-α → PGE2 in hypothalamus → raised set point

---

## J. ENDOCRINOLOGY AND REPRODUCTION

### Major Endocrine Glands and Hormones
| Gland | Hormone | Function |
|-------|---------|---------|
| Anterior pituitary | GH, TSH, ACTH, FSH, LH, Prolactin | Master gland |
| Posterior pituitary | ADH (Vasopressin), Oxytocin | Released from hypothalamic neurons |
| Thyroid | T3, T4 (iodine-containing), Calcitonin | Metabolism, growth; Ca²+ lowering |
| Parathyroid | PTH | ↑Ca²+; ↑bone resorption, ↑renal Ca reabsorption |
| Adrenal cortex | Glucocorticoids (cortisol), Mineralocorticoids (aldosterone), Androgens | Stress; Na+ balance |
| Adrenal medulla | Epinephrine, Norepinephrine | Fight or flight; catecholamines |
| Pancreas | Insulin (β cells), Glucagon (α cells) | Blood glucose regulation |
| Gonads | Estrogen, Progesterone (ovary); Testosterone (testis) | Reproduction |

### Hormone Mechanism of Action
- **Hydrophilic (peptide, catecholamines):** Cannot cross membrane → surface receptors → second messengers
- **Lipophilic (steroids, thyroid):** Cross membrane → intracellular receptors → direct gene regulation

### Reproductive Axis
- **GnRH (hypothalamus)** → FSH + LH (anterior pituitary) → Gonads → Sex steroids (feedback)
- **Menstrual cycle:**
  - Follicular phase (days 1-13): FSH → follicle development; Estrogen ↑
  - LH surge (day 14) → Ovulation
  - Luteal phase (days 15-28): LH → Corpus luteum → Progesterone; supports endometrium
  - If no fertilization: Corpus luteum degenerates → Progesterone ↓ → Menstruation

---

## K. GUT MICROBIOME (METAORGANISM CONCEPT)

- **Holobiont:** Host + all associated microorganisms
- **Gut microbiome:** ~3.8×10¹³ bacteria; Firmicutes, Bacteroidetes (dominant phyla)
- **Functions:** Fermentation of dietary fibers → SCFAs (propionate, butyrate, acetate); vitamin K and B12 synthesis; immune training; metabolize xenobiotics
- **Gut-brain axis:** Vagus nerve, enteric nervous system, metabolites, immune signals
- **Dysbiosis:** Imbalance in gut microbiota; associated with IBD, obesity, T2DM, depression
- **Germ-free animals:** Raised without microbiota; underdeveloped immune system; larger cecum; useful for microbiome research

---

# UNIT 8: INHERITANCE BIOLOGY

## A. MENDELIAN AND CHROMOSOMAL INHERITANCE

### Mendel's Laws
- **Law of Segregation:** Two alleles separate during gamete formation
- **Law of Independent Assortment:** Genes on different chromosomes assort independently (NOT valid for linked genes)

### Deviations from 9:3:3:1
| Ratio | Type | Example |
|-------|------|---------|
| 9:7 | Complementary (two dominant needed) | Flower color in peas |
| 9:3:4 | Recessive epistasis | Labrador coat color |
| 12:3:1 | Dominant epistasis | Squash color |
| 15:1 | Duplicate dominant | Shepherd's purse fruit shape |
| 13:3 | Dominant suppressor | Maize pigmentation |

- **Penetrance:** Proportion of individuals with genotype showing phenotype
- **Expressivity:** Degree to which phenotype is expressed in individual
- **Pleiotropy:** One gene affects multiple phenotypes (e.g., PKU, sickle cell anemia)

### Sex-Linked Inheritance
- **X-linked recessive:** More common in males (hemizygous); carrier females; example: Hemophilia A (Factor VIII), color blindness
- **X-linked dominant:** Affected father → all daughters affected; Rett syndrome (MECP2)
- **Y-linked:** Male-to-male transmission; azoospermia factor (AZF)

### Mitochondrial and Chloroplast Inheritance
- **Maternal inheritance:** mtDNA from egg cytoplasm; no paternal contribution
- **Heteroplasmy:** Mix of mutant and normal mtDNA in a cell
- **Mitochondrial diseases:** MELAS (mitochondrial encephalomyopathy), MERRF, Leber's optic neuropathy
- **Chloroplast inheritance:** Often maternal; shoot color follows maternal parent (variegation)

---

## B. GENES AND MUTATIONS

### Types of Mutations
| Type | Example | Effect |
|------|---------|--------|
| Missense | Sickle cell (E6V) | Different AA |
| Nonsense | UAA/UAG/UGA | Premature stop |
| Frameshift | Insertion/deletion of non-3 bases | Altered reading frame |
| Silent | Synonymous codon change | No AA change |
| Transition | Purine↔Purine or Pyrimidine↔Pyrimidine | |
| Transversion | Purine↔Pyrimidine | More disruptive |
| Deletion/Duplication | cDNA level | |

### Mutagens
- **Physical:** UV (pyrimidine dimers - CPDs), ionizing radiation (DSBs)
- **Chemical:**
  - Base analogs: 5-BU (T analog), 2-AP (A analog)
  - Alkylating agents: EMS, MMS; O⁶-methylguanine pairs with T
  - Intercalating agents: Proflavin, EtBr → frameshift
  - Deaminating: Nitrous acid (C→U, A→HX)
- **Ames test:** Uses Salmonella his- mutants to test chemical mutagenicity

---

## C. GENETIC ANALYSIS

### Genetic Mapping
- **Recombination frequency (RF) = (recombinant offspring / total offspring) × 100%**
- **1 cM (centimorgan) = 1% recombination**
- **Three-point cross:** Determine gene order from double crossover classes (rarest class)
- **Interference = 1 - Coefficient of coincidence (CoC)**
- **CoC = observed DCO / expected DCO**

### Tetrad Analysis (Fungi: Neurospora, Saccharomyces)
- **Ordered tetrad (Neurospora):** Linear arrangement reflects position relative to centromere
- **Second division segregation:** Crossover between gene and centromere → 2:2:2:2 or 2:4:2 pattern
- **Gene-centromere distance = (½ × second division tetrads / total tetrads) × 100**

### Gene Transfer in Bacteria
| Method | Vehicle | Features |
|--------|---------|---------|
| Transformation | Naked DNA | Competent cells; Ca²+ treatment; natural or artificial |
| Conjugation | F factor (pilus) | Requires cell contact; Hfr × F- → partial diploids |
| Transduction | Bacteriophage | Generalized (P1 in E. coli) or Specialized (λ phage - gal, bio) |
| Sexduction (F-duction) | F' plasmid | F+ gene transfer; merodiploids |

### Bacterial Mapping
- **Interrupted mating (time of entry):** Hfr × F-; mix broken at specific times → gene order by time of entry
- **Cotransduction frequency:** Used to map genes within 2 min (~90 kb) of each other
- **Complementation test (cis-trans test):** Two mutations in SAME gene → no complementation (mutant); DIFFERENT genes → complementation (wild-type)

---

## D. HUMAN GENETICS

### Pedigree Analysis Rules
- **Autosomal Dominant:** Affected parent → 50% affected offspring; both sexes; no skip generations; vertical pattern
- **Autosomal Recessive:** Both parents carriers; 25% affected; horizontal pattern; consanguinity increases risk
- **X-linked Recessive:** Males affected; carrier females; no male-to-male transmission
- **X-linked Dominant:** Affected females often > males; affected father → all daughters affected
- **Mitochondrial:** Maternal transmission; all children of affected mother may be affected

### Genetic Disorders Quick Reference
| Disorder | Gene/Mutation | Inheritance | Features |
|---------|--------------|-------------|---------|
| Cystic fibrosis | CFTR (ΔF508 most common) | AR | Thick mucus; lung/pancreas disease |
| Huntington's | HTT (CAG repeat expansion) | AD | Neurodegeneration; onset 30s-40s |
| Phenylketonuria (PKU) | PAH (phenylalanine hydroxylase) | AR | Mental retardation if untreated |
| Down syndrome | Trisomy 21 | Sporadic/chromosome | Intellectual disability; heart defects |
| Fragile X | FMR1 (CGG repeat expansion) | X-linked | Most common inherited intellectual disability |
| Sickle cell | HBB (E6V) | AR (codominant) | Hemolytic anemia; malaria protection |
| DMD (Duchenne) | Dystrophin (frameshift deletion) | X-linked recessive | Progressive muscle wasting |

### Karyotyping
- **Normal human:** 46 chromosomes (44 autosomes + 2 sex chromosomes)
- **Trisomies:** 21 (Down), 18 (Edwards), 13 (Patau), X (Klinefelter: 47,XXY; Turner: 45,X)
- **LOD score:** Log of odds; LOD > 3 = significant linkage; LOD < -2 = exclude linkage

