Master every high-yield biochemistry topic for NEET PG 2026: enzymology, carbohydrate metabolism, lipid metabolism, amino acid metabolism, molecular biology, vitamins, hormones, and genetic disorders with real exam facts and study strategies.
Version 1.0 — Published April 2026
Biochemistry contributes 12-18 questions to NEET PG and rewards candidates who master metabolic regulation and clinical correlations rather than memorizing every intermediate. The eight high-yield areas that return with the highest frequency are:
This guide covers each area with the clinical facts that NBE tests, the enzyme names and pathways you must know cold, and a practical study strategy to secure 10+ marks from Biochemistry alone.
Biochemistry is the subject where molecular precision meets clinical reasoning. Unlike Anatomy, where spatial visualization carries you through stems, Biochemistry demands that you know specific enzymes, their regulators, and the clinical consequence when they fail. There is no way to derive the rate-limiting enzyme of glycolysis from first principles under exam pressure. You either know it is phosphofructokinase-1 or you do not.
That specificity is what makes Biochemistry both challenging and predictable. NBE returns to the same metabolic pathways, enzyme defects, and vitamin associations year after year. A candidate who has drilled the eight high-yield areas in this guide will recognize the majority of Biochemistry stems on sight.
This guide is structured around those eight areas. Each section gives you the clinical correlations that NBE tests, the enzyme details that distinguish correct from close-but-wrong options, and the common trap patterns. Pair it with the full Biochemistry subject hub and daily MCQ practice to convert reading into retrievable exam knowledge.
Enzymology is the study of enzyme structure, kinetics, and regulation — and it forms the foundation for understanding every metabolic pathway question in NEET PG. Without a firm grip on Michaelis-Menten kinetics and inhibition patterns, you cannot solve clinical pharmacology or metabolism questions that test enzyme modulation.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Start practicing NEET PG MCQs with AI-powered explanations.
Start Free PracticeBuild a personal NEET PG mistake-bank with AI flashcards: error taxonomy, mock-test extraction, Anki vs RemNote vs NEETPGAI, spaced repetition cadence, leech card management, last-week protocol.
Build a personalised AI-powered NEET PG study plan: diagnostic baseline, subject prioritisation by weightage, spaced repetition, AI tutor, mock analysis, 12/6/3/1-month templates.
Master cholesterol, beta-oxidation, ketogenesis, urea cycle, transamination, PKU, MSUD, homocystinuria, G6PD and one-carbon metabolism for NEET PG 2026.
Daily MCQs, study tips, and topper strategies on Telegram.
Join on Telegram →The Michaelis-Menten equation describes the relationship between substrate concentration [S] and reaction velocity (V):
V = Vmax [S] / (Km + [S])
At low [S], the reaction is first-order (velocity proportional to [S]). At high [S], the reaction is zero-order (velocity independent of [S] because the enzyme is saturated). This transition is a favorite conceptual question in NBE.
The Lineweaver-Burk plot transforms the Michaelis-Menten curve into a straight line by plotting 1/V against 1/[S]:
NBE tests this plot primarily through inhibition patterns:
| Inhibition Type | Km (apparent) | Vmax (apparent) | Lineweaver-Burk Pattern |
|---|---|---|---|
| Competitive | Increased | Unchanged | Lines intersect on Y-axis |
| Non-competitive | Unchanged | Decreased | Lines intersect on X-axis |
| Uncompetitive | Decreased | Decreased | Parallel lines |
Clinical correlations: Methotrexate is a competitive inhibitor of dihydrofolate reductase. Organophosphates are irreversible inhibitors of acetylcholinesterase. Allopurinol inhibits xanthine oxidase (used in gout). Statins competitively inhibit HMG-CoA reductase. Each of these connects enzymology to pharmacology questions.
