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Here are your high-yield MBBS Biochemistry Paper 2 notes, sourced from Lippincott, Basic Medical Biochemistry (6e), and Harper's Illustrated Biochemistry:

Biochemistry Paper 2 - High-Yield Exam Notes


1. METABOLISM

Glycolysis

(Basic Medical Biochemistry 6e; Lippincott Biochemistry 8e)
  • Occurs in cytoplasm of all cells
  • Converts 1 glucose → 2 pyruvate
  • Net yield: 2 ATP + 2 NADH (aerobic) | 2 ATP only (anaerobic)
  • Two phases:
    • Preparatory phase (investment): 2 ATP consumed; glucose → fructose-1,6-bisphosphate
    • Payoff phase (generation): 4 ATP produced
  • Key irreversible enzymes (rate-limiting):
    1. Hexokinase (glucose → glucose-6-phosphate) - inhibited by G6P
    2. Phosphofructokinase-1 (PFK-1) - THE main regulatory enzyme; activated by AMP/ADP, inhibited by ATP/citrate
    3. Pyruvate kinase - inhibited by ATP, activated by fructose-1,6-bisphosphate
  • Anaerobic fate: Pyruvate → Lactate (by lactate dehydrogenase); regenerates NAD+ for continued glycolysis
  • Aerobic fate: Pyruvate → Acetyl-CoA (by pyruvate dehydrogenase complex, requires B1/thiamine)
Key facts for MCQs:
  • RBCs: glycolysis only (no mitochondria)
  • Brain: dependent on glucose; cannot use fatty acids
  • PFK-1 is the committed step in glycolysis

TCA Cycle (Krebs / Citric Acid Cycle)

(Basic Medical Biochemistry 6e; Ganong's)
  • Location: mitochondrial matrix
  • Substrate: Acetyl-CoA (2C) + Oxaloacetate (4C) → Citrate (6C)
  • Per turn of the cycle:
    • 3 NADH
    • 1 FADH2
    • 1 GTP
    • 2 CO2 released
  • Total ATP from 1 acetyl-CoA: ~10 ATP (3 NADH × 2.5 + 1 FADH2 × 1.5 + 1 GTP)
  • Total ATP from 1 glucose (complete oxidation): ~30-32 ATP
Key enzymes:
EnzymeReactionCofactor
Citrate synthaseOAA + Acetyl-CoA → Citrate-
Isocitrate dehydrogenaseIsocitrate → α-KGNAD+ (rate-limiting)
α-KG dehydrogenaseα-KG → Succinyl-CoAB1, B2, B3, lipoate
Succinate dehydrogenaseSuccinate → FumarateFAD (only ETC-linked enzyme)
Regulation: Inhibited by high NADH/NAD+, high ATP; activated by ADP, Ca2+

Electron Transport Chain (ETC) & Oxidative Phosphorylation

(Lippincott Biochemistry 8e)
  • Location: inner mitochondrial membrane (Complex I-IV + ATP synthase)
  • Electrons flow: NADH → Complex I → CoQ → Complex III → Cyt c → Complex IV → O2
  • FADH2 enters at Complex II (bypasses Complex I, so yields less ATP)
Complexes:
ComplexNamePumps H+?
INADH dehydrogenaseYes
IISuccinate dehydrogenaseNo
IIICytochrome bc1Yes
IVCytochrome c oxidaseYes
VATP synthase (F0F1)Driven by H+ gradient
  • Chemiosmotic theory (Mitchell): Proton gradient across inner membrane drives ATP synthesis
  • Uncouplers (e.g., DNP, thermogenin/UCP1 in brown fat): dissipate gradient as heat without making ATP
Inhibitors to remember:
  • Rotenone - blocks Complex I
  • Antimycin A - blocks Complex III
  • CN-, CO, azide - block Complex IV
  • Oligomycin - blocks ATP synthase

Gluconeogenesis (key points)

(Basic Medical Biochemistry 6e)
  • Occurs mainly in liver (also kidney cortex)
  • From: lactate, glycerol, amino acids (glucogenic), propionate
  • Bypasses the 3 irreversible glycolytic steps with unique enzymes:
    1. Pyruvate carboxylase (pyruvate → OAA; requires biotin, B7)
    2. PEPCK (OAA → PEP)
    3. Fructose-1,6-bisphosphatase (F1,6-bisP → F6P)
    4. Glucose-6-phosphatase (G6P → glucose; only in liver/kidney)

2. LIPIDS & MEMBRANES

Membrane Structure

(Harper's Illustrated Biochemistry 32e)
  • Fluid mosaic model (Singer-Nicolson): Phospholipid bilayer + proteins
  • Membrane lipids are amphipathic - polar head (hydrophilic) + nonpolar tails (hydrophobic)
  • Phospholipid types: Phosphatidylcholine, phosphatidylserine, sphingomyelin, cardiolipin (in mitochondria)
  • Membrane fluidity influenced by:
    • Unsaturated fatty acids → increase fluidity (cis double bonds create kinks)
    • Saturated FA → decrease fluidity (straight, tightly packed)
    • Cholesterol → acts as fluidity buffer (prevents excessive fluidity at high temp, excessive rigidity at low temp)
Asymmetry of membrane:
  • Outer leaflet: phosphatidylcholine, sphingomyelin, glycolipids
  • Inner leaflet: phosphatidylserine (negatively charged), phosphatidylethanolamine

Fatty Acid Oxidation (Beta-oxidation)

(Lippincott; Goldman-Cecil)
  • Location: mitochondrial matrix
  • Requires: CoA, FAD, NAD+
  • Activation: Fatty acid + CoA + ATP → Acyl-CoA (on outer mitochondrial membrane)
  • Transport into mitochondria: via carnitine shuttle (rate-limiting step; inhibited by malonyl-CoA)
  • Each cycle removes 2C as acetyl-CoA; produces 1 NADH + 1 FADH2
ATP yield from palmitate (C16):
  • 7 cycles of beta-oxidation
  • Produces 8 acetyl-CoA + 7 NADH + 7 FADH2
  • Total ~106 ATP (net ~129 - 2 for activation)
Odd-chain FA: Final product is propionyl-CoA → succinyl-CoA (requires B12)

Fatty Acid Synthesis

  • Location: cytoplasm (opposite to beta-oxidation)
  • Rate-limiting enzyme: Acetyl-CoA carboxylase (ACC) - adds CO2 to acetyl-CoA using biotin to form malonyl-CoA
  • Activated by insulin + citrate; inhibited by glucagon, palmitoyl-CoA
  • Requires: NADPH (from pentose phosphate pathway and malic enzyme)
Key contrast - Beta-oxidation vs Synthesis:
Beta-oxidationFA Synthesis
LocationMitochondriaCytoplasm
CarrierCoAACP
CofactorFAD, NAD+NADPH
DirectionDegradationAnabolism

Cholesterol Metabolism

  • Rate-limiting step: HMG-CoA reductase (target of statins)
  • Cholesterol is precursor to: bile acids, steroid hormones, vitamin D
  • Transported in blood as:
    • VLDL → delivers TG to peripheral tissues
    • LDL → delivers cholesterol to cells ("bad")
    • HDL → reverse cholesterol transport ("good")

3. MOLECULAR BIOLOGY & GENETICS

DNA Replication

  • Template: antiparallel (3'→5' template reads 5'→3' new strand)
  • Enzyme: DNA polymerase III (prokaryotes); DNA pol α, δ, ε (eukaryotes)
  • Requires: RNA primer (made by primase)
  • Leading strand: continuous synthesis; Lagging strand: Okazaki fragments
  • Helicase: unwinds DNA at replication fork
  • Topoisomerase: relieves supercoiling ahead of fork
  • DNA ligase: joins Okazaki fragments

Transcription (mRNA synthesis)

  • Template strand read 3'→5; mRNA synthesized 5'→3'
  • Enzyme: RNA polymerase (no primer needed)
  • Prokaryotes: RNA pol holoenzyme (sigma factor for promoter recognition); promoters at -10 (Pribnow box) and -35
  • Eukaryotes: 3 RNA polymerases:
    • RNA pol I - rRNA (28S, 18S, 5.8S)
    • RNA pol II - mRNA (most important; target of alpha-amanitin)
    • RNA pol III - tRNA, 5S rRNA
Post-transcriptional processing (eukaryotes):
  1. 5' 7-methylguanosine cap (protects, aids translation)
  2. 3' poly-A tail (protects, aids export)
  3. Splicing of introns by spliceosomes; exons remain

Translation (Protein Synthesis)

Genetic code:
  • 64 codons; 61 code for amino acids; 3 are stop codons (UAA, UAG, UGA)
  • AUG = start codon (methionine)
  • Code is degenerate (multiple codons per amino acid), unambiguous, universal
Ribosome sites: A (aminoacyl), P (peptidyl), E (exit)
Steps:
  1. Initiation: mRNA + small subunit + initiator tRNA (Met-tRNA)
  2. Elongation: Aminoacyl-tRNA enters A site; peptide bond formed by peptidyl transferase (part of 23S rRNA); translocation
  3. Termination: Stop codon recognized by release factors
Antibiotics targeting translation (high-yield!)
AntibioticTargetMechanism
Streptomycin30SMisreading of mRNA
Tetracycline30SBlocks aminoacyl-tRNA binding
Chloramphenicol50SInhibits peptidyl transferase
Erythromycin50SBlocks translocation
Linezolid70SBlocks initiation

Gene Regulation

  • Operon model (prokaryotes): Lac operon - inducible; Trp operon - repressible
  • Eukaryotic regulation: Enhancers, silencers, transcription factors
  • Epigenetics: DNA methylation (silencing), histone acetylation (activation), histone methylation (variable)
  • Post-translational modifications: phosphorylation, glycosylation, ubiquitination

4. ACID-BASE & FLUIDS

Basic Definitions

(Greenfield's Surgery; Lippincott)
  • Acid = H+ donor; Base = H+ acceptor
  • pH = -log[H+]
  • Normal arterial blood pH: 7.35-7.45 (slightly alkaline)
  • Henderson-Hasselbalch equation: pH = pKa + log ([HCO3-] / [CO2])
  • Normal values: HCO3- = 22-26 mEq/L; PaCO2 = 35-45 mmHg