---

## E. QUANTITATIVE GENETICS

### Hardy-Weinberg Equilibrium
- **p² + 2pq + q² = 1** (genotype frequencies)
- **p + q = 1** (allele frequencies)
- **Assumptions (MARRIAGE acronym):** No Migration, No Assortative mating, Random mating, No selection, Infinite population size, No mutation, Genetic equilibrium
- **Violations:** Small populations (genetic drift), selection, mutation, migration, non-random mating

### Heritability
- **Broad sense heritability (H²) = VG / VP** (total genetic variance / total phenotypic variance)
- **Narrow sense heritability (h²) = VA / VP** (additive variance; predicts response to selection)
- **VP = VG + VE + VGE** (Phenotypic = Genetic + Environmental + interaction variance)
- **VG = VA + VD + VI** (Additive + Dominance + Epistatic interaction variance)
- **Response to selection (R) = h² × selection differential (S)**

### Population Genetics
- **Genetic drift:** Random changes in allele frequency; greater in small populations
- **Bottleneck effect:** Population size reduced drastically; loss of diversity
- **Founder effect:** Small founding population; non-representative allele frequencies
- **Gene flow:** Movement of alleles between populations; reduces differentiation
- **Natural selection:** Directional, stabilizing, disruptive (diversifying)

---

## F. CHROMOSOMAL ALTERATIONS

### Structural Aberrations
| Type | Description | Effect |
|------|-------------|--------|
| Deletion | Loss of chromosomal segment | Haploinsufficiency; uncovers recessive alleles |
| Duplication | Extra copy of segment | Gene dosage effects |
| Inversion | Segment inverted | Paracentric (within arm); Pericentric (includes centromere) |
| Translocation | Segment moved to another chromosome | Reciprocal; Robertsonian (acrocentric chromosomes) |

- **Position effect:** Gene expression changes due to new chromosomal environment
- **Cri-du-chat syndrome:** Deletion of 5p; high-pitched cry; intellectual disability

### Numerical Aberrations
| Type | Description |
|------|-------------|
| Monosomy | 2n-1; usually lethal except 45,X (Turner) |
| Trisomy | 2n+1; Down, Patau, Edwards |
| Polyploidy | 3n (triploid), 4n (tetraploid); common in plants; rare in animals |
| Autopolyploidy | Multiple sets from same species |
| Allopolyploidy | Sets from different species (amphidiploid); e.g., wheat (6n=42) |

- **Endoreduplication:** DNA replication without division → polytene chromosomes (Drosophila salivary glands)

~/csir-net-notes/CSIR_NET_LifeScience_Notes_Part3.md

# CSIR-NET LIFE SCIENCE NOTES - PART 3
### Units 9-14: Evolution | Ecology | Bioinformatics | Biochem Engineering | Biotechnology | Methods in Biology

---

# UNIT 9: EVOLUTION AND DIVERSITY OF LIFE FORMS

## A. EVOLUTION OF LIFE

### Origin of Life
- **Early Earth atmosphere:** Reducing (NH₃, CH₄, H₂, H₂O) - no free O₂
- **Miller-Urey experiment (1953):** Simulated early conditions → amino acids formed (chemical evolution)
- **Oparin-Haldane hypothesis:** "Primordial soup" - organic molecules accumulated in oceans
- **RNA world hypothesis:** RNA first (self-replicating + catalytic); DNA and proteins evolved later
- **Ribozymes:** Catalytic RNAs (Tetrahymena rRNA, RNase P); support RNA world
- **First cells:** Protocells; lipid vesicles enclosing self-replicating RNA
- **LUCA (Last Universal Common Ancestor):** ~3.5-3.8 billion years ago

### Major Evolutionary Events (Timeline)
| Event | Time (Bya) |
|-------|-----------|
| Formation of Earth | 4.6 |
| First life (prokaryotes) | ~3.5-3.8 |
| Great Oxidation Event | ~2.4 |
| First eukaryotes | ~2.1 |
| Multicellular organisms | ~0.6 |
| Cambrian Explosion | ~0.54 |
| Land plants | ~0.47 |
| Land vertebrates | ~0.37 |
| Mammals | ~0.2 |
| Humans (Homo sapiens) | ~0.0003 |

### Endosymbiotic Theory (Margulis)
- **Mitochondria:** From α-proteobacteria engulfed by archaeal host
- **Chloroplasts:** From cyanobacteria
- **Evidence:** Double membrane, circular DNA, 70S ribosomes, binary fission, similar size

---

## B. MECHANISMS OF EVOLUTION

### Natural Selection (Darwin)
- **Variation** exists in populations
- Variation is **heritable**
- More offspring produced than can survive (**overproduction**)
- Individuals with favorable traits **survive and reproduce** more
- **Types:**
  - Directional: Favors one extreme phenotype
  - Stabilizing: Favors intermediate; reduces variation (birth weight in humans)
  - Disruptive (diversifying): Favors both extremes; may lead to speciation

### Genetic Drift
- Random change in allele frequencies; more pronounced in small populations
- **Bottleneck effect:** Sudden reduction in population size → loss of alleles
- **Founder effect:** Small founding group → non-representative gene pool
- Example: High frequency of certain diseases in isolated populations (e.g., Ellis-van Creveld in Amish)

### Gene Flow
- Movement of alleles between populations via migration
- Tends to **homogenize** populations and reduce divergence
- Counteracts local adaptation by natural selection

### Mutation
- Ultimate source of all new genetic variation
- Most mutations neutral or deleterious; some beneficial
- **Mutation rate** in humans: ~60 new point mutations per generation

### Speciation
- **Allopatric speciation:** Geographic barrier → reproductive isolation → new species (most common)
- **Sympatric speciation:** New species arise in same geographic area
  - Polyploidy (common in plants): Allopolyploidy (bread wheat)
  - Ecological specialization
- **Peripatric speciation:** Small peripheral population becomes isolated
- **Parapatric speciation:** Adjacent populations with some gene flow
- **Reproductive Isolation:**
  - Pre-zygotic: Temporal, habitat, behavioral, mechanical, gametic
  - Post-zygotic: Hybrid inviability, hybrid sterility (mule), hybrid breakdown

### Biological Species Concept (Mayr)
- Species = groups of actually or potentially interbreeding populations that are reproductively isolated from other groups
- **Limitations:** Cannot apply to asexual organisms, fossils

### Adaptive Radiation
- Rapid diversification from common ancestor into many ecological niches
- **Examples:** Darwin's finches (Galápagos), Hawaiian honeycreepers, cichlid fish (African Rift lakes), placental mammals after K-Pg extinction

### Convergent Evolution
- Unrelated organisms evolve similar traits in similar environments
- Examples: Wings (birds vs bats vs insects), eyes (vertebrates vs cephalopods), streamlined body (sharks vs dolphins)

### Coevolution
- Two species reciprocally influence each other's evolution
- **Arms race:** Host-parasite coevolution (Red Queen hypothesis)
- **Mutualistic coevolution:** Flowers and pollinators, figs and fig wasps
- **Mimicry:** Batesian (harmless mimics toxic), Müllerian (both toxic, mutual benefit)

### Extinction
- **Background extinction rate** vs. **Mass extinctions**
- **Five major mass extinctions:** End-Ordovician, Late Devonian, End-Permian (largest; 96% marine species), End-Triassic, K-Pg (asteroid impact; killed non-avian dinosaurs)
- **Sixth mass extinction:** Currently ongoing; human-caused

---

## C. MICROBIAL LIFE

### Bacteria
- **Phylogenetic domains:** Bacteria, Archaea, Eukarya (Woese & Fox; based on 16S rRNA)
- **Major phyla:** Proteobacteria (α,β,γ,δ,ε), Firmicutes, Bacteroidetes, Actinobacteria, Cyanobacteria
- **Archaea:** No peptidoglycan; ether-linked lipids; live in extreme environments
  - Methanogens (CO₂ + H₂ → CH₄), Halophiles, Thermoacidophiles

### Viruses
- **Not alive** (no cells, no metabolism)
- **Baltimore classification (7 groups):** Based on genome type and replication strategy
  - I: dsDNA (Herpes, Adenovirus)
  - II: ssDNA (Parvoviruses, Phage M13)
  - III: dsRNA (Reoviruses)
  - IV: +ssRNA (Picornaviruses, Coronaviruses)
  - V: -ssRNA (Influenza, Rabies)
  - VI: ssRNA-RT (HIV - retroviruses)
  - VII: dsDNA-RT (Hepatitis B)
- **Lytic vs Lysogenic cycles (bacteriophage λ):**
  - Lytic: Phage replicates → lyses cell
  - Lysogenic: Phage integrates as prophage (Int/Xis); CI repressor maintains lysogeny; SOS response → induction

---

## D-G. DIVERSITY OF PROTISTS, FUNGI, PLANTS, ANIMALS

### Protists
- **Algae:** Chlorophyta (green), Rhodophyta (red), Phaeophyta (brown/kelp)
- **Protozoa:** Amoeba, Paramecium, Plasmodium (malaria - Apicomplexa), Trypanosoma
- **Slime molds:** Cellular (Dictyostelium; model organism) and plasmodial
- **Oomycetes (water molds):** NOT fungi; cellulose wall; caused Irish potato famine (Phytophthora infestans)