Allosteric enzymes do not follow Michaelis-Menten kinetics — they show a sigmoidal velocity curve. They have regulatory sites distinct from the active site. Key examples:
Carbohydrate metabolism encompasses glycolysis, the TCA cycle, gluconeogenesis, glycogenesis, glycogenolysis, and the HMP shunt. Together, these pathways generate 4-6 questions per NEET PG paper. The key to scoring is knowing rate-limiting enzymes and their clinical diseases.
Glycolysis is the cytoplasmic pathway that converts one molecule of glucose into two molecules of pyruvate, generating 2 ATP (net) and 2 NADH.
Rate-limiting enzyme: Phosphofructokinase-1 (PFK-1) — the committed step. Activated by AMP and fructose-2,6-bisphosphate. Inhibited by ATP and citrate. This is the most frequently tested regulatory enzyme in NEET PG biochemistry.
Key enzymes to know:
Clinical correlation: Pyruvate kinase deficiency causes chronic hemolytic anemia — the most common enzyme deficiency of glycolysis. RBCs depend entirely on glycolysis for ATP (no mitochondria), making them uniquely vulnerable.
The TCA cycle operates in the mitochondrial matrix and is the final common pathway for oxidation of carbohydrates, fats, and proteins.
Rate-limiting enzyme: Isocitrate dehydrogenase — activated by ADP, inhibited by ATP and NADH.
Net yield per acetyl-CoA: 3 NADH, 1 FADH2, 1 GTP. Per glucose molecule: multiply by 2 (two acetyl-CoA per glucose).
Clinical correlation: Arsenic poisoning inhibits the pyruvate dehydrogenase complex (and alpha-ketoglutarate dehydrogenase) because arsenic binds to lipoic acid, a required cofactor. This is a classic NEET PG association — "arsenic + metabolic acidosis + garlic breath" in a stem points to PDH complex inhibition.
The HMP shunt operates in the cytoplasm and has two phases:
Rate-limiting enzyme: Glucose-6-phosphate dehydrogenase (G6PD) — the oxidative phase enzyme.
G6PD deficiency is the most common enzymopathy worldwide. X-linked recessive. NADPH depletion leads to inability to regenerate reduced glutathione, causing oxidative damage to RBC membranes. Triggered by oxidant drugs (primaquine, sulfonamides, dapsone), fava beans, and infections. Peripheral smear shows Heinz bodies (denatured hemoglobin) and bite cells. This is tested almost every year in NEET PG.
| Disease | Enzyme Defect | Glycogen Pattern | Key Clinical Feature |
|---|---|---|---|
| Von Gierke (Type I) | Glucose-6-phosphatase | Hepatomegaly, hypoglycemia | Severe fasting hypoglycemia, lactic acidosis, hyperuricemia |
| Pompe (Type II) | Acid maltase (lysosomal alpha-1,4-glucosidase) | Cardiomegaly | Only GSD with lysosomal involvement; cardiac failure in infants |
| Cori (Type III) | Debranching enzyme | Short outer chains | Milder hypoglycemia than von Gierke (gluconeogenesis intact) |
| McArdle (Type V) | Muscle glycogen phosphorylase | Muscle glycogen accumulation | Exercise intolerance, myoglobinuria, no rise in lactate on exercise |
NBE trap: Pompe disease is the only glycogen storage disease that involves lysosomes — if the stem mentions "lysosomal enzyme deficiency with cardiomegaly," the answer is Pompe. McArdle disease is tested through the ischemic forearm exercise test — no rise in blood lactate (because muscle cannot break down glycogen) but a normal rise in ammonia.
Master NEET PG with AI-powered practice — adaptive MCQs with instant explanations.
Start Free Practice →Lipid metabolism questions test three areas: fatty acid oxidation, ketone body synthesis, and lipoprotein classification with familial dyslipidemias. Together, these account for 2-4 questions per paper.
Beta-oxidation occurs in the mitochondrial matrix and involves four repeating steps: oxidation (FAD), hydration, oxidation (NAD+), and thiolysis. Each cycle removes 2 carbons as acetyl-CoA.