Buffer Systems

(Greenfield's Surgery)
  • Bicarbonate buffer (main extracellular): HCO3-/H2CO3 (pKa 6.1) - most physiologically important despite not being the strongest buffer
  • Phosphate buffer (intracellular, urine): H2PO4-/HPO42-
  • Protein/Hemoglobin buffer (RBCs): Hb is a major blood buffer
  • Ammonia buffer (renal): NH3 + H+ → NH4+ (excreted in urine)
Regulation:
  • Lungs: regulate CO2 (fast response, minutes)
  • Kidneys: regulate HCO3- (slow response, hours-days)

Acid-Base Disorders

(Greenfield's Surgery; Tietz Laboratory Medicine)
DisorderpHPrimary ChangeCompensation
Metabolic acidosisHCO3- ↓PaCO2 ↓ (hyperventilation)
Metabolic alkalosisHCO3- ↑PaCO2 ↑ (hypoventilation)
Respiratory acidosisPaCO2 ↑HCO3- ↑ (renal)
Respiratory alkalosisPaCO2 ↓HCO3- ↓ (renal)
Common causes:
  • Metabolic acidosis: MUDPILES mnemonic - Methanol, Uremia, DKA, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates
  • Metabolic alkalosis: vomiting (loss of HCl), diuretics (loss of K+, H+), hyperaldosteronism
  • Respiratory acidosis: COPD, opioids, chest wall disease
  • Respiratory alkalosis: anxiety, hyperventilation, high altitude, fever, pregnancy
Anion Gap = Na+ - (Cl- + HCO3-); normal = 8-12 mEq/L
  • High AG acidosis: lactic acidosis, DKA, uremia, toxins
  • Normal AG acidosis: diarrhea, RTA, saline infusion

Body Fluids

  • Total body water (TBW) = ~60% body weight in males; ~50% in females
  • Intracellular fluid (ICF): 2/3 of TBW; major cation = K+
  • Extracellular fluid (ECF): 1/3 of TBW; major cation = Na+
    • Plasma: 1/4 of ECF
    • Interstitial: 3/4 of ECF
  • Osmolality = mainly determined by Na+ (normal ~285-295 mOsm/kg)

Quick High-Yield Mnemonics

MnemonicMeaning
GLUT transportersGLUT1 (RBC/brain), GLUT2 (liver/pancreas, bidirectional), GLUT4 (muscle/fat, insulin-dependent)
Vitamins for PDHB1 (TPP), B2 (FAD), B3 (NAD+), B5 (CoA), lipoic acid
ALASAminolevulinic acid synthase = rate-limiting in heme synthesis
TCA cofactors"Tender Loving Care For Nerves" = Thiamine, Lipoate, CoA, FAD, NAD
Stop codonsUAA (U Are Away), UAG (U Are Gone), UGA (U Go Away)

Sources: Lippincott Illustrated Reviews Biochemistry 8e | Basic Medical Biochemistry: A Clinical Approach 6e | Harper's Illustrated Biochemistry 32e | Greenfield's Surgery 7e

That covers all four topic areas. Which section would you like me to go deeper on? I can also generate practice MCQs for any topic if that would help you prepare!Paper Analysis - Most Repeated Topics Across All 4 Papers:
TopicTimes Asked
Allopurinol / Gout / Uric acid4/4 papers
Acid-base case (vomiting = metabolic alkalosis, DKA = metabolic acidosis)3/4 papers
TCA cycle (amphibolic role, steps, inhibitors)4/4 papers
DNA replication / transcription / translation4/4 papers
LDL/Cholesterol/Lipoprotein fractions4/4 papers
PCR (principle, technique, applications)3/4 papers
Collagen structure & disorders3/4 papers
Ketogenesis / ketone bodies / DKA3/4 papers
Renal acid-base regulation4/4 papers
Clearance tests / creatinine clearance3/4 papers
Tumor markers3/4 papers
PUFA / Fish oil3/4 papers
Aspirin in MI prevention3/4 papers
ELISA3/4 papers
Thyroid function tests (T3, T4, TSH)3/4 papers
Fatty liver / lipotropic factors2/4 papers
Antioxidants / free radicals2/4 papers
Mutations2/4 papers
Now here are comprehensive model answers for every major question:

AMRITA MBBS BIOCHEMISTRY PAPER 2 - MODEL ANSWERS


SECTION A - CASE QUESTIONS


Q: ACID-BASE CASE - Vomiting patient (Sep 2025 paper)

Results: HCO3- = 38 (high), H+ = 28 nmol/L (low = pH ~7.55), pCO2 = 8.6 kPa (high), K+ = 2.9 (low)
A. Nature of disturbance: Metabolic alkalosis with respiratory compensation
  • pH elevated (low [H+] = 28 nmol/L vs normal 36-44)
  • HCO3- elevated (38 vs normal 21-28 mmol/L) - primary change
  • pCO2 elevated (8.6 kPa = ~64.5 mmHg, vs normal 4.7-6 kPa) - compensatory retention
B. Cause: Persistent vomiting causes loss of HCl from the stomach → loss of H+ and Cl- → blood becomes alkalotic. The kidneys compensate by retaining H+ and excreting HCO3-, but vomiting volume overwhelmed this. Hypokalemia (K+ = 2.9) worsens alkalosis because K+ shifts out of cells in exchange for H+ moving in.
C. Buffer systems (4 marks):
Buffer SystemLocationMechanism
Bicarbonate/Carbonic acidExtracellularH+ + HCO3- ⇌ H2CO3 ⇌ CO2 + H2O; most important ECF buffer
PhosphateIntracellular & urineH2PO4- ⇌ HPO42- + H+; important in renal tubules
Protein/HemoglobinIntracellular (RBCs)Imidazole groups of histidine; Hb is major RBC buffer
AmmoniaRenal tubulesNH3 + H+ → NH4+ (excreted in urine)
Bicarbonate buffer is the most important physiologically because: (1) its components are regulated separately - lungs control CO2, kidneys control HCO3-; (2) it is present in high concentration in ECF.
D. Role of renal system in acid-base balance (3 marks): The kidneys maintain acid-base balance by three mechanisms:
  1. Reabsorption of filtered HCO3-: ~4500 mEq/day of HCO3- is filtered; 85% reabsorbed in proximal tubule via H+ secretion + carbonic anhydrase
  2. Titratable acid excretion: H+ secreted in tubules combines with HPO42- → H2PO4- (excreted); this reclaims HCO3- into blood
  3. Ammonia synthesis: Glutamine in tubular cells → NH3 + H+ → NH4+ (excreted); generates new HCO3- for blood
In alkalosis: kidneys excrete HCO3- and retain H+ In acidosis: kidneys retain HCO3- and excrete H+ (as NH4+ and titratable acid)

Q: DKA CASE (Jul/Aug 2024 paper)

Results: pH 7.12, pCO2 40 mmHg, HCO3- 12 mEq/L, glucose 620 mg/dl, ketones+++ in urine
A. Condition: Diabetic Ketoacidosis (DKA) - Type 1 DM patient (skipped insulin doses)
B. Justification:
  • Hyperglycemia (620 mg/dl): Insulin deficiency → glucose cannot enter cells → hyperglycemia → glucosuria + osmotic diuresis
  • Metabolic acidosis (pH 7.12, HCO3- 12): Insulin deficiency → lipolysis → excess fatty acids → ketogenesis → ketone bodies (acetoacetate, β-hydroxybutyrate are acids) → high AG metabolic acidosis
  • pCO2 = 40 (normal but relatively high for the degree of acidosis): Kussmaul breathing (deep rapid) is the compensatory hyperventilation; pCO2 should be lower - suggests mixed or inadequate compensation
  • Ketonuria: Overflow of ketones in urine
  • Vomiting → further fluid/electrolyte loss
C. Ketone bodies - Names and synthesis:
Names: (1) Acetoacetate, (2) β-hydroxybutyrate (most abundant in DKA), (3) Acetone (volatile, exhaled - fruity breath)
Synthesis (Ketogenesis) - in liver mitochondria:
  1. 2 Acetyl-CoA → Acetoacetyl-CoA (thiolase)
  2. Acetoacetyl-CoA + Acetyl-CoA → HMG-CoA (HMG-CoA synthase) - rate-limiting step
  3. HMG-CoA → Acetoacetate + Acetyl-CoA (HMG-CoA lyase)
  4. Acetoacetate → β-hydroxybutyrate (β-hydroxybutyrate dehydrogenase, needs NADH)
  5. Acetoacetate → Acetone (spontaneous decarboxylation)
Trigger: Insulin deficiency → excess glucagon → malonyl-CoA decreases → carnitine shuttle opens → FA flood into mitochondria → TCA overwhelmed → acetyl-CoA diverted to ketogenesis
D. Test for ketone bodies in urine: Rothera's test (sodium nitroprusside + ammonia; purple/violet color = positive for acetoacetate/acetone). Also Gerhardt's test (FeCl3, burgundy color).
E. Other conditions with ketonuria: Prolonged starvation/fasting, alcoholic ketoacidosis, high-fat low-carb diet, pregnancy, glycogen storage diseases

SECTION A - SHORT ESSAYS


Q: Fatty Liver - Causes and Lipotropic Factors (Sep 2025 paper) [5 marks]

Definition (1 mark): Fatty liver (hepatic steatosis) is the abnormal accumulation of triglycerides within hepatocytes, exceeding 5% of liver weight.
Causes (2 marks): Fatty liver results from any imbalance between TG synthesis and export from liver:
  1. Alcoholism - most common cause; alcohol inhibits FA oxidation, increases NADH (favors TG synthesis), inhibits VLDL synthesis
  2. Obesity/Type 2 DM - excess free fatty acids delivered to liver
  3. Protein deficiency (kwashiorkor) - lack of apoprotein B → cannot form VLDL → TG accumulates
  4. Starvation - excess FA mobilization from adipose overwhelms liver
  5. Drugs - tetracycline, methotrexate, valproate inhibit mitochondrial FA oxidation
  6. Choline/methionine deficiency - cannot synthesize phosphatidylcholine for VLDL assembly
Lipotropic factors (2 marks): Lipotropic factors are substances that prevent fat accumulation in the liver by promoting VLDL formation and export of TG:
FactorMechanism
CholineComponent of phosphatidylcholine (lecithin) in VLDL shell
MethionineMethyl donor → forms choline via transmethylation
InositolComponent of phosphatidylinositol for VLDL
BetaineMethyl donor, regenerates methionine
Vitamin B12 & FolateNeeded for methionine synthesis
Essential fatty acidsPromote phospholipid synthesis
Deficiency of lipotropic factors → cannot make VLDL → TG trapped in liver → fatty liver.