### Fungi
| Group | Features | Examples |
|-------|---------|---------|
| Chytrids | Flagellated spores; aquatic | Batrachochytrium (frog pathogen) |
| Zygomycetes | Zygospores; coenocytic hyphae | Rhizopus (bread mold) |
| Glomeromycetes | AM mycorrhizal fungi | Glomus |
| Ascomycetes | Ascospores in asci; septate hyphae | Penicillium, Aspergillus, Saccharomyces, Neurospora |
| Basidiomycetes | Basidiospores on basidia | Mushrooms, Puccinia (wheat rust), Ustilago (corn smut) |

- **Mycorrhizae:** AM (Arbuscular; Glomeromycetes) - most plants; ECM (Ectomycorrhizal; Basidiomycetes) - trees
- **Lichens:** Fungus (Ascomycete mainly) + cyanobacteria or green algae symbiosis

### Plant Life - Major Groups
| Group | Key Feature | Example |
|-------|------------|---------|
| Bryophytes | Non-vascular; dominant gametophyte | Mosses, liverworts, hornworts |
| Pteridophytes | Vascular; no seeds; dominant sporophyte | Ferns, horsetails |
| Gymnosperms | Vascular; naked seeds; no fruit | Pine, fir, Ginkgo, Cycads |
| Angiosperms | Vascular; enclosed seeds; flowers/fruits | All flowering plants |

- **Alternation of generations:** Gametophyte (n) ↔ Sporophyte (2n)
- **Trend in plant evolution:** Reduction in gametophyte; dominance of sporophyte

### Animal Phylogeny (Key synapomorphies)
- **Porifera:** No true tissues; choanocytes; spicules
- **Cnidaria:** Radial symmetry; two body layers; cnidocytes (nematocysts); polyp and medusa stages
- **Platyhelminthes:** Acoelomate; flatworms; liver fluke (Fasciola), tapeworm (Taenia)
- **Annelida:** Segmented; coelom; setae (earthworms, leeches)
- **Mollusca:** Mantle, radula; most diverse invertebrate phylum by species after arthropods
- **Arthropoda:** Exoskeleton (chitin); jointed appendages; largest phylum
- **Echinodermata:** Radial symmetry (adults); water vascular system; deuterostomes; spiny skin
- **Chordata:** Notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail

---

# UNIT 10: ECOLOGY AND BEHAVIOURAL BIOLOGY

## A. POPULATION ECOLOGY

### Population Growth Models
- **Exponential (J-curve):** dN/dt = rN (r = intrinsic rate of increase; unlimited resources)
  - N(t) = N₀ × e^(rt)
  - λ (finite rate) = e^r
- **Logistic (S-curve):** dN/dt = rN[(K-N)/K] (K = carrying capacity)
  - Maximum growth rate when N = K/2
  - As N → K, growth → 0

### Life History Strategies
| Feature | r-selected | K-selected |
|---------|-----------|-----------|
| Population size | Variable; below K | Near K |
| Body size | Small | Large |
| Lifespan | Short | Long |
| Reproductive rate | High; many offspring | Low; few offspring |
| Parental care | Little | Extensive |
| Examples | Insects, weeds, bacteria | Elephants, whales, humans |

### Life Tables
- **Cohort life table:** Follow single cohort from birth to death
- **lx (survivorship):** Proportion surviving to age x
- **mx (fecundity):** Female offspring produced at age x
- **R₀ (net reproductive rate) = Σ(lx × mx)** ; R₀ > 1 = growing; < 1 = declining
- **Generation time (T) = Σ(x × lx × mx) / R₀**
- **Survivorship curves:**
  - Type I (convex): Low early mortality; high late (humans, large mammals)
  - Type II (diagonal): Constant mortality at all ages (birds, some reptiles)
  - Type III (concave): High early mortality; survivors live long (fish, invertebrates, plants)

### Metapopulations
- Network of local populations linked by dispersal
- **Levins model:** dp/dt = mp(1-p) - ep (p = proportion occupied patches; m = colonization; e = extinction)
- **Rescue effect:** Immigration reduces extinction probability of small populations
- Important for conservation: Habitat fragmentation creates metapopulations

---

## B. COMMUNITY ECOLOGY

### Species Interactions
| Interaction | Species A | Species B | Example |
|------------|---------|---------|---------|
| Competition | - | - | Two species competing for food |
| Predation | + | - | Lion and wildebeest |
| Herbivory | + | - | Caterpillar and plant |
| Parasitism | + | - | Tick and host |
| Mutualism | + | + | Clownfish and anemone |
| Commensalism | + | 0 | Barnacles on whale |
| Amensalism | 0 | - | Penicillin vs bacteria |

### Competition
- **Competitive Exclusion Principle (Gause):** Two species competing for identical resources cannot coexist indefinitely
- **Lotka-Volterra competition:** Coexistence when intraspecific competition > interspecific
- **Character displacement:** Competing species evolve different morphology when sympatric vs allopatric (Darwin's finches)
- **Ecological niche:** Fundamental niche (potential) vs Realized niche (actual, with competition)
- **Niche partitioning:** Resource division reduces competition; promotes coexistence

### Predator-Prey Dynamics (Lotka-Volterra)
- **dN/dt = rN - aNP** (prey growth - predation)
- **dP/dt = baNP - mP** (predator growth - mortality)
- Oscillating cycles; classic example: Canada lynx and snowshoe hare

### Keystone Species
- Species with disproportionately large effect on community structure relative to biomass
- Examples: Sea otter (controls sea urchins → kelp forest), wolves in Yellowstone (trophic cascade)

### Succession
- **Primary succession:** On bare substrate (no soil); pioneer species → climax community
  - Example: After glacier retreat; volcanic island; bare rock colonized by lichens
- **Intermediate disturbance hypothesis:** Intermediate disturbance frequency maximizes species diversity
- **Facilitation:** Early species make conditions suitable for later species
- **Inhibition:** Early species prevent establishment of later ones
- **Tolerance:** Later species resist early ones but establish regardless

---

## C. ECOSYSTEM ECOLOGY

### Energy Flow
- **Primary production:** Gross PP (GPP) - Respiration = Net PP (NPP)
- **Trophic efficiency:** ~10% energy transferred between levels (Lindeman's rule)
- **Ecological pyramids:** Pyramid of numbers, biomass, energy
- **Inverted biomass pyramid:** Phytoplankton (low biomass) supports larger zooplankton biomass (marine)

### Biogeochemical Cycles

**Carbon Cycle:**
- **Photosynthesis:** CO₂ → organic C
- **Respiration:** Organic C → CO₂
- **Decomposition:** Organic C → CO₂ (microbes)
- **Human impact:** Fossil fuel burning → ↑ atmospheric CO₂ → global warming

**Nitrogen Cycle:**
- **Fixation:** N₂ → NH₃ (Rhizobium, Azobacter, Cyanobacteria; lightning)
- **Nitrification:** NH₃ → NO₂⁻ (Nitrosomonas) → NO₃⁻ (Nitrobacter)
- **Denitrification:** NO₃⁻ → N₂ (Pseudomonas, Paracoccus; anaerobic)
- **Assimilation:** NO₃⁻/NH₄⁺ → organic N (plants)
- **Ammonification:** Organic N → NH₃ (decomposers)

**Phosphorus Cycle:**
- No gaseous phase; weathering of rocks → soil → uptake → decomposition
- **Limiting nutrient** in many freshwater ecosystems

---

## D. BIODIVERSITY AND CONSERVATION

### Biodiversity Levels
- **Genetic diversity:** Variation within species
- **Species diversity:** Number of species
- **Ecosystem diversity:** Variety of habitats/ecosystems
- **Alpha diversity:** Species richness within a habitat
- **Beta diversity:** Change in species composition between habitats
- **Gamma diversity:** Regional species richness

### Threats to Biodiversity (HIPPO)
- **H**abitat destruction (GREATEST threat)
- **I**nvasive species
- **P**ollution
- **P**opulation (human)
- **O**verhunting/overexploitation
- + Climate change

### IUCN Red List Categories
- Extinct (EX) → Extinct in Wild (EW) → Critically Endangered (CR) → Endangered (EN) → Vulnerable (VU) → Near Threatened (NT) → Least Concern (LC)

### Conservation Strategies
- **In-situ:** Protection in natural habitat (national parks, biosphere reserves, wildlife sanctuaries)
- **Ex-situ:** Protection outside habitat (zoos, botanical gardens, seed banks, cryopreservation)
- **Minimum Viable Population (MVP):** Smallest population with >99% chance of persisting for 1000 years
- **Population Viability Analysis (PVA):** Modeling extinction probability
- **Conservation genetics:** Inbreeding depression, effective population size (Ne), genetic diversity maintenance

