HomeFMGEBiochemistry

Master Biochemistry
for FMGE

Access 50+ high-yield questions tailored for the 2026 syllabus. Includes AI-powered explanations and performance tracking.

Start Free Practice View Full Syllabus
HIGH YIELD NOTES ~5 min read

Core Concepts

Biochemistry is the study of chemical processes within and relating to living organisms. It underpins all physiological functions and disease states. High-yield areas for FMGE include:

  • Carbohydrate Metabolism:
    • Glycolysis: Glucose → Pyruvate. Energy production. Key enzyme: PFK-1. Aerobic vs. Anaerobic metabolism (Lactate).
    • Gluconeogenesis: Non-carb precursors → Glucose (liver, kidney). Activated by glucagon, cortisol. Imp. enzymes: Pyruvate carboxylase, PEPCK, F-1,6-BPase, G-6-Phosphatase.
    • Glycogenesis & Glycogenolysis: Synthesis/breakdown of glycogen. Regulated by insulin/glucagon. GSDs – e.g., Von Gierke (G-6-Pase), McArdle (Muscle Glycogen Phosphorylase).
    • HMP Shunt (Pentose Phosphate Pathway): Produces NADPH (reductive biosynthesis, antioxidant) and Ribose-5-Phosphate. Key enzyme: G-6-PD. G6PD deficiency: Hemolytic anemia with oxidant stress.
    • TCA Cycle (Krebs Cycle): Central hub for aerobic metabolism, generates ATP, NADH, FADH2.
    • Fructose & Galactose Metabolism: Inborn errors include Hereditary Fructose Intolerance (aldolase B def), Galactosemia (GALT def).
  • Lipid Metabolism:
    • Fatty Acid Synthesis & Beta-oxidation: Synthesis (cytosol), Breakdown (mitochondria, Carnitine shuttle).
    • Ketone Bodies: Acetoacetate, β-hydroxybutyrate. Synthesized in liver during fasting/starvation. Diabetic Ketoacidosis (DKA).
    • Cholesterol Synthesis: Key enzyme HMG-CoA Reductase.
    • Lipoproteins: Chylomicrons, VLDL, LDL, HDL. Transport lipids. Disorders: Familial Hypercholesterolemias.
  • Protein & Amino Acid Metabolism:
    • Urea Cycle: Detoxifies ammonia to urea. Disorders: Hyperammonemia.
    • Amino Acid Catabolism: Carbon skeletons feed into TCA/gluconeogenesis. Nitrogen removed via transamination/deamination.
    • Disorders: Phenylketonuria (PKU - Phenylalanine hydroxylase def), Maple Syrup Urine Disease (MSUD), Alkaptonuria (Homogentisate oxidase def).
  • Nucleic Acid Metabolism:
    • Purine & Pyrimidine Synthesis/Degradation. Salvage pathways.
    • Disorders: Gout (hyperuricemia), Lesch-Nyhan syndrome (HGPRT def).
  • Enzymology:
    • Enzyme Kinetics: Michaelis-Menten (Km, Vmax). Factors: pH, temp, substrate conc.
    • Inhibition: Competitive (Vmax unchanged, Km ↑), Non-competitive (Vmax ↓, Km unchanged).
    • Regulation: Allosteric, covalent modification.
  • Vitamins & Minerals:
    • Fat-soluble (A, D, E, K): Functions, deficiency. Vit D (Ca/P), Vit K (clotting).
    • Water-soluble (B complex, C): Functions, deficiency. B1 (pyruvate dehydrogenase), B3 (NAD/NADP), B12 & Folate (one-carbon).
    • Minerals: Ca, P, Na, K, Mg, Fe, Cu, Zn.
  • Molecular Biology:
    • DNA Replication, Transcription, Translation: Central dogma.
    • Mutations: Point, frameshift.
    • Recombinant DNA: PCR, Gel electrophoresis, Blotting (Southern-DNA, Northern-RNA, Western-Protein).
  • Hormones & Signal Transduction: Insulin/Glucagon regulate blood glucose. Steroid hormones.
  • Clinical Biochemistry Markers: LFTs, RFTs, Cardiac enzymes (CK-MB, Troponins), Electrolytes, ABG.

Clinical Presentation

  • Often non-specific: Failure to thrive, developmental delay, neurological dysfunction (seizures, hypotonia), recurrent infections.
  • Specific signs: Unusual body/urine odor (e.g., MSUD, PKU), hepatosplenomegaly, jaundice, cardiomyopathy, acidosis/alkalosis.
  • Triggered by stress: Fasting, infection, certain foods/drugs can exacerbate symptoms in metabolic disorders.