Q: Gout / Uric Acid / Lesch-Nyhan (Sep 2025 paper) [5 marks]

A. Diagnosis & cause (2 marks): Gout - Deposition of monosodium urate crystals in joints (first MTP joint = podagra is classic). Cause: Hyperuricemia from increased purine synthesis or decreased uric acid excretion. Uric acid is the end product of purine catabolism in humans (humans lack uricase enzyme).
B. What is uric acid? (1 mark): Uric acid (2,6,8-trioxypurine) is the final oxidation product of purine metabolism in humans. Formed from xanthine by xanthine oxidase. Normal serum levels: males < 7 mg/dL; females < 6 mg/dL.
C. Lesch-Nyhan Syndrome (2 marks):
  • X-linked recessive disorder
  • Caused by complete deficiency of HGPRT (Hypoxanthine-Guanine Phosphoribosyltransferase)
  • HGPRT normally salvages hypoxanthine and guanine back to IMP/GMP (salvage pathway)
  • Without HGPRT: hypoxanthine and guanine are all converted to uric acid → severe hyperuricemia
  • Features: gout, severe intellectual disability, choreoathetosis, self-mutilation (biting fingers/lips - pathognomonic), aggressive behavior
  • Treatment: allopurinol (reduces uric acid), but neurological features do not respond

SECTION A - SHORT NOTES (4 marks each)


Q: Antioxidants in health (Sep 2025 paper)

Role of antioxidants: Free radicals (superoxide O2•-, hydroxyl •OH, peroxyl ROO•) are generated during normal metabolism (ETC leak, phagocytosis, radiation). They cause:
  • Lipid peroxidation of cell membranes
  • Protein oxidation
  • DNA strand breaks → mutations, cancer Antioxidants neutralize free radicals and prevent oxidative damage.
Therapeutic antioxidants:
  • Vitamin E (tocopherol) - lipid-soluble; protects membranes
  • Vitamin C (ascorbic acid) - water-soluble; regenerates Vitamin E
  • Beta-carotene (pro-vitamin A)
  • N-acetylcysteine (NAC) - replenishes glutathione
  • Selenium compounds
Free radical scavenging enzymes:
  1. Superoxide dismutase (SOD) - converts O2•- → H2O2
  2. Catalase - converts H2O2 → H2O + O2
  3. Glutathione peroxidase (GPx) - uses GSH to reduce H2O2 and lipid peroxides (requires selenium)

Q: Types of RNA and their role in protein synthesis

RNA type% of totalSynthesized byFunction
rRNA (ribosomal)80%RNA pol I (28S,18S,5.8S); RNA pol III (5S)Structural component of ribosomes; peptidyl transferase activity (23S/28S rRNA is a ribozyme)
mRNA (messenger)5%RNA pol IICarries genetic code from DNA to ribosomes; template for translation
tRNA (transfer)15%RNA pol IIIAdaptor molecule; carries amino acids to ribosome; anticodon matches mRNA codon
snRNA (small nuclear)TraceRNA pol II/IIIPart of spliceosome; removes introns from pre-mRNA
miRNA/siRNATraceRNA pol IIPost-transcriptional gene silencing
hnRNAPrecursorRNA pol IIPrimary transcript (pre-mRNA) before processing

Q: Chemiosmotic theory + ETC Inhibitors

Chemiosmotic Theory (Peter Mitchell, 1961): As electrons pass through Complexes I, III, and IV of the ETC, protons (H+) are pumped from the mitochondrial matrix to the intermembrane space, creating:
  1. A proton gradient (ΔpH)
  2. An electrochemical gradient (membrane potential, negative inside)
Together = proton motive force (PMF). H+ flows back into matrix through ATP synthase (Complex V/F0F1 ATPase), driving rotation of the F0 subunit → conformational change in F1 → ADP + Pi → ATP (rotational catalysis).
Inhibitors of ETC:
InhibitorSite of actionEffect
Rotenone, amobarbitalComplex IBlocks NADH oxidation
TTFA, carboxinComplex IIBlocks FADH2 entry
Antimycin AComplex IIIBlocks electron flow to cyt c
CN-, CO, azide, H2SComplex IVBlocks O2 reduction; fatal
OligomycinATP synthase (F0)Blocks H+ channel; stops ATP synthesis
DNP, FCCPUncouplers (not direct inhibitors)Dissipate H+ gradient as heat; O2 consumed but no ATP

Q: Renal Clearance Tests

Definition: Clearance (C) = the volume of plasma completely cleared of a substance by the kidneys per minute. Formula: C = (U × V) / P (U = urine conc, V = urine flow rate, P = plasma conc)
Types of clearance tests:
TestSubstanceNormal valueWhat it measures
Inulin clearanceInulin125 mL/minGold standard for GFR (filtered only, not secreted/reabsorbed)
Creatinine clearanceCreatinine97-137 mL/min (male)Practical GFR estimate
PAH clearancep-Aminohippurate600 mL/minRenal plasma flow (filtered + secreted)
Urea clearanceUrea75 mL/minHistorical; underestimates GFR (urea reabsorbed)
Creatinine clearance (most asked):
  • Creatinine is produced from creatine phosphate in muscle at constant rate
  • Freely filtered; slightly secreted (overestimates GFR by ~10%)
  • 24-hour urine collection + serum creatinine
  • Normal: males ~120 mL/min; females ~100 mL/min
  • Declines with age and with progressive kidney disease
  • Used to stage CKD and adjust drug doses

Q: T3, T4, TSH in Hyper and Hypothyroidism

ParameterNormalHyperthyroidismHypothyroidism
T4 (thyroxine)5-12 μg/dL↑↑
T3 (triiodothyronine)80-180 ng/dL↑↑
TSH0.4-4.0 mIU/L↓ (suppressed by feedback)↑ (pituitary trying to stimulate)
Radioactive iodine uptakeNormal
Primary hypothyroidism (e.g., Hashimoto's): T3/T4 low, TSH very high Secondary hypothyroidism (pituitary failure): T3/T4 low, TSH low Primary hyperthyroidism (e.g., Graves'): T3/T4 high, TSH suppressed

SECTION B


Q: LDL - Transport of cholesterol from liver to peripheral tissues (Sep 2025) [4 marks]

LDL pathway:
  1. Liver secretes VLDL (Very Low Density Lipoprotein) into blood; contains TG + cholesterol + apoB-100
  2. In capillaries, lipoprotein lipase (LPL) hydrolyzes TG from VLDL → IDL (Intermediate Density Lipoprotein)
  3. IDL → further TG removal by hepatic lipase → LDL (mostly cholesterol + apoB-100, little TG)
  4. LDL receptor (LDL-R) on peripheral cells (and liver) recognizes apoB-100
  5. LDL binds LDL-R → endocytosis → lysosomal degradation → releases free cholesterol
  6. Free cholesterol: used for membrane synthesis, steroid hormone synthesis, bile acids
  7. Intracellular cholesterol inhibits HMG-CoA reductase (feedback) and downregulates LDL-R
Atherogenicity: Excess LDL undergoes oxidation → taken up by macrophages via scavenger receptors → foam cells → atherosclerotic plaques

Q: Substances derived from cholesterol + cholesterol-lowering drug

Substances derived from cholesterol:
  1. Bile acids (chenodeoxycholic, cholic acid) - bile salts for fat digestion
  2. Steroid hormones:
    • Glucocorticoids (cortisol)
    • Mineralocorticoids (aldosterone)
    • Sex hormones (testosterone, estrogen, progesterone)
  3. Vitamin D3 (cholecalciferol) - from 7-dehydrocholesterol in skin
  4. Oxysterols - regulatory molecules
Drug: Statins (e.g., Atorvastatin)
  • Mechanism: Competitive inhibitors of HMG-CoA reductase (rate-limiting enzyme of cholesterol synthesis: HMG-CoA → Mevalonate)
  • Effect: ↓ intracellular cholesterol → upregulation of LDL receptors → ↑ LDL clearance from blood → ↓ plasma LDL by 30-50%
  • Also have pleiotropic effects: anti-inflammatory, plaque stabilization

Q: Cardiac markers in MI (Sep 2025) [3 marks]

MarkerRises atPeaksNormalizesNote
Troponin I/T3-6 hrs12-24 hrs7-14 daysMost specific; gold standard
CK-MB4-6 hrs18-24 hrs2-3 daysUsed for reinfarction detection
Myoglobin1-2 hrs6-9 hrs24-36 hrsEarliest; not cardiac-specific
LDH12-24 hrs2-3 days7-10 daysLate marker
Earliest: Myoglobin → Most specific: Troponin I/T → Reinfarction: CK-MB

Q: PCR - Principle, Technique, Applications

Principle: PCR (Polymerase Chain Reaction) amplifies a specific DNA sequence exponentially in vitro using thermostable DNA polymerase (Taq polymerase from Thermus aquaticus).
Components:
  • Template DNA
  • Two primers (flanking the target sequence)
  • Taq polymerase
  • dNTPs (dATP, dTTP, dGTP, dCTP)
  • Buffer with MgCl2
  • Thermocycler
Technique - 3 steps repeated 30-40 cycles:
  1. Denaturation: 94-95°C - H-bonds broken, double-stranded DNA → single strands
  2. Annealing: 50-65°C - primers bind to complementary sequences on template
  3. Extension: 72°C - Taq polymerase extends from 3' end of primer using dNTPs
Each cycle doubles the target → 2^n copies after n cycles (1 copy → >1 billion copies in 30 cycles)
Applications:
  • Diagnosis of infectious diseases (HIV, TB, COVID-19, hepatitis)
  • Genetic disease diagnosis (sickle cell anemia, cystic fibrosis)
  • Forensic DNA fingerprinting
  • Prenatal diagnosis
  • Cancer detection (oncogene mutations)
  • RFLP analysis, DNA sequencing
  • Paternity testing

