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I now have all the key data I need from Lippincott, Robbins, and Harrison's. Let me compile the full viva guide.
⚡ MBBS 1st Year Biochemistry Viva: Vitamins & Minerals
Sources: Lippincott Illustrated Reviews Biochemistry 8th ed, Robbins Pathology, Harrison's 22E
🔑 QUICK RULE: Classification First
| Type | Vitamins |
|---|---|
| Fat-soluble | A, D, E, K (stored in liver/adipose, toxicity possible) |
| Water-soluble | B-complex (B1,B2,B3,B5,B6,B7,B9,B12) + C (daily requirement, minimal storage) |
FAT-SOLUBLE VITAMINS
Vitamin A (Retinol)
| Point | Detail |
|---|---|
| Active forms | Retinol (storage), Retinal (vision), Retinoic acid (gene regulation) |
| Provitamin | β-Carotene (plants) - 12:1 ratio to retinol activity |
| Storage | 90% in liver (Ito/stellate cells), sufficient for 6 months |
| Transport | Retinol-Binding Protein (RBP) |
| Functions | Vision (rhodopsin), epithelial maintenance, immune function, growth |
| Vision mechanism | Retinal + opsin → rhodopsin; light → 11-cis to all-trans isomerization |
| Deficiency | Night blindness (1st sign), xerophthalmia, Bitot's spots, keratomalacia |
| Toxicity | Teratogenic (avoid in pregnancy), pseudotumor cerebri, hypervitaminosis A |
Viva Q: "What is the role of vitamin A in vision?" → Retinal forms rhodopsin in rod cells. Photon converts 11-cis-retinal → all-trans-retinal → nerve impulse.
Vitamin D (Cholecalciferol)
| Point | Detail |
|---|---|
| D3 source | Skin (7-dehydrocholesterol + UV light) or diet (animal) |
| D2 source | Plants (ergocalciferol) |
| Activation | D3 → 25-OH-D3 (liver, calcidiol) → 1,25-(OH)₂D3 (kidney, calcitriol - active) |
| Enzyme | 25-hydroxylase (liver), 1α-hydroxylase (kidney) - both CYP450 |
| Regulation | ↑PTH, ↓Ca²⁺, ↓PO₄³⁻ → ↑calcitriol; feedback inhibition by calcitriol itself |
| Function | ↑Ca²⁺ & PO₄ absorption (gut), bone mineralization, renal Ca reabsorption |
| Deficiency | Rickets (children - bow legs, rachitic rosary) / Osteomalacia (adults) |
| Toxicity | Hypercalcemia, metastatic calcification, nephrolithiasis |
Viva Q: "Difference between rickets and osteomalacia?" → Same biochemical defect, different presentation. Rickets in growing children (affects growth plates). Osteomalacia in adults (bone pain, fractures, pseudofractures/Looser zones).
Vitamin E (Tocopherol)
| Point | Detail |
|---|---|
| Form | α-Tocopherol is most active |
| Function | Antioxidant - protects polyunsaturated FA & cell membranes from free radicals; works with selenium (glutathione peroxidase) |
| Deficiency | Rare; seen in fat malabsorption - hemolytic anemia, spinocerebellar ataxia, peripheral neuropathy |
| Newborns | Premature infants: hemolytic anemia due to low vitamin E |
Vitamin K
| Point | Detail |
|---|---|
| Forms | K1 (phylloquinone, green leafy veg), K2 (menaquinone, gut bacteria), K3 (menadione, synthetic) |
| Active form | Vitamin K hydroquinone (KH₂) |
| Function | Co-factor for γ-carboxylase → carboxylates glutamate residues of clotting factors II, VII, IX, X and proteins C, S, Z |
| Cycle | KH₂ → KO (epoxide) after each carboxylation → regenerated by VKOR (target of warfarin) |
| Deficiency | Bleeding tendency, prolonged PT; newborns (no gut bacteria) → hemorrhagic disease of newborn → give IM at birth |
| Antagonist | Warfarin blocks VKOR |
Viva Q: "Why do newborns get vitamin K injection at birth?" → Gut is sterile at birth, no bacterial K2 synthesis; breast milk is low in K1; risk of hemorrhagic disease of newborn.