Diagnosis (Gold Standard)

Primarily based on identifying abnormal metabolites or enzyme deficiencies:

  • Newborn Screening (NBS): Tandem Mass Spectrometry (MS/MS) for amino acidopathies, organic acidemias, fatty acid oxidation defects.
  • Specific Enzyme Assays: Confirm enzyme deficiency in affected tissues (e.g., fibroblasts, WBCs).
  • Genetic Testing: Targeted gene sequencing or whole exome sequencing (WES) to identify causative mutations.
  • Metabolic Panels: Plasma amino acids, urine organic acids, serum acylcarnitines, plasma lactate/ammonia, CSF studies.

Management (First Line)

Focuses on dietary modification, removing toxic substances, and supplementing deficient products:

  • Dietary Restrictions: Limiting intake of problematic precursors (e.g., phenylalanine in PKU, lactose/galactose in galactosemia).
  • Cofactor Supplementation: High-dose vitamins/cofactors if the enzyme defect is responsive (e.g., B6 in some homocystinurias, B12 for methylmalonic acidemia).
  • Enzyme Replacement Therapy (ERT): For specific lysosomal storage disorders.
  • Symptomatic Support: Addressing acute metabolic crises (e.g., IV glucose for hypoglycemia, dialysis for hyperammonemia).

Exam Red Flags

  • Pathways vs. Enzymes: Know key regulatory enzymes (e.g., PFK-1 in glycolysis, HMG-CoA reductase in cholesterol synthesis) and their clinical correlations.
  • Vitamin Deficiencies: High yield on B-complex vitamins (B1-Thiamine, B3-Niacin, B12-Cobalamin, Folate) and their associated clinical syndromes.
  • Inborn Errors of Metabolism (IEMs): Common ones like PKU, MSUD, G6PD deficiency, Galactosemia, Von Gierke are frequently tested. Focus on defective enzyme and accumulating metabolite.
  • Molecular Biology Basics: Central dogma, types of blotting (Southern, Northern, Western) and what they detect, PCR principles.
  • Acid-Base Balance: Metabolic acidosis causes and compensation related to biochemical disorders (e.g., DKA, lactic acidosis, urea cycle defects).

Sample Practice Questions

Question 1

A 25-year-old male presents to the emergency department with a 2-day history of polyuria, polydipsia, and fatigue. He is found to be tachypneic with deep, rapid breaths (Kussmaul respiration). Arterial blood gas shows pH 7.18, pCO2 25 mmHg, HCO3- 10 mEq/L. His blood glucose is 450 mg/dL, and urine ketones are strongly positive. Which of the following is the primary biochemical mechanism leading to his profound acidosis?

A) Impaired renal acid excretion.
B) Excessive production of lactic acid.
C) Increased fatty acid oxidation leading to ketone body accumulation.
D) Bicarbonate loss through the gastrointestinal tract.
Explanation: This area is hidden for preview users.
Question 2

A 6-month-old infant is brought to the clinic by her parents who are concerned about her developmental delay, fair hair, and a 'mousy' odor detected from her urine. Newborn screening results, recently reviewed, showed significantly elevated phenylalanine levels. Dietary modifications are being discussed.

A) Deficiency of Tyrosinase
B) Deficiency of Phenylalanine hydroxylase
C) Deficiency of Homogentisate oxidase
D) Deficiency of Branched-chain alpha-keto acid dehydrogenase
Explanation: This area is hidden for preview users.
Question 3

A 55-year-old obese male presents with sudden onset of excruciating pain, swelling, and redness in his right great toe. He reports a similar episode a year ago that resolved spontaneously. His serum uric acid level is 9.2 mg/dL (normal range 3.5-7.2 mg/dL). Aspiration of the affected joint reveals needle-shaped, negatively birefringent crystals. The enzyme primarily responsible for the terminal step in the synthesis of uric acid, and thus a key target for pharmacotherapy in this condition, is:

A) Adenosine deaminase
B) Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
C) Xanthine oxidase
D) Phosphoribosyl pyrophosphate (PRPP) synthetase
Explanation: This area is hidden for preview users.

Ready to see the answers?

Unlock All Answers

FMGE

  • ✓ 50+ Biochemistry Questions
  • ✓ AI Tutor Assistance
  • ✓ Detailed Explanations
  • ✓ Performance Analytics
Get Full Access