### Indian Acts and Policies
- **Wildlife Protection Act, 1972:** Schedule I-VI species protection
- **Forest Conservation Act, 1980:** Prior approval for forest diversion
- **Biodiversity Act, 2002:** ABS (Access and Benefit Sharing); NBA (National Biodiversity Authority)
- **PPVFR Act, 2001:** Farmers' rights, Plant Breeders' rights
- **International:** CBD (Convention on Biological Diversity), CITES, Ramsar Convention (wetlands), Nagoya Protocol (ABS)
- **PGRFA Treaty:** International Treaty on Plant Genetic Resources for Food and Agriculture

---

## E. BEHAVIOURAL ECOLOGY

### Proximate vs Ultimate Causes
- **Proximate:** HOW behaviour works (mechanism, development) - Tinbergen's questions
- **Ultimate:** WHY behaviour evolved (function, evolutionary history)
- **Tinbergen's 4 questions:** Causation, Development, Function, Evolution

### Foraging Theory
- **Optimal Foraging Theory:** Animals maximize energy intake per unit time
- **Marginal Value Theorem:** Leave patch when foraging rate = average habitat foraging rate

### Communication
- **Chemical:** Pheromones (sex, alarm, trail); highly species-specific
- **Visual:** Displays (threat, courtship); bioluminescence (Photinus firefly)
- **Acoustic:** Birdsong; ultrasound (bats, whales); stridulation (insects)
- **Tactile:** Bee waggle dance (Karl von Frisch, Nobel 1973) - communicates distance and direction of food

### Bee Waggle Dance
- **Waggle run duration ∝ distance to food**
- **Angle relative to vertical = angle of food relative to sun**
- **Round dance:** Short distance (<50m)
- **Waggle dance:** >50m

### Altruism and Kin Selection
- **Hamilton's rule:** Altruistic behavior evolves when rB > C
  - r = coefficient of relatedness; B = benefit to recipient; C = cost to actor
- **Kin selection:** Inclusive fitness (direct + indirect fitness)
- **Eusociality:** Haplodiploid hypothesis (Hamilton); worker bees more related to sisters (r=0.75) than own offspring (r=0.5)
- **Reciprocal altruism (Trivers):** Help non-relatives with expectation of return

### Sexual Selection (Darwin)
- **Intrasexual selection:** Competition within same sex (male-male competition → antlers)
- **Intersexual selection (mate choice):** Females choose males with honest signals
- **Runaway selection (Fisher):** Arbitrary preferences coevolve with traits
- **Handicap principle (Zahavi):** Costly signals are honest (peacock's tail)

### Migration
- **Navigation mechanisms:** Sun compass, star compass, magnetic compass (magnetite), landmarks
- **Long-distance migrants:** Arctic tern (longest migration; Arctic to Antarctic)
- **Imprinting:** Salmon return to birth stream; geese imprint on mother (Lorenz)

---

# UNIT 11: BIOINFORMATICS AND COMPUTATIONAL BIOLOGY

## A. MAJOR BIOINFORMATICS DATABASES

| Database | Content |
|---------|---------|
| GenBank (NCBI) | DNA/RNA sequences |
| UniProt/Swiss-Prot | Protein sequences (curated) |
| PDB (Protein Data Bank) | 3D protein structures |
| EMBL | European nucleotide sequences |
| KEGG | Metabolic pathways |
| GO (Gene Ontology) | Functional annotation |
| Pfam | Protein families and domains |
| PROSITE | Protein patterns and profiles |
| GEO | Gene expression data |
| OMIM | Human genetic diseases |
| PubChem/ChEMBL | Chemical compounds |
| RefSeq | Reference sequences (NCBI) |

---

## B. SEQUENCE ANALYSIS

### BLAST (Basic Local Alignment Search Tool)
- **Heuristic** algorithm; finds local alignments
- **BLASTN:** Nucleotide vs nucleotide
- **BLASTP:** Protein vs protein
- **BLASTX:** Translated nucleotide vs protein
- **TBLASTN:** Protein vs translated nucleotide
- **TBLASTX:** Translated nt vs translated nt
- **E-value:** Expected number of random hits with equal or better score; E < 0.001 = significant
- **Bit score:** Normalized alignment score
- **FASTA:** Older algorithm; similar to BLAST; uses k-tuples

### Homology Terms
- **Homologues:** Share common ancestor
- **Orthologues:** Diverged by speciation; same function in different species (β-globin in mouse and human)
- **Paralogues:** Diverged by duplication within same genome; may have different functions (α- and β-globin)
- **Analogues:** Similar function but different evolutionary origin (convergent)
- **Xenologues:** Similarity due to horizontal gene transfer

### Sequence Alignment
- **Pairwise:** Two sequences; global (Needleman-Wunsch) or local (Smith-Waterman)
- **Global alignment:** Best for similar-length sequences (full alignment)
- **Local alignment:** Best for finding conserved domains within otherwise different sequences
- **Gap penalty:** Affine gap penalty (gap opening + extension)
- **Scoring matrices:**
  - **PAM (Point Accepted Mutation):** PAM1 = 1 AA change per 100 residues; PAM250 for distant homologues
  - **BLOSUM:** Blocks Substitution Matrix; BLOSUM62 (most used; 62% identity in blocks); BLOSUM80 for closely related
- **MSA (Multiple Sequence Alignment):** ClustalW, MUSCLE, MAFFT; progressive or iterative
- **Phylogenetics from MSA:** Distance methods (UPGMA, Neighbor-Joining), parsimony, maximum likelihood, Bayesian

---

## C. GENE ANNOTATION AND PHYLOGENETICS

### Phylogenetic Trees
- **Cladogram:** Shows branching pattern only; branch lengths not proportional to change
- **Phylogram:** Branch lengths proportional to amount of change
- **Ultrametric tree (dendrogram):** Tips equidistant from root; assumes molecular clock
- **Rooted vs Unrooted:** Rooted has common ancestor; outgroup used to root
- **Bootstrap values:** Statistical support (>70-80% acceptable)
- **Parsimony:** Minimizes total number of evolutionary changes
- **Maximum Likelihood:** Finds tree maximizing probability of observed data given model
- **Bayesian:** Uses prior probabilities; posterior probability for each tree

### Molecular Clock
- Proteins and DNA evolve at approximately constant rate over time
- Used to date divergence events
- Not always constant (rate variation)

### Genetic Variation
- **SNP (Single Nucleotide Polymorphism):** Most common variant; >1% frequency in population
- **Indel:** Insertion or deletion
- **CNV (Copy Number Variation):** Deleted or duplicated segments (>1 kb)
- **LOH (Loss of Heterozygosity):** Loss of one allele; common in cancers

---

## D. MOLECULAR MODELLING AND DRUG DESIGN

### Protein Structure Prediction
- **Homology modelling:** Template with known structure used to build model of target (>30% identity)
- **Fold recognition (threading):** Profile of known fold matched to target sequence
- **Ab initio:** Structure predicted from sequence alone (energy minimization); computationally expensive
- **AlphaFold (DeepMind, 2020):** AI-based; near-experimental accuracy; revolutionized structural biology
- **Molecular dynamics (MD) simulation:** Newton's equations of motion; force fields (AMBER, CHARMM, GROMOS)
- **Energy minimization:** Finds nearest energy minimum; removes bad contacts
- **RMSD (Root Mean Square Deviation):** Structural similarity measure

### Drug Design
- **Structure-based drug design:** Target structure known → dock ligand
- **Molecular docking:** AutoDock, Glide; finds optimal ligand pose
- **ADMET:** Absorption, Distribution, Metabolism, Excretion, Toxicity
- **Lipinski's Rule of 5:** MW ≤500, logP ≤5, H-bond donors ≤5, H-bond acceptors ≤10 → oral bioavailability
- **QSAR (Quantitative Structure-Activity Relationship):** Mathematical model relating structure to activity
- **Pharmacophore:** Minimal structural features required for activity
- **Virtual screening:** In silico library screening against target

---

## E. SYSTEMS BIOLOGY

- **Systems biology:** Integrative approach; studies emergent properties of biological systems
- **Omics integration:** Genomics + transcriptomics + proteomics + metabolomics
- **Network biology:** Protein-protein interaction (PPI) networks; metabolic networks
- **Hub proteins:** Highly connected nodes; often essential
- **Synthetic lethality:** Two mutations lethal together but not individually (BRCA + PARP inhibitors)
- **Digital health:** Wearable sensors, EHR, AI diagnostics
- **Personalized medicine:** Treatment based on individual genomics/omics profile

---

# UNIT 12: BIOCHEMICAL ENGINEERING AND INDUSTRIAL BIOTECHNOLOGY

## A. ENGINEERING PRINCIPLES

### Material and Energy Balance
- **Mass balance:** Input = Output + Accumulation (± generation)
- **Steady state:** dAccumulation/dt = 0
- **Yield coefficient (YX/S):** g cells / g substrate consumed
- **Stoichiometry:** Elemental balances for C, H, O, N in fermentation