WATER-SOLUBLE VITAMINS (B-Complex)
Vitamin B1 - Thiamine
| Point | Detail |
|---|---|
| Active form | Thiamine pyrophosphate (TPP) |
| Enzymes requiring TPP | Pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, Transketolase (HMP shunt), branched-chain α-keto acid dehydrogenase |
| Deficiency test | ↑Erythrocyte transketolase activity with added TPP |
| Beriberi | Dry = peripheral neuropathy; Wet = dilated cardiomyopathy + edema |
| Wernicke-Korsakoff | Alcoholism; Wernicke = confusion + ophthalmoplegia + ataxia; Korsakoff = memory loss + confabulation |
Viva Q: "What is the biochemical basis of Wernicke's encephalopathy?" → Thiamine deficiency → impaired pyruvate dehydrogenase & α-ketoglutarate dehydrogenase → ↓ATP in CNS → neuronal damage, especially mammillary bodies.
Vitamin B2 - Riboflavin
| Point | Detail |
|---|---|
| Active forms | FMN (flavin mononucleotide), FAD (flavin adenine dinucleotide) |
| Function | Electron carriers in oxidative metabolism |
| Deficiency | "Oro-oculo-genital syndrome": angular cheilitis, glossitis (magenta tongue), corneal vascularization, scrotal/vulval dermatitis, normochromic anemia |
Vitamin B3 - Niacin (Nicotinic Acid)
| Point | Detail |
|---|---|
| Active forms | NAD⁺ / NADH, NADP⁺ / NADPH |
| Synthesis | From tryptophan (60 mg Trp = 1 mg niacin); requires B6 |
| Deficiency | Pellagra - 3 D's: Dermatitis, Diarrhea, Dementia (+ 4th D = Death) |
| Dermatitis | Casal's necklace (photosensitive rash around neck) |
| Causes | Alcoholism, corn diet (maize low in niacin & tryptophan), carcinoid syndrome, Hartnup disease (Trp malabsorption) |
| Pharmacologic dose | Lowers LDL, TG; raises HDL - side effect: flushing (prostaglandin-mediated) |
Vitamin B5 - Pantothenic Acid
| Active form | Coenzyme A (CoA) - needed for acyl group transfer |
|---|---|
| Deficiency | Rare; "burning feet" syndrome |
Vitamin B6 - Pyridoxine
| Point | Detail |
|---|---|
| Active form | Pyridoxal phosphate (PLP) |
| Functions | Transamination, decarboxylation, glycogenolysis (glycogen phosphorylase), synthesis of heme, niacin from Trp, neurotransmitters (serotonin, dopamine, GABA) |
| Deficiency | Convulsions (↓GABA), peripheral neuropathy, sideroblastic anemia, glossitis |
| Drug interaction | Isoniazid (INH) is a B6 antagonist → give pyridoxine with INH |
Viva Q: "Why do patients on INH get peripheral neuropathy?" → INH antagonizes vitamin B6 (PLP) → ↓GABA & neurotransmitter synthesis → neuropathy. Prevented by pyridoxine supplementation.
Vitamin B7 - Biotin
| Point | Detail |
|---|---|
| Function | CO₂ carrier in carboxylation reactions |
| Key enzymes | Pyruvate carboxylase, Acetyl-CoA carboxylase, Propionyl-CoA carboxylase |
| Deficiency | Rare; raw egg white (avidin binds biotin) → dermatitis, alopecia, neurologic symptoms |
Vitamin B9 - Folic Acid
| Point | Detail |
|---|---|
| Active form | Tetrahydrofolate (THF) - one carbon donor |
| Functions | Purine & pyrimidine synthesis, methylation reactions |
| Deficiency | Megaloblastic anemia (↑MCV, hypersegmented neutrophils), neural tube defects (spina bifida) |
| Key point | Folate vs B12 anemia: SAME blood picture, BUT B12 deficiency also causes subacute combined degeneration of spinal cord |
| Folate trap | B12 deficiency → folate trapped as N5-methyl THF → functional folate deficiency |
Viva Q: "Why should you not treat B12 deficiency with folate alone?" → Folate corrects anemia but neurologic damage (SACD) continues to progress because B12 is still deficient.
Vitamin B12 - Cobalamin
| Point | Detail |
|---|---|
| Structure | Corrin ring with cobalt; physiologic forms: methylcobalamin, 5'-deoxyadenosylcobalamin |
| Source | Only animal products & gut bacteria (absent in plants) |
| Absorption | Requires Intrinsic Factor (IF) from gastric parietal cells; absorbed in terminal ileum |
| Reactions | (1) Homocysteine → Methionine (methylcobalamin), (2) Methylmalonyl-CoA → Succinyl-CoA (adenosylcobalamin) |
| Deficiency | Megaloblastic anemia + subacute combined degeneration (posterior & lateral columns) |
| Causes | Pernicious anemia (anti-IF antibodies), veganism, terminal ileum disease (Crohn's), gastrectomy |
Viva Q: "What is pernicious anemia?" → Autoimmune destruction of gastric parietal cells → ↓IF → ↓B12 absorption → megaloblastic anemia + neurologic features.