Q: Collagen - Structure & Disorders

Structure:
  • Most abundant protein in the body (30% of total protein)
  • Primary structure: repeating Gly-X-Y triplets (X = proline, Y = hydroxyproline)
  • Glycine at every 3rd position is essential (smallest AA fits inside triple helix)
  • Three polypeptide chains coil around each other in a right-handed triple helix
  • Stabilized by hydrogen bonds between chains + covalent lysine cross-links
Synthesis steps:
  1. Pre-pro-collagen synthesized on ribosomes
  2. Hydroxylation of proline/lysine (requires Vitamin C + O2 + Fe2+)
  3. Glycosylation in ER
  4. Triple helix formation → procollagen
  5. Secreted → procollagen peptidases cleave propeptides → tropocollagen
  6. Self-assembly into fibrils; cross-linking by lysyl oxidase (requires Cu2+)
Disorders:
DiseaseDefectFeatures
ScurvyVitamin C deficiency → impaired hydroxylationBleeding gums, poor wound healing, perifollicular hemorrhages
Osteogenesis imperfectaMutation in COL1A1/A2 (Type I collagen)Brittle bones, blue sclera, hearing loss
Ehlers-Danlos syndromeDefects in collagen cross-linking or type III collagenHyperextensible skin, hypermobile joints
Marfan syndromeFibrillin-1 defect (not collagen directly)Tall, arachnodactyly, aortic dissection
Alport syndromeType IV collagen mutationHereditary nephritis + deafness

Q: Tumor Markers - What they are + clinical applications

Definition: Tumor markers are substances (proteins, enzymes, hormones, antigens) produced by tumor cells or normal cells in response to a tumor, detected in blood/urine/tissues.
Important tumor markers:
MarkerCancerNotes
PSA (Prostate specific antigen)Prostate cancerScreening + monitoring
AFP (Alpha-fetoprotein)Hepatocellular carcinoma, testicular (yolk sac)Also elevated in pregnancy
CEA (Carcinoembryonic antigen)Colorectal, lung, breastMonitoring recurrence
CA-125Ovarian cancerScreening + response monitoring
CA 19-9Pancreatic cancer, cholangiocarcinoma
β-hCGChoriocarcinoma, testicular (non-seminoma)
Bence-Jones proteinMultiple myelomaDetected in urine (light chains)
CA 15-3Breast cancerMonitoring
Clinical applications: Screening (PSA), diagnosis, staging, monitoring treatment response, detecting recurrence, predicting prognosis

Q: ELISA - Principle and Technique (3 marks)

ELISA (Enzyme-Linked Immunosorbent Assay):
Principle: Uses an enzyme-labeled antibody to detect antigen-antibody binding. The enzyme converts colorless substrate to colored product (quantifiable by spectrophotometry).
Types and technique (Sandwich ELISA - most common):
  1. Coat microplate wells with capture antibody (primary Ab against target antigen)
  2. Add patient sample → antigen binds to capture Ab
  3. Wash (removes unbound material)
  4. Add enzyme-labeled detection antibody (binds another epitope of antigen)
  5. Wash again
  6. Add enzyme substrate → color develops proportional to antigen concentration
  7. Stop reaction (H2SO4); read absorbance at 450 nm
Common enzyme-substrate pairs: HRP (horseradish peroxidase) + TMB; AP (alkaline phosphatase) + pNPP
Applications: HIV diagnosis, hepatitis B/C, pregnancy test (hCG), allergy testing (IgE), TORCH infections, autoantibody detection

"GIVE REASONS" - ALL REPEATED ONES


A. Allopurinol is used to treat Gout (asked in ALL 4 papers)
  • Gout is caused by hyperuricemia (excess uric acid deposition as monosodium urate crystals)
  • Uric acid is formed from xanthine by xanthine oxidase
  • Allopurinol is a structural analog of hypoxanthine → competitively inhibits xanthine oxidase → blocks conversion of hypoxanthine → xanthine → uric acid
  • Result: reduced uric acid synthesis; hypoxanthine/xanthine accumulate (more soluble than uric acid, excreted easily)
  • Also acts as a suicide substrate (irreversible inhibition after oxidation to oxypurinol)
B. Aspirin is useful in prevention of heart attacks/MI
  • Platelets play key role in thrombus formation in MI
  • Aspirin irreversibly inhibits COX-1 (cyclooxygenase-1) by acetylating a serine residue
  • This blocks synthesis of TXA2 (thromboxane A2) in platelets
  • TXA2 normally promotes platelet aggregation and vasoconstriction
  • Since platelets have no nucleus, they cannot synthesize new COX → effect lasts platelet's lifetime (7-10 days)
  • Low-dose aspirin (75-100 mg/day) selectively inhibits platelet TXA2 more than endothelial prostacyclin (PGI2, which inhibits platelets)
  • Net effect: anti-platelet aggregation → prevents coronary thrombosis → prevents MI
C. Statins treat hypercholesterolemia / Hypercholesterolemia in hypothyroidism
  • In hypothyroidism: low T3/T4 → reduced expression of LDL receptors on liver cells → less LDL cleared from blood → hypercholesterolemia
  • Also: reduced lipoprotein lipase activity → reduced TG clearance
  • Statins block HMG-CoA reductase → reduced intracellular cholesterol → upregulation of LDL receptors → increased LDL clearance
D. Trans fatty acids are bad for health
  • Produced by partial hydrogenation of vegetable oils (margarine, processed foods)
  • Trans double bonds make FA straight (like saturated FA) → pack tightly → raise LDL ("bad"), lower HDL ("good")
  • Increase inflammation (raise CRP, IL-6)
  • Incorporated into cell membranes → alter membrane fluidity and receptor function
  • Increase cardiovascular disease, insulin resistance, type 2 DM risk
E. PUFA (Polyunsaturated Fatty Acids) are beneficial for health
  • Omega-3 PUFA (EPA, DHA from fish oil) and Omega-6 (linoleic acid)
  • Benefits:
    1. Lower TG (↓ VLDL synthesis)
    2. Lower LDL, raise HDL
    3. Anti-inflammatory: EPA/DHA → resolvins, protectins (anti-inflammatory eicosanoids) instead of pro-inflammatory prostaglandins
    4. Antithrombotic: reduce platelet aggregation
    5. Membrane fluidity: maintain fluidity of cell membranes (cis double bonds = kinked chains)
    6. DHA essential for brain and retinal development
    7. Lower risk of cardiovascular disease
F. Hyperkalaemia is treated with glucose and insulin
  • In hyperkalemia, K+ is dangerously high in blood → risk of cardiac arrhythmia
  • Insulin stimulates Na+/K+-ATPase on cell membranes → drives K+ into cells (ICF)
  • Glucose is given simultaneously to prevent hypoglycemia from insulin
  • Net effect: shifts K+ from ECF to ICF → lowers serum K+ within 30-60 minutes
  • Temporary measure (does not remove K+ from body - dialysis does that)
G. During starvation, free fatty acid is the preferred fuel for muscle
  • In starvation, insulin falls and glucagon rises → adipose lipolysis → free FA released
  • Muscles preferentially oxidize FFA via beta-oxidation (yield ~129 ATP from palmitate)
  • This spares glucose for the brain (which cannot use FA)
  • FFA also generates ketone bodies (acetoacetate, β-hydroxybutyrate) in liver → after ~2-3 days of starvation, brain shifts to using ketone bodies → further spares glucose → prevents protein catabolism
H. Purine synthesis inhibitors used as anti-cancer drugs (Methotrexate)
  • Rapidly dividing cancer cells require large amounts of purines/pyrimidines for DNA/RNA synthesis
  • Methotrexate inhibits dihydrofolate reductase (DHFR) → blocks regeneration of THF → depletes folate coenzymes needed for purine ring synthesis (C2 and C8 of purine ring donated by formyl-THF)
  • 5-Fluorouracil inhibits thymidylate synthase → blocks dTMP synthesis
  • 6-Mercaptopurine → incorporated as fraudulent nucleotide; inhibits PRPP amidotransferase (rate-limiting step of de novo purine synthesis)
  • Result: DNA synthesis cannot proceed → cancer cell death (more sensitive because they divide faster)

EXTRA HIGH-YIELD TOPICS

Amphibolic Role of TCA Cycle (asked in 3 papers)

TCA cycle is amphibolic because it functions in both catabolism AND anabolism:
Catabolic (energy-generating): Oxidizes acetyl-CoA → CO2 + NADH + FADH2 → ATP
Anabolic (biosynthetic): TCA intermediates drawn off for biosynthesis:
IntermediateBiosynthetic use
CitrateFA synthesis (exported to cytoplasm)
α-KetoglutarateGlutamate, other amino acids
Succinyl-CoAHeme synthesis, amino acids
OxaloacetateGluconeogenesis, aspartate
FumarateAmino acid synthesis (via aspartate)
This removal = cataplerosis (draining intermediates out). Must be replenished by anaplerosis (filling intermediates back in): e.g., pyruvate carboxylase (pyruvate → OAA), transamination

Renal Clearance - Creatinine Clearance (3 papers)

Formula: CCr = (Ucr × V) / Pcr
  • Ucr = urine creatinine (mg/dL), V = urine volume (mL/min), Pcr = plasma creatinine (mg/dL)
  • Normal male: 97-137 mL/min; Female: 88-128 mL/min
  • Correlates with GFR; used to detect and stage kidney disease

DNA Replication Enzymes (4 papers asked this)

  1. Helicase - unwinds double helix at replication fork
  2. Topoisomerase (Gyrase in prokaryotes) - relieves positive supercoiling ahead of fork
  3. Primase - synthesizes RNA primer
  4. DNA Pol III (prokaryotes) / DNA Pol δ, ε (eukaryotes) - main synthesis enzyme (5'→3')
  5. DNA Pol I (prokaryotes) - removes RNA primer, fills in gap
  6. DNA Ligase - joins Okazaki fragments (seals 3'-OH to 5'-phosphate with phosphodiester bond)
  7. Single-strand binding proteins (SSBPs) - stabilize unwound single strands
  8. Telomerase (eukaryotes) - extends chromosome ends using RNA template

These notes cover every question from all 4 of your past papers. The highest priority topics for tomorrow are: Allopurinol/Gout, Acid-base cases, TCA cycle (especially amphibolic role), LDL/cholesterol, Collagen, PCR, and the "Give Reasons" section. Good luck! You've got this.