Rate-limiting step: Carnitine palmitoyltransferase-1 (CPT-1) — controls entry of long-chain fatty acids into mitochondria via the carnitine shuttle. Inhibited by malonyl-CoA (the first committed intermediate of fatty acid synthesis). This reciprocal regulation ensures that synthesis and oxidation do not run simultaneously.
Energy yield from palmitate (C16): 7 cycles of beta-oxidation produce 8 acetyl-CoA, 7 FADH2, and 7 NADH. Total ATP: 106 (gross) or 104 (net, after subtracting 2 ATP equivalents for initial activation).
Clinical correlation: Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common inherited defect of fatty acid oxidation. Presents with hypoketotic hypoglycemia during fasting — the inability to oxidize fatty acids means both ketogenesis and gluconeogenesis are impaired. This "hypoketotic hypoglycemia" pattern is a classic NEET PG clue.
Ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) are synthesized in the liver mitochondria from acetyl-CoA when oxaloacetate is diverted to gluconeogenesis during prolonged fasting or uncontrolled diabetes.
Rate-limiting enzyme: HMG-CoA synthase (mitochondrial — distinct from the cytoplasmic HMG-CoA synthase used in cholesterol synthesis).
Key fact: The liver produces ketone bodies but cannot use them (lacks succinyl-CoA:acetoacetate CoA transferase, also called thiophorase). The brain, heart, and skeletal muscle are the primary consumers. During prolonged starvation, ketone bodies supply up to 75% of the brain's energy needs (Harper's Illustrated Biochemistry, 31st Edition).
| Lipoprotein | Primary Lipid | Origin | Key Apolipoprotein | Clinical Significance |
|---|---|---|---|---|
| Chylomicrons | Dietary triglycerides | Intestine | ApoB-48, ApoCII, ApoE | Cleared by LPL; deficiency causes Type I hyperlipidemia |
| VLDL | Endogenous triglycerides | Liver | ApoB-100, ApoCII, ApoE | Precursor of LDL |
| LDL | Cholesterol | VLDL catabolism | ApoB-100 | "Bad cholesterol"; target of statins |
| HDL | Phospholipids | Liver, intestine | ApoA-I | "Good cholesterol"; reverse cholesterol transport via LCAT |
Familial hypercholesterolemia (Type IIa): Autosomal dominant. Defect in LDL receptor. Elevated LDL cholesterol. Tendon xanthomas, xanthelasma, premature atherosclerosis. Homozygotes develop coronary artery disease before age 20. This is one of the most frequently tested genetic disorders in NEET PG biochemistry.
| Type | Elevated Lipoprotein | Defect | Serum Appearance |
|---|---|---|---|
| I | Chylomicrons | LPL or ApoCII deficiency | Creamy supernatant |
| IIa | LDL | LDL receptor defect | Clear |
| IIb | LDL + VLDL | Multiple | Clear to turbid |
| III | IDL (beta-VLDL) | ApoE deficiency | Turbid |
| IV | VLDL | Overproduction | Turbid |
| V | Chylomicrons + VLDL | Multiple | Creamy supernatant + turbid |
Amino acid metabolism generates 2-4 NEET PG questions annually. The questions cluster around the urea cycle, transamination, and inborn errors of metabolism — conditions where a single enzyme defect produces a recognizable clinical phenotype.
The urea cycle converts toxic ammonia to urea for renal excretion. It spans two compartments: the first two reactions occur in the mitochondrial matrix, and the remaining three in the cytoplasm.
Rate-limiting enzyme: Carbamoyl phosphate synthetase I (CPS-I) — requires N-acetylglutamate as an obligate activator. This is a frequently tested fact: N-acetylglutamate is synthesized by N-acetylglutamate synthase, activated by arginine.
