Based on the fact that tomorrow is my biochemistry exam help me make notes on the topics given below and due to multiple reasons i was unaable to study anything so i know nothing therefore based on your understanding of me make the notes easy to memorize remember and understand also keep in mids these are all important topics so they should have all the information required in 1st year MBBS while not adding excess [04/07, 3:19 pm] Dr. Zahid: There will be a special class on Endocrinology by Dr Kamran Khan, professor physiology at 10 am. All students are required to be present in the lecture. [04/07, 3:30 pm] Dr. Zahid: Sunday 5th July at 10 am [04/07, 7:04 pm] Dr. Zahid: Tumour Marker, Oncogene [04/07, 7:04 pm] Dr. Zahid: Mechanism of Oncogene activation [04/07, 7:04 pm] Dr. Zahid: Lac operon [04/07, 7:04 pm] Dr. Zahid: Inhibitors of replication, transcription and translation [04/07, 7:04 pm] Dr. Zahid: Post transcriptional and post translational modifications [04/07, 7:04 pm] Dr. Zahid: Mutation, types of mutation Details of point mutations [04/07, 7:04 pm] Dr. Zahid: Different DNA repair mechanism and it's defect causing genetic disorder [04/07, 7:18 pm] Dr. Zahid: Beta oxidation Alfa and omega oxidation. Fatty acid synthesis and regulation. Sources of NADPH. Ketogenesis in starvation and Diabetes mellitus. Regulation of ketogenesis. Lipoproteins. Functions of apolipoproteins. Lipoprotein metabolism. Lipoprotein (a). Fatty liver Regulation of cholesterol biosynthesis. Products derived from cholesterol. Biosynthesis of heme. Bilirubin metabolism. Jaundice. Only 5 hours for everything as a whole

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Here are your complete, exam-ready notes. Everything is organized to be fast to read, easy to memorize, and covers 1st year MBBS requirements. I've used mnemonics, bullet points, and tables to make them stick quickly.

BIOCHEMISTRY EXAM NOTES - 1st Year MBBS

Time budget: ~15 min per section


1. TUMOUR MARKERS & ONCOGENES

What is a Tumour Marker?

A substance (protein, hormone, enzyme, etc.) produced by tumour cells or by the body in response to a tumour, found in blood/urine/tissue. Used for screening, diagnosis, monitoring response to treatment, and detecting recurrence.
Mnemonic - "A PIECE of Cake" for common markers:
MarkerCancer
AFP (Alpha-fetoprotein)Hepatocellular carcinoma, testicular germ cell
PSA (Prostate-specific antigen)Prostate cancer
CEA (Carcinoembryonic antigen)Colorectal, lung, breast
CA-125Ovarian cancer
CA 19-9Pancreatic cancer
hCG (human chorionic gonadotropin)Choriocarcinoma, testicular
CalcitoninMedullary thyroid carcinoma
Bence Jones proteinMultiple myeloma
S-100Melanoma
Ideal tumour marker: 100% sensitive and specific (none exists currently). Must be present only in tumour, measurable easily, levels correlate with tumour burden.

What is an Oncogene?

  • Proto-oncogene: Normal gene that regulates cell growth and division.
  • Oncogene: Mutated/overactivated proto-oncogene that drives uncontrolled cell proliferation (gain-of-function mutation - only ONE allele needs to be affected).
  • Acts like a stuck accelerator in a car.
Tumour Suppressor Genes = like brakes (BOTH alleles must be lost - loss of function). Examples: p53, Rb.

Mechanisms of Oncogene Activation (4 ways - mnemonic "PAINT")

MechanismHowExample
Point mutationSingle base change → constitutively active proteinKRAS (codon 12/13/61) in pancreatic (>95%), colon (40%) cancer
AmplificationMultiple copies of gene → overexpressionMYC in breast/prostate; MYCN in neuroblastoma; MDM2 in sarcoma
Insertion (retroviral)Retrovirus inserts near proto-oncogene, activating itHIV, HTLV
Non-disjunction / TranslocationChromosome rearrangement puts gene near active promoterBCR-ABL t(9;22) Philadelphia chromosome in CML; MYC-IgH t(8;14) in Burkitt lymphoma
Transcription factor dysregulationMultiple cancers
Key exam point: KRAS mutations are gain-of-function - they lock RAS in active (GTP-bound) form, constantly signalling cell division even without growth factors.
Oncogene categories by function:
  • Growth factors (e.g., SIS/PDGF)
  • Growth factor receptors (e.g., EGFR/HER2)
  • Signal transducers (e.g., RAS, RAF)
  • Transcription factors (e.g., MYC, JUN)
  • Cell cycle regulators (e.g., Cyclin D1)
  • Anti-apoptotic proteins (e.g., BCL-2)

2. LAC OPERON

The Concept

The lac operon is a model of gene regulation in prokaryotes (E. coli). It controls the genes for metabolizing lactose. It has two controls: negative (repressor) and positive (CAP/CRP).

Structure of the Lac Operon

[Promoter] - [Operator] - [lacZ] - [lacY] - [lacA]
  • lacZ → β-galactosidase (hydrolyzes lactose to glucose + galactose)
  • lacY → Permease (transports lactose into cell)
  • lacA → Transacetylase (acetylates β-galactosides, function unclear)

Negative Control (Repressor System)

  • A repressor protein (coded by lacI gene) normally binds the operator → blocks transcription
  • When lactose is present: lactose is converted to allolactose (the inducer)
  • Allolactose binds repressor → repressor changes shape → cannot bind operator → transcription proceeds
  • "Lactose unlocks the block"

Positive Control (CAP/CRP System)

  • When glucose is absent, cAMP levels rise
  • cAMP binds CRP (cAMP Receptor Protein = CAP) → activates it
  • cAMP-CRP complex binds promoter → enhances RNA polymerase binding → more transcription
  • When glucose is present → cAMP is low → CRP inactive → low transcription even if lactose present
  • "No glucose = more cAMP = more lactose genes" (catabolite repression)

Summary Table

GlucoseLactosecAMPRepressorTranscription
HighAbsentLowBound (active)OFF
HighPresentLowInactiveLow
LowAbsentHighActiveOFF
LowPresentHighInactiveMAX ON
The cell only makes lactose-metabolizing enzymes when it NEEDS them (lactose present) and when they are the BEST option (glucose absent).

Trp Operon Contrast (corepression)

  • Tryptophan = corepressor that ACTIVATES the repressor → shuts off trp synthesis when Trp is abundant.
  • Opposite to lac operon induction.

3. INHIBITORS OF REPLICATION, TRANSCRIPTION & TRANSLATION

A. Inhibitors of DNA Replication

Drug/AgentMechanism
HydroxyureaInhibits ribonucleotide reductase (blocks dNTP supply)
Cytarabine (Ara-C)False nucleoside → terminates chain
Nucleoside analogs (acyclovir, AZT)Inhibit viral DNA polymerase / chain termination
Fluoroquinolones (ciprofloxacin)Inhibit bacterial DNA gyrase (topoisomerase II)
Nalidixic acidInhibits bacterial DNA gyrase
CamptothecinInhibits topoisomerase I
EtoposideInhibits topoisomerase II
AphidicolinInhibits DNA polymerase α
UV radiationCreates pyrimidine dimers (TT dimers)

B. Inhibitors of Transcription (RNA synthesis)

Drug/AgentMechanism
RifampicinInhibits bacterial RNA polymerase (binds β subunit) - used in TB
Actinomycin DIntercalates in DNA → blocks RNA polymerase movement
α-Amanitin (mushroom toxin)Inhibits eukaryotic RNA polymerase II (mRNA synthesis)
DoxorubicinIntercalates in DNA → inhibits both replication and transcription
Rifampicin is the classic exam drug - inhibits prokaryotic RNA polymerase.

C. Inhibitors of Translation (Protein synthesis)

Bacteria have 70S ribosomes (50S + 30S subunits) - targeted selectively by antibiotics.
Mnemonic - "30S Cowboys Always Try Eating Tomorrow" → 30S inhibitors
  • Chloramphenicol (actually 50S - watch out!)
  • Aminoglycosides (Streptomycin, Gentamicin) → block 30S A site, cause misreading
  • Tetracycline → blocks aminoacyl-tRNA binding to 30S A site
Mnemonic - "50S is the BIG boss" → 50S inhibitors - "CCEL"
  • Chloramphenicol → inhibits peptidyl transferase on 23S rRNA of 50S
  • Clindamycin/Lincomycin → block 50S
  • Erythromycin (macrolides) → block translocation on 50S
  • Linezolid → 50S
Eukaryote-specific inhibitors:
  • Cycloheximide → inhibits peptidyl transferase on 60S (eukaryotes only)
  • Puromycin → structural analog of tyrosinyl-tRNA → causes premature chain termination (BOTH prokaryotes and eukaryotes)
  • Diphtheria toxin → ADP-ribosylates EF-2 (elongation factor) → stops translocation (eukaryotes only)
  • Ricin → cleaves 28S rRNA from 60S subunit
Easy trick: "Some Antibiotics That Don't Cure Everyone" - 30S: Streptomycin, Aminoglycosides, Tetracycline. 50S: macrolides, Chloramphenicol, Erythromycin

4. POST-TRANSCRIPTIONAL & POST-TRANSLATIONAL MODIFICATIONS

Post-Transcriptional Modifications (Processing of pre-mRNA → mature mRNA)

In eukaryotes, the primary transcript (pre-mRNA/hnRNA) must be processed before leaving the nucleus.
Three main modifications:
1. 5' Capping
  • A 7-methylguanosine (m7G) cap is added to the 5' end
  • Functions: protects mRNA from degradation, helps in ribosome binding (initiation of translation), export from nucleus
2. 3' Polyadenylation
  • A poly-A tail (100-250 adenine residues) is added to the 3' end
  • Functions: stability/protection from exonucleases, export, translation efficiency
  • Signal: AAUAAA sequence just before the cleavage site
3. Splicing (Removal of Introns)
  • Introns (intervening sequences) = removed
  • Exons (expressed sequences) = kept and joined
  • Done by the spliceosome (complex of snRNPs - small nuclear ribonucleoproteins)
  • Splice sites: 5' end of intron starts with GU, 3' end ends with AG (GU-AG rule)
  • Alternative splicing = one gene can produce multiple proteins (e.g., tropomyosin)
Other modifications:
  • RNA editing (e.g., ApoB mRNA - different proteins in liver vs intestine)
  • Export from nucleus via nuclear pores

Post-Translational Modifications (PTMs)

After protein synthesis, proteins are modified for proper function, localization, or regulation.
Common PTMs (mnemonic "GPS-MUG"):
ModificationWhat happensExample/Function
GlycoylationSugar added (N-linked or O-linked)Antibodies, cell surface proteins, blood groups
PhosphorylationPhosphate added (Ser, Thr, Tyr) by kinases; removed by phosphatasesSignal transduction, enzyme regulation
Signal peptide cleavageN-terminal signal sequence removedTargets protein to ER/membrane
MethylationMethyl groups added to Lys/Arg or DNAHistone modification, gene regulation
UbiquitinationUbiquitin tags proteinMarks for proteasomal degradation
GPI anchor additionGlycophosphatidylinositol links protein to membraneCD55, CD59 (absent in PNH)
Additional important ones:
  • Hydroxylation - proline & lysine in collagen (requires Vitamin C) → deficiency causes scurvy
  • Carboxylation - Glu → Gla, requires Vitamin K → clotting factors (II, VII, IX, X)
  • Acetylation - N-terminal; histone modification
  • Disulfide bond formation - in ER; stabilizes protein structure (insulin)
  • Proteolytic cleavage - zymogen activation (e.g., pepsinogen → pepsin, proinsulin → insulin)

5. MUTATION & TYPES OF MUTATION

What is a Mutation?

