Biochemistry
MBBS Biochemistry question bank: biomolecules, enzymes, metabolism, molecular biology, vitamins, nutrition and clinical biochemistry.
12chapters144questions75High-Yield
Definition
Calcium and phosphate metabolism maintains plasma levels of these minerals — essential for bone, nerve and muscle — under hormonal control.
Calcium Functions
- Bone / teeth mineralisation
- Muscle contraction, nerve conduction
- Blood clotting, enzyme cofactor
Regulation (hormones)
- PTH — ↑ Ca²⁺
- Calcitriol (vitamin D) — ↑ absorption
- Calcitonin — ↓ Ca²⁺
Phosphate
- In bone, ATP, nucleic acids, phospholipids
- Regulated inversely with calcium
Hormones restore calcium by acting on bone, gut and kidney. Hormone Effect on Ca²⁺ PTH ↑ Calcitriol ↑ Calcitonin ↓ Applied
- Rickets, tetany
- Hyper / hypoparathyroidism
🔑KEY POINTS TO REMEMBER- PTH & calcitriol raise Ca²⁺; calcitonin lowers it.
- Calcium: bone, muscle, nerve, clotting.
- Phosphate regulated inversely.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Iron metabolism governs the absorption, transport, storage and use of iron, essential for haemoglobin and enzymes.
Absorption
- In the duodenum (Fe²⁺ better absorbed)
- Enhanced by vitamin C, reduced by phytates
- Regulated (no active excretion)
Transport & Storage
- Transport: transferrin
- Storage: ferritin, haemosiderin (liver, spleen)
Functions
- Haemoglobin, myoglobin
- Cytochromes, enzymes
Iron is absorbed, carried by transferrin, stored as ferritin and used for haem. Protein Role Transferrin Transport Ferritin Storage Haemoglobin O₂ carriage Applied
- Iron-deficiency anaemia
- Haemochromatosis (overload)
🔑KEY POINTS TO REMEMBER- Iron absorbed in duodenum (↑ by vitamin C).
- Transferrin (transport), ferritin (storage).
- Deficiency → anaemia; excess → haemochromatosis.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Haemoglobin is the oxygen-carrying protein of red cells; haem metabolism covers its synthesis and degradation.
Structure
- Four globin chains (2α + 2β in HbA)
- Each with a haem (Fe²⁺ + porphyrin)
- Binds four O₂ molecules
Haem Synthesis
- From glycine + succinyl-CoA
- Rate-limiting: ALA synthase
- In liver & bone marrow
Haem Degradation
- Haem → biliverdin → bilirubin
- Bilirubin → liver → conjugated → bile
Haem is built from glycine and succinyl-CoA and degraded to bilirubin. Process Key point Synthesis ALA synthase (rate-limiting) Degradation → bilirubin Applied
- Porphyrias (haem synthesis defects)
- Jaundice (bilirubin)
🔑KEY POINTS TO REMEMBER- Haemoglobin: 2α + 2β globin + haem (Fe²⁺).
- Synthesis rate enzyme = ALA synthase.
- Degradation → bilirubin (jaundice).
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Nutrition concerns nutrient intake for energy and health; BMR is basal energy expenditure and a balanced diet provides all nutrients.
Energy
- Carbohydrate / protein — 4 kcal/g
- Fat — 9 kcal/g
- Alcohol — 7 kcal/g
Basal Metabolic Rate (BMR)
- Energy at complete rest
- Affected by thyroid, body mass, age, sex
- Measured in the post-absorptive state
Balanced Diet
- Carbohydrate 50–60%, fat 20–30%, protein 10–15%
- + vitamins, minerals, fibre, water
Balancing energy intake against BMR and activity maintains health. Nutrient kcal/g Carbohydrate 4 Protein 4 Fat 9 Applied
- Obesity, malnutrition
- Diet planning
🔑KEY POINTS TO REMEMBER- Energy: carbohydrate/protein 4, fat 9, alcohol 7 kcal/g.
- BMR = resting energy (thyroid-dependent).
- Balanced diet: 50–60% carb, 20–30% fat, 10–15% protein.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Trace elements are minerals required in small amounts, functioning mainly as enzyme cofactors.
Important Trace Elements
- Iron — haemoglobin
- Iodine — thyroid hormones
- Zinc — many enzymes, wound healing
- Copper — ceruloplasmin, enzymes
- Fluoride — teeth / bone
Though needed in tiny amounts, trace elements are vital enzyme cofactors. Element Function Deficiency Iodine Thyroid Goitre Zinc Enzymes Poor healing Copper Ceruloplasmin Anaemia Applied
- Iodine deficiency (goitre)
- Zinc deficiency (dermatitis)
🔑KEY POINTS TO REMEMBER- Trace elements = enzyme cofactors (iron, iodine, zinc, copper, fluoride).
- Iodine → thyroid; zinc → healing.
- Deficiencies: goitre, poor healing.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Protein energy malnutrition (PEM) results from inadequate protein and/or energy intake; the two severe forms are kwashiorkor and marasmus.