Urea cycle steps (mnemonic: "Ordinarily, Clever Children Argue Furiously"):
Clinical correlation: Ornithine transcarbamoylase (OTC) deficiency is the most common urea cycle disorder. X-linked. Presents with hyperammonemia, respiratory alkalosis (ammonia stimulates the respiratory center), and elevated orotic acid in urine (excess carbamoyl phosphate diverts into pyrimidine synthesis). The orotic acid finding distinguishes OTC deficiency from CPS-I deficiency (no orotic aciduria in CPS-I deficiency) — a classic NEET PG differentiator.
| Disease | Enzyme Defect | Accumulated Metabolite | Key Clinical Feature |
|---|---|---|---|
| PKU (Phenylketonuria) | Phenylalanine hydroxylase | Phenylalanine, phenylpyruvate | Musty/mousy odor, intellectual disability, fair skin (decreased melanin), eczema |
| Alkaptonuria | Homogentisic acid oxidase | Homogentisic acid | Dark urine on standing, ochronosis (blue-black discoloration of cartilage), arthritis |
| Maple syrup urine disease | Branched-chain alpha-keto acid dehydrogenase | Leucine, isoleucine, valine (branched-chain amino acids) | Maple syrup odor of urine, neurological deterioration, neonatal onset |
| Homocystinuria | Cystathionine beta-synthase | Homocysteine | Marfanoid habitus, downward lens subluxation (Marfan is upward), thromboembolism, intellectual disability |
| Cystinuria | Defective renal tubular reabsorption of COLA (cystine, ornithine, lysine, arginine) | Cystine in urine | Hexagonal crystals in urine, recurrent renal calculi |
NBE trap on homocystinuria vs Marfan syndrome: Both present with tall stature and long limbs, but the lens subluxation direction is the discriminator — upward and temporal in Marfan (fibrillin-1 defect), downward and nasal in homocystinuria. Additionally, Marfan patients have normal intelligence and no thrombotic tendency, while homocystinuria causes intellectual disability and thromboembolic events.
PKU screening: The Guthrie test (bacterial inhibition assay) or tandem mass spectrometry on newborn blood spots is used for neonatal screening. Treatment is a phenylalanine-restricted diet with tyrosine supplementation. Maternal PKU (uncontrolled phenylalanine in a pregnant woman with PKU) causes microcephaly and congenital heart disease in the fetus — even if the fetus does not have PKU.
Molecular biology questions have increased in NEET PG since 2022. NBE tests enzyme functions in replication and transcription, mutation types, and the genetic code properties. This section is conceptually dense but highly predictable — the same enzymes and definitions recur.
DNA replication is semiconservative (Meselson-Stahl experiment), bidirectional, and occurs in the S phase of the cell cycle.
Key enzymes and their functions:
| Enzyme | Function | Key Fact |
|---|---|---|
| Helicase | Unwinds double helix | Creates replication fork |
| Topoisomerase (gyrase) | Relieves supercoiling ahead of the fork | Target of fluoroquinolones (ciprofloxacin) |
| Primase | Synthesizes RNA primer | Required because DNA polymerase cannot initiate synthesis de novo |
| DNA Polymerase III | Main replicative polymerase (prokaryotes) | 5'→3' synthesis, 3'→5' proofreading (exonuclease) |
| DNA Polymerase I | Removes RNA primers, fills gaps | 5'→3' exonuclease activity (unique) |
| DNA Ligase | Joins Okazaki fragments on the lagging strand | Seals phosphodiester bonds |
| SSB proteins | Stabilize single-stranded DNA | Prevent re-annealing |
Clinical correlations: Fluoroquinolones inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV. This connects molecular biology directly to pharmacology. Methotrexate inhibits dihydrofolate reductase, blocking thymidylate synthesis and thus DNA replication.
Transcription is the synthesis of mRNA from a DNA template by RNA polymerase.
Eukaryotic RNA polymerases:
Post-transcriptional modifications of mRNA:
Translation occurs on ribosomes (80S in eukaryotes: 60S + 40S subunits).