Most repeated question

Based on my analysis of all 4 of your Amrita papers, here are the most repeated questions ranked by frequency:

🔥 APPEARED IN ALL 4 PAPERS

#TopicHow it's asked
1Allopurinol / Gout / Uric acid"Give reason: Allopurinol used in Gout" + Lesch-Nyhan
2TCA CycleAmphibolic role, steps, energy-releasing steps, inhibitors
3DNA Replication / Transcription / TranslationSteps + enzymes + inhibitors + post-translational modifications
4Renal acid-base regulationRole of kidneys in maintaining pH
5Cholesterol / LipoproteinLDL transport, products of cholesterol, lipoprotein fractions

🔴 APPEARED IN 3 OUT OF 4 PAPERS

#TopicHow it's asked
6Acid-base case (vomiting = metabolic alkalosis)Case + identify disturbance + buffer systems
7Ketogenesis / DKA caseKetone bodies synthesis, ketosis conditions
8PCRPrinciple, technique, applications
9CollagenStructure + disorders (Scurvy, OI, EDS)
10Tumor markersList + clinical applications
11PUFA / Fish oil"Give reason" why beneficial
12Aspirin in MI prevention"Give reason"
13ELISAPrinciple + technique
14Thyroid function testsT3, T4, TSH table in hyper/hypothyroidism
15Creatinine clearance testDefinition + formula + clinical use

THE SINGLE MOST REPEATED QUESTION:

"Allopurinol is used in the treatment of Gout - Give reason"
  • Asked in Sep 2025, Jul/Aug 2024, Jan 2024 Supp, Nov/Dec 2023 - every single paper without exception.
Write this answer in your sleep:
Gout = uric acid excess. Uric acid formed by xanthine oxidase. Allopurinol = structural analog of hypoxanthine → competitively + irreversibly inhibits xanthine oxidase → blocks hypoxanthine → xanthine → uric acid → less urate crystal deposition → treats gout.

Your Priority Study Order for Tonight:

  1. Allopurinol/Gout/Uric acid/Lesch-Nyhan (100% coming)
  2. TCA cycle - amphibolic role (every paper)
  3. DNA replication enzymes + post-translational modifications (every paper)
  4. Acid-base case (metabolic alkalosis from vomiting is the classic)
  5. LDL transport + cholesterol products + statins (every paper)
  6. Ketogenesis / DKA (3/4 papers, Section B long question)
  7. PCR (3/4 papers)
  8. Collagen structure + disorders (3/4 papers)
  9. Renal acid-base (every paper)
  10. Aspirin + PUFA give reasons (quick 2-mark answers)
All the detailed answers for these are already written above - just revise them! 💪

Generate a PDF cheat sheet of top 15 repeated topics for quick review

Reading File
Running Command

ls /home/daytona/workspace/ 2>/dev/null || mkdir -p /home/daytona/workspace/bioc…

Running Command

mkdir -p /home/daytona/workspace/biochem-cheatsheet && ls /home/daytona/workspac…

Writing File

~/biochem-cheatsheet/generate_cheatsheet.py

from reportlab.lib.pagesizes import A4
from reportlab.lib import colors
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.units import cm, mm
from reportlab.platypus import (SimpleDocTemplate, Paragraph, Spacer, Table,
                                 TableStyle, HRFlowable, PageBreak)
from reportlab.lib.enums import TA_LEFT, TA_CENTER, TA_JUSTIFY
from reportlab.platypus import KeepTogether

OUTPUT = "/home/daytona/workspace/biochem-cheatsheet/Biochem_Paper2_CheatSheet.pdf"

doc = SimpleDocTemplate(
    OUTPUT,
    pagesize=A4,
    leftMargin=1.5*cm, rightMargin=1.5*cm,
    topMargin=1.8*cm, bottomMargin=1.8*cm
)

W, H = A4

# ── Colour palette ──────────────────────────────────────────────────────────
C_RED    = colors.HexColor("#C0392B")
C_ORANGE = colors.HexColor("#E67E22")
C_BLUE   = colors.HexColor("#1A5276")
C_TEAL   = colors.HexColor("#148F77")
C_GREEN  = colors.HexColor("#1E8449")
C_PURPLE = colors.HexColor("#6C3483")
C_GREY   = colors.HexColor("#F2F3F4")
C_LTBLUE = colors.HexColor("#D6EAF8")
C_LTYEL  = colors.HexColor("#FEF9E7")
C_LTRED  = colors.HexColor("#FDEDEC")
C_LTGRN  = colors.HexColor("#E9F7EF")
C_WHITE  = colors.white
C_BLACK  = colors.HexColor("#1C2833")
C_BADGE  = colors.HexColor("#922B21")

styles = getSampleStyleSheet()

def S(name, **kw):
    base = styles["Normal"]
    return ParagraphStyle(name, parent=base, **kw)

# ── Style definitions ────────────────────────────────────────────────────────
sTITLE  = S("sTITLE",  fontSize=20, leading=24, textColor=C_WHITE,
            fontName="Helvetica-Bold", alignment=TA_CENTER, spaceAfter=2)
sSUB    = S("sSUB",    fontSize=10, leading=13, textColor=C_WHITE,
            fontName="Helvetica", alignment=TA_CENTER)
sH1     = S("sH1",     fontSize=13, leading=16, textColor=C_WHITE,
            fontName="Helvetica-Bold", spaceBefore=4, spaceAfter=2)
sH2     = S("sH2",     fontSize=10, leading=13, textColor=C_BLUE,
            fontName="Helvetica-Bold", spaceBefore=4, spaceAfter=1)
sH3     = S("sH3",     fontSize=9,  leading=12, textColor=C_TEAL,
            fontName="Helvetica-Bold", spaceBefore=3, spaceAfter=1)
sBODY   = S("sBODY",   fontSize=8,  leading=11, textColor=C_BLACK,
            fontName="Helvetica", spaceAfter=1)
sBULL   = S("sBULL",   fontSize=8,  leading=11, textColor=C_BLACK,
            fontName="Helvetica", leftIndent=10, spaceAfter=1)
sKEY    = S("sKEY",    fontSize=8,  leading=11, textColor=C_RED,
            fontName="Helvetica-Bold", leftIndent=10, spaceAfter=1)
sTABH   = S("sTABH",   fontSize=7.5,leading=10, textColor=C_WHITE,
            fontName="Helvetica-Bold", alignment=TA_CENTER)
sTABC   = S("sTABC",   fontSize=7.5,leading=10, textColor=C_BLACK,
            fontName="Helvetica", alignment=TA_LEFT)
sFOOT   = S("sFOOT",   fontSize=7,  leading=9,  textColor=colors.grey,
            fontName="Helvetica-Oblique", alignment=TA_CENTER)

def badge(text, bg=C_RED):
    return Table([[Paragraph(text, S("b", fontSize=7, fontName="Helvetica-Bold",
                                     textColor=C_WHITE, alignment=TA_CENTER))]],
                 colWidths=[1.6*cm],
                 style=[("BACKGROUND",(0,0),(-1,-1), bg),
                        ("ROUNDEDCORNERS",[3]),
                        ("TOPPADDING",(0,0),(-1,-1),1),
                        ("BOTTOMPADDING",(0,0),(-1,-1),1)])

def section_header(title, color=C_BLUE):
    tbl = Table([[Paragraph(title, sH1)]],
                colWidths=[doc.width],
                style=[("BACKGROUND",(0,0),(-1,-1), color),
                       ("TOPPADDING",(0,0),(-1,-1),4),
                       ("BOTTOMPADDING",(0,0),(-1,-1),4),
                       ("LEFTPADDING",(0,0),(-1,-1),8),
                       ("ROUNDEDCORNERS",[4])])
    return tbl

def two_col(left_items, right_items):
    """Put two lists of flowables side-by-side."""
    half = (doc.width - 0.4*cm) / 2
    lt = [[item] for item in left_items]
    rt = [[item] for item in right_items]
    # Build inner tables
    def inner(rows, w):
        return Table(rows, colWidths=[w],
                     style=[("TOPPADDING",(0,0),(-1,-1),0),
                            ("BOTTOMPADDING",(0,0),(-1,-1),0),
                            ("LEFTPADDING",(0,0),(-1,-1),0),
                            ("RIGHTPADDING",(0,0),(-1,-1),0)])
    return Table([[inner(lt, half), inner(rt, half)]],
                 colWidths=[half+0.2*cm, half+0.2*cm],
                 style=[("VALIGN",(0,0),(-1,-1),"TOP"),
                        ("LEFTPADDING",(0,0),(-1,-1),0),
                        ("RIGHTPADDING",(0,0),(-1,-1),0),
                        ("TOPPADDING",(0,0),(-1,-1),0),
                        ("BOTTOMPADDING",(0,0),(-1,-1),0)])

def card(content_rows, bg=C_GREY, border_color=C_BLUE):
    inner = Table([[r] for r in content_rows], colWidths=[doc.width - 0.6*cm],
                  style=[("TOPPADDING",(0,0),(-1,-1),0),
                         ("BOTTOMPADDING",(0,0),(-1,-1),0),
                         ("LEFTPADDING",(0,0),(-1,-1),0),
                         ("RIGHTPADDING",(0,0),(-1,-1),0)])
    outer = Table([[inner]],
                  colWidths=[doc.width],
                  style=[("BACKGROUND",(0,0),(-1,-1), bg),
                         ("BOX",(0,0),(-1,-1),1, border_color),
                         ("TOPPADDING",(0,0),(-1,-1),5),
                         ("BOTTOMPADDING",(0,0),(-1,-1),5),
                         ("LEFTPADDING",(0,0),(-1,-1),6),
                         ("RIGHTPADDING",(0,0),(-1,-1),6)])
    return outer

def make_table(headers, rows, col_widths, header_color=C_BLUE):
    data = [[Paragraph(h, sTABH) for h in headers]]
    for row in rows:
        data.append([Paragraph(str(c), sTABC) for c in row])
    t = Table(data, colWidths=col_widths)
    style = [
        ("BACKGROUND",(0,0),(-1,0), header_color),
        ("ROWBACKGROUNDS",(0,1),(-1,-1),[C_WHITE, C_LTBLUE]),
        ("GRID",(0,0),(-1,-1),0.4, colors.HexColor("#BFC9CA")),
        ("TOPPADDING",(0,0),(-1,-1),3),
        ("BOTTOMPADDING",(0,0),(-1,-1),3),
        ("LEFTPADDING",(0,0),(-1,-1),4),
        ("RIGHTPADDING",(0,0),(-1,-1),4),
        ("VALIGN",(0,0),(-1,-1),"TOP"),
    ]
    t.setStyle(TableStyle(style))
    return t

# ════════════════════════════════════════════════════════════════════════════
# BUILD STORY
# ════════════════════════════════════════════════════════════════════════════
story = []