A permanent change in DNA sequence. Can be heritable or somatic.

Classification

A. By extent:
  • Point mutation = single base affected
  • Large-scale mutations = deletions, insertions, inversions, translocations
B. Point Mutations (most important for exam):
1. Substitutions
  • Transition: Purine ↔ Purine (A↔G) OR Pyrimidine ↔ Pyrimidine (C↔T) - same type
  • Transversion: Purine ↔ Pyrimidine - different type
Types by effect on protein:
TypeWhat happensExample
Silent/SynonymousCodon changes but same amino acid (due to degeneracy of code)GAA → GAG (both = Glu)
MissenseCodon changes → different amino acidSickle cell: Glu→Val in β-globin (GAG→GTG)
NonsenseCodon changes → STOP codon → truncated proteinCGA→TGA
FrameshiftInsertion/deletion of non-multiples of 3 bases → reading frame shiftsAlmost always deleterious
2. Insertions & Deletions (Indels)
  • If number of bases NOT a multiple of 3 → frameshift mutation
  • If multiple of 3 → in-frame insertion/deletion (protein may retain some function)
3. Trinucleotide Repeat Expansions
  • Expansion of 3-base repeats beyond normal limits
  • Examples:
    • Huntington's disease: CAG repeats in HTT gene
    • Fragile X: CGG repeats in FMR1
    • Myotonic dystrophy: CTG repeats
Key exam point - Sickle cell disease: A→T transversion at codon 6 of β-globin. GAG (Glu) → GTG (Val). This single missense mutation causes the entire disease.

6. DNA REPAIR MECHANISMS & DISORDERS

Why repair? DNA is constantly damaged by UV light, chemicals, radiation, and replication errors.

Repair Mechanisms (mnemonic "BEN MRD")

1. Base Excision Repair (BER)
  • Fixes small, non-bulky damage (oxidized bases, alkylated bases, deaminated cytosine)
  • Steps: DNA glycosylase removes the damaged base → AP endonuclease cuts backbone → DNA polymerase fills gap → ligase seals
  • Example: Uracil in DNA (from deamination of cytosine) is removed
2. Nucleotide Excision Repair (NER)
  • Fixes bulky lesions that distort DNA helix (UV-induced pyrimidine dimers, chemical adducts)
  • Steps: Recognise → cut out ~25-30 nucleotide patch including the lesion → fill by DNA polymerase → seal with ligase
  • Defect: Xeroderma Pigmentosum (XP) → extreme UV sensitivity, skin cancers, neurological defects
3. Mismatch Repair (MMR)
  • Fixes replication errors (mismatched base pairs, small insertions/deletions that escaped proofreading)
  • Occurs within minutes of replication
  • Uses methylation pattern to distinguish new (daughter) strand from template
  • Proteins: MutS (recognizes mismatch), MutL, MutH (cuts unmethylated daughter strand) in E. coli; homologs in humans (MSH2, MLH1)
  • Reduces error rate from 1 in 10^7 to 1 in 10^9
  • Defect: Hereditary Non-Polyposis Colorectal Cancer (HNPCC/Lynch Syndrome) → MSH2, MLH1 mutations → microsatellite instability
4. Direct Repair
  • Photolyase: repairs pyrimidine dimers directly using light energy (photo-reactivation) - mainly in bacteria and plants
  • O6-methylguanine methyltransferase (MGMT): removes alkyl groups from O6 position of guanine directly
5. Recombination Repair (Double-strand break repair)
Two pathways:
  • Homologous Recombination (HR): uses sister chromatid as template; accurate; active in S/G2 phase. BRCA1/BRCA2 involved.
  • Non-Homologous End Joining (NHEJ): rejoins broken ends directly; error-prone; active throughout cell cycle
Defect of HR: BRCA1/BRCA2 mutations → hereditary breast and ovarian cancer syndrome

Summary Table - Repair Defects

Repair Type DefectiveDiseaseKey Features
NERXeroderma PigmentosumUV sensitivity, skin cancers early in life
MMRHNPCC (Lynch Syndrome)Colon cancer, microsatellite instability
HR (BRCA1/2)Hereditary breast/ovarian cancerEarly-onset breast & ovarian cancer
NER (partial)Cockayne SyndromePhotosensitivity, premature aging, NO cancer
NER + NHEJTrichothiodystrophyBrittle hair, photosensitivity

7. BETA OXIDATION, ALPHA & OMEGA OXIDATION

Beta Oxidation (main pathway)

Fatty acids are degraded 2 carbons at a time as acetyl-CoA in mitochondria.
Before entering mitochondria:
  • Long-chain fatty acids are activated: FA + CoA + ATP → Fatty acyl-CoA (by thiokinase/acyl-CoA synthetase)
  • Transport into mitochondria requires Carnitine shuttle:
    • Carnitine palmitoyltransferase I (CPT-I) on outer membrane - rate-limiting, regulated step
    • Carnitine translocase transports acyl-carnitine across inner membrane
    • CPT-II on inner membrane regenerates fatty acyl-CoA inside
Regulation: CPT-I is inhibited by malonyl-CoA (the first product of fatty acid synthesis) - this prevents simultaneous synthesis and breakdown.
The 4-step cycle (OHAB):
  1. Oxidation (FAD-dependent) → trans-Δ2-enoyl-CoA (produces FADH2)
  2. Hydration → L-3-hydroxyacyl-CoA
  3. Another oxidation (NAD-dependent) → 3-ketoacyl-CoA (produces NADH)
  4. Beta-ketothiolase (thiolysis) → acetyl-CoA + shortened acyl-CoA (by 2C)
Energy yield from palmitate (16C):
  • 7 cycles → 8 acetyl-CoA + 7 FADH2 + 7 NADH
  • Total ~106 ATP (net ~129 ATP before subtracting activation cost)
Special cases:
  • Odd-chain fatty acids: final product is propionyl-CoA → converted to succinyl-CoA (enters TCA) via propionyl-CoA carboxylase (requires Biotin + Vit B12)
  • Unsaturated fatty acids: require additional isomerase/reductase enzymes, produce slightly less ATP

Alpha Oxidation

  • Occurs in peroxisomes
  • Removes one carbon from the alpha (2nd) carbon as CO2
  • Important for branched-chain fatty acids (e.g., phytanic acid from plant food)
  • Defect: Refsum disease → accumulation of phytanic acid → peripheral neuropathy, ataxia, retinitis pigmentosa

Omega Oxidation

  • Occurs in endoplasmic reticulum (microsomes)
  • Oxidation starts at the omega (last/methyl) end → produces dicarboxylic acids
  • Minor pathway; important in fatty acid oxidation disorders (when beta and alpha oxidation are impaired)
  • Products excreted in urine as dicarboxylic acids (diagnostic clue)

8. FATTY ACID SYNTHESIS & REGULATION

Key Features (opposite of beta oxidation)

  • Site: cytosol (beta oxidation is in mitochondria)
  • Acetyl-CoA cannot cross mitochondrial membrane directly → exits as citrate → cleaved by ATP-citrate lyase in cytosol
  • Requires: NADPH (not NADH), biotin, Mn2+
  • Product: Palmitate (16:0) - all other fatty acids made from this

Steps

Step 1: Acetyl-CoA → Malonyl-CoA (COMMITTED & RATE-LIMITING STEP)
  • Enzyme: Acetyl-CoA Carboxylase (ACC) - requires biotin
  • Reaction: Acetyl-CoA + CO2 + ATP → Malonyl-CoA
Step 2: Palmitate synthesis on Fatty Acid Synthase (FAS) complex
  • FAS is a multifunctional enzyme (in animals, one large polypeptide with 7 enzymatic activities)
  • Has two SH groups: ACP-SH (acyl carrier protein, prosthetic group = pantothenic acid/Vit B5) and Cys-SH
  • Cycle: Load acetyl (2C) → load malonyl (3C) → condensation releases CO2 → ketoreduction (NADPH) → dehydration → enoylreduction (NADPH) → product is 4C acyl chain
  • Repeat 6 more times → palmitate (16C)
  • Each cycle adds 2C, uses 2 NADPH, 1 malonyl-CoA
Overall equation for palmitate:
8 Acetyl-CoA + 7 ATP + 14 NADPH → Palmitate + 8 CoA + 6 H2O + 7 ADP + 14 NADP+

Regulation of Fatty Acid Synthesis

ACC is the key regulatory enzyme:
FactorEffect on ACCEffect on FA Synthesis
Citrate (high energy signal)Allosteric activation
Palmitoyl-CoA (product feedback)Allosteric inhibition
Malonyl-CoA-Inhibits CPT-I (prevents beta-oxidation)
InsulinActivates ACC (dephosphorylation)
Glucagon/EpinephrineInhibits ACC (phosphorylation via cAMP-PKA)
AMP-kinase (AMPK)Phosphorylates & inhibits ACC

Sources of NADPH (important!)

NADPH is used for reductive biosynthesis (fatty acid synthesis, cholesterol synthesis) and antioxidant defense (glutathione reductase).
SourcePathwayDetail
Pentose Phosphate Pathway (PPP)G6PD → NADPHMajor source - glucose 6-phosphate dehydrogenase (G6PD); G6PD deficiency → hemolytic anemia
Malic enzymeMalate → Pyruvate + CO2OAA from citrate cleavage → malate → pyruvate + NADPH
Isocitrate dehydrogenase (cytosolic)Isocitrate → α-ketoglutarateMinor
Glutamate dehydrogenaseGlutamate → α-ketoglutarateMinor
Folate pathwayMTHFRProduces NADPH in one-carbon metabolism

9. KETOGENESIS

Where & When

  • Occurs in liver mitochondria
  • Liver produces ketone bodies; liver cannot use them (lacks succinyl-CoA transferase/thiophorase)
  • Extrahepatic tissues (brain, heart, kidney, muscle) USE ketone bodies for energy

Ketone bodies (3 types):

  1. Acetoacetate (first formed, also called acetoacetic acid)
  2. β-Hydroxybutyrate (reduced form; major form in blood; not technically a "ketone")
  3. Acetone (formed by spontaneous decarboxylation of acetoacetate; exhaled - gives fruity breath)

Pathway of Ketogenesis

2 Acetyl-CoA → Acetoacetyl-CoA (by thiolase)
↓
+ Acetyl-CoA → HMG-CoA (by HMG-CoA synthase) [RATE-LIMITING STEP]
↓
HMG-CoA → Acetoacetate + Acetyl-CoA (by HMG-CoA lyase)
↓
Acetoacetate ⇌ β-Hydroxybutyrate (by β-hydroxybutyrate dehydrogenase; requires NADH)
Acetoacetate → Acetone (spontaneous decarboxylation)

Conditions that trigger Ketogenesis (= high acetyl-CoA + low oxaloacetate)

  1. Starvation/Fasting: Low glucose → low insulin → increased lipolysis → high fatty acids → high acetyl-CoA. Also OAA is used for gluconeogenesis.
  2. Diabetes Mellitus (Type 1): No insulin → same mechanism. Much more severe ketogenesis → diabetic ketoacidosis (DKA).
  3. High-fat, low-carbohydrate diet

Regulation of Ketogenesis

  • Insulin inhibits ketogenesis (inhibits lipolysis, activates malonyl-CoA → blocks CPT-I)
  • Glucagon promotes ketogenesis (promotes lipolysis)
  • The key rate-limiting enzyme is HMG-CoA synthase in mitochondria
  • When OAA is depleted (used for gluconeogenesis), acetyl-CoA cannot enter TCA → diverted to ketogenesis

Utilization of Ketone Bodies (extrahepatic)

β-Hydroxybutyrate → Acetoacetate (by β-hydroxybutyrate dehydrogenase)
Acetoacetate + Succinyl-CoA → Acetoacetyl-CoA + Succinate (by succinyl-CoA transferase = THIOPHORASE)
Acetoacetyl-CoA → 2 Acetyl-CoA → TCA cycle
Brain normally uses glucose but switches to ketone bodies during prolonged starvation (60-70% of brain fuel after 4+ days of fasting) - this is why people survive prolonged starvation.