Antibiotics that target translation (connects to Pharmacology):
| Antibiotic | Target | Subunit |
|---|---|---|
| Chloramphenicol | Peptidyl transferase | 50S |
| Erythromycin | Translocation | 50S |
| Clindamycin | Translocation | 50S |
| Tetracycline | Aminoacyl-tRNA binding to A site | 30S |
| Aminoglycosides | Misreading of mRNA | 30S |
Sickle cell disease is the single most tested molecular biology clinical correlation. A single nucleotide change (A→T) in the beta-globin gene on chromosome 11 changes codon 6 from GAG (glutamic acid) to GTG (valine). The resulting HbS polymerizes under hypoxic conditions, causing the sickle shape.
Vitamins are tested with high frequency in NEET PG — 3-5 questions per paper. NBE tests the active coenzyme form, the metabolic pathway each vitamin participates in, and the clinical deficiency syndrome. This is pure recall territory: you either know the associations or you lose marks.
| Vitamin | Active Form | Key Pathway | Deficiency Disease | Classic Feature |
|---|---|---|---|---|
| B1 (Thiamine) | TPP (thiamine pyrophosphate) | PDH complex, alpha-KG dehydrogenase, transketolase | Beriberi (dry/wet), Wernicke-Korsakoff | Wet beriberi: cardiac failure; Wernicke: ataxia, ophthalmoplegia, confusion |
| B2 (Riboflavin) | FAD, FMN | Electron transport, fatty acid oxidation | Ariboflavinosis | Cheilosis, angular stomatitis, corneal vascularization |
| B3 (Niacin) | NAD+, NADP+ | Glycolysis, TCA, HMP shunt, beta-oxidation | Pellagra | 3 Ds: Dermatitis (Casal necklace), Diarrhea, Dementia |
| B5 (Pantothenic acid) | Coenzyme A | Acetyl-CoA formation, TCA, fatty acid synthesis | Rare (burning feet syndrome) | Component of CoA and ACP |
| B6 (Pyridoxine) | PLP (pyridoxal phosphate) | Transamination, decarboxylation, heme synthesis (ALA synthase) | Sideroblastic anemia, peripheral neuropathy | INH-induced deficiency (always co-prescribe pyridoxine with INH) |
| B7 (Biotin) | Biotin-CO2 | Carboxylation reactions (pyruvate carboxylase, acetyl-CoA carboxylase) | Dermatitis, alopecia | Raw egg whites (avidin) bind biotin |
| B9 (Folate) | THF (tetrahydrofolate) | One-carbon transfers, thymidylate synthesis, purine synthesis | Megaloblastic anemia, neural tube defects | Methotrexate inhibits DHFR, blocking THF regeneration |
| B12 (Cobalamin) | Methylcobalamin, adenosylcobalamin | Methionine synthase (homocysteine→methionine), methylmalonyl-CoA mutase | Megaloblastic anemia + neurological symptoms | Methylmalonic aciduria distinguishes B12 from folate deficiency |
| C (Ascorbic acid) | Ascorbate | Collagen synthesis (proline and lysine hydroxylation), iron absorption | Scurvy | Bleeding gums, perifollicular hemorrhage, poor wound healing |
NBE trap on B12 vs folate deficiency: Both cause megaloblastic anemia. However, B12 deficiency also causes neurological symptoms (subacute combined degeneration of the spinal cord — posterior columns and lateral corticospinal tracts) and methylmalonic aciduria. Folate deficiency does not cause neurological symptoms or methylmalonic aciduria. If the stem mentions "megaloblastic anemia + paresthesias + ataxia," the answer is B12 deficiency.
| Vitamin | Active Form | Deficiency | Toxicity |
|---|---|---|---|
| A (Retinol) | Retinal (vision), retinoic acid (gene expression) | Night blindness (nyctalopia), Bitot spots, xerophthalmia, keratomalacia | Pseudotumor cerebri (raised intracranial pressure), teratogenicity, hepatotoxicity |
| D (Cholecalciferol) | 1,25-(OH)2-D3 (calcitriol) | Rickets (children), osteomalacia (adults) | Hypercalcemia, metastatic calcification, renal stones |
| E (Tocopherol) | Alpha-tocopherol | Hemolytic anemia in premature infants, spinocerebellar degeneration | Rare; may potentiate anticoagulant effect of warfarin |
| K (Phylloquinone) | Menadione | Hemorrhagic disease of newborn, prolonged PT | Not applicable for dietary forms |
Vitamin K is the cofactor for gamma-carboxylation of glutamate residues in clotting factors II, VII, IX, and X (and proteins C and S). Warfarin inhibits vitamin K epoxide reductase, blocking this carboxylation. This is one of the most frequently tested connections between biochemistry and pharmacology.