# ── COVER BANNER ─────────────────────────────────────────────────────────────
banner = Table([
    [Paragraph("AMRITA MBBS · BIOCHEMISTRY PAPER 2", sTITLE)],
    [Paragraph("TOP 15 MOST REPEATED TOPICS · QUICK REVISION CHEAT SHEET", sSUB)],
    [Paragraph("Based on Nov/Dec 2023 | Jan 2024 (Supp) | Jul/Aug 2024 | Sep 2025 papers", sSUB)],
], colWidths=[doc.width],
style=[("BACKGROUND",(0,0),(-1,-1), C_BLUE),
       ("TOPPADDING",(0,0),(-1,-1),8),
       ("BOTTOMPADDING",(0,0),(-1,-1),8),
       ("ROUNDEDCORNERS",[5])])
story.append(banner)
story.append(Spacer(1, 0.3*cm))

# ── FREQUENCY TABLE ──────────────────────────────────────────────────────────
story.append(section_header("📋  FREQUENCY MAP — How Often Each Topic Appears", C_RED))
story.append(Spacer(1, 0.15*cm))
freq_data = [
    ["Allopurinol / Gout / Uric acid / Lesch-Nyhan", "4/4 🔥🔥🔥"],
    ["TCA Cycle (amphibolic, steps, inhibitors)", "4/4 🔥🔥🔥"],
    ["DNA Replication / Transcription / Translation", "4/4 🔥🔥🔥"],
    ["Renal acid-base regulation", "4/4 🔥🔥🔥"],
    ["Cholesterol / LDL / Lipoproteins", "4/4 🔥🔥🔥"],
    ["Acid-base case (Metabolic Alkalosis — vomiting)", "3/4 🔥🔥"],
    ["Ketogenesis / DKA case", "3/4 🔥🔥"],
    ["PCR (principle, technique, applications)", "3/4 🔥🔥"],
    ["Collagen structure + disorders", "3/4 🔥🔥"],
    ["Tumor markers", "3/4 🔥🔥"],
    ["PUFA / Fish oil — give reason", "3/4 🔥🔥"],
    ["Aspirin in MI prevention — give reason", "3/4 🔥🔥"],
    ["ELISA", "3/4 🔥🔥"],
    ["Thyroid function tests (T3, T4, TSH)", "3/4 🔥🔥"],
    ["Creatinine clearance / Renal clearance tests", "3/4 🔥🔥"],
]
story.append(make_table(["Topic", "Frequency"],
             freq_data, [13*cm, 3.5*cm], C_RED))
story.append(Spacer(1, 0.3*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 1 — ALLOPURINOL / GOUT
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("1.  ALLOPURINOL / GOUT / URIC ACID / LESCH-NYHAN  [Asked ALL 4 papers]", C_RED),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Uric acid</b> = final product of purine catabolism in humans (lack uricase). Normal: males &lt;7 mg/dL.", sBODY),
        Paragraph("<b>Pathway:</b> Hypoxanthine → Xanthine → Uric acid   [enzyme: <b>Xanthine oxidase</b>]", sKEY),
        Paragraph("<b>Allopurinol mechanism:</b> Structural analog of hypoxanthine → competitively + irreversibly inhibits xanthine oxidase → ↓ uric acid synthesis → prevents urate crystal deposition in joints.", sBODY),
        Paragraph("<b>Gout:</b> Deposition of monosodium urate crystals in joints (1st MTP = podagra). Causes: overproduction or underexcretion of uric acid.", sBODY),
        Paragraph("<b>Lesch-Nyhan Syndrome:</b> X-linked recessive. Complete deficiency of <b>HGPRT</b> (Hypoxanthine-Guanine PhosphoRibosylTransferase). Features: severe hyperuricemia, gout, intellectual disability, choreoathetosis, <b>self-mutilation</b> (pathognomonic). Tx: allopurinol (controls uric acid only; neuro features persist).", sBODY),
    ], C_LTRED, C_RED),
]))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 2 — TCA CYCLE
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("2.  TCA CYCLE — Amphibolic Role, Steps, Inhibitors  [All 4 papers]", C_TEAL),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Location:</b> Mitochondrial matrix. Substrate: Acetyl-CoA (2C) + OAA (4C) → Citrate (6C).", sBODY),
        Paragraph("<b>Per turn yield:</b> 3 NADH + 1 FADH₂ + 1 GTP + 2 CO₂ → ~10 ATP", sKEY),
    ], C_LTGRN, C_TEAL),
]))
story.append(Spacer(1, 0.1*cm))
tca_enzymes = [
    ["Citrate synthase", "OAA + Acetyl-CoA → Citrate", "—"],
    ["Isocitrate dehydrogenase", "Isocitrate → α-KG", "NAD⁺ (rate-limiting)"],
    ["α-KG dehydrogenase", "α-KG → Succinyl-CoA", "B1, B2, B3, Lipoate"],
    ["Succinate dehydrogenase", "Succinate → Fumarate", "FAD (Complex II of ETC)"],
    ["Malate dehydrogenase", "Malate → OAA", "NAD⁺"],
]
story.append(make_table(["Enzyme","Reaction","Cofactor"], tca_enzymes,
             [5.5*cm, 5.5*cm, 5.5*cm], C_TEAL))
story.append(Spacer(1, 0.1*cm))
story.append(card([
    Paragraph("<b>Amphibolic role</b> (catabolic + anabolic):", sH3),
    Paragraph("• Citrate → FA synthesis  |  • α-KG → Glutamate  |  • Succinyl-CoA → Heme synthesis", sBULL),
    Paragraph("• OAA → Gluconeogenesis  |  • Fumarate → Amino acids", sBULL),
    Paragraph("<b>Anaplerosis</b> (refilling cycle): Pyruvate carboxylase (pyruvate → OAA, requires biotin/B7)", sBODY),
    Paragraph("<b>Inhibitors:</b> Fluoroacetate (→ fluorocitrate, blocks aconitase) | Arsenite (inhibits α-KG dehydrogenase)", sKEY),
], C_LTGRN, C_TEAL))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 3 — DNA REPLICATION / TRANSCRIPTION / TRANSLATION
# ═══════════════════════════════════════════════════════════
story.append(section_header("3.  DNA REPLICATION / TRANSCRIPTION / TRANSLATION  [All 4 papers]", C_PURPLE))
story.append(Spacer(1, 0.1*cm))
replic_enzymes = [
    ["Helicase","Unwinds double helix at replication fork"],
    ["Topoisomerase / Gyrase","Relieves supercoiling ahead of fork"],
    ["Primase","Synthesizes RNA primer (required to start)"],
    ["DNA Pol III (prokaryotes)","Main synthesis enzyme; 5'→3' synthesis"],
    ["DNA Pol I (prokaryotes)","Removes RNA primer, fills in gap"],
    ["DNA Ligase","Joins Okazaki fragments; seals nick"],
    ["SSBPs","Stabilize single-stranded DNA"],
    ["Telomerase (eukaryotes)","Extends telomeres using RNA template"],
]
story.append(make_table(["Enzyme","Function"], replic_enzymes,
             [5*cm, 11.5*cm], C_PURPLE))
story.append(Spacer(1, 0.1*cm))

transl_inh = [
    ["Streptomycin","30S","Misreads mRNA"],
    ["Tetracycline","30S","Blocks aminoacyl-tRNA binding to A site"],
    ["Chloramphenicol","50S","Inhibits peptidyl transferase"],
    ["Erythromycin","50S","Blocks translocation"],
    ["Linezolid","70S","Blocks initiation complex"],
]
story.append(card([Paragraph("<b>Translation inhibitor antibiotics:</b>", sH3)],
             C_GREY, C_PURPLE))
story.append(make_table(["Antibiotic","Target","Mechanism"], transl_inh,
             [5*cm, 2.5*cm, 9*cm], C_PURPLE))
story.append(Spacer(1, 0.1*cm))
story.append(card([
    Paragraph("<b>Post-translational modifications:</b> Phosphorylation | Glycosylation | Hydroxylation (collagen — needs Vit C) | Ubiquitination (protein degradation) | Acetylation | Methylation", sBODY),
    Paragraph("<b>Stop codons:</b> UAA · UAG · UGA  |  <b>Start:</b> AUG (Met)  |  Genetic code: degenerate, unambiguous, universal, non-overlapping", sKEY),
], C_GREY, C_PURPLE))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 4 — ACID-BASE CASE (Metabolic Alkalosis)
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("4.  ACID-BASE CASE — Metabolic Alkalosis (Vomiting)  [3/4 papers]", C_ORANGE),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Classic case:</b> Young man, persistent vomiting, dehydrated, shallow respiration, ↑HCO₃⁻, ↓H⁺ (high pH), ↑pCO₂, ↓K⁺.", sBODY),
        Paragraph("<b>Disturbance:</b> Metabolic alkalosis with respiratory compensation.", sKEY),
        Paragraph("<b>Cause:</b> Vomiting → loss of HCl → loss of H⁺ and Cl⁻ → ↑pH. Hypokalemia (K⁺ 2.9) worsens alkalosis (K⁺ exits cells, H⁺ enters cells).", sBODY),
        Paragraph("<b>Compensation:</b> Lungs hypoventilate → retain CO₂ (↑pCO₂). Kidneys excrete HCO₃⁻.", sBODY),
    ], C_LTYEL, C_ORANGE),
]))
story.append(Spacer(1, 0.1*cm))

abdisordr = [
    ["Metabolic acidosis","↓","↓ (primary)","—","↓ (compensation)"],
    ["Metabolic alkalosis","↑","↑ (primary)","—","↑ (compensation)"],
    ["Respiratory acidosis","↓","—","↑ (primary)","↑ (compensation)"],
    ["Respiratory alkalosis","↑","—","↓ (primary)","↓ (compensation)"],
]
story.append(make_table(["Disorder","pH","HCO₃⁻","pCO₂","Compensation"],
             abdisordr, [4.5*cm, 1.5*cm, 2.8*cm, 2.5*cm, 5.2*cm], C_ORANGE))
story.append(Spacer(1, 0.1*cm))
story.append(card([
    Paragraph("<b>Buffer systems:</b>", sH3),
    Paragraph("1. Bicarbonate/H₂CO₃ — main ECF buffer (regulated by lungs + kidneys)", sBULL),
    Paragraph("2. Phosphate (H₂PO₄⁻/HPO₄²⁻) — intracellular & urine", sBULL),
    Paragraph("3. Protein/Hemoglobin — intracellular (RBCs)", sBULL),
    Paragraph("4. Ammonia — renal tubules (NH₃ + H⁺ → NH₄⁺ excreted)", sBULL),
    Paragraph("<b>Renal role:</b> ① Reabsorb filtered HCO₃⁻ (proximal tubule) ② Titratable acid excretion (H⁺ + HPO₄²⁻ → H₂PO₄⁻) ③ Ammonia synthesis → new HCO₃⁻", sKEY),
], C_LTYEL, C_ORANGE))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 5 — CHOLESTEROL / LDL / LIPOPROTEINS
# ═══════════════════════════════════════════════════════════
story.append(section_header("5.  CHOLESTEROL / LDL / LIPOPROTEINS  [All 4 papers]", C_BLUE))
story.append(Spacer(1, 0.1*cm))

