Biochemistry
MBBS Biochemistry question bank: biomolecules, enzymes, metabolism, molecular biology, vitamins, nutrition and clinical biochemistry.
12chapters144questions75High-Yield
Definition
Acid–base balance maintains blood pH within 7.35–7.45 through buffers, the lungs and the kidneys; disorders are acidosis or alkalosis.
Regulation
- Buffers — bicarbonate (immediate)
- Lungs — CO₂ (minutes)
- Kidneys — HCO₃⁻, H⁺ (slow)
Disorders
- Metabolic acidosis — ↓ HCO₃⁻ (DKA)
- Respiratory acidosis — ↑ CO₂ (hypoventilation)
- Metabolic alkalosis — ↑ HCO₃⁻ (vomiting)
- Respiratory alkalosis — ↓ CO₂ (hyperventilation)
Three lines of defence — buffers, lungs, kidneys — hold pH steady. Disorder Change Metabolic acidosis ↓ HCO₃⁻ Respiratory acidosis ↑ CO₂ Metabolic alkalosis ↑ HCO₃⁻ Applied
- DKA (metabolic acidosis)
- Compensation mechanisms
🔑KEY POINTS TO REMEMBER- pH 7.35–7.45 held by buffers, lungs, kidneys.
- Acidosis/alkalosis: metabolic (HCO₃⁻) or respiratory (CO₂).
- DKA = metabolic acidosis.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Liver function tests (LFTs) are biochemical tests that assess hepatic synthesis, excretion and cell integrity.
Categories
- Enzymes — ALT, AST (hepatocellular); ALP, GGT (cholestasis)
- Bilirubin — conjugated / unconjugated
- Synthetic — albumin, prothrombin time
- Total protein, A:G ratio
LFTs sample enzymes, bilirubin and synthetic markers together. Test Indicates ALT/AST Hepatocellular damage ALP Cholestasis Albumin Synthetic function Applied
- Hepatitis (↑ ALT/AST)
- Obstruction (↑ ALP, bilirubin)
🔑KEY POINTS TO REMEMBER- LFTs: enzymes (ALT/AST, ALP), bilirubin, synthetic (albumin, PT).
- ALT/AST ↑ in hepatocellular damage.
- ALP ↑ in cholestasis.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Renal function tests assess the kidney’s excretory and filtration capacity.
Tests
- Blood urea, serum creatinine — ↑ in renal failure
- GFR / creatinine clearance — filtration
- Urine analysis — protein, cells
- Electrolytes
Clearance
- Inulin — gold standard for GFR
- Creatinine clearance — practical estimate
Renal tests combine blood markers, clearance and urine analysis. Test Assesses Creatinine GFR (↑ in failure) Urea Excretion Clearance Filtration Applied
- Chronic kidney disease staging
- ↑ creatinine in renal failure
🔑KEY POINTS TO REMEMBER- RFTs: urea, creatinine, GFR/clearance, urine analysis.
- Inulin = gold standard; creatinine clearance practical.
- ↑ creatinine → renal failure.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Free radicals are reactive molecules with unpaired electrons that cause cell damage; antioxidants neutralise them.
Free Radicals
- Reactive oxygen species (superoxide, H₂O₂, hydroxyl)
- Damage lipids, proteins, DNA
- From metabolism, radiation, toxins
Antioxidants
- Enzymes — superoxide dismutase, catalase, glutathione peroxidase
- Vitamins — C, E, β-carotene
- Glutathione
Antioxidants counter the cell damage caused by reactive free radicals. Antioxidant Type SOD, catalase Enzyme Vitamin E, C Vitamin Glutathione Molecule Applied
- Ageing, cancer, atherosclerosis
- Oxidative stress
🔑KEY POINTS TO REMEMBER- Free radicals (ROS) damage lipids, DNA, protein.
- Antioxidants: SOD, catalase, vitamins C/E, glutathione.
- Imbalance → oxidative stress.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Biochemical techniques are laboratory methods used to separate, identify and quantify biomolecules.
Common Techniques
- Chromatography — separation (paper, column, HPLC)
- Electrophoresis — separation by charge / size
- Spectrophotometry — quantification (colour)
- ELISA — antigen / antibody detection
- PCR — DNA amplification
Biomolecules are first separated, then detected and quantified. Technique Use Electrophoresis Separate by charge ELISA Detect antigen Spectrophotometry Quantify Applied
- Diagnostic assays
- Research
🔑KEY POINTS TO REMEMBER- Techniques: chromatography, electrophoresis, spectrophotometry, ELISA, PCR.
- Separate → detect → quantify.
- Basis of diagnostic assays.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Tumour markers are substances (often proteins) produced by cancer cells or by the body in response, used in diagnosis and monitoring.
