Chapter 5 — Vitamins and Nucleic Acids
Key Concepts — Vitamins
| Vitamin | Chemical Name | Deficiency Disease |
|---|
| A | Retinol | Night blindness, Xerophthalmia |
| D | Calciferol | Rickets (children), Osteomalacia (adults) |
| E | Tocopherol | Sterility, haemolytic anaemia |
| K | Phylloquinone | Impaired blood clotting |
| B₁ | Thiamine | Beriberi (peripheral neuropathy) |
| B₂ | Riboflavin | Ariboflavinosis (cheilosis, glossitis) |
| B₃ | Niacin | Pellagra (3 D's: Dermatitis, Diarrhoea, Dementia) |
| B₆ | Pyridoxine | Anaemia, dermatitis |
| B₁₂ | Cyanocobalamin | Pernicious anaemia |
| C | Ascorbic acid | Scurvy (bleeding gums, impaired wound healing) |
| Folic acid | Pteroylglutamic acid | Megaloblastic anaemia, neural tube defects |
I. Choose the Best Answer (MCQs)
1. Vitamin C deficiency causes: (a) Rickets (b) Scurvy (c) Pellagra (d) Beriberi
Answer(b) Scurvy Vitamin C (ascorbic acid): required for collagen synthesis (hydroxylation of proline and lysine). Deficiency → weakened collagen → bleeding gums, poor wound healing, joint pain.
2. The "anti-sterility" vitamin is: (a) Vitamin A (b) Vitamin D (c) Vitamin E (d) Vitamin K
Answer(c) Vitamin E Vitamin E (tocopherol): fat-soluble antioxidant. Deficiency → sterility in rats (classic experiment); in humans → haemolytic anaemia, neurological symptoms. Called anti-sterility vitamin.
3. Rickets is caused by deficiency of: (a) Vitamin A (b) Vitamin B₁ (c) Vitamin C (d) Vitamin D
Answer(d) Vitamin D Vitamin D: required for calcium and phosphate absorption from intestine (activates calcium-binding protein). Deficiency → poor bone mineralisation → rickets (children: bowed legs), osteomalacia (adults: soft bones).
4. DNA differs from RNA in that DNA contains: (a) Adenine (b) Uracil instead of thymine (c) Thymine instead of uracil (d) Guanine
Answer(c) Thymine instead of uracil DNA contains: Adenine, Guanine (purines) + Cytosine, Thymine (pyrimidines) + deoxyribose. RNA contains: Adenine, Guanine + Cytosine, Uracil (no thymine) + ribose (has 2'-OH).
5. The base pairing in DNA: Adenine pairs with: (a) Cytosine with 2 H-bonds (b) Guanine with 3 H-bonds (c) Thymine with 2 H-bonds (d) Uracil with 2 H-bonds
Answer(c) Thymine with 2 H-bonds Chargaff's rules: A=T (2 H-bonds); G≡C (3 H-bonds). In RNA: A pairs with U (2 H-bonds).
6. A nucleotide consists of: (a) Base + Sugar (b) Base + Phosphate (c) Base + Sugar + Phosphate (d) Sugar + Phosphate only
Answer(c) Base + Sugar + Phosphate Nucleotide = nucleoside + phosphate = (base + sugar) + phosphate. DNA nucleotides: dAMP, dGMP, dCMP, dTMP. RNA nucleotides: AMP, GMP, CMP, UMP.
7. Pellagra (deficiency of Niacin/Vitamin B₃) is characterised by the "3 D's": (a) Dizziness, Deafness, Drowsiness (b) Dermatitis, Diarrhoea, Dementia (c) Diplopia, Dysphagia, Depression (d) Dandruff, Dryness, Dehydration
Answer(b) Dermatitis, Diarrhoea, Dementia Pellagra: Niacin (Vitamin B₃) deficiency. Classic triad: Dermatitis (sun-sensitive rash), Diarrhoea, Dementia. A 4th D: Death if untreated. Tryptophan is precursor of niacin (60 mg Trp → 1 mg niacin).
II. Short Answer Questions
Q1. Compare DNA and RNA.
Answer
| Feature | DNA | RNA |
|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, G, C, T | A, G, C, U |
| Structure | Double helix | Single-stranded (mostly) |
| Location | Nucleus (mainly); mitochondria | Nucleus, cytoplasm, ribosomes |
| Function | Genetic information storage | Protein synthesis (mRNA, tRNA, rRNA) |
| Stability | More stable | Less stable |
| Size | Larger | Smaller |
Q2. What are the water-soluble vitamins and their coenzyme roles?
Answer
Water-soluble B vitamins act as coenzymes in metabolism:
- B₁ (Thiamine): TPP (thiamine pyrophosphate) → pyruvate decarboxylation in Krebs cycle.
- B₂ (Riboflavin): FAD, FMN → electron transport chain, β-oxidation.
- B₃ (Niacin): NAD⁺, NADP⁺ → redox reactions in glycolysis, Krebs cycle, ETC.
- B₅ (Pantothenic acid): Coenzyme A → fatty acid metabolism, Krebs cycle.
- B₆ (Pyridoxine): PLP (pyridoxal phosphate) → amino acid transamination and decarboxylation.
- B₁₂ (Cobalamin): methyl group transfer; required for folate metabolism and myelin synthesis.
- Folic acid: tetrahydrofolate → one-carbon transfer reactions; essential for DNA synthesis.
Exam Checklist
- Fat-soluble vitamins (ADEK): stored in body fat; can cause toxicity if excess.
- Water-soluble (B complex + C): not stored; excess excreted in urine.
- Vitamin deficiencies: A (night blindness), D (rickets), C (scurvy), B₁ (beriberi), B₃ (pellagra), B₁₂ (pernicious anaemia).
- DNA: deoxyribose, thymine; double helix; A=T (2 H-bonds), G≡C (3 H-bonds).
- Nucleotide = base + sugar + phosphate.
- Chargaff's rules: A=T, G=C (in double-stranded DNA).