lipo_data = [
    ["Chylomicron","Dietary TG","Apo B-48","Delivers dietary fat to tissues"],
    ["VLDL","Endogenous TG","Apo B-100","Delivers liver TG to periphery"],
    ["IDL","TG + Chol","Apo B-100","Intermediate; → LDL"],
    ["LDL","Cholesterol","Apo B-100","Delivers cholesterol to cells (\"bad\")"],
    ["HDL","Protein-rich","Apo A-I","Reverse cholesterol transport (\"good\")"],
]
story.append(make_table(["Lipoprotein","Main Lipid","Apoprotein","Function"],
             lipo_data, [3*cm, 3*cm, 2.8*cm, 7.7*cm]))
story.append(Spacer(1, 0.1*cm))
story.append(card([
    Paragraph("<b>LDL pathway:</b> VLDL → (LPL removes TG) → IDL → (Hepatic lipase) → LDL → binds LDL receptor (Apo B-100) → endocytosis → releases cholesterol → feedback inhibits HMG-CoA reductase.", sBODY),
    Paragraph("<b>Products of cholesterol:</b> Bile acids | Steroid hormones (cortisol, aldosterone, estrogen, testosterone) | Vitamin D₃ | Oxysterols", sBODY),
    Paragraph("<b>Statins:</b> Competitive inhibitors of HMG-CoA reductase (rate-limiting step) → ↓ intracellular cholesterol → ↑ LDL receptor expression → ↑ LDL clearance from blood.", sKEY),
], C_LTBLUE, C_BLUE))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 6 — KETOGENESIS / DKA
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("6.  KETOGENESIS / DKA CASE  [3/4 papers]", C_ORANGE),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Ketone bodies:</b> ① Acetoacetate ② β-Hydroxybutyrate (most abundant in DKA) ③ Acetone (exhaled — fruity breath)", sBODY),
        Paragraph("<b>Synthesis (liver mitochondria):</b>", sH3),
        Paragraph("2 Acetyl-CoA → Acetoacetyl-CoA → + Acetyl-CoA → <b>HMG-CoA</b> (rate-limiting step: HMG-CoA synthase) → Acetoacetate → β-Hydroxybutyrate / Acetone", sBULL),
        Paragraph("<b>DKA trigger:</b> ↓ Insulin + ↑ Glucagon → lipolysis → FA flood liver → ↓ malonyl-CoA → carnitine shuttle open → β-oxidation overwhelms TCA → acetyl-CoA → ketogenesis.", sBODY),
        Paragraph("<b>DKA ABG:</b> pH ↓, HCO₃⁻ ↓ (primary), pCO₂ ↓ (Kussmaul compensation) = High anion gap metabolic acidosis.", sKEY),
        Paragraph("<b>Test for ketones in urine:</b> Rothera's test (sodium nitroprusside + ammonia → purple/violet for acetoacetate).", sBODY),
        Paragraph("<b>Other causes of ketonuria:</b> Starvation | Alcoholic ketoacidosis | High-fat diet | Pregnancy | Glycogen storage disease", sBODY),
    ], C_LTYEL, C_ORANGE),
]))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 7 — PCR
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("7.  PCR — Principle, Technique, Applications  [3/4 papers]", C_TEAL),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Principle:</b> In vitro amplification of specific DNA sequences using thermostable Taq DNA polymerase + specific primers + thermocycler.", sBODY),
        Paragraph("<b>Components:</b> Template DNA | Two primers (flanking target) | Taq polymerase | dNTPs | MgCl₂ buffer", sBODY),
        Paragraph("<b>3 Steps (30-40 cycles):</b>", sH3),
        Paragraph("① Denaturation 94°C: strands separate   ② Annealing 50-65°C: primers bind   ③ Extension 72°C: Taq extends new strand 5'→3'", sBULL),
        Paragraph("<b>Result:</b> 2ⁿ copies after n cycles (1 molecule → >1 billion in 30 cycles)", sKEY),
        Paragraph("<b>Applications:</b> Infectious disease diagnosis (HIV, TB, COVID) | Genetic disease (sickle cell, CF) | Forensic DNA fingerprinting | Prenatal diagnosis | Cancer mutation detection | RFLP analysis | Paternity testing", sBODY),
    ], C_LTGRN, C_TEAL),
]))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 8 — COLLAGEN
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("8.  COLLAGEN — Structure & Disorders  [3/4 papers]", C_BLUE),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Structure:</b> Repeating Gly-X-Y triplets (X=Pro, Y=Hydroxyproline). Three chains form right-handed triple helix. Stabilized by H-bonds + covalent Lys cross-links.", sBODY),
        Paragraph("<b>Synthesis:</b> Ribosomes → Hydroxylation of Pro/Lys (<b>Vit C + Fe²⁺ + O₂</b>) → Glycosylation → Triple helix (procollagen) → Secreted → Peptidases → Tropocollagen → Fibrils (Lysyl oxidase + Cu²⁺)", sBODY),
    ], C_LTBLUE, C_BLUE),
]))
story.append(Spacer(1, 0.1*cm))
collagen_dis = [
    ["Scurvy","Vit C deficiency → ↓ hydroxylation","Bleeding gums, poor wound healing, perifollicular hemorrhage"],
    ["Osteogenesis Imperfecta","COL1A1/A2 mutation (Type I collagen)","Brittle bones, blue sclera, hearing loss"],
    ["Ehlers-Danlos","Defective cross-linking / Type III collagen","Hyperextensible skin, hypermobile joints"],
    ["Alport Syndrome","Type IV collagen mutation","Hereditary nephritis + deafness"],
]
story.append(make_table(["Disease","Defect","Features"], collagen_dis,
             [3.5*cm, 6*cm, 7*cm]))
story.append(Spacer(1, 0.25*cm))