### Transport Phenomena
- **Momentum transfer:** Fluid flow; Reynolds number Re = ρvd/μ (laminar <2100; turbulent >4000)
- **Heat transfer:** Conduction (Fourier's law), convection, radiation
- **Mass transfer:** Fick's law: J = -D(dC/dx)
- **Overall mass transfer coefficient (KLa):** Critical for O₂ supply in bioreactors

---

## B. THERMODYNAMICS IN BIOLOGICAL SYSTEMS

- **First Law:** Energy is conserved (ΔU = q - w)
- **Second Law:** Entropy of isolated system always increases (ΔS ≥ 0)
- **Biological systems:** Open, non-equilibrium; maintain low entropy by exporting entropy
- **Gibbs Free Energy:** ΔG = ΔH - TΔS; ΔG = ΔG° + RT ln Q
- **ATP hydrolysis:** ΔG = -30.5 kJ/mol (standard); more negative in cell (-50 to -60 kJ/mol)
- **Glycolytic oscillations:** Allosteric regulation of PFK1 → sustained oscillations in yeast
- **Entropy production:** Irreversible processes produce entropy; living systems are entropy exporters

---

## C. BIOPROCESS ENGINEERING

### Bioreactor Types
| Type | Description | Use |
|------|-------------|-----|
| Batch | Closed system; substrate added at start | Antibiotics, most fermentations |
| Fed-batch | Substrate added intermittently; no removal | Insulin, high-cell density cultures |
| Continuous (Chemostat) | Constant input/output; steady state | Research; enzyme production |
| Plug Flow | Tubular; no back-mixing | Enzyme reactions |
| CSTR | Continuous stirred tank; well-mixed | Wastewater; enzyme reactions |

### Chemostat Theory
- **Dilution rate (D) = F/V** (F = flow rate; V = volume)
- **At steady state:** D = μ (specific growth rate)
- **Washout:** D > μmax → cells washed out
- **Monod equation:** μ = μmax × S/(Ks + S)

### Oxygen Transfer
- **DO (Dissolved Oxygen)** critical limiting nutrient
- **OTR (Oxygen Transfer Rate) = KLa × (C* - C)** (C* = saturation; C = actual)
- **Aeration:** Sparger + impeller (Rushton turbine)
- **Scale-up challenges:** Maintaining KLa; heat transfer; shear stress on cells

### Industrial Fermentation Products
| Product | Organism | Notes |
|---------|---------|-------|
| Penicillin | Penicillium chrysogenum | Fed-batch; high cell density |
| Citric acid | Aspergillus niger | Low pH, high sugar |
| Ethanol | Saccharomyces cerevisiae | Anaerobic; sugarcane/corn |
| Lactic acid | Lactobacillus | Homo/heterofermentative |
| Glutamic acid | Corynebacterium glutamicum | Biotin limitation |
| Vitamin B12 | Propionibacterium, Pseudomonas | |
| Insulin | Recombinant E. coli or S. cerevisiae | |

### Sterilization
- **Thermal sterilization:** 121°C, 15 psi, 15-20 min (autoclave) - kills by protein denaturation
- **Del factor (∇):** Measure of sterilization; ln(N₀/N)
- **HTST (High Temp Short Time):** Better for heat-sensitive media

---

## D. DOWNSTREAM PROCESSING

1. **Biomass removal:** Centrifugation, microfiltration
2. **Cell disruption:** Homogenization, bead milling, sonication, enzymatic (lysozyme)
3. **Clarification:** Centrifugation, filtration
4. **Precipitation:** Ammonium sulfate (salting out), isoelectric precipitation, organic solvents
5. **Chromatography:**
   - Ion exchange (IEX): Charge-based separation
   - Size exclusion (SEC/GFC): Molecular weight separation
   - Affinity: Specific ligand (Protein A for IgG, Ni-NTA for His-tag)
   - Hydrophobic interaction (HIC): Binds at high salt, elutes at low salt
6. **Ultrafiltration/Dialysis:** Membrane separation; concentration; buffer exchange
7. **Drying:** Spray drying, freeze-drying (lyophilization); lyophilization preserves protein activity

---

## E. ENZYME TECHNOLOGY

### Enzyme Immobilization
- **Methods:** Adsorption, covalent attachment, entrapment (alginate beads), crosslinking (with glutaraldehyde)
- **Advantages:** Reusable, stable, easy product separation, continuous use
- **Carriers:** Sepharose, silica, polyacrylamide, alginate, DEAE-cellulose
- **Thiele modulus (φ):** Ratio of reaction rate to diffusion rate
  - High φ → diffusion-limited; low φ → kinetically limited
  - External diffusion resistance: Stagnant film around carrier
  - Internal diffusion resistance: Within porous matrix

### Protein Engineering
- **Random mutagenesis (directed evolution):** Error-prone PCR → mutant library → screening/selection
- **Rational design:** Site-directed mutagenesis based on structure-function knowledge
- **Enzyme in organic solvents:** Increases hydrophobic substrate solubility; reverse reactions possible
- **Ionic liquids:** Designer solvents; enzyme stability; green chemistry

---

## F. METABOLIC ENGINEERING AND SYNTHETIC BIOLOGY

- **Metabolic engineering:** Directed modification of metabolic networks to improve cellular properties
- **Tools:** Gene knockouts, overexpression, promoter engineering, cofactor engineering
- **Synthetic biology:** Design and construction of new biological parts, devices, systems
- **BioBrick parts:** Standardized biological parts (iGEM)
- **Gene circuits:** Toggle switches (Gardner et al.), oscillators (Elowitz & Leibler), logic gates
- **CRISPR/Cas9:** Powerful tool for metabolic engineering; precise gene editing
- **Whole-cell biocatalysis:** Using whole cells for biotransformations
- **Flux balance analysis (FBA):** Constraint-based modeling of metabolic networks

---

# UNIT 13: ADVANCES IN BIOTECHNOLOGY

## A. RECOMBINANT DNA TECHNOLOGY

### Cloning Vectors
| Vector | Insert size | Host | Use |
|--------|------------|------|-----|
| Plasmid | <10 kb | E. coli | Small genes, expression |
| Lambda phage | 10-20 kb | E. coli | cDNA/genomic libraries |
| Cosmid | 25-50 kb | E. coli | Genomic libraries |
| BAC | 100-300 kb | E. coli | Physical mapping, genome sequencing |
| YAC | 100-1000 kb | Yeast | Very large inserts |

### Restriction Enzymes
- **Type II RE:** Cut within or near recognition sequence; generate blunt or sticky ends
- **Palindromic recognition sequences:** EcoRI (GAATTC), HindIII (AAGCTT), BamHI (GGATCC)
- **Sticky ends:** Easier ligation; direction-specific cloning
- **Blunt ends:** Less efficient; require higher ligase concentration

### PCR (Polymerase Chain Reaction)
- **Steps:** Denaturation (94°C) → Annealing (55-65°C) → Extension (72°C)
- **2^n amplification** (n = cycles)
- **Taq polymerase:** Heat-stable (from Thermus aquaticus); no proofreading
- **Pfu polymerase:** High-fidelity; 3'→5' exonuclease
- **RT-PCR:** RNA → cDNA (reverse transcriptase) → PCR; quantifies mRNA
- **qPCR (Real-time PCR):** SYBR Green or TaqMan probes; quantitative
- **Other variants:** Nested PCR, Touchdown PCR, LAMP

### DNA Sequencing
- **Sanger sequencing:** Chain-termination; ddNTPs; fluorescent labels; ~1 kb reads; Gold standard
- **NGS (Next Generation Sequencing):**
  - **Illumina (SBS):** Short reads (150 bp); high accuracy; most widely used
  - **454 (pyrosequencing):** Medium reads; retired
  - **Ion Torrent:** pH changes; semiconductor detection
  - **PacBio (SMRT):** Long reads (10-30 kb); single molecule; higher error rate
  - **Oxford Nanopore:** Longest reads; real-time; portable; measures current change

### Genome Editing
- **ZFN (Zinc Finger Nucleases):** First gen; complex design
- **TALEN (Transcription Activator-Like Effector Nucleases):** Second gen; easier design
- **CRISPR-Cas9:** Most widely used; sgRNA (guide RNA) directs Cas9 to target; cuts both strands
  - **Cas9 (from Streptococcus pyogenes):** Requires PAM sequence (NGG)
  - **Repair:** NHEJ (error-prone; gene KO) or HDR (precise; needs template)
  - **Base editing:** CBA (cytosine base editor), ABE (adenine base editor) - no DSB needed
  - **Prime editing:** Search-and-replace genome editing; uses pegRNA + reverse transcriptase
  - **CRISPRi/CRISPRa:** dCas9-based transcriptional repression/activation
  - Nobel Prize 2020: Jennifer Doudna and Emmanuelle Charpentier