10. LIPOPROTEINS

Why lipoproteins? Lipids are hydrophobic and need protein carriers to travel in aqueous blood.

Structure

A lipoprotein = hydrophobic core (TAG, cholesterol esters) + hydrophilic shell (phospholipids, free cholesterol) + apolipoproteins on the surface.

Classification (by density, which is inversely related to fat content)

LipoproteinMade inCarries mainlyKey ApoFunction
ChylomicronsIntestineDietary TAG (exogenous)ApoB-48, ApoC-II, ApoEDelivers dietary fat to tissues
VLDLLiverEndogenous TAGApoB-100, ApoC-II, ApoEDelivers liver-made TAG to tissues
IDLFrom VLDLTAG + CholesterolApoB-100, ApoEIntermediate; taken up by liver or → LDL
LDLFrom IDLCholesterol esters (main)ApoB-100 onlyDelivers cholesterol to cells ("bad")
HDLLiver + IntestineCholesterol (picks up from tissues)ApoA-IReverse cholesterol transport ("good")

Functions of Key Apolipoproteins

ApolipoproteinFunction
ApoA-IActivates LCAT (Lecithin-Cholesterol AcylTransferase); major HDL protein; reverse cholesterol transport
ApoB-100Binds LDL receptor (receptor-mediated endocytosis)
ApoB-48Structural for chylomicrons (intestine makes only this truncated form)
ApoC-IIActivates Lipoprotein Lipase (LPL) → hydrolyzes TAG in chylomicrons and VLDL
ApoC-IIIInhibits LPL
ApoEMediates receptor-mediated uptake of remnants (chylomicron remnants, IDL) by liver

Lipoprotein Metabolism

Exogenous pathway (dietary fat): Intestine → Chylomicrons → lymph → blood → LPL (activated by ApoC-II) hydrolyzes TAG → tissues take up fatty acids → Chylomicron remnant → taken up by liver (via ApoE binding to LDL-related receptors)
Endogenous pathway (liver-made): Liver → VLDL → blood → LPL hydrolyzes TAG → IDL → either taken up by liver (ApoE) OR → LDL (after more TAG removal, IDL loses ApoE, retains ApoB-100)
LDL receptor pathway: LDL → binds LDL receptor (via ApoB-100) → receptor-mediated endocytosis → cholesterol released inside cell → inhibits HMG-CoA reductase (blocks cholesterol synthesis) + downregulates LDL receptors
Reverse cholesterol transport (HDL): HDL (ApoA-I) → picks up cholesterol from peripheral tissues → LCAT esterifies it → HDL delivers cholesterol esters to liver (via SR-B1 receptor) or transfers to VLDL/LDL (via CETP)

Lipoprotein (a) - Lp(a)

  • LDL-like particle with an extra protein: Apo(a) linked to ApoB-100 by disulfide bond
  • Apo(a) is structurally similar to plasminogen → competes with plasminogen → inhibits fibrinolysis
  • Result: Prothrombotic + proatherogenic (independent cardiovascular risk factor)
  • Levels are genetically determined (not much affected by diet or lifestyle)

11. FATTY LIVER

Definition

Accumulation of fat (mainly TAG) in hepatocytes > 5% of liver weight (steatosis). Seen on histology as fat droplets in cells.

Causes (mnemonic "ABCD of fatty liver")

  • Alcohol - #1 cause in developed countries
  • Besity (Obesity) - NAFLD (Non-Alcoholic Fatty Liver Disease)
  • Corticosteroids / Drugs (methotrexate, amiodarone, tamoxifen)
  • Diabetes mellitus type 2 / Dyslipidemia
  • Also: starvation, total parenteral nutrition, pregnancy (AFLP)

Mechanism of fatty liver in Alcoholism

  1. Alcohol → acetaldehyde → excess NADH (shifts NAD+/NADH ratio)
  2. Excess NADH inhibits gluconeogenesis and beta-oxidation
  3. OAA is diverted → malate; pyruvate → lactate
  4. Acetyl-CoA accumulates → increased fatty acid synthesis
  5. Decreased VLDL secretion (alcohol impairs apolipoprotein synthesis)
  6. Net result: fat accumulates in liver

12. CHOLESTEROL BIOSYNTHESIS & REGULATION

Synthesis overview

  • Site: liver primarily (also intestine, adrenal, gonads)
  • All carbons from acetyl-CoA
  • Requires NADPH and ATP

Key steps

Mevalonate pathway:
3 Acetyl-CoA → HMG-CoA (by HMG-CoA synthase in cytosol - different from mitochondrial one)
↓
HMG-CoA → Mevalonate [RATE-LIMITING STEP, by HMG-CoA reductase]
↓
Mevalonate → Isoprene units (IPP, DMAPP)
↓
6 Isoprene units → Squalene
↓
Squalene → Lanosterol → Cholesterol (many steps)
HMG-CoA reductase is the target of STATINS (e.g., atorvastatin, simvastatin).

Regulation of Cholesterol Synthesis

FactorEffect on HMG-CoA reductaseMechanism
Intracellular cholesterol ↑InhibitsDecreases transcription (via SREBP) and increases degradation of the enzyme
InsulinActivatesPromotes dephosphorylation (active form)
GlucagonInhibitsPromotes phosphorylation (inactive form)
StatinsCompetitive inhibitStructural analog of HMG-CoA → blocks active site
High cholesterol dietInhibitsAlso downregulates LDL receptors
SREBP (Sterol Regulatory Element Binding Protein): When cholesterol is low → SREBP is activated → goes to nucleus → increases transcription of HMG-CoA reductase AND LDL receptor gene.

Products Derived from Cholesterol

ProductDetails
Bile acids/saltsPrimary: cholic acid, chenodeoxycholic acid. Rate-limiting: cholesterol 7α-hydroxylase
Steroid hormonesGlucocorticoids (cortisol), mineralocorticoids (aldosterone), sex hormones (estrogen, testosterone, DHEA)
Vitamin DCholesterol → 7-dehydrocholesterol → UV light in skin → cholecalciferol (D3)
Cell membranesStructural component; regulates fluidity

13. BIOSYNTHESIS OF HEME

Overview

  • Main sites: liver and erythroid bone marrow (>85% in erythroid tissue)
  • Pathway spans both mitochondria and cytosol

Pathway (simplified)

In mitochondria (start):
  1. Succinyl-CoA + Glycineδ-ALA (δ-aminolevulinic acid)
    • Enzyme: ALA synthase (ALAS) - RATE-LIMITING STEP
    • Requires: Pyridoxal phosphate (PLP/Vit B6)
    • Two isoforms: ALAS1 (liver, all tissues), ALAS2 (erythroid only)
In cytosol: 2. 2 ALA → Porphobilinogen (PBG) - by ALA dehydratase (inhibited by lead) 3. 4 PBG → Hydroxymethylbilane → Uroporphyrinogen III 4. Uroporphyrinogen III → Coproporphyrinogen III
Back into mitochondria (end): 5. Coproporphyrinogen → Protoporphyrinogen IX → Protoporphyrin IX 6. Protoporphyrin IX + Fe²⁺ → Heme (by ferrochelatase - also inhibited by lead)

Regulation

  • Heme/Hemin inhibits ALAS1 (negative feedback) by:
    • Repressing ALAS1 gene transcription
    • Increasing ALAS1 mRNA degradation
    • Blocking import of ALAS1 into mitochondria
  • Drugs increase ALAS1 by depleting hepatic heme (via increased CYP enzyme synthesis)

Porphyrias (enzyme defects in heme synthesis)

PorphyriaEnzyme DefectKey Features
AIP (Acute Intermittent Porphyria)HMB synthaseAbdominal pain, neuropathy, NO skin symptoms; elevated ALA + PBG
PCT (Porphyria Cutanea Tarda)Uroporphyrinogen decarboxylaseBlistering skin photosensitivity (most common porphyria)
Lead poisoningInhibits ALA dehydratase AND ferrochelataseAnemia, abdominal pain, neuropathy, elevated ALA

14. BILIRUBIN METABOLISM & JAUNDICE

Formation

RBC breakdown (mainly in spleen macrophages) → hemoglobin → heme + globin
Heme → Biliverdin (by heme oxygenase; releases Fe²⁺ and CO)
Biliverdin → Bilirubin (by biliverdin reductase; requires NADPH)
~85% from RBC breakdown (~250-350 mg/day in adults); 15% from other heme proteins (myoglobin, CYPs)

Bilirubin Transport to Liver

  • Unconjugated bilirubin = insoluble in water, lipid-soluble, toxic to brain (kernicterus)
  • Travels in blood bound to albumin (cannot be filtered by kidney)
  • Enters hepatocyte via OATP transporters
  • Inside hepatocyte: bound to ligandin (Y protein)

Conjugation in Liver

  • Bilirubin + UDP-glucuronic acid → Bilirubin diglucuronide (conjugated bilirubin)
  • Enzyme: UDP-glucuronosyltransferase (UGT1A1)
  • Conjugated bilirubin = water-soluble, non-toxic, can be excreted in bile

Excretion

  • Conjugated bilirubin → bile → intestine
  • Intestinal bacteria convert it: bilirubin → urobilinogen
  • Urobilinogen fates:
    • Mostly → stercobilin (brown colour of feces)
    • Some reabsorbed → portal blood → liver (enterohepatic circulation) → small amount in urine as urobilinogen