# PAGE BREAK before remaining topics
story.append(PageBreak())

# ═══════════════════════════════════════════════════════════
# TOPIC 9 — TUMOR MARKERS
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("9.  TUMOR MARKERS  [3/4 papers]", C_RED),
    Spacer(1, 0.1*cm),
]))
tm_data = [
    ["PSA","Prostate cancer","Screening + monitoring"],
    ["AFP (α-Fetoprotein)","Hepatocellular ca., testicular (yolk sac)","↑ in pregnancy too"],
    ["CEA","Colorectal, lung, breast","Monitoring recurrence"],
    ["CA-125","Ovarian cancer","Treatment response"],
    ["CA 19-9","Pancreatic, cholangiocarcinoma","Prognosis"],
    ["β-hCG","Choriocarcinoma, testicular","Also pregnancy test"],
    ["Bence Jones protein","Multiple myeloma","Detected in urine (light chains)"],
    ["CA 15-3","Breast cancer","Monitoring"],
]
story.append(make_table(["Marker","Cancer","Note"], tm_data,
             [3.5*cm, 5.5*cm, 7.5*cm], C_RED))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 10 — ELISA
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("10.  ELISA — Principle & Technique  [3/4 papers]", C_PURPLE),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Principle:</b> Enzyme-labeled antibody detects antigen-antibody binding. Enzyme converts colorless substrate → colored product (quantified by spectrophotometry at 450 nm).", sBODY),
        Paragraph("<b>Sandwich ELISA steps:</b> Coat plate with capture Ab → Add sample (Ag binds) → Wash → Add enzyme-linked detection Ab → Wash → Add substrate → Color proportional to Ag concentration → Stop + read OD.", sBODY),
        Paragraph("<b>Enzyme-substrate pairs:</b> HRP + TMB | Alkaline phosphatase + pNPP", sBODY),
        Paragraph("<b>Applications:</b> HIV diagnosis | Hepatitis B/C | hCG (pregnancy) | Allergy (IgE) | TORCH infections | Autoantibody detection | Drug levels", sKEY),
    ], C_GREY, C_PURPLE),
]))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 11 — THYROID FUNCTION TESTS
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("11.  THYROID FUNCTION TESTS — T3, T4, TSH  [3/4 papers]", C_TEAL),
    Spacer(1, 0.1*cm),
]))
tft_data = [
    ["T4 (Thyroxine)","5-12 μg/dL","↑↑","↓"],
    ["T3 (Triiodothyronine)","80-180 ng/dL","↑↑","↓"],
    ["TSH","0.4-4.0 mIU/L","↓ (suppressed by -ve feedback)","↑ (pituitary stimulating)"],
    ["RAI Uptake","Normal","↑","↓"],
]
story.append(make_table(["Parameter","Normal","Hyperthyroidism","Hypothyroidism"],
             tft_data, [4*cm, 3*cm, 5*cm, 4.5*cm], C_TEAL))
story.append(Spacer(1, 0.1*cm))
story.append(card([
    Paragraph("<b>Hypercholesterolemia in hypothyroidism:</b> ↓T3/T4 → ↓LDL receptor expression → ↓LDL clearance → ↑plasma LDL. Also ↓lipoprotein lipase → ↑TG.", sBODY),
], C_LTGRN, C_TEAL))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 12 — CREATININE CLEARANCE
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("12.  CLEARANCE TESTS / CREATININE CLEARANCE  [3/4 papers]", C_BLUE),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Clearance formula:</b>  C = (U × V) / P   where U = urine conc, V = urine flow (mL/min), P = plasma conc", sKEY),
        Paragraph("<b>Creatinine clearance:</b> Produced at constant rate from creatine phosphate in muscle. Freely filtered; slightly secreted (~10% overestimates GFR). Normal: male ~120 mL/min, female ~100 mL/min.", sBODY),
        Paragraph("<b>Inulin clearance:</b> Gold standard for GFR (freely filtered only, not secreted/reabsorbed) = 125 mL/min.", sBODY),
        Paragraph("<b>PAH clearance:</b> Measures renal plasma flow (filtered + completely secreted) = ~600 mL/min.", sBODY),
        Paragraph("<b>Clinical use:</b> Detect + stage CKD | Drug dose adjustment | Monitor transplant function | Pre-op assessment", sBODY),
    ], C_LTBLUE, C_BLUE),
]))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 13 — FATTY LIVER + LIPOTROPIC FACTORS
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("13.  FATTY LIVER & LIPOTROPIC FACTORS  [2/4 papers]", C_ORANGE),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Fatty liver:</b> Abnormal accumulation of TG in hepatocytes (>5% liver weight).", sBODY),
        Paragraph("<b>Causes:</b> Alcoholism (most common) | Obesity/T2DM | Protein deficiency (↓ApoB → can't form VLDL) | Starvation | Drugs (tetracycline, valproate) | Choline/methionine deficiency", sBODY),
        Paragraph("<b>Lipotropic factors</b> (prevent fat in liver by promoting VLDL synthesis):", sH3),
        Paragraph("Choline (phosphatidylcholine for VLDL shell) | Methionine (methyl donor → choline) | Inositol | Betaine | Vitamin B12 + Folate | Essential fatty acids", sBULL),
        Paragraph("<b>Key point:</b> Deficiency of lipotropic factors → cannot assemble VLDL → TG trapped in liver → steatosis.", sKEY),
    ], C_LTYEL, C_ORANGE),
]))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 14 — ANTIOXIDANTS
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("14.  ANTIOXIDANTS — Role, Therapeutic Agents, Scavenging Enzymes  [2/4 papers]", C_GREEN),
    Spacer(1, 0.1*cm),
    card([
        Paragraph("<b>Free radicals:</b> O₂•⁻ (superoxide), •OH (hydroxyl), ROO• (peroxyl) — generated by ETC leakage, phagocytosis, radiation, smoking.", sBODY),
        Paragraph("<b>Damage:</b> Lipid peroxidation | Protein oxidation | DNA strand breaks → mutations, cancer, aging, atherosclerosis", sBODY),
        Paragraph("<b>Therapeutic antioxidants:</b> Vitamin E (lipid-soluble, protects membranes) | Vitamin C (water-soluble, regenerates Vit E) | β-Carotene | N-Acetylcysteine (NAC, replenishes GSH) | Selenium", sBODY),
        Paragraph("<b>Scavenging enzymes (MOST IMPORTANT):</b>", sH3),
        Paragraph("① <b>Superoxide dismutase (SOD)</b>: 2O₂•⁻ + 2H⁺ → H₂O₂ + O₂", sKEY),
        Paragraph("② <b>Catalase</b>: 2H₂O₂ → 2H₂O + O₂", sKEY),
        Paragraph("③ <b>Glutathione peroxidase (GPx)</b>: H₂O₂ + 2GSH → GSSG + 2H₂O (requires <b>selenium</b>)", sKEY),
    ], C_LTGRN, C_GREEN),
]))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# TOPIC 15 — ETC + CHEMIOSMOTIC THEORY
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("15.  ETC & CHEMIOSMOTIC THEORY + INHIBITORS  [All 4 papers]", C_TEAL),
    Spacer(1, 0.1*cm),
]))
etc_data = [
    ["Complex I","NADH dehydrogenase","NADH → CoQ","Yes","Rotenone, Amobarbital"],
    ["Complex II","Succinate dehydrogenase","FADH₂ → CoQ","No","TTFA, Carboxin"],
    ["Complex III","Cytochrome bc₁","CoQ → Cyt c","Yes","Antimycin A"],
    ["Complex IV","Cytochrome c oxidase","Cyt c → O₂","Yes","CN⁻, CO, Azide, H₂S"],
    ["Complex V","ATP Synthase (F₀F₁)","H⁺ gradient → ATP","—","Oligomycin"],
]
story.append(make_table(["Complex","Name","Electron flow","Pumps H⁺?","Inhibitor"],
             etc_data, [2.5*cm, 4*cm, 3.5*cm, 2*cm, 4.5*cm], C_TEAL))
story.append(Spacer(1, 0.1*cm))
story.append(card([
    Paragraph("<b>Chemiosmotic Theory (Peter Mitchell):</b> Complexes I, III, IV pump H⁺ from matrix → intermembrane space → creates proton motive force (ΔpH + membrane potential). H⁺ flows back through ATP synthase → drives rotational synthesis of ATP.", sBODY),
    Paragraph("<b>Uncouplers</b> (e.g., DNP, thermogenin/UCP1 in brown fat): dissipate H⁺ gradient as heat — O₂ consumed but no ATP made. Basis of thermogenesis in newborns.", sKEY),
], C_LTGRN, C_TEAL))
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# GIVE REASONS QUICK REFERENCE
# ═══════════════════════════════════════════════════════════
story.append(section_header("⚡  GIVE REASONS — QUICK REFERENCE (2-3 marks each)", C_RED))
story.append(Spacer(1, 0.1*cm))
gr_data = [
    ["Allopurinol treats Gout","Structural analog of hypoxanthine → competitively + irreversibly inhibits xanthine oxidase → ↓ uric acid synthesis → prevents urate crystal deposition"],
    ["Aspirin prevents MI","Irreversibly acetylates COX-1 → ↓TXA₂ (platelet aggregator) → anti-platelet → prevents coronary thrombosis"],
    ["PUFA beneficial for health","↓TG, ↓LDL, ↑HDL | Anti-inflammatory (resolvins, protectins) | Anti-thrombotic | ↑membrane fluidity | DHA essential for brain development"],
    ["Trans FA bad for health","Straight chain like saturated FA → ↑LDL, ↓HDL | Pro-inflammatory (↑CRP) | ↑cardiovascular risk, insulin resistance"],
    ["Hypercholesterolemia in hypothyroidism","↓T3/T4 → ↓LDL receptor expression → ↓LDL clearance → ↑plasma LDL. Also ↓LPL → ↑TG"],
    ["Hyperkalaemia treated with glucose + insulin","Insulin activates Na⁺/K⁺-ATPase → drives K⁺ into cells (ICF). Glucose prevents hypoglycemia. Rapid, temporary shift of K⁺"],
    ["Starvation: FFA preferred fuel for muscle","↓Insulin, ↑Glucagon → adipose lipolysis → FFA released → muscle β-oxidation → spares glucose for brain"],
    ["Purine synthesis inhibitors as anti-cancer drugs","Rapidly dividing cancer cells need purines for DNA synthesis. Methotrexate inhibits DHFR → ↓THF → ↓purine synthesis. 6-MP inhibits PRPP amidotransferase"],
    ["Bicarbonate is the most important buffer","Regulated by both lungs (CO₂) and kidneys (HCO₃⁻) independently. High concentration in ECF. Open system allows rapid adjustment"],
    ["Fish oil good for health","Omega-3 FA (EPA, DHA): ↓TG, ↓LDL, ↑HDL, anti-inflammatory, anti-thrombotic, prevents arrhythmias, ↓CV disease risk"],
]
gr_table = Table(
    [[Paragraph("<b>"+r[0]+"</b>", S("g1", fontSize=7.5, fontName="Helvetica-Bold", textColor=C_BLUE)),
      Paragraph(r[1], sBODY)] for r in gr_data],
    colWidths=[5.5*cm, 11*cm],
    style=[
        ("ROWBACKGROUNDS",(0,0),(-1,-1),[C_WHITE, C_LTBLUE]),
        ("GRID",(0,0),(-1,-1),0.3, colors.HexColor("#BFC9CA")),
        ("TOPPADDING",(0,0),(-1,-1),3),
        ("BOTTOMPADDING",(0,0),(-1,-1),3),
        ("LEFTPADDING",(0,0),(-1,-1),4),
        ("RIGHTPADDING",(0,0),(-1,-1),4),
        ("VALIGN",(0,0),(-1,-1),"TOP"),
    ]
)
story.append(gr_table)
story.append(Spacer(1, 0.25*cm))

# ═══════════════════════════════════════════════════════════
# CARDIAC MARKERS TABLE
# ═══════════════════════════════════════════════════════════
story.append(KeepTogether([
    section_header("🫀  BONUS: CARDIAC MARKERS IN MI  [Sep 2025 paper]", C_RED),
    Spacer(1, 0.1*cm),
]))
cm_data = [
    ["Myoglobin","1-2 hrs","6-9 hrs","24-36 hrs","Earliest; not cardiac-specific"],
    ["CK-MB","4-6 hrs","18-24 hrs","2-3 days","Reinfarction detection"],
    ["Troponin I/T","3-6 hrs","12-24 hrs","7-14 days","GOLD STANDARD; most specific"],
    ["LDH","12-24 hrs","2-3 days","7-10 days","Late marker"],
]
story.append(make_table(["Marker","Rises","Peaks","Normalizes","Note"],
             cm_data, [3*cm, 2.5*cm, 2.5*cm, 2.5*cm, 6*cm], C_RED))
story.append(Spacer(1, 0.2*cm))

# ── FOOTER ───────────────────────────────────────────────────────────────────
story.append(HRFlowable(width="100%", thickness=0.5, color=colors.grey))
story.append(Spacer(1, 0.1*cm))
story.append(Paragraph(
    "Amrita MBBS Biochemistry Paper 2 · Cheat Sheet · Based on Nov/Dec 2023 | Jan 2024 (Supp) | Jul/Aug 2024 | Sep 2025 Past Papers · For exam preparation only",
    sFOOT))

# ── BUILD ─────────────────────────────────────────────────────────────────────
doc.build(story)
print(f"PDF generated: {OUTPUT}")
Running Command

cd /home/daytona/workspace/biochem-cheatsheet && python generate_cheatsheet.py 2…

Your cheat sheet PDF is ready! 🎉

Biochem Paper2 CheatSheet

PDF Document · PDF

What's inside (2 pages, print-friendly):
  • Frequency map - all 15 topics ranked by how often they appear across your 4 papers
  • 15 topic cards with color-coded sections:
    • Allopurinol/Gout/Lesch-Nyhan
    • TCA Cycle (steps, enzymes, amphibolic role, inhibitors)
    • DNA Replication/Transcription/Translation + antibiotic table
    • Acid-base disorders table + buffer systems
    • Lipoprotein fractions + LDL pathway + Statins
    • Ketogenesis/DKA
    • PCR
    • Collagen + disorders table
    • Tumor markers table
    • ELISA
    • Thyroid function tests table
    • Creatinine clearance
    • Fatty liver + lipotropic factors
    • Antioxidants + scavenging enzymes
    • ETC + chemiosmotic theory + inhibitors
  • "Give Reasons" quick reference table - all 10 common ones
  • Cardiac markers in MI bonus table
Good luck tomorrow - you've got this! 💪
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