### Mutagenesis Techniques
- **Site-directed mutagenesis (SDM):** Kunkel method, QuikChange method; specific base changes
- **Random mutagenesis:** EMS (chemical), UV, error-prone PCR
- **Insertional mutagenesis:** T-DNA insertion (Agrobacterium), transposon tagging

---

## B. MEDICAL BIOTECHNOLOGY

### Vaccines
| Type | Description | Example |
|------|-------------|---------|
| Live attenuated | Weakened pathogen | BCG, MMR, Oral polio |
| Killed/inactivated | Killed pathogen | Salk polio, influenza, rabies |
| Toxoid | Inactivated toxin | Diphtheria, tetanus |
| Subunit | Purified antigen | HBV (HBsAg), acellular pertussis |
| Recombinant | rDNA-produced antigen | HBV vaccine (S. cerevisiae) |
| mRNA | mRNA encoding antigen | COVID-19 (Pfizer/BNT162b2, Moderna) |
| Viral vector | Viral delivery of antigen | COVID-19 (AstraZeneca/ChAdOx1) |

### Monoclonal Antibodies (mAbs)
- **Hybridoma technology (Köhler & Milstein, 1975; Nobel 1984):**
  - B cell (antibody producing) + Myeloma cell (immortal) → Hybridoma
  - HAT selection medium
- **mAb naming:** -mab suffix; source (-o- mouse, -xi- chimeric, -zu- humanized, -u- human)
- **Therapeutic mAbs:** Trastuzumab (HER2+, breast cancer), Rituximab (CD20, lymphoma), Nivolumab (PD-1, immune checkpoint)
- **Antibody engineering:** Chimeric (mouse V + human C), Humanized, Fully human (phage display, transgenic mice)

### Stem Cell Technology
- **ESC:** Pluripotent; from ICM; ethical concerns
- **iPSC (Yamanaka, 2006):** Oct4 + Sox2 + Klf4 + c-Myc reprogram somatic cells; Nobel 2012
- **Applications:** Disease modeling, drug screening, cell therapy, organoids
- **Organoids:** Stem cell-derived 3D self-organizing structures; brain organoids, gut organoids, liver organoids
- **Directed differentiation:** Growth factors guide iPSCs to specific cell types (e.g., dopaminergic neurons for Parkinson's)

### Gene Therapy
- **Ex vivo:** Cells removed, modified, returned (CAR-T cells)
- **In vivo:** Vector delivered directly (AAV-based; LNP for mRNA)
- **Vectors:** Retrovirus (integrates; risk of insertional mutagenesis), Adeno-associated virus (AAV; non-integrating; low immunogenicity), Lentivirus (integrates into non-dividing cells)
- **CAR-T cells:** T cells engineered with chimeric antigen receptor; CD19 CAR-T for B cell leukemia

### Diagnostics
- **ELISA:** Enzyme-linked immunosorbent assay; 4 types (direct, indirect, sandwich, competitive)
- **PCR-based:** RT-PCR (COVID-19 diagnosis), allele-specific PCR
- **Biosensors:** Glucose sensor (electrochemical; GOx enzyme)
- **Flow cytometry:** Cell counting; surface marker analysis; FACS (sorting)
- **Lateral flow assay (LFA):** Rapid antigen/antibody tests; colloidal gold

---

## C. TRANSGENIC ORGANISMS

### Transgenic Plants
- **Agrobacterium-mediated transformation:** Ti plasmid; T-DNA integrates into plant genome
  - Disarmed Ti plasmid used in research
  - Binary vector system: T-DNA genes on separate plasmid
- **Biolistic (gene gun):** Gold particles coated with DNA; high-velocity delivery; for monocots
- **Bt crops:** Bacillus thuringiensis toxin (Cry proteins) → insect resistance; Bt cotton, Bt corn
- **Herbicide-tolerant crops (Roundup Ready):** CP4-EPSPS gene; glyphosate tolerance
- **Golden rice:** β-carotene (provitamin A) in endosperm; psy + crtI genes
- **Virus-resistant papaya:** Coat protein gene from PRSV

### Transgenic Animals
- **Pronuclear microinjection:** DNA injected into pronucleus of fertilized egg
- **ES cell targeting:** Knockin/knockout via homologous recombination in ES cells
- **CRISPR KO animals:** More efficient; direct zygote editing
- **Cre-lox system:** Conditional knockouts; tissue-specific deletion
- **Knockin:** Replace gene with modified version (e.g., humanized mice)
- **Applications:** Disease models (ApoE mice for atherosclerosis), biopharmaceutical production (ATryn - antithrombin from goat milk)

---

## D. AGRICULTURAL BIOTECHNOLOGY

### Molecular Markers in Plant Breeding
| Marker | PCR required | Dominant/Codominant | Use |
|--------|-------------|--------------------|----|
| RFLP | No | Codominant | First-generation |
| RAPD | Yes | Dominant | Fingerprinting |
| AFLP | Yes | Dominant | High resolution |
| SSR (Microsatellite) | Yes | Codominant | Breeding; mapping |
| SNP | Yes | Codominant | High-throughput; GWAS |
| DArT | No | Dominant | High-throughput |

- **Marker Assisted Selection (MAS):** Select for trait using linked marker; faster than phenotypic
- **Foreground selection:** Track target gene/QTL
- **Background selection:** Recover recurrent parent genome (backcross breeding)
- **Gene introgression:** Transfer single gene from donor to elite line
- **Gene pyramiding:** Stack multiple genes (e.g., multiple disease resistance genes)

### Genomics Applications
- **EST (Expressed Sequence Tag):** Partial cDNA sequence; identify expressed genes
- **QTL mapping:** Quantitative Trait Locus; identify genomic regions controlling quantitative traits
- **GWAS (Genome-wide association study):** Associate SNPs with traits in diverse populations
- **Genomic selection:** Genome-wide markers for prediction of breeding value

---

## E. ENVIRONMENTAL BIOTECHNOLOGY

### Bioremediation
- **In situ:** Treatment at contaminated site (bioaugmentation, biostimulation)
- **Ex situ:** Contaminated material removed and treated (bioreactors, composting)
- **Phytoremediation:** Plants + root zone microbes remove/detoxify pollutants
  - Phytoextraction: Plant accumulates metal in shoot (Thlaspi, Arabidopsis halleri)
  - Phytostabilization: Immobilize pollutant in root zone
  - Rhizofiltration: Root absorption from water
- **Metal hyperaccumulators:** Accumulate >1000 ppm metal in shoots

### Wastewater Treatment
- **Primary treatment:** Physical (screening, sedimentation); removes ~60% SS
- **Secondary treatment:** Biological (aerobic activated sludge; anaerobic digestion)
  - **BOD (Biological Oxygen Demand):** Measure of organic pollution
  - **Activated sludge:** Mixed culture aerobic treatment; removes 85-95% BOD
- **Tertiary treatment:** Advanced; removes N, P, pathogens (filtration, chlorination, UV)

### Biofuels
- **1st gen:** Sugarcane ethanol, corn ethanol; food vs fuel debate
- **2nd gen:** Lignocellulosic biomass; cellulose → sugars → ethanol
- **3rd gen:** Algal biofuels; high lipid content; raceway ponds/photobioreactors
- **Biogas:** Anaerobic digestion; CH₄ + CO₂; 4 stages (hydrolysis, acidogenesis, acetogenesis, methanogenesis)

---

# UNIT 14: METHODS IN BIOLOGY

## A. MOLECULAR BIOLOGY TECHNIQUES

### Chromatography
| Type | Principle | Examples |
|------|-----------|---------|
| IEX (Ion Exchange) | Charge | DEAE (anion), CM (cation) |
| SEC (Size Exclusion) | Molecular size | Sephadex, Superdex |
| Affinity | Specific ligand | Protein A (IgG), Ni-NTA (His-tag), GST |
| HIC (Hydrophobic Interaction) | Hydrophobicity | Phenyl Sepharose |
| Reverse phase (HPLC) | Hydrophobicity | C18, C8 columns |

### Electrophoresis
- **Agarose gel:** DNA/RNA separation; ethidium bromide or SYBR staining; migration ∝ 1/log(MW)
- **SDS-PAGE:** Protein separation by MW; SDS denatures; β-mercaptoethanol reduces disulfide bonds
- **Native PAGE:** Separation by charge + size + shape; preserves activity
- **2D-PAGE:** IEF (pI) + SDS-PAGE (MW); proteomics
- **Pulse-field gel electrophoresis (PFGE):** Very large DNA (chromosomes)

### Centrifugation
- **Differential centrifugation:** Sequential steps at increasing g-forces
  - 600g: Cell debris, nuclei
  - 10,000g: Mitochondria, chloroplasts
  - 100,000g: Ribosomes, microsomes, ER vesicles
- **Density gradient:** Sucrose gradient (rate-zonal) or CsCl/Cs₂SO₄ (isopycnic/equilibrium)
  - CsCl equilibrium: Separates DNA by buoyant density (G-C rich DNA denser)