Kwashiorkor
- Protein deficiency (calories adequate)
- Oedema, fatty liver
- Skin / hair changes, apathy
Marasmus
- Overall calorie deficiency
- Severe wasting (no oedema)
- ‘Old man’ face
Kwashiorkor is protein-deficient (oedema); marasmus is energy-deficient (wasting). Feature Kwashiorkor Marasmus Deficiency Protein Energy Oedema Yes No Wasting Some Severe Applied
- Nutritional rehabilitation
🔑KEY POINTS TO REMEMBER- Kwashiorkor = protein deficiency (oedema, fatty liver).
- Marasmus = energy deficiency (severe wasting).
- Both are PEM.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Jaundice is the yellowish discoloration of skin, sclera and mucosa due to raised bilirubin.
Types
- Prehepatic (haemolytic) — ↑ unconjugated bilirubin
- Hepatic — liver-cell damage
- Posthepatic (obstructive) — ↑ conjugated bilirubin
Raised bilirubin from any of three levels yellows the skin and sclera. Type Bilirubin Haemolytic ↑ unconjugated Hepatic Both Obstructive ↑ conjugated Applied
- Neonatal jaundice
- Gallstones (obstructive)
🔑KEY POINTS TO REMEMBER- Jaundice = ↑ bilirubin.
- Prehepatic (unconjugated), hepatic, posthepatic (conjugated).
- Neonatal & obstructive causes common.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Sodium is the main extracellular cation and potassium the main intracellular cation; both are vital for fluid balance and excitability.
Sodium
- Main ECF cation
- Fluid / osmotic balance, nerve conduction
- Regulated by aldosterone
Potassium
- Main ICF cation
- Resting membrane potential, cardiac function
- Imbalance → arrhythmias
The Na⁺/K⁺ gradient underlies fluid balance and excitability. Ion Compartment Sodium Extracellular Potassium Intracellular Applied
- Hyper / hypokalaemia (arrhythmia)
- Hyponatraemia
🔑KEY POINTS TO REMEMBER- Na⁺ = main ECF cation; K⁺ = main ICF cation.
- Maintained by Na⁺/K⁺ pump; aldosterone regulates Na⁺.
- K⁺ imbalance → arrhythmias.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
The respiratory quotient (RQ) is the ratio of CO₂ produced to O₂ consumed, indicating the type of fuel being oxidised.
Values
- Carbohydrate — RQ = 1.0
- Fat — RQ = 0.7
- Protein — RQ = 0.8
- Mixed diet — ~0.85
The RQ value reveals which fuel the body is burning. Fuel RQ Carbohydrate 1.0 Fat 0.7 Protein 0.8 Applied
- Assess metabolism
- Indirect calorimetry
🔑KEY POINTS TO REMEMBER- RQ = CO₂ / O₂.
- Carbohydrate 1.0, fat 0.7, protein 0.8.
- Used in indirect calorimetry.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Wilson’s disease is an autosomal recessive disorder of copper metabolism causing copper accumulation in tissues.
Mechanism
- Defective copper excretion into bile
- ↓ Ceruloplasmin
- Copper deposits in liver, brain, eye
Features
- Liver disease (cirrhosis)
- Neurological (tremor, dystonia)
- Kayser-Fleischer rings (cornea)
Copper that cannot be excreted builds up in liver, brain and eyes. Organ Sign Liver Cirrhosis Brain Tremor Eye KF rings Applied
- ↓ Serum ceruloplasmin
- Penicillamine (chelation)
🔑KEY POINTS TO REMEMBER- Wilson’s = copper accumulation (↓ biliary excretion, ↓ ceruloplasmin).
- Liver, brain, KF rings.
- Treated with penicillamine.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
The biological value (BV) of a protein is the proportion of absorbed protein nitrogen retained by the body, reflecting protein quality.
Principle
- Depends on essential amino acid content
- High BV — egg, milk (complete proteins)
- Low BV — cereals (incomplete proteins)
Concepts
- Complete vs incomplete proteins
- Mutual supplementation (complementary proteins)
BV reflects how well a protein’s amino acids match the body’s needs. Protein BV Egg ~100 (high) Cereal Low Applied
- Complementary proteins (rice + dal)
🔑KEY POINTS TO REMEMBER- BV = fraction of absorbed nitrogen retained.
- High (egg, milk) vs low (cereal).
- Complementary proteins improve BV.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).Definition
Fetal haemoglobin (HbF) is the main haemoglobin during fetal life, with higher oxygen affinity than adult HbA.
Structure
- Two α + two γ chains (α2γ2)
- Replaced by HbA (α2β2) after birth
Features
- Higher O₂ affinity (↓ 2,3-BPG binding)
- Draws O₂ from maternal blood
- Resists alkali denaturation
HbF’s higher affinity lets the fetus pull oxygen from maternal blood. Haemoglobin Chains HbF α2γ2 HbA α2β2 Applied
- ↑ HbF in thalassaemia, sickle cell
- Hydroxyurea ↑ HbF
🔑KEY POINTS TO REMEMBER- HbF = α2γ2; higher O₂ affinity than HbA.
- Extracts O₂ from maternal blood.
- ↑ in thalassaemia; hydroxyurea raises it.
📚SOURCES: Textbook of Biochemistry (U. Satyanarayana); Harper’s Illustrated Biochemistry; Textbook of Medical Biochemistry (M.N. Chatterjea).