Examples
- AFP — liver cancer, germ-cell tumours
- CEA — colorectal cancer
- PSA — prostate cancer
- CA-125 — ovarian; CA 19-9 — pancreatic
- β-hCG — germ-cell, choriocarcinoma
Markers shed into blood help track a cancer’s presence and response. Marker Cancer AFP Liver CEA Colorectal PSA Prostate CA-125 Ovarian Applied
- Monitor treatment response
- Mostly not for screening
🔑KEY POINTS TO REMEMBER- Tumour markers: AFP, CEA, PSA, CA-125, CA 19-9, β-hCG.
- Used for diagnosis & monitoring.
- Generally not screening tools.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Oncogenes promote cancer when overactive; tumour suppressor genes normally restrain growth and cause cancer when lost.
Oncogenes
- Mutated proto-oncogenes
- Gain of function → uncontrolled growth
- E.g. RAS, MYC
Tumour Suppressor Genes
- Loss of function → cancer
- Both alleles must be lost (Knudson hypothesis)
- E.g. p53, Rb
Cancer arises from activated oncogenes or lost tumour suppressors. Gene type Example Oncogene RAS, MYC Suppressor p53, Rb Applied
- p53 — commonest mutation in cancer
- Retinoblastoma (Rb)
🔑KEY POINTS TO REMEMBER- Oncogenes: gain of function (RAS, MYC).
- Tumour suppressors: loss of function (p53, Rb).
- Knudson two-hit for suppressors.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
The anion gap is the difference between measured cations and anions in plasma, used to classify metabolic acidosis.
Formula & Value
- Anion gap = Na⁺ – (Cl⁻ + HCO₃⁻)
- Normal ~8–12 mEq/L
- Represents unmeasured anions
Uses
- High anion gap acidosis — ketoacidosis, lactic, uraemia
- Normal anion gap acidosis — diarrhoea, RTA
The gap sorts metabolic acidosis into high- and normal-gap causes. Anion gap Cause High DKA, lactic, uraemia Normal Diarrhoea, RTA Applied
- Classify metabolic acidosis
- MUDPILES causes
🔑KEY POINTS TO REMEMBER- Anion gap = Na⁺ – (Cl⁻ + HCO₃⁻); normal 8–12.
- High-gap: DKA, lactic, uraemia.
- Normal-gap: diarrhoea, RTA.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
The glomerular filtration rate (GFR) is the volume of plasma filtered by the glomeruli per minute — the best index of kidney function.
Features
- Normal ~120 mL/min
- Measured by clearance (inulin, creatinine)
- ↓ GFR in kidney disease
Estimation
- Creatinine clearance (practical)
- eGFR from serum creatinine (formulas)
GFR gauges how much plasma the glomeruli clear each minute. Marker Use Inulin Gold standard Creatinine Practical Applied
- CKD staging by GFR
- ↓ GFR = renal impairment
🔑KEY POINTS TO REMEMBER- GFR = plasma filtered per minute (~120 mL/min).
- Measured by clearance (inulin gold standard).
- ↓ GFR stages CKD.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Reactive oxygen species (ROS) are oxygen-derived free radicals; oxidative stress is an imbalance between ROS and antioxidants.
ROS
- Superoxide (O₂⁻), hydrogen peroxide, hydroxyl radical
- From mitochondria, phagocytes
- Damage lipids, DNA, proteins
Oxidative Stress
- ROS > antioxidant capacity
- Linked to ageing, cancer, atherosclerosis, diabetes
When ROS outpace antioxidants, oxidative stress damages the cell. ROS Note Superoxide From ETC Hydroxyl Most reactive Applied
- Ageing, degenerative disease
- Antioxidant defence
🔑KEY POINTS TO REMEMBER- ROS = superoxide, H₂O₂, hydroxyl radical.
- Oxidative stress = ROS > antioxidants.
- Linked to ageing, cancer, atherosclerosis.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Cardiac markers are biochemical substances released into blood after myocardial injury, used to diagnose myocardial infarction.
Markers
- Troponin I/T — most specific, rises 3–6 h
- CK-MB — rises early, normalises in 2–3 days
- Myoglobin — earliest but non-specific
- LDH — late (historical)
Injured myocardium leaks markers whose pattern confirms infarction. Marker Note Troponin Most specific CK-MB Early, returns fast Myoglobin Earliest Applied
- Troponin = gold standard for MI
- Serial measurement
🔑KEY POINTS TO REMEMBER- Cardiac markers: troponin (most specific), CK-MB, myoglobin.
- Troponin rises 3–6 h; gold standard for MI.
- Measured serially.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
ELISA (enzyme-linked immunosorbent assay) detects and quantifies antigens or antibodies using an enzyme-linked colour reaction.
Principle
- Antigen-antibody binding
- Enzyme-linked antibody added
- Substrate → colour change
- Colour ∝ amount of antigen / antibody
An enzyme-linked antibody turns substrate to colour in proportion to antigen. Feature Detail Basis Antigen-antibody Detection Enzyme colour Applied
- HIV testing
- Hormone / antibody assays
🔑KEY POINTS TO REMEMBER- ELISA: antigen-antibody + enzyme colour reaction.
- Colour ∝ amount of antigen/antibody.
- Used in HIV testing, hormone assays.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).