Vitamin C (Ascorbic Acid)
| Point | Detail |
|---|---|
| Function | Antioxidant; hydroxylation of proline & lysine in collagen synthesis (prolyl hydroxylase, requires Fe²⁺); Fe³⁺→Fe²⁺ absorption; dopamine β-hydroxylase |
| Deficiency | Scurvy - perifollicular hemorrhages, corkscrew hairs, bleeding gums, poor wound healing, periosteal hemorrhages, "woody leg" |
| Mechanism | ↓Collagen hydroxylation → weak triple helix → defective collagen |
Viva Q: "What is the biochemical basis of scurvy?" → Ascorbic acid is required to keep prolyl hydroxylase active (reduces Fe to Fe²⁺). Deficiency → inadequate collagen hydroxylation → unstable collagen → perivascular connective tissue weakness → bleeding.
MINERALS & TRACE ELEMENTS
| Element | Key Function | Deficiency |
|---|---|---|
| Iron (Fe) | Hemoglobin, myoglobin, cytochromes, Fe-S enzymes | Hypochromic microcytic anemia |
| Iodine | Thyroid hormone (T3/T4) synthesis | Goiter, hypothyroidism, cretinism |
| Zinc | Component of >100 enzymes (oxidases, carbonic anhydrase) | Acrodermatitis enteropathica (rash around eyes/mouth/anus), growth retardation, impaired wound healing, loss of taste/smell, night blindness, infertility |
| Copper | Cytochrome c oxidase, ceruloplasmin, tyrosinase, lysyl oxidase, dopamine β-hydroxylase | Muscle weakness, neurologic defects, anemia, abnormal collagen cross-linking |
| Selenium | Glutathione peroxidase (antioxidant, works with Vit E) | Keshan disease (cardiomyopathy), myopathy |
| Fluoride | Bone & tooth mineralization | Dental caries |
| Calcium | Bone, muscle contraction, nerve conduction, blood clotting | Tetany, osteoporosis |
| Magnesium | Cofactor for 300+ enzymes, ATP stabilization | Muscle cramps, cardiac arrhythmia |
HIGH-YIELD VIVA ASSOCIATIONS
| Deficiency | Classic Feature |
|---|---|
| Vitamin A | Night blindness, Bitot's spots |
| Vitamin D | Rickets / Rachitic rosary / Harrison's sulcus |
| Vitamin E | Hemolytic anemia (premature infants), Spinocerebellar ataxia |
| Vitamin K | Bleeding + normal platelet count (prolonged PT) |
| B1 (Thiamine) | Wernicke-Korsakoff, wet/dry Beriberi |
| B2 (Riboflavin) | Angular cheilitis, magenta tongue |
| B3 (Niacin) | Pellagra - 4 D's + Casal's necklace |
| B6 (Pyridoxine) | Convulsions in INH therapy, sideroblastic anemia |
| B9 (Folate) | Megaloblastic anemia + NTDs |
| B12 (Cobalamin) | Megaloblastic anemia + SACD of cord |
| Vitamin C | Scurvy - bleeding gums, corkscrew hairs |
| Zinc | Acrodermatitis enteropathica |
| Iodine | Goiter |
| Selenium | Keshan disease (cardiomyopathy) |
MUST-KNOW COENZYME FORMS (Viva Favourites)
| Vitamin | Coenzyme Form |
|---|---|
| B1 | TPP (Thiamine Pyrophosphate) |
| B2 | FMN, FAD |
| B3 | NAD⁺, NADP⁺ |
| B5 | CoA (Coenzyme A) |
| B6 | PLP (Pyridoxal Phosphate) |
| B7 | Biocytin (Biotin-lysine) |
| B9 | THF (Tetrahydrofolate) |
| B12 | Methylcobalamin, Adenosylcobalamin |
COMMON VIVA TRAPS
- Vitamin A vs Zinc - both cause night blindness (zinc needed to mobilize retinol from liver via RBP)
- Folate vs B12 - same megaloblastic anemia, but only B12 deficiency causes neurologic damage
- Vitamin D - the sun doesn't give you vitamin D directly; skin makes cholecalciferol, liver & kidney activate it
- Niacin from tryptophan - requires B6; so B6 deficiency can also precipitate pellagra
- Vitamin K newborns - treat with IM K (not oral) because gut bacteria not yet established
- Warfarin - blocks VKOR, NOT vitamin K itself
Good luck with your viva! These are the highest-yield points from Lippincott Biochemistry 8th ed, Robbins Pathology, and Harrison's 22E - exactly what examiners ask.
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