Practice Biochemistry MCQs on vitamin deficiency diseases — the coenzyme-pathway-disease triplet is the fastest route to marks in this section.
Hormone biochemistry generates 1-3 questions per NEET PG paper. The questions focus on signal transduction mechanisms, second messenger systems, and the molecular basis of hormone action.
Insulin is synthesized as preproinsulin in pancreatic beta cells. It is cleaved to proinsulin (removal of signal peptide), then to insulin + C-peptide (removal of connecting peptide). C-peptide levels are used clinically to distinguish endogenous from exogenous insulin.
Insulin receptor: A receptor tyrosine kinase (RTK). Insulin binding activates the intrinsic tyrosine kinase activity, which phosphorylates insulin receptor substrate-1 (IRS-1). This activates the PI3K/Akt pathway, leading to:
NBE tests which enzymes insulin activates versus inhibits. The rule is simple: insulin activates anabolic pathways and inhibits catabolic pathways.
| Insulin Activates | Insulin Inhibits |
|---|---|
| Glucokinase | Glucose-6-phosphatase |
| Phosphofructokinase-1 | Fructose-1,6-bisphosphatase |
| Pyruvate kinase | Phosphoenolpyruvate carboxykinase (PEPCK) |
| Glycogen synthase | Glycogen phosphorylase |
| Acetyl-CoA carboxylase | Hormone-sensitive lipase |
| Pyruvate dehydrogenase | — |
Thyroid hormone synthesis occurs in the thyroid follicular cells and involves:
Clinical correlation: Propylthiouracil (PTU) and methimazole both inhibit TPO (blocking organification and coupling). PTU additionally inhibits peripheral conversion of T4 to T3 by inhibiting 5'-deiodinase. This is why PTU is preferred in thyroid storm — it has a dual mechanism. Methimazole is preferred otherwise because of lower hepatotoxicity risk.
| Hormone | Receptor Type | Second Messenger |
|---|---|---|
| Glucagon, ACTH, TSH, LH, FSH, ADH (V2) | Gs-coupled GPCR | cAMP (adenylyl cyclase) |
| Insulin, EGF, PDGF | Receptor tyrosine kinase | Tyrosine phosphorylation cascade |
| ADH (V1), oxytocin, angiotensin II | Gq-coupled GPCR | IP3/DAG (phospholipase C) |
| ANP, NO | Guanylyl cyclase | cGMP |
| Thyroid hormone, steroids, vitamin D, retinoic acid | Intracellular (nuclear) receptor | Direct gene transcription |
Genetic disorders in biochemistry focus on two categories: trinucleotide repeat expansion diseases and lysosomal storage diseases. Both are tested with high frequency because they produce distinctive clinical phenotypes linked to specific molecular defects.
| Disease | Repeat | Gene/Protein | Inheritance | Key Feature |
|---|---|---|---|---|
| Huntington disease | CAG | Huntingtin (chromosome 4) | AD | Chorea, dementia, caudate atrophy, onset age 30-50 |
| Fragile X syndrome | CGG | FMR1 (X chromosome) | X-linked | Most common inherited cause of intellectual disability, macro-orchidism, long face |
| Myotonic dystrophy | CTG | DMPK | AD | Most common adult muscular dystrophy, myotonia, cataracts, frontal balding |
| Friedreich ataxia | GAA | Frataxin | AR | Only AR trinucleotide repeat disease; ataxia, hypertrophic cardiomyopathy |
Anticipation: Trinucleotide repeat diseases show anticipation — the disease becomes more severe and has earlier onset in successive generations because the number of repeats expands during meiosis. This is a frequently tested genetic concept.