Jaundice

Definition: Yellow discoloration of skin, sclera, mucous membranes when serum bilirubin >2.5-3 mg/dL (normal <1 mg/dL).
Three Types:
FeaturePre-hepatic (Hemolytic)Hepatic (Hepatocellular)Post-hepatic (Obstructive/Cholestatic)
CauseExcess RBC breakdownLiver diseaseBile duct obstruction
ExamplesHemolytic anemia, malaria, G6PD deficiencyHepatitis, cirrhosisGallstones, pancreatic cancer, cholangiocarcinoma
Bilirubin typeUnconjugated ↑↑Both ↑Conjugated ↑↑
Urine bilirubinAbsent (unconjugated can't pass)PresentPresent
Urine urobilinogenIncreasedVariableAbsent (no bilirubin reaches gut)
Fecal colorNormal/DarkPalePale/Clay-coloured (acholic)
PruritusNoVariableYes (bile salts in skin)
ALPNormalMild ↑Markedly ↑
Named syndromes:
  • Gilbert's syndrome: Mild ↓ UGT1A1 activity → mild unconjugated hyperbilirubinemia with fasting/stress. Benign. Most common hereditary cause.
  • Crigler-Najjar type I: Complete absence of UGT1A1 → severe unconjugated hyperbilirubinemia → kernicterus → fatal without liver transplant
  • Crigler-Najjar type II (Arias): Partial UGT1A1 deficiency → treatable with phenobarbital
  • Dubin-Johnson: Defective conjugated bilirubin secretion into bile (MRP2 transporter mutation) → conjugated hyperbilirubinemia, dark liver (black pigment), benign
  • Rotor syndrome: Similar to Dubin-Johnson but no dark pigment, different defect

QUICK SUMMARY MNEMONICS

Oncogene activation: PAINT (Point mutation, Amplification, Insertion, Non-disjunction/Translocation, Transcription factor dysregulation)
DNA Repair Disorders: NER→XP, MMR→HNPCC, BRCA→Hereditary breast/ovarian
Beta oxidation: OHAB cycle (Oxidation-Hydration-Another oxidation-Beta-ketothiolysis)
Lipoprotein mnemonic for order of density: "Cows (Chylomicron) Venture (VLDL) Into (IDL) Large (LDL) Herds (HDL)" - density increases left to right
Ketogenesis: Liver makes it, extrahepatic uses it; HMG-CoA synthase is rate-limiting; triggered by starvation/DM
Heme synthesis rate-limiting enzyme: ALA synthase (needs PLP/B6); inhibited by heme; lead blocks ALA dehydratase and ferrochelatase
Jaundice types: Pre-hepatic=unconjugated↑, dark urine absent; Post-hepatic=conjugated↑, pale stools, pruritus, dark urine
50S inhibitors: "Big MACE" - Macrolides (erythromycin), Amphenicols (chloramphenicol), Clindamycin, Everninomicins/Linezolid
30S inhibitors: Aminoglycosides, Tetracyclines, Spectinomycin

Good luck on your exam tomorrow! Start with the topics you find hardest - likely ketogenesis/lipoproteins and DNA repair - since those have the most detail. The mnemonics in this sheet are designed to help you reconstruct entire tables from single words during the exam.

Make a pdf of this

Reading File
Running Command

ls -la /tmp/workspace/ 2>/dev/null || mkdir -p /tmp/workspace && echo "created"