---

## B. BIOPHYSICAL METHODS

### Spectroscopy
| Method | Principle | Application |
|--------|-----------|-------------|
| UV-Vis | Absorption of UV/visible light | Protein (280 nm; Trp,Tyr), DNA (260 nm), enzyme assays |
| Fluorescence | Emission after excitation | Protein folding, FRET, GFP-based assays |
| CD (Circular Dichroism) | Differential absorption of L/R circularly polarized light | Secondary structure of proteins; DNA conformation |
| NMR | Nuclear spin in magnetic field | Solution structure of proteins <50 kDa; dynamics |
| ESR/EPR | Electron spin | Radical detection; spin-labeled probes |

### Structure Determination
- **X-ray crystallography:** Diffraction pattern from crystal; electron density map; most structures in PDB
- **Cryo-EM:** Frozen hydrated samples; single particle analysis; near-atomic resolution; large complexes; Nobel 2017 (Henderson, Dubochet, Frank)
- **NMR spectroscopy:** Solution structures; dynamics; <50 kDa proteins

### Mass Spectrometry
- **ESI-MS (Electrospray Ionization):** Intact proteins/peptides; soft ionization
- **MALDI-TOF:** Matrix-assisted laser desorption/ionization; PMF (peptide mass fingerprinting)
- **Tandem MS (MS/MS):** Peptide fragmentation; protein identification (proteomics); de novo sequencing
- **Applications:** Protein identification, PTM analysis, metabolomics, drug discovery

### Other Methods
- **SPR (Surface Plasmon Resonance):** Real-time binding kinetics; KD measurement; label-free (BIAcore)
- **ITC (Isothermal Titration Calorimetry):** Binding thermodynamics; ΔH, ΔS, KD, stoichiometry
- **DLS (Dynamic Light Scattering):** Hydrodynamic radius; particle size distribution

---

## C. GENOMICS, TRANSCRIPTOMICS, PROTEOMICS, METABOLOMICS

### Genomics
- **Shotgun sequencing:** Random fragmentation → sequence → assemble (Celera approach for human genome)
- **Hierarchical (clone-by-clone):** BAC clone maps → sequence each BAC (HGP approach)
- **Human Genome Project:** Completed 2003; ~3.2 billion bp; ~20,000-25,000 protein-coding genes; ~1.5% coding
- **Comparative genomics:** Compare genomes across species; conserved elements = functionally important
- **DNA barcoding:** Short DNA sequence (COI gene for animals; rbcL+matK for plants) identifies species

### Transcriptomics
- **Microarray:** Hybridization-based; compare two conditions; limited to known sequences
- **RNA-seq:** Sequencing-based; unbiased; quantifies all transcripts; detects novel transcripts/splicing
- **Single-cell RNA-seq (scRNA-seq):** Gene expression in individual cells; reveals cell heterogeneity
- **ATAC-seq:** Chromatin accessibility mapping

### Proteomics
- **2D-PAGE + MS:** Classic proteomics
- **SILAC:** Stable isotope labeling; quantitative proteomics
- **iTRAQ/TMT:** Chemical labeling for multiplexed quantification
- **Protein-protein interaction (PPI):** Y2H (yeast two-hybrid), co-IP, pull-down, proximity ligation
- **ChIP-seq:** Chromatin immunoprecipitation + sequencing; maps DNA-binding protein sites

### Metabolomics
- **NMR-based:** Quantitative; non-destructive; structural identification
- **LC-MS/GC-MS:** Higher sensitivity and resolution
- **Targeted:** Measure known metabolites (quantitative)
- **Untargeted:** Discover all metabolites (qualitative/semi-quantitative)
- **Flux analysis (13C labeling):** Trace metabolic pathways

---

## D. RADIOLABELING TECHNIQUES

### Common Radioisotopes in Biology
| Isotope | Half-life | Emission | Use |
|---------|----------|---------|-----|
| ³H (Tritium) | 12.3 years | β⁻ (weak) | Autoradiography, RIA, scintillation counting |
| ¹⁴C | 5730 years | β⁻ | Carbon dating, metabolic tracing |
| ³²P | 14.3 days | β⁻ (strong) | DNA/RNA labeling, kinase assays |
| ³⁵S | 87.4 days | β⁻ | Protein labeling, DNA sequencing (old) |
| ¹²⁵I | 60 days | γ | RIA, protein labeling |
| ⁵¹Cr | 27.7 days | γ | Cytotoxicity assays (chromium release) |

- **Scintillation counting:** Liquid scintillation for β emitters; uses scintillation cocktail
- **Autoradiography:** Film or phosphorimager; detects radiation in gels/sections
- **Safety:** ALARA principle (As Low As Reasonably Achievable); lead shielding (γ), plexiglass (β)

---

## E. HISTOCHEMICAL AND IMMUNOTECHNIQUES

### ELISA Formats
| Format | Use |
|--------|-----|
| Direct ELISA | Antigen coated; enzyme-labeled Ab |
| Indirect ELISA | Antigen coated; unlabeled 1° Ab + enzyme-labeled 2° Ab; more sensitive |
| Sandwich ELISA | Two Abs; most specific and sensitive; quantitative |
| Competitive ELISA | Inhibition of binding; for small molecules |

### Western Blot
- SDS-PAGE → Transfer to nitrocellulose/PVDF → Block → 1° Ab → 2° Ab (HRP/AP conjugate) → Detection
- **ECL (Enhanced Chemiluminescence):** Most common detection

### Flow Cytometry
- **Measures:** Cell size (FSC), granularity (SSC), fluorescence intensity
- **FACS (Fluorescence Activated Cell Sorting):** Sorts cells based on fluorescence
- **Applications:** Immunophenotyping, cell cycle analysis, apoptosis (Annexin V), intracellular cytokines

### FISH (Fluorescence In Situ Hybridization)
- DNA probe hybridizes to chromosomal target; fluorescent label
- **Applications:** Gene mapping, chromosomal abnormalities, copy number changes
- **GISH (Genomic FISH):** Whole genome DNA as probe; identifies alien chromosomes

### Immunofluorescence
- **Direct:** Labeled primary antibody
- **Indirect:** Unlabeled 1° Ab + labeled 2° Ab; more sensitive; signal amplification

---

## F. MICROSCOPY

### Types of Microscopes
| Type | Principle | Resolution | Use |
|------|-----------|-----------|-----|
| Brightfield | Transmitted light | ~200 nm | Fixed stained specimens |
| Phase contrast | Phase differences | ~200 nm | Living cells |
| DIC (Nomarski) | Differential interference | ~200 nm | Fine structures; living cells |
| Fluorescence | Excitation/emission | ~200 nm | GFP-tagged proteins, immunofluorescence |
| Confocal | Laser; pinhole; optical sections | ~200 nm | 3D reconstruction; live imaging |
| TIRF | Evanescent wave | ~100 nm | Membrane events; single molecules |
| TEM | Electron beam; transmission | ~0.1 nm | Ultrastructure; internal organelles |
| SEM | Electron beam; surface scanning | ~1-20 nm | Surface morphology |
| STED | Stimulated emission depletion | ~30-80 nm | Super-resolution |
| STORM/PALM | Single molecule localization | ~10-20 nm | Super-resolution (Nobel 2014: Betzig, Hell, Moerner) |

- **Abbe resolution limit:** d = 0.61λ/NA (NA = numerical aperture)
- **Sample preparation for EM:** Fixation (glutaraldehyde + OsO₄) → dehydration → embedding → sectioning → staining (heavy metals)

---

## G. ELECTROPHYSIOLOGICAL METHODS

- **Patch-clamp (Neher & Sakmann, Nobel 1991):** Record current through single ion channels
  - Cell-attached, inside-out, outside-out, whole-cell configurations
- **Single neuron recording:** Extracellular (population) or intracellular (sharp electrode)
- **EEG (Electroencephalogram):** Brain surface electrical activity; epilepsy, sleep staging
- **MEG (Magnetoencephalography):** Magnetic fields from brain currents
- **fMRI:** Blood oxygenation level-dependent (BOLD) signal; functional brain imaging
- **PET (Positron Emission Tomography):** Radiotracer; metabolic imaging; ¹⁸F-FDG glucose metabolism
- **CAT/CT:** X-ray computed tomography; anatomical imaging

---

## H. FIELD BIOLOGY METHODS

### Population Estimation
- **Mark-Recapture (Lincoln-Petersen):** N = M × n / m (M = marked; n = recaptured; m = marked in recapture)
- **Quadrat method:** Count organisms in defined area; multiple quadrats → estimate total density
- **Transect method:** Count along line or belt transect; line transect, point transect
- **Distance sampling:** Detections at varying distances; detection probability modeled

### Remote Sensing
- **GPS tracking:** Animal movement; home range analysis
- **Camera traps:** Non-invasive; wildlife surveys; mark-recapture
- **Satellite imagery:** Habitat mapping; land use change; NDVI (vegetation index)
- **Acoustic monitoring:** Bat echolocation; bird calls; underwater acoustics