NBE trap: Friedreich ataxia is the only autosomal recessive trinucleotide repeat disease. All others are autosomal dominant or X-linked. If the stem describes "ataxia + cardiomyopathy + autosomal recessive inheritance," the answer is Friedreich ataxia.
Lysosomal storage diseases result from deficiency of specific lysosomal enzymes, causing accumulation of undigested substrates within lysosomes.
| Disease | Enzyme Defect | Accumulated Substrate | Key Clinical Feature |
|---|---|---|---|
| Gaucher disease | Glucocerebrosidase | Glucocerebroside | Most common lysosomal storage disease; "crumpled tissue paper" macrophages (Gaucher cells), hepatosplenomegaly, bone crises |
| Tay-Sachs disease | Hexosaminidase A | GM2 ganglioside | Cherry-red spot on macula, progressive neurodegeneration, no hepatosplenomegaly |
| Niemann-Pick disease (A/B) | Sphingomyelinase | Sphingomyelin | Foam cells, hepatosplenomegaly, cherry-red spot (type A). Type A: severe infantile neurovisceral |
| Fabry disease | Alpha-galactosidase A | Globotriaosylceramide | X-linked; angiokeratomas, peripheral neuropathy (burning hands/feet), renal failure |
| Krabbe disease | Galactocerebrosidase | Galactocerebroside | Globoid cells, severe neurodegeneration in infancy |
| Metachromatic leukodystrophy | Arylsulfatase A | Sulfatide | Demyelination, metachromatic granules on biopsy |
| Hunter syndrome (MPS II) | Iduronate sulfatase | Heparan sulfate, dermatan sulfate | X-linked (only X-linked MPS); mild Hurler-like features, no corneal clouding |
| Hurler syndrome (MPS I) | Alpha-L-iduronidase | Heparan sulfate, dermatan sulfate | AR; corneal clouding (distinguishes from Hunter), gargoylism, hepatosplenomegaly |
Discriminating Tay-Sachs from Niemann-Pick: Both can have cherry-red spot on macula. The distinguishing feature is hepatosplenomegaly — present in Niemann-Pick, absent in Tay-Sachs. If the stem says "cherry-red spot + hepatosplenomegaly," the answer is Niemann-Pick. If "cherry-red spot without organomegaly," it is Tay-Sachs.
Gaucher disease is the most common lysosomal storage disease worldwide. It is treatable with enzyme replacement therapy (imiglucerase) — one of the few lysosomal storage diseases with effective treatment. This therapeutic fact is tested in Pharmacology.
Knowing the content is necessary but not sufficient. Biochemistry in NEET PG rewards candidates who can retrieve specific enzyme names and clinical associations under time pressure. The strategy below is designed for exactly that conversion.
Cover the eight high-yield areas in this guide using Vasudevan's Textbook of Biochemistry or Lehninger's Principles of Biochemistry (selectively). Spend two days on each major topic. For each topic, build a one-page summary with the rate-limiting enzymes, clinical correlations, and deficiency diseases. Do not take extensive notes — the one-page summary is your revision tool.
Solve 15 biochemistry MCQs daily on the topic you studied that day. Mark every question you get wrong and note the specific enzyme or pathway you were missing.
Increase to 25-30 biochemistry MCQs daily. Mix topics — do not cluster by pathway. Use previous year question banks and clinical vignettes. For each wrong answer, trace the error to one of three categories:
Read our spaced repetition guide for NEET PG and build a deck of rate-limiting enzymes, inborn errors, and vitamin coenzyme forms. Review the deck daily.
In the final week, solve one full-length biochemistry mock under timed conditions. Revise your one-page summaries in reverse order. On the day before the exam, review only three things: the glycogen storage diseases table, the inborn errors of metabolism table, and the vitamin coenzyme-deficiency table.