Running Command

mkdir -p /tmp/workspace/biochem-notes && cat > /tmp/workspace/biochem-notes/make_pdf.py << 'PYEOF' from reportlab.lib.pagesizes import A4 from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle from reportlab.lib.units import cm from reportlab.lib import colors from reportlab.platypus import (SimpleDocTemplate, Paragraph, Spacer, Table, TableStyle, HRFlowable, PageBreak, KeepTogether) from reportlab.lib.enums import TA_LEFT, TA_CENTER, TA_JUSTIFY from reportlab.platypus.flowables import HRFlowable output_path = "/tmp/workspace/biochem-notes/Biochemistry_Exam_Notes.pdf" doc = SimpleDocTemplate( output_path, pagesize=A4, leftMargin=1.8*cm, rightMargin=1.8*cm, topMargin=2*cm, bottomMargin=2*cm ) W = A4[0] - 3.6*cm # usable width # ── Styles ────────────────────────────────────────────────────────────────── styles = getSampleStyleSheet() TITLE_S = ParagraphStyle("title_s", parent=styles["Title"], fontSize=22, leading=28, textColor=colors.HexColor("#1a237e"), spaceAfter=4, alignment=TA_CENTER) SUBTITLE_S = ParagraphStyle("subtitle_s", parent=styles["Normal"], fontSize=10, textColor=colors.HexColor("#5c6bc0"), alignment=TA_CENTER, spaceAfter=12) H1 = ParagraphStyle("h1", parent=styles["Heading1"], fontSize=13, leading=16, textColor=colors.white, backColor=colors.HexColor("#1a237e"), spaceBefore=14, spaceAfter=4, leftIndent=-8, rightIndent=-8, borderPad=5) H2 = ParagraphStyle("h2", parent=styles["Heading2"], fontSize=11, leading=14, textColor=colors.HexColor("#1a237e"), spaceBefore=10, spaceAfter=3, borderPad=2) H3 = ParagraphStyle("h3", parent=styles["Heading3"], fontSize=10, leading=13, textColor=colors.HexColor("#283593"), spaceBefore=7, spaceAfter=2, fontName="Helvetica-Bold") BODY = ParagraphStyle("body", parent=styles["Normal"], fontSize=9, leading=13, spaceAfter=4, alignment=TA_JUSTIFY) BULLET = ParagraphStyle("bullet", parent=styles["Normal"], fontSize=9, leading=13, leftIndent=14, spaceAfter=2, bulletIndent=4) MNEMONIC = ParagraphStyle("mnemonic", parent=styles["Normal"], fontSize=9, leading=13, leftIndent=12, spaceAfter=4, backColor=colors.HexColor("#fff9c4"), borderPad=4, borderColor=colors.HexColor("#f9a825"), borderWidth=1) HIGHLIGHT = ParagraphStyle("highlight", parent=styles["Normal"], fontSize=9, leading=13, leftIndent=12, spaceAfter=4, backColor=colors.HexColor("#e3f2fd"), borderPad=4) CODE = ParagraphStyle("code", parent=styles["Code"], fontSize=8, leading=12, leftIndent=12, spaceAfter=4, backColor=colors.HexColor("#f5f5f5"), borderPad=4, fontName="Courier") # ── Helpers ────────────────────────────────────────────────────────────────── def h1(text): return Paragraph(f" {text}", H1) def h2(text): return Paragraph(text, H2) def h3(text): return Paragraph(text, H3) def p(text): return Paragraph(text, BODY) def b(text): return Paragraph(f"• {text}", BULLET) def mn(text): return Paragraph(f"<b>Mnemonic:</b> {text}", MNEMONIC) def hl(text): return Paragraph(text, HIGHLIGHT) def sp(h=6): return Spacer(1, h) def hr(): return HRFlowable(width="100%", thickness=0.5, color=colors.HexColor("#5c6bc0"), spaceAfter=4, spaceBefore=4) TH_BG = colors.HexColor("#283593") TH_FG = colors.white ALT_ROW = colors.HexColor("#e8eaf6") GRID = colors.HexColor("#9fa8da") def make_table(headers, rows, col_widths=None): data = [[Paragraph(f"<b><font color='white'>{h}</font></b>", ParagraphStyle("th", parent=BODY, fontSize=8, leading=11, alignment=TA_CENTER)) for h in headers]] for i, row in enumerate(rows): data.append([Paragraph(str(c), ParagraphStyle("td", parent=BODY, fontSize=8, leading=11)) for c in row]) style = TableStyle([ ("BACKGROUND", (0,0), (-1,0), TH_BG), ("ROWBACKGROUNDS", (0,1), (-1,-1), [colors.white, ALT_ROW]), ("GRID", (0,0), (-1,-1), 0.4, GRID), ("VALIGN", (0,0), (-1,-1), "TOP"), ("TOPPADDING", (0,0), (-1,-1), 4), ("BOTTOMPADDING", (0,0), (-1,-1), 4), ("LEFTPADDING", (0,0), (-1,-1), 5), ("RIGHTPADDING", (0,0), (-1,-1), 5), ]) t = Table(data, colWidths=col_widths, style=style, repeatRows=1) return t # ═══════════════════════════════════════════════════════════════════════════ # CONTENT # ═══════════════════════════════════════════════════════════════════════════ story = [] # ── Cover ── story += [ sp(20), Paragraph("BIOCHEMISTRY EXAM NOTES", TITLE_S), Paragraph("1st Year MBBS | All Topics | Exam Ready", SUBTITLE_S), Paragraph("Prepared for your exam — concise, complete, easy to memorize", ParagraphStyle("sub2", parent=BODY, alignment=TA_CENTER, textColor=colors.grey)), sp(10), HRFlowable(width="60%", thickness=2, color=colors.HexColor("#1a237e"), hAlign="CENTER"), sp(40), ] # ════════════════════════════════════════════════════════════════════════════ # SECTION 1: TUMOUR MARKERS & ONCOGENES # ════════════════════════════════════════════════════════════════════════════ story += [h1("1. TUMOUR MARKERS & ONCOGENES"), sp(4)] story += [h2("What is a Tumour Marker?"), sp(2)] story += [p("A substance (protein, hormone, enzyme, etc.) produced <b>by tumour cells or by the body in response to a tumour</b>, found in blood/urine/tissue. Used for: screening, diagnosis, monitoring treatment response, and detecting recurrence."), sp(4)] story += [make_table( ["Marker", "Cancer"], [ ["AFP (Alpha-fetoprotein)", "Hepatocellular carcinoma, testicular germ cell"], ["PSA (Prostate-specific antigen)", "Prostate cancer"], ["CEA (Carcinoembryonic antigen)", "Colorectal, lung, breast"], ["CA-125", "Ovarian cancer"], ["CA 19-9", "Pancreatic cancer"], ["hCG", "Choriocarcinoma, testicular cancer"], ["Calcitonin", "Medullary thyroid carcinoma"], ["Bence Jones protein", "Multiple myeloma"], ["S-100", "Melanoma"], ], col_widths=[W*0.35, W*0.65] ), sp(6)] story += [mn("AFP → 'A Father's Pain' (liver/testis); CEA → 'Colon Eats Away'; CA-125 → Ovarian (O = 125 shape); PSA → Prostate")] story += [hl("<b>Ideal tumour marker:</b> 100% sensitive and specific. None currently exists. Levels should correlate with tumour burden."), sp(4)] story += [h2("What is an Oncogene?"), sp(2)] story += [ b("<b>Proto-oncogene:</b> Normal gene regulating cell growth/division."), b("<b>Oncogene:</b> Mutated/overactivated proto-oncogene → uncontrolled proliferation. <b>Gain-of-function</b> — only ONE allele needs to be affected."), b("Acts like a <b>stuck accelerator</b> in a car."), b("<b>Tumour Suppressor Genes</b> (p53, Rb) = brakes. BOTH alleles must be lost."), sp(6), ] story += [h2("Mechanisms of Oncogene Activation"), sp(2)] story += [mn("PAINT: Point mutation | Amplification | Insertion | Non-disjunction/Translocation | Transcription dysregulation")] story += [make_table( ["Mechanism", "How", "Example"], [ ["Point mutation", "Single base change → constitutively active protein", "KRAS (codon 12/13/61) in pancreatic >95%, colon 40%"], ["Amplification", "Multiple gene copies → overexpression", "MYC in breast/prostate; MYCN in neuroblastoma"], ["Retroviral insertion", "Retrovirus inserts near proto-oncogene", "HIV, HTLV"], ["Translocation", "Chromosome rearrangement near active promoter", "BCR-ABL t(9;22) in CML; MYC-IgH t(8;14) Burkitt"], ], col_widths=[W*0.22, W*0.38, W*0.40] ), sp(4)] story += [hl("<b>KRAS key point:</b> Mutations lock RAS in GTP-bound (active) form → constitutive signalling even without growth factors.")] story += [h3("Oncogene categories:"), sp(2)] story += [make_table( ["Category", "Examples"], [ ["Growth factors", "SIS (PDGF)"], ["Growth factor receptors", "EGFR, HER2/neu"], ["Signal transducers", "RAS, RAF, ABL"], ["Transcription factors", "MYC, JUN, FOS"], ["Cell cycle regulators", "Cyclin D1"], ["Anti-apoptotic", "BCL-2"], ], col_widths=[W*0.4, W*0.6] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 2: LAC OPERON # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("2. LAC OPERON"), sp(4)] story += [h2("Concept"), sp(2)] story += [p("Model of <b>gene regulation in prokaryotes (E. coli)</b>. Controls lactose-metabolizing genes. Has two controls: <b>negative</b> (repressor) and <b>positive</b> (CAP/CRP)."), sp(4)] story += [h2("Structure"), sp(2)] story += [Paragraph("<font face='Courier'>[Promoter] — [Operator] — [lacZ] — [lacY] — [lacA]</font>", CODE), sp(2)] story += [make_table( ["Gene", "Product", "Function"], [ ["lacZ", "β-galactosidase", "Hydrolyzes lactose → glucose + galactose"], ["lacY", "Permease", "Transports lactose into cell"], ["lacA", "Transacetylase", "Acetylates β-galactosides (function unclear)"], ], col_widths=[W*0.15, W*0.3, W*0.55] ), sp(6)] story += [h2("Negative Control (Repressor System)"), sp(2)] story += [ b("Repressor protein (from lacI gene) binds operator → blocks transcription"), b("Lactose present → converted to <b>allolactose</b> (the inducer)"), b("Allolactose binds repressor → shape change → cannot bind operator → transcription ON"), mn('"Lactose unlocks the block"'), sp(4), ] story += [h2("Positive Control (CAP/CRP System)"), sp(2)] story += [ b("Glucose absent → cAMP rises"), b("cAMP binds CRP (CAP) → activates it"), b("cAMP-CRP complex binds promoter → enhances RNA polymerase binding → MORE transcription"), b("Glucose present → low cAMP → CRP inactive → low transcription even with lactose"), mn('"No glucose = more cAMP = max lactose gene expression" (catabolite repression)'), sp(4), ] story += [make_table( ["Glucose", "Lactose", "cAMP", "Repressor", "Transcription"], [ ["High", "Absent", "Low", "Active (bound)", "OFF"], ["High", "Present", "Low", "Inactive", "Low"], ["Low", "Absent", "High", "Active (bound)", "OFF"], ["Low ✓", "Present ✓", "High ✓", "Inactive ✓", "MAXIMUM ON ✓"], ], col_widths=[W*0.17, W*0.17, W*0.15, W*0.25, W*0.26] ), sp(4)] story += [hl("<b>Trp Operon contrast:</b> Tryptophan = COREPRESSOR that ACTIVATES the repressor → shuts off trp synthesis when Trp is abundant. Opposite to lac induction.")] # ════════════════════════════════════════════════════════════════════════════ # SECTION 3: INHIBITORS # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("3. INHIBITORS OF REPLICATION, TRANSCRIPTION & TRANSLATION"), sp(4)] story += [h2("A. Inhibitors of DNA Replication"), sp(2)] story += [make_table( ["Drug/Agent", "Mechanism"], [ ["Hydroxyurea", "Inhibits ribonucleotide reductase (blocks dNTP supply)"], ["Cytarabine (Ara-C)", "False nucleoside → chain termination"], ["Fluoroquinolones (ciprofloxacin)", "Inhibit bacterial DNA gyrase (Topoisomerase II)"], ["Camptothecin", "Inhibits Topoisomerase I"], ["Etoposide", "Inhibits Topoisomerase II"], ["Acyclovir / AZT", "Inhibit viral DNA polymerase / chain termination"], ["UV radiation", "Creates pyrimidine (TT) dimers"], ], col_widths=[W*0.38, W*0.62] ), sp(6)] story += [h2("B. Inhibitors of Transcription"), sp(2)] story += [make_table( ["Drug/Agent", "Mechanism"], [ ["Rifampicin", "Inhibits BACTERIAL RNA polymerase (β subunit) — used in TB"], ["Actinomycin D", "Intercalates in DNA → blocks RNA polymerase movement"], ["α-Amanitin (mushroom toxin)", "Inhibits eukaryotic RNA polymerase II (mRNA synthesis)"], ["Doxorubicin", "Intercalates in DNA → inhibits replication AND transcription"], ], col_widths=[W*0.35, W*0.65] ), sp(4)] story += [hl("<b>Exam tip:</b> Rifampicin = classic — inhibits PROKARYOTIC RNA polymerase only."), sp(6)] story += [h2("C. Inhibitors of Translation (Protein Synthesis)"), sp(2)] story += [p("Bacteria have <b>70S ribosomes</b> (50S + 30S subunits) — targeted selectively by antibiotics."), sp(4)] story += [h3("30S Inhibitors:"), sp(2)] story += [mn("AAT: Aminoglycosides, Tetracycline (+ Spectinomycin)")] story += [make_table( ["Drug", "Mechanism"], [ ["Aminoglycosides (Streptomycin, Gentamicin)", "Block 30S A site; cause misreading of mRNA"], ["Tetracycline", "Blocks aminoacyl-tRNA binding to 30S A site"], ], col_widths=[W*0.45, W*0.55] ), sp(6)] story += [h3("50S Inhibitors:"), sp(2)] story += [mn('"Big MACE": Macrolides | Amphenicols (Chloramphenicol) | Clindamycin | Everninomicins/Linezolid')] story += [make_table( ["Drug", "Mechanism"], [ ["Chloramphenicol", "Inhibits peptidyl transferase on 23S rRNA of 50S"], ["Erythromycin (macrolides)", "Blocks translocation on 50S"], ["Clindamycin/Lincomycin", "Block 50S translocation"], ["Linezolid", "Inhibits 50S — prevents 70S initiation complex"], ], col_widths=[W*0.38, W*0.62] ), sp(6)] story += [h3("Eukaryote-specific inhibitors:"), sp(2)] story += [make_table( ["Drug", "Target", "Notes"], [ ["Cycloheximide", "60S (eukaryotes only)", "Inhibits peptidyl transferase; NOT clinical"], ["Puromycin", "Both 70S and 80S", "Analog of tyrosinyl-tRNA; premature chain release"], ["Diphtheria toxin", "EF-2 (eukaryotes only)", "ADP-ribosylates EF-2 → stops translocation"], ["Ricin", "28S rRNA of 60S", "Cleaves single adenine from 28S rRNA"], ], col_widths=[W*0.28, W*0.32, W*0.40] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 4: POST-TRANSCRIPTIONAL & POST-TRANSLATIONAL MODIFICATIONS # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("4. POST-TRANSCRIPTIONAL & POST-TRANSLATIONAL MODIFICATIONS"), sp(4)] story += [h2("Post-Transcriptional Modifications (pre-mRNA → mature mRNA)"), sp(2)] story += [p("In eukaryotes, pre-mRNA (hnRNA) must be processed before leaving the nucleus. Three main modifications:"), sp(4)] story += [h3("1. 5' Capping"), sp(2)] story += [ b("A <b>7-methylguanosine (m7G) cap</b> is added to the 5' end"), b("Functions: protects from degradation, helps ribosome binding (translation initiation), aids nuclear export"), sp(4), ] story += [h3("2. 3' Polyadenylation"), sp(2)] story += [ b("A <b>poly-A tail</b> (100-250 adenine residues) added to the 3' end"), b("Signal: <b>AAUAAA</b> sequence just upstream of cleavage site"), b("Functions: mRNA stability (protects from exonucleases), export, translation efficiency"), sp(4), ] story += [h3("3. Splicing — Removal of Introns"), sp(2)] story += [ b("<b>Introns</b> (intervening) = removed | <b>Exons</b> (expressed) = kept and joined"), b("Done by the <b>spliceosome</b> (complex of snRNPs)"), b("Splice sites: intron starts with <b>GU</b>, ends with <b>AG</b> (GU-AG rule)"), b("<b>Alternative splicing</b> = one gene → multiple proteins (e.g., tropomyosin)"), mn('"I Got Excited" = Introns Gone, Exons stay'), sp(6), ] story += [h2("Post-Translational Modifications (PTMs)"), sp(2)] story += [mn("GPS-MUG: Glycosylation | Phosphorylation | Signal cleavage | Methylation | Ubiquitination | GPI anchor")] story += [make_table( ["Modification", "What happens", "Example / Clinical"], [ ["Glycosylation", "Sugar added (N-linked or O-linked)", "Antibodies, blood groups, cell surface"], ["Phosphorylation", "Phosphate added to Ser/Thr/Tyr by kinases", "Signal transduction, enzyme regulation"], ["Signal peptide cleavage", "N-terminal signal sequence removed", "Targets protein to ER/membrane"], ["Methylation", "Methyl groups on Lys/Arg", "Histone modification, gene regulation"], ["Ubiquitination", "Ubiquitin tags protein", "Marks for proteasomal degradation"], ["GPI anchor", "Glycophosphatidylinositol links protein to membrane", "CD55, CD59 — absent in PNH"], ["Hydroxylation", "Pro & Lys in collagen hydroxylated", "Requires Vit C — deficiency = SCURVY"], ["Carboxylation", "Glu → Gla", "Requires Vit K — clotting factors II, VII, IX, X"], ["Proteolytic cleavage", "Zymogen activation", "Pepsinogen→Pepsin; Proinsulin→Insulin"], ["Disulfide bonds", "Cys-Cys bond in ER", "Stabilizes proteins (e.g., insulin, IgG)"], ], col_widths=[W*0.25, W*0.35, W*0.40] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 5: MUTATION # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("5. MUTATION & TYPES OF MUTATION"), sp(4)] story += [h2("Definition"), sp(2)] story += [p("A <b>permanent change in DNA sequence</b>. Can be heritable (germline) or somatic (acquired)."), sp(4)] story += [h2("A. Point Mutations (Single base affected)"), sp(2)] story += [h3("Types of Substitution:"), sp(2)] story += [ b("<b>Transition:</b> Purine ↔ Purine (A↔G) OR Pyrimidine ↔ Pyrimidine (C↔T) — same type"), b("<b>Transversion:</b> Purine ↔ Pyrimidine — different type (e.g., A→T)"), sp(4), ] story += [h3("Effects on protein:"), sp(2)] story += [make_table( ["Type", "What happens", "Example"], [ ["Silent/Synonymous", "Codon changes but SAME amino acid (code degeneracy)", "GAA→GAG (both Glu)"], ["Missense", "Codon changes → DIFFERENT amino acid", "Sickle cell: GAG→GTG (Glu→Val)"], ["Nonsense", "Codon changes → STOP codon → truncated protein", "CGA→TGA"], ["Frameshift", "Indel of non-multiple-of-3 bases → frame shifts", "Almost always deleterious"], ], col_widths=[W*0.25, W*0.45, W*0.30] ), sp(4)] story += [hl("<b>Sickle cell disease exam classic:</b> A→T TRANSVERSION at codon 6 of β-globin gene. GAG (Glu) → GTG (Val). One missense mutation causes the entire disease."), sp(4)] story += [h2("B. Insertions & Deletions (Indels)"), sp(2)] story += [ b("NOT a multiple of 3 → <b>frameshift mutation</b> (severe)"), b("Multiple of 3 → in-frame insertion/deletion (protein may retain partial function)"), sp(6), ] story += [h2("C. Trinucleotide Repeat Expansions"), sp(2)] story += [make_table( ["Disease", "Repeat", "Gene"], [ ["Huntington's disease", "CAG", "HTT"], ["Fragile X syndrome", "CGG", "FMR1"], ["Myotonic dystrophy", "CTG", "DMPK"], ], col_widths=[W*0.4, W*0.2, W*0.4] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 6: DNA REPAIR # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("6. DNA REPAIR MECHANISMS & GENETIC DISORDERS"), sp(4)] story += [mn("BEN-MRD: Base Excision | Excision (Nucleotide) | Non-homologous End Joining | Mismatch Repair | Recombination | Direct repair")] story += [h2("1. Base Excision Repair (BER)"), sp(2)] story += [ b("Fixes <b>small, non-bulky damage</b>: oxidized bases, alkylated bases, deaminated cytosine (→ uracil)"), b("Steps: DNA glycosylase removes base → AP endonuclease cuts backbone → DNA pol fills gap → ligase seals"), sp(6), ] story += [h2("2. Nucleotide Excision Repair (NER)"), sp(2)] story += [ b("Fixes <b>bulky helix-distorting lesions</b>: UV-induced pyrimidine dimers, chemical adducts"), b("Removes ~25-30 nucleotide patch around lesion → DNA pol fills → ligase seals"), b("<b>Defect → Xeroderma Pigmentosum (XP):</b> extreme UV sensitivity, skin cancers early in life, neurological defects"), sp(6), ] story += [h2("3. Mismatch Repair (MMR)"), sp(2)] story += [ b("Fixes <b>replication errors</b>: mismatched base pairs that escaped proofreading"), b("Uses methylation to distinguish template (methylated) from new daughter strand"), b("Proteins: MutS (recognizes) → MutL → MutH (cuts unmethylated strand) in E.coli"), b("Human homologs: <b>MSH2, MLH1</b>"), b("Reduces error rate: 1 in 10<super>7</super> → 1 in 10<super>9</super>"), b("<b>Defect → HNPCC/Lynch Syndrome:</b> colorectal cancer + microsatellite instability"), sp(6), ] story += [h2("4. Double-Strand Break Repair"), sp(2)] story += [make_table( ["Type", "Mechanism", "When active", "Accuracy"], [ ["Homologous Recombination (HR)", "Uses sister chromatid as template; BRCA1/2 involved", "S/G2 phase", "Accurate"], ["Non-Homologous End Joining (NHEJ)", "Rejoins broken ends directly", "All cell cycle phases", "Error-prone"], ], col_widths=[W*0.28, W*0.38, W*0.18, W*0.16] ), sp(4)] story += [hl("<b>BRCA1/BRCA2 mutations:</b> Defective HR → hereditary breast and ovarian cancer syndrome"), sp(6)] story += [h2("5. Direct Repair"), sp(2)] story += [ b("<b>Photolyase:</b> repairs pyrimidine dimers using light energy (mainly bacteria/plants)"), b("<b>MGMT (O6-methylguanine methyltransferase):</b> removes alkyl groups from O6-guanine directly"), sp(6), ] story += [h2("Summary Table — Repair Defects"), sp(2)] story += [make_table( ["Repair Defect", "Disease", "Key Features"], [ ["NER", "Xeroderma Pigmentosum", "UV sensitivity, early skin cancers, neurological defects"], ["MMR", "HNPCC/Lynch Syndrome", "Colon cancer, microsatellite instability"], ["HR (BRCA1/2)", "Hereditary Breast/Ovarian Cancer", "Early-onset breast & ovarian cancer"], ["NER (partial)", "Cockayne Syndrome", "Photosensitivity, premature aging, NO cancer"], ["NER+NHEJ", "Trichothiodystrophy", "Brittle hair, photosensitivity"], ], col_widths=[W*0.20, W*0.30, W*0.50] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 7: BETA / ALPHA / OMEGA OXIDATION # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("7. BETA, ALPHA & OMEGA OXIDATION"), sp(4)] story += [h2("Beta Oxidation — Main Pathway"), sp(2)] story += [ b("Site: <b>Mitochondria</b>"), b("Degradation: 2 carbons removed at a time as <b>acetyl-CoA</b>"), sp(4), ] story += [h3("Entry into mitochondria — Carnitine Shuttle:"), sp(2)] story += [ b("FA + CoA + ATP → Fatty acyl-CoA (by acyl-CoA synthetase/thiokinase)"), b("CPT-I (outer membrane): rate-limiting, regulated — transfers acyl to carnitine"), b("Carnitine-acylcarnitine translocase: moves acylcarnitine across inner membrane"), b("CPT-II (inner membrane): regenerates fatty acyl-CoA inside"), hl("<b>CPT-I is inhibited by malonyl-CoA</b> — prevents simultaneous synthesis + breakdown"), sp(4), ] story += [h3("The 4-step Beta Oxidation Cycle (OHAB):"), sp(2)] story += [mn("OHAB: Oxidation | Hydration | Another oxidation | Beta-ketothiolysis")] story += [make_table( ["Step", "Reaction", "Product", "Coenzyme"], [ ["1. Oxidation", "Acyl-CoA → trans-Δ2-enoyl-CoA", "FADH2", "FAD"], ["2. Hydration", "→ L-3-hydroxyacyl-CoA", "—", "H2O"], ["3. Oxidation", "→ 3-ketoacyl-CoA", "NADH", "NAD+"], ["4. Thiolysis", "→ Acetyl-CoA + shorter acyl-CoA (2C less)", "Acetyl-CoA", "CoA"], ], col_widths=[W*0.22, W*0.38, W*0.18, W*0.22] ), sp(4)] story += [hl("<b>Palmitate (16C) energy yield:</b> 7 cycles → 8 acetyl-CoA + 7 FADH2 + 7 NADH → ~106 net ATP")] story += [h3("Special cases:"), sp(2)] story += [ b("<b>Odd-chain fatty acids:</b> Final product = propionyl-CoA → succinyl-CoA (requires Biotin + Vit B12)"), b("<b>Unsaturated FAs:</b> Need extra isomerase/reductase → slightly less ATP"), sp(6), ] story += [h2("Alpha Oxidation"), sp(2)] story += [ b("Site: <b>Peroxisomes</b>"), b("Removes ONE carbon (as CO2) from the alpha (2nd) carbon"), b("Important for <b>branched-chain FAs</b> (e.g., phytanic acid from plant food)"), b("<b>Defect → Refsum disease:</b> phytanic acid accumulates → peripheral neuropathy, ataxia, retinitis pigmentosa"), sp(6), ] story += [h2("Omega Oxidation"), sp(2)] story += [ b("Site: <b>Endoplasmic reticulum</b> (microsomes)"), b("Oxidation at the omega (last methyl) end → produces <b>dicarboxylic acids</b>"), b("Minor pathway; important when beta-oxidation is impaired"), b("Dicarboxylic acids found in urine = diagnostic clue for fatty acid oxidation disorders"), sp(4), ] # ════════════════════════════════════════════════════════════════════════════ # SECTION 8: FATTY ACID SYNTHESIS & NADPH # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("8. FATTY ACID SYNTHESIS & REGULATION"), sp(4)] story += [h2("Key Features (contrast with Beta Oxidation)"), sp(2)] story += [make_table( ["Feature", "Fatty Acid Synthesis", "Beta Oxidation"], [ ["Site", "Cytosol", "Mitochondria"], ["Coenzyme", "NADPH (reducing)", "NAD+, FAD (oxidizing)"], ["Acetyl-CoA source", "Via citrate shuttle from mitochondria", "Direct in mitochondria"], ["Product", "Palmitate (16:0)", "Acetyl-CoA"], ], col_widths=[W*0.25, W*0.38, W*0.37] ), sp(6)] story += [h2("Step 1: COMMITTED Rate-Limiting Step"), sp(2)] story += [hl("<b>Acetyl-CoA + CO2 + ATP → Malonyl-CoA</b> (by Acetyl-CoA Carboxylase / ACC) — requires BIOTIN"), sp(4)] story += [h2("Step 2: Palmitate on Fatty Acid Synthase (FAS)"), sp(2)] story += [ b("FAS = multifunctional enzyme (one large polypeptide in animals, 7 enzymatic activities)"), b("Prosthetic group: <b>ACP (Acyl Carrier Protein)</b> — uses <b>pantothenic acid (Vit B5)</b>"), b("Each elongation cycle: adds 2C from malonyl-CoA, uses 2 NADPH, releases CO2"), b("7 cycles → <b>Palmitate (16C)</b>"), sp(4), ] story += [hl("<b>Overall:</b> 8 Acetyl-CoA + 7 ATP + 14 NADPH → Palmitate + 8 CoA + 7 ADP + 14 NADP+"), sp(6)] story += [h2("Regulation of Fatty Acid Synthesis (ACC is key)"), sp(2)] story += [make_table( ["Factor", "Effect on ACC", "Net effect on FA synthesis"], [ ["Citrate (high energy signal)", "Allosteric ACTIVATION", "↑ Synthesis"], ["Palmitoyl-CoA (product)", "Allosteric INHIBITION", "↓ Synthesis (feedback)"], ["Malonyl-CoA", "—", "Inhibits CPT-I → prevents beta-oxidation"], ["Insulin", "Activates (dephosphorylation)", "↑ Synthesis"], ["Glucagon/Epinephrine", "Inhibits (phosphorylation via PKA)", "↓ Synthesis"], ["AMP-kinase (AMPK)", "Phosphorylates → inhibits", "↓ Synthesis (low energy state)"], ], col_widths=[W*0.30, W*0.35, W*0.35] ), sp(6)] story += [h2("Sources of NADPH"), sp(2)] story += [make_table( ["Source", "Pathway", "Note"], [ ["Pentose Phosphate Pathway (PPP)", "G6PD → NADPH (x2 per glucose)", "MAJOR SOURCE — G6PD deficiency → hemolytic anemia"], ["Malic enzyme", "Malate → Pyruvate + CO2 + NADPH", "OAA from citrate cleavage → malate → pyruvate"], ["Isocitrate dehydrogenase (cytosolic)", "Isocitrate → α-ketoglutarate", "Minor"], ["Folate pathway (MTHFR)", "One-carbon metabolism", "Minor"], ], col_widths=[W*0.33, W*0.37, W*0.30] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 9: KETOGENESIS # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("9. KETOGENESIS"), sp(4)] story += [h2("Where & When"), sp(2)] story += [ b("Site: <b>Liver mitochondria</b> (ONLY)"), b("Liver <b>PRODUCES</b> ketone bodies; liver <b>CANNOT USE</b> them (lacks succinyl-CoA transferase/thiophorase)"), b("<b>Extrahepatic tissues</b> (brain, heart, kidney, muscle) USE ketone bodies"), sp(4), ] story += [h2("The Three Ketone Bodies"), sp(2)] story += [make_table( ["Ketone Body", "Notes"], [ ["Acetoacetate", "First formed; the 'true' ketone"], ["β-Hydroxybutyrate", "Reduced form (NADH-dependent); major form in blood during ketosis; NOT technically a ketone"], ["Acetone", "Spontaneous decarboxylation of acetoacetate; exhaled → FRUITY BREATH (diagnostic!)"], ], col_widths=[W*0.35, W*0.65] ), sp(6)] story += [h2("Pathway of Ketogenesis"), sp(2)] story += [Paragraph( """2 Acetyl-CoA → Acetoacetyl-CoA (thiolase)<br/> + Acetyl-CoA → HMG-CoA (HMG-CoA synthase) ← RATE-LIMITING STEP<br/> HMG-CoA → Acetoacetate + Acetyl-CoA (HMG-CoA lyase)<br/> Acetoacetate ⇌ β-Hydroxybutyrate (β-hydroxybutyrate dehydrogenase; needs NADH)<br/> Acetoacetate → Acetone (spontaneous decarboxylation)""", CODE), sp(4)] story += [hl("<b>Note:</b> HMG-CoA synthase in MITOCHONDRIA (ketogenesis) is different from HMG-CoA synthase in CYTOSOL (cholesterol synthesis)"), sp(6)] story += [h2("Triggers for Ketogenesis"), sp(2)] story += [make_table( ["Condition", "Mechanism"], [ ["Starvation/Fasting", "Low glucose → low insulin → lipolysis ↑ → high acetyl-CoA. OAA used for gluconeogenesis → can't enter TCA"], ["Diabetes Mellitus (Type 1)", "No insulin → uncontrolled lipolysis → massive acetyl-CoA. Can cause DIABETIC KETOACIDOSIS (DKA)"], ["High-fat, low-carb diet", "Same mechanism as starvation, milder"], ], col_widths=[W*0.30, W*0.70] ), sp(6)] story += [h2("Regulation of Ketogenesis"), sp(2)] story += [ b("<b>Insulin:</b> inhibits ketogenesis (inhibits lipolysis; activates ACC → malonyl-CoA → blocks CPT-I)"), b("<b>Glucagon:</b> promotes ketogenesis (promotes lipolysis)"), b("Rate-limiting enzyme: <b>HMG-CoA synthase</b> (mitochondrial)"), sp(6), ] story += [h2("Utilization in Extrahepatic Tissues"), sp(2)] story += [Paragraph( "β-Hydroxybutyrate → Acetoacetate (β-hydroxybutyrate dehydrogenase)<br/>Acetoacetate + Succinyl-CoA → Acetoacetyl-CoA + Succinate (THIOPHORASE — absent in liver!)<br/>Acetoacetyl-CoA → 2 Acetyl-CoA → TCA cycle → ATP", CODE), sp(4)] story += [hl("<b>Brain adaptation:</b> Uses glucose normally, but switches to ketone bodies after 4+ days of fasting (provides 60-70% of brain fuel in prolonged starvation).")] # ════════════════════════════════════════════════════════════════════════════ # SECTION 10: LIPOPROTEINS # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("10. LIPOPROTEINS"), sp(4)] story += [h2("Structure"), sp(2)] story += [p("Lipoprotein = hydrophobic core (TAG, cholesterol esters) + hydrophilic shell (phospholipids, free cholesterol) + <b>apolipoproteins</b> on surface."), sp(4)] story += [h2("Classification"), sp(2)] story += [mn("Cows Venture Into Large Herds: Chylomicron | VLDL | IDL | LDL | HDL (density increases ↑, size decreases ↓)")] story += [make_table( ["Lipoprotein", "Made in", "Carries mainly", "Key Apo", "Function"], [ ["Chylomicrons", "Intestine", "Dietary TAG (exogenous)", "ApoB-48, ApoC-II, ApoE", "Delivers dietary fat to tissues"], ["VLDL", "Liver", "Endogenous TAG", "ApoB-100, ApoC-II, ApoE", "Delivers liver-made TAG to tissues"], ["IDL", "From VLDL", "TAG + Cholesterol", "ApoB-100, ApoE", "Intermediate; → liver or LDL"], ["LDL", "From IDL", "Cholesterol esters (mainly)", "ApoB-100 ONLY", "Delivers cholesterol to cells ('bad')"], ["HDL", "Liver + Intestine", "Picks up cholesterol", "ApoA-I", "Reverse cholesterol transport ('good')"], ], col_widths=[W*0.16, W*0.14, W*0.20, W*0.22, W*0.28] ), sp(6)] story += [h2("Functions of Key Apolipoproteins"), sp(2)] story += [make_table( ["Apolipoprotein", "Function"], [ ["ApoA-I", "Activates LCAT (Lecithin-Cholesterol AcylTransferase); major HDL protein; reverse cholesterol transport"], ["ApoB-100", "Binds LDL receptor → receptor-mediated endocytosis"], ["ApoB-48", "Structural for chylomicrons (intestinal truncated form)"], ["ApoC-II", "Activates Lipoprotein Lipase (LPL) → hydrolyzes TAG in chylomicrons/VLDL"], ["ApoC-III", "Inhibits LPL"], ["ApoE", "Mediates receptor uptake of chylomicron remnants & IDL by liver"], ], col_widths=[W*0.20, W*0.80] ), sp(6)] story += [h2("Lipoprotein Metabolism"), sp(2)] story += [h3("Exogenous pathway (dietary fat):"), sp(2)] story += [ b("Intestine → Chylomicrons → lymph → blood → LPL (activated by ApoC-II) hydrolyzes TAG"), b("Tissues take up fatty acids → Chylomicron remnant → liver via ApoE binding"), sp(4), ] story += [h3("Endogenous pathway (liver-made):"), sp(2)] story += [ b("Liver → VLDL → LPL hydrolyzes TAG → IDL → either liver (ApoE) OR → LDL (loses ApoE, keeps ApoB-100)"), sp(4), ] story += [h3("LDL receptor pathway:"), sp(2)] story += [ b("LDL → binds LDL receptor via ApoB-100 → receptor-mediated endocytosis"), b("Cholesterol released inside cell → inhibits HMG-CoA reductase + downregulates LDL receptors (feedback)"), sp(4), ] story += [h3("Reverse cholesterol transport (HDL):"), sp(2)] story += [ b("HDL (ApoA-I) → picks up cholesterol from peripheral tissues → LCAT esterifies it"), b("HDL delivers cholesterol esters to liver (SR-B1 receptor) or transfers to VLDL/LDL via CETP"), sp(6), ] story += [h2("Lipoprotein (a) — Lp(a)"), sp(2)] story += [ b("LDL-like particle with extra protein: <b>Apo(a)</b> linked to ApoB-100 by disulfide bond"), b("Apo(a) structurally similar to <b>plasminogen</b> → competes → inhibits fibrinolysis"), b("Result: <b>Prothrombotic + proatherogenic</b> — independent cardiovascular risk factor"), b("Levels are <b>genetically determined</b> (not much affected by diet/lifestyle)"), sp(4), ] # ════════════════════════════════════════════════════════════════════════════ # SECTION 11: FATTY LIVER # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("11. FATTY LIVER"), sp(4)] story += [h2("Definition"), sp(2)] story += [p("Accumulation of fat (mainly TAG) in hepatocytes <b>>5% of liver weight</b> (steatosis). Seen histologically as fat droplets in cells."), sp(4)] story += [h2("Causes"), sp(2)] story += [mn("ABCD: Alcohol | Besity (Obesity/NAFLD) | Corticosteroids/drugs | Diabetes type 2")] story += [make_table( ["Cause", "Notes"], [ ["Alcohol", "#1 cause in developed countries"], ["Obesity (NAFLD/NASH)", "Non-alcoholic fatty liver disease; associated with insulin resistance"], ["Drugs", "Methotrexate, amiodarone, tamoxifen, corticosteroids"], ["Diabetes mellitus type 2", "Insulin resistance → increased lipolysis → hepatic fat"], ["Starvation/TPN", "Reduced apolipoprotein synthesis → decreased VLDL secretion"], ["Pregnancy (AFLP)", "Acute Fatty Liver of Pregnancy — rare, serious"], ], col_widths=[W*0.30, W*0.70] ), sp(6)] story += [h2("Mechanism in Alcoholism"), sp(2)] story += [ b("Alcohol → acetaldehyde → excess <b>NADH</b> (shifts NAD+/NADH ratio)"), b("Excess NADH inhibits gluconeogenesis and <b>beta-oxidation</b>"), b("OAA → malate; pyruvate → lactate (lactic acidosis)"), b("Acetyl-CoA accumulates → <b>increased fatty acid synthesis</b>"), b("Acetaldehyde impairs apolipoprotein synthesis → <b>decreased VLDL secretion</b>"), b("<b>Net: fat accumulates in liver</b>"), sp(4), ] # ════════════════════════════════════════════════════════════════════════════ # SECTION 12: CHOLESTEROL BIOSYNTHESIS # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("12. CHOLESTEROL BIOSYNTHESIS & REGULATION"), sp(4)] story += [h2("Overview"), sp(2)] story += [ b("Site: <b>Liver</b> primarily (also intestine, adrenal, gonads)"), b("All carbons from <b>Acetyl-CoA</b>; requires NADPH and ATP"), sp(4), ] story += [h2("Mevalonate Pathway — Key Steps"), sp(2)] story += [Paragraph( "3 Acetyl-CoA → HMG-CoA (cytosolic HMG-CoA synthase)<br/>" "↓<br/>" "<b>HMG-CoA → Mevalonate</b> [by HMG-CoA REDUCTASE — RATE-LIMITING STEP] ← STATINS target here<br/>" "↓<br/>" "Mevalonate → Isoprene units (IPP, DMAPP)<br/>" "↓<br/>" "6 Isoprene units → Squalene → Lanosterol → Cholesterol", CODE), sp(6)] story += [h2("Regulation of HMG-CoA Reductase"), sp(2)] story += [make_table( ["Factor", "Effect", "Mechanism"], [ ["Intracellular cholesterol ↑", "Inhibits", "Decreases transcription (via SREBP); increases enzyme degradation"], ["Insulin", "Activates", "Dephosphorylation → active form"], ["Glucagon", "Inhibits", "Phosphorylation → inactive form"], ["Statins", "Competitive inhibition", "Structural analog of HMG-CoA; competitive inhibitor"], ], col_widths=[W*0.28, W*0.18, W*0.54] ), sp(4)] story += [hl("<b>SREBP</b> (Sterol Regulatory Element Binding Protein): When cholesterol is low → SREBP activated → increases transcription of HMG-CoA reductase AND LDL receptor genes simultaneously."), sp(6)] story += [h2("Products Derived from Cholesterol"), sp(2)] story += [make_table( ["Product", "Details"], [ ["Bile acids", "Primary: cholic acid, chenodeoxycholic acid. Rate-limiting enzyme: cholesterol 7α-hydroxylase"], ["Steroid hormones", "Glucocorticoids (cortisol), mineralocorticoids (aldosterone), sex hormones (testosterone, estrogen, DHEA)"], ["Vitamin D3", "Cholesterol → 7-dehydrocholesterol → UV in skin → cholecalciferol (D3) → kidney/liver activation"], ["Cell membranes", "Structural component; regulates membrane fluidity"], ], col_widths=[W*0.25, W*0.75] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 13: HEME BIOSYNTHESIS # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("13. BIOSYNTHESIS OF HEME"), sp(4)] story += [h2("Overview"), sp(2)] story += [ b("Main sites: <b>Liver</b> and <b>Erythroid bone marrow</b> (>85% in erythroid tissue)"), b("Pathway spans <b>mitochondria AND cytosol</b>"), b("Mature RBCs lack mitochondria → CANNOT synthesize heme"), sp(4), ] story += [h2("Pathway"), sp(2)] story += [Paragraph( "<b>IN MITOCHONDRIA:</b><br/>" "Succinyl-CoA + Glycine → δ-ALA (by ALA synthase, needs PLP/B6) ← RATE-LIMITING STEP<br/>" "<b>IN CYTOSOL:</b><br/>" "2 ALA → Porphobilinogen / PBG (by ALA dehydratase) ← Inhibited by LEAD<br/>" "4 PBG → Hydroxymethylbilane → Uroporphyrinogen III → Coproporphyrinogen III<br/>" "<b>BACK TO MITOCHONDRIA:</b><br/>" "Coproporphyrinogen → Protoporphyrinogen IX → Protoporphyrin IX<br/>" "Protoporphyrin IX + Fe²⁺ → <b>HEME</b> (by ferrochelatase) ← Also inhibited by LEAD", CODE), sp(6)] story += [h2("Regulation of ALA Synthase (ALAS1)"), sp(2)] story += [ b("Heme/Hemin (excess) → inhibits ALAS1 (negative feedback) by:"), b("1) Repressing ALAS1 gene transcription", ), b("2) Increasing ALAS1 mRNA degradation"), b("3) Blocking import of ALAS1 into mitochondria"), b("Drugs (e.g., barbiturates, griseofulvin) → increase CYP synthesis → consume heme → reduce free heme → INCREASE ALAS1"), sp(6), ] story += [h2("Porphyrias — Key Enzyme Defects"), sp(2)] story += [make_table( ["Porphyria", "Deficient Enzyme", "Key Features"], [ ["AIP (Acute Intermittent Porphyria)", "HMB synthase (PBG deaminase)", "Abdominal pain, neuropathy, NO skin involvement; elevated ALA + PBG in urine"], ["PCT (Porphyria Cutanea Tarda)", "Uroporphyrinogen decarboxylase", "Blistering skin photosensitivity (most common porphyria); no neurological symptoms"], ["Lead poisoning", "Inhibits ALA dehydratase + ferrochelatase", "Anemia (microcytic), abdominal pain, neuropathy; elevated ALA"], ], col_widths=[W*0.28, W*0.30, W*0.42] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # SECTION 14: BILIRUBIN METABOLISM & JAUNDICE # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("14. BILIRUBIN METABOLISM & JAUNDICE"), sp(4)] story += [h2("Formation"), sp(2)] story += [Paragraph( "RBC breakdown (mainly spleen macrophages) → Hb → Heme + Globin<br/>" "Heme → Biliverdin (by heme oxygenase; releases Fe²⁺ and CO)<br/>" "Biliverdin → Bilirubin (by biliverdin reductase; requires NADPH)<br/>" "~85% from RBC; 15% from myoglobin, CYPs, etc. (~250-350 mg/day in adults)", CODE), sp(6)] story += [h2("Transport to Liver"), sp(2)] story += [ b("Unconjugated bilirubin = <b>water-insoluble, lipid-soluble, TOXIC</b> to brain (kernicterus)"), b("Travels in blood <b>bound to albumin</b> — cannot be filtered by kidney → no urinary bilirubin"), b("Enters hepatocyte via OATP transporters; binds <b>ligandin (Y protein)</b> inside"), sp(6), ] story += [h2("Conjugation in Liver"), sp(2)] story += [ b("Bilirubin + UDP-glucuronic acid → <b>Bilirubin diglucuronide</b> (conjugated bilirubin)"), b("Enzyme: <b>UDP-glucuronosyltransferase (UGT1A1)</b>"), b("Conjugated bilirubin = <b>water-soluble, non-toxic</b>, excreted in bile"), sp(6), ] story += [h2("Excretion & Enterohepatic Circulation"), sp(2)] story += [ b("Conjugated bilirubin → bile → intestine → bacteria convert to <b>urobilinogen</b>"), b("Most urobilinogen → <b>stercobilin</b> (brown color of feces)"), b("Some urobilinogen reabsorbed → liver (enterohepatic circulation) → small amount in urine"), sp(6), ] story += [h2("Jaundice"), sp(2)] story += [p("<b>Definition:</b> Yellow discoloration of skin/sclera when serum bilirubin >2.5-3 mg/dL (normal <1 mg/dL)."), sp(4)] story += [make_table( ["Feature", "Pre-hepatic (Hemolytic)", "Hepatic", "Post-hepatic (Obstructive)"], [ ["Cause", "Excess RBC breakdown", "Hepatitis, cirrhosis", "Gallstones, pancreatic cancer"], ["Bilirubin", "Unconjugated ↑↑", "Both ↑", "Conjugated ↑↑"], ["Urine bilirubin", "ABSENT", "Present", "Present"], ["Urine urobilinogen", "Increased", "Variable", "ABSENT"], ["Fecal color", "Normal/Dark", "Pale", "PALE/Clay-coloured"], ["Pruritus", "No", "Variable", "YES (bile salts)"], ["ALP", "Normal", "Mild ↑", "Markedly ↑↑"], ], col_widths=[W*0.22, W*0.26, W*0.26, W*0.26] ), sp(6)] story += [h2("Named Syndromes"), sp(2)] story += [make_table( ["Syndrome", "Defect", "Bilirubin type", "Key feature"], [ ["Gilbert's syndrome", "Mild ↓ UGT1A1", "Unconjugated ↑ (mild)", "Most common hereditary; benign; triggered by fasting/stress"], ["Crigler-Najjar Type I", "Complete UGT1A1 absence", "Unconjugated ↑↑ (severe)", "Kernicterus → fatal without liver transplant"], ["Crigler-Najjar Type II (Arias)", "Partial UGT1A1 deficiency", "Unconjugated ↑ (moderate)", "Treatable with phenobarbital"], ["Dubin-Johnson", "MRP2 transporter mutation (bile secretion defect)", "Conjugated ↑", "Benign; dark liver on biopsy (black pigment)"], ["Rotor syndrome", "OATP1B1/1B3 deficiency", "Conjugated ↑", "Similar to Dubin-Johnson but NO dark pigment"], ], col_widths=[W*0.22, W*0.28, W*0.20, W*0.30] ), sp(4)] # ════════════════════════════════════════════════════════════════════════════ # QUICK SUMMARY & MNEMONICS PAGE # ════════════════════════════════════════════════════════════════════════════ story += [PageBreak(), h1("QUICK SUMMARY & MNEMONICS"), sp(4)] story += [h2("Master Mnemonic Sheet"), sp(4)] mnemonics = [ ("Oncogene activation", "PAINT: Point mutation | Amplification | Insertion | Non-disjunction/Translocation | Transcription factor"), ("Tumour markers", "AFP=liver/testis | CEA=colon | CA-125=ovary | CA19-9=pancreas | PSA=prostate | Calcitonin=medullary thyroid"), ("DNA Repair → Disease", "NER→XP | MMR→HNPCC/Lynch | BRCA→Hereditary breast/ovarian"), ("Beta oxidation cycle", "OHAB: Oxidation (FAD) | Hydration | Another oxidation (NAD) | Beta-ketothiolysis"), ("30S antibiotic inhibitors", "AAT: Aminoglycosides, Aminoglycosides, Tetracycline"), ("50S antibiotic inhibitors", "Big MACE: Macrolides, Amphenicols (chloramphenicol), Clindamycin, Everninomicins/Linezolid"), ("Lipoprotein order", "Cows Venture Into Large Herds: Chylomicrons|VLDL|IDL|LDL|HDL (density ↑)"), ("ApoC-II function", "ApoC-II = Calls LPL to work (activates lipoprotein lipase)"), ("Ketogenesis trigger", "Low OAA + High Acetyl-CoA = Ketones"), ("Jaundice types", "Pre=unconjugated↑(no urine Bil); Post=conjugated↑(pale stools, pruritus, dark urine)"), ("Heme rate-limiting enzyme", "ALA Synthase (needs PLP/B6); inhibited by heme; LEAD blocks ALA dehydratase + ferrochelatase"), ("Fatty acid synthesis site", "FAS in Cytosol; beta-oxidation in Mitochondria (OPPOSITE!)"), ("Sources of NADPH", "PPP (G6PD) = major; Malic enzyme; Isocitrate DH (cytosolic)"), ("Post-transcriptional mods", "5' cap (m7G) | 3' poly-A tail | Splicing (GU-AG rule)"), ("Post-translational mods", "GPS-MUG: Glycosylation|Phosphorylation|Signal cleavage|Methylation|Ubiquitination|GPI anchor"), ("Fatty liver in alcohol", "Alcohol→NADH↑→beta-oxidation↓, gluconeogenesis↓, FA synthesis↑, VLDL secretion↓→FAT in liver"), ] for topic, mnemonic in mnemonics: story += [ Paragraph(f"<b>{topic}:</b>", H3), Paragraph(mnemonic, MNEMONIC), sp(4), ] # ── Build ── doc.build(story) print(f"SUCCESS: PDF created at {output_path}") PYEOF echo "Script written."

Running Command

cd /tmp/workspace/biochem-notes && python make_pdf.py 2>&1

Your PDF is ready! Here it is:

Biochemistry Exam Notes

PDF Document · PDF

What's inside:
  • All 14 topics fully covered across organized pages
  • Every topic has its own color-coded section header (dark blue)
  • Tables for every major classification (tumour markers, lipoproteins, jaundice types, DNA repair disorders, inhibitors, etc.)
  • Yellow mnemonic boxes throughout
  • Blue highlight boxes for key exam points
  • A dedicated Quick Summary & Mnemonics page at the end - perfect for last-minute revision right before the exam
Download it, open it on your phone or print it, and good luck tomorrow!
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