---

## I. STATISTICAL METHODS

### Key Concepts
- **Type I error (α):** False positive; reject true null hypothesis
- **Type II error (β):** False negative; fail to reject false null hypothesis
- **p-value:** Probability of observed result (or more extreme) if null hypothesis is true; p < 0.05 = significant
- **Confidence Interval:** Range within which true value lies with specified probability (usually 95%)

### Probability Distributions
- **Normal (Gaussian):** Bell-shaped; mean ± SD; 68-95-99.7 rule
- **Binomial:** Discrete; n trials; probability p; X ~ B(n,p)
- **Poisson:** Count data; rare events; mean = variance = λ

### Tests
| Test | Use |
|------|-----|
| t-test (Student's) | Compare means of 2 groups (paired or unpaired) |
| ANOVA (Analysis of Variance) | Compare means of >2 groups; F-test |
| Chi-square (χ²) | Categorical data; goodness of fit; independence |
| Mann-Whitney U | Non-parametric; compare 2 groups |
| Kruskal-Wallis | Non-parametric; compare >2 groups |
| Pearson correlation | Linear relationship; parametric |
| Spearman correlation | Rank correlation; non-parametric |
| Linear regression | Predict Y from X; y = mx + c |

- **Parametric tests:** Assume normal distribution; t-test, ANOVA, Pearson
- **Non-parametric tests:** No distribution assumption; Mann-Whitney, Kruskal-Wallis, χ²

---

## J. IPR, BIOSAFETY AND BIOETHICS

### Intellectual Property Rights
- **Patent:** 20-year protection; novel, non-obvious, useful; requires full disclosure
- **Copyright:** Literary, artistic works; automatic; life + 60 years in India
- **Trademark:** Brand identification; renewable
- **Trade secret:** Confidential business information; no registration needed
- **Geographical Indication (GI):** Product associated with geographic origin (Darjeeling tea)
- **Plant variety protection:** PPVFR Act 2001 in India; Plant Breeders' Rights + Farmers' Rights
- **Patent databases:** USPTO, EPO, WIPO (PCT), Indian Patent Office (IPO)

### Biosafety
| BSL Level | Examples | Containment |
|-----------|---------|-------------|
| BSL-1 | Non-pathogenic E. coli | Basic lab practices |
| BSL-2 | S. aureus, Hepatitis A, Toxoplasma | BSL-1 + restricted access, eye protection |
| BSL-3 | M. tuberculosis, SARS-CoV-2, HIV | BSL-2 + controlled air; special ventilation |
| BSL-4 | Ebola, Marburg, Smallpox | Full-body positive pressure suits; maximum containment |

- **rDNA safety (NIH guidelines):** RAC (Recombinant DNA Advisory Committee) reviews
- **IBC (Institutional Biosafety Committee):** Oversees rDNA research
- **IBSC (Institutional Biosafety Committee, India):** DBT guidelines
- **GEAC (Genetic Engineering Appraisal Committee):** Approves GM crop field trials/release in India

### Research Ethics
- **3Rs in Animal Research:** Replacement (alternative methods), Reduction (fewer animals), Refinement (minimize suffering)
- **IACUC (Institutional Animal Care and Use Committee):** Reviews animal protocols
- **Informed consent:** Voluntary, informed, competent participant
- **Plagiarism:** Presenting others' work as own; multiple forms (verbatim, mosaic, self-plagiarism)
- **Data fabrication vs falsification:** Inventing vs manipulating data; research misconduct
- **Authorship criteria (ICMJE):** Substantial contribution + drafting/revision + approval + accountability
- **AI in research:** Disclosure of AI tool use; AI cannot be listed as author (no accountability)

---

# QUICK REVISION: HIGH-YIELD FACTS FOR CSIR-NET

## Nobel Prizes (Biology - Frequently Asked)
| Year | Laureates | Work |
|------|----------|------|
| 1958 | Beadle & Tatum | One gene-one enzyme |
| 1962 | Watson, Crick, Wilkins | DNA structure |
| 1965 | Jacob, Monod, Lwoff | Operon and gene regulation |
| 1975 | Baltimore, Dulbecco, Temin | Reverse transcriptase; tumor viruses |
| 1978 | Arber, Smith, Nathans | Restriction enzymes |
| 1980 | Berg, Gilbert, Sanger | Recombinant DNA; DNA sequencing |
| 1983 | McClintock | Transposons |
| 1984 | Köhler & Milstein + Jerne | Monoclonal antibodies |
| 1993 | Roberts & Sharp | Split genes/RNA splicing |
| 1993 | Mullis | PCR |
| 1994 | Gilman & Rodbell | G-proteins |
| 1995 | Lewis, Nüsslein-Volhard, Wieschaus | Drosophila development; Hox genes |
| 2002 | Brenner, Horvitz, Sulston | C. elegans; programmed cell death |
| 2006 | Fire & Mello | RNA interference (RNAi) |
| 2006 | Kornberg | Eukaryotic transcription |
| 2009 | Ramakrishnan, Steitz, Yonath | Ribosome structure |
| 2012 | Gurdon & Yamanaka | Nuclear reprogramming; iPSCs |
| 2013 | Rothman, Schekman, Südhof | Vesicle trafficking |
| 2014 | Betzig, Hell, Moerner | Super-resolution microscopy |
| 2017 | Henderson, Dubochet, Frank | Cryo-EM |
| 2020 | Doudna & Charpentier | CRISPR-Cas9 |

---

## CSIR-NET Common Exam Tips

### Unit-wise Weightage (Approximate)
- **High weightage:** Unit 1 (Biomolecules), Unit 3 (Fundamental Processes), Unit 4 (Cell Signaling), Unit 8 (Inheritance), Unit 14 (Methods)
- **Moderate weightage:** Unit 2 (Cell Biology), Unit 5 (Developmental), Unit 6 (Plant Physiology), Unit 7 (Animal Physiology)
- **Conceptual heavy:** Unit 9 (Evolution), Unit 10 (Ecology), Unit 11 (Bioinformatics), Unit 13 (Biotechnology)

### Common Traps
1. A-DNA vs Z-DNA handedness (A = right; Z = LEFT)
2. E. coli RNA Pol - 5 subunits in core (α₂ββ'ω), sigma needed for promoter recognition
3. Meiosis I = reductional; Meiosis II = equational
4. Hardy-Weinberg: Allele frequency p+q=1; genotype p²+2pq+q²=1
5. Competitive inhibition: Km increases, Vmax unchanged (MOST COMMON MCQ!)
6. Cyclin D/CDK4,6 phosphorylates Rb (not CDK2)
7. Oxygen evolution in PSII (P680), not PSI
8. Leghemoglobin = plant protein (not bacterial); encoded by plant genome
9. Sickle cell = AR, but codominant at molecular level
10. CRISPR Nobel was 2020 (not chemistry Nobel - actually it was Chemistry Nobel 2020)

### Key Numbers to Remember
- Human genome: 3.2 billion bp; ~20,000-25,000 genes; 1.5% coding
- Human chromosomes: 46 (22 pairs autosomes + XX or XY)
- DNA replication speed: ~1000 bp/sec (E. coli); ~50-100 bp/sec (eukaryotes)
- E. coli genome: 4.6 Mb; ~4,300 genes; circular
- ATP yield glycolysis: 2 ATP net; 2 NADH; 2 pyruvate
- Human mtDNA: 16,569 bp; 37 genes (13 protein-coding, 22 tRNA, 2 rRNA)
- Nucleosome: 147 bp DNA + histone octamer; 1.65 turns of DNA
- Average protein: ~300 AAs; ~110 Da/AA; ~33 kDa
- Km of hexokinase (~0.1 mM glucose); Glucokinase (~10 mM; liver)

cat /home/daytona/workspace/csir-net-notes/CSIR_NET_LifeScience_Notes_Part1.md \…

cd /home/daytona/workspace/csir-net-notes && pandoc CSIR_NET_LifeScience_COMPLET…

# Try with wkhtmltopdf or weasyprint which wkhtmltopdf weasyprint pandoc 2>/dev/…

# Try reportlab to make PDF from the markdown python3 -c " from reportlab.lib.pa…

python3 << 'PYEOF' from reportlab.lib.pagesizes import A4 from reportlab.lib.sty…

python3 << 'PYEOF' from reportlab.lib.pagesizes import A4 from reportlab.lib.sty…

ls -lh /home/daytona/workspace/csir-net-notes/

python3 -c " import pdfplumber files = [ '/home/daytona/workspace/attachment…

python3 -c " import pdfplumber, fitz # PyMuPDF # Try fitz for image extraction …

# Convert PDF pages to images using pdftoppm, then OCR with tesseract which pdft…

# OCR first 5 pages of PYQ file 1 mkdir -p /home/daytona/workspace/csir-net-note…