For a comprehensive study plan that integrates Biochemistry with other subjects, explore the Pathology high-yield topics guide — pathology and biochemistry share significant overlap in metabolic diseases and genetic disorders.
Biochemistry contributes 12-18 questions in NEET PG, covering enzymology, metabolism, molecular biology, and vitamins. Metabolism-based questions (glycolysis, TCA, beta-oxidation, urea cycle) account for roughly half. Inborn errors of metabolism and vitamin deficiency diseases are tested almost every year.
Enzyme kinetics (Michaelis-Menten, Lineweaver-Burk), glycogen storage diseases, inborn errors of amino acid metabolism (PKU, alkaptonuria, maple syrup urine disease), lipoproteins, and vitamin deficiency diseases dominate. Molecular biology questions on DNA replication, transcription, and mutations have increased since 2022.
Harper's Illustrated Biochemistry is the gold standard reference but is too detailed for first-pass reading. Use Vasudevan's Textbook of Biochemistry for a concise overview, then refer to Harper's selectively for enzyme regulation, metabolic integration, and molecular biology chapters where depth is needed.
Focus on rate-limiting enzymes and their regulators — NBE tests regulatory steps, not every intermediate. Draw each pathway once from memory, then use spaced repetition for the key enzymes. Link pathways to clinical diseases: G6PD deficiency to HMP shunt, von Gierke disease to glycogenolysis, PKU to phenylalanine metabolism.
Competitive inhibition (increased Km, unchanged Vmax), non-competitive inhibition (unchanged Km, decreased Vmax), and uncompetitive inhibition (both Km and Vmax decreased) are the three core types. NBE tests Lineweaver-Burk plot interpretation — know where the lines intersect for each type.
PKU (phenylalanine hydroxylase deficiency, musty odor), alkaptonuria (homogentisic acid oxidase deficiency, dark urine), maple syrup urine disease (branched-chain alpha-keto acid dehydrogenase deficiency), homocystinuria (cystathionine beta-synthase deficiency, Marfanoid habitus), and cystinuria (defective renal tubular reabsorption, hexagonal crystals) are perennial favorites.
Vitamins account for 3-5 questions per paper. Water-soluble vitamin deficiencies (B1 beriberi, B3 pellagra, B12 megaloblastic anemia, C scurvy) and fat-soluble vitamin toxicities (A teratogenicity, D hypercalcemia) are high-yield. Know each vitamin's active coenzyme form and the pathway it participates in.
In the final two weeks, focus on three tables: rate-limiting enzymes of all major pathways, inborn errors of metabolism with their enzyme defects and clinical features, and vitamin coenzyme forms with deficiency diseases. Solve 20-30 biochemistry MCQs daily under timed conditions. Use your self-made one-page summaries for each of the eight sections in this guide.
Yes. Gaucher disease (glucocerebrosidase deficiency, crumpled tissue paper macrophages), Tay-Sachs (hexosaminidase A deficiency, cherry-red spot on macula), Niemann-Pick (sphingomyelinase deficiency, foam cells), and Fabry disease (alpha-galactosidase A deficiency, angiokeratomas) are tested regularly. Know the enzyme defect, accumulated substrate, and one key clinical feature for each.
Know that insulin binds a receptor tyrosine kinase, activates the IRS-1/PI3K/Akt pathway, and promotes GLUT4 translocation for glucose uptake. Key downstream effects: activates glycogen synthase, activates pyruvate dehydrogenase, inhibits hormone-sensitive lipase. NBE tests which enzymes insulin activates versus inhibits — make a two-column table and memorize it.
Start your biochemistry prep today. Open the Biochemistry subject page and solve your first 15 MCQs — the enzyme names you drill now are the enzyme names you will retrieve on exam day. Want unlimited AI-powered biochemistry MCQs with detailed explanations? Explore NEETPGAI Pro.
Written by: NEETPGAI Editorial Team Reviewed by: Pending SME Review Last reviewed: April 2026
This article is reviewed by qualified medical professionals for clinical accuracy and exam relevance. For corrections or updates, contact the editorial team.