ANWSER
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Question 1(a):
Answer:
Enzymes are biological catalysts with the following properties:
– (i) Biochemical nature: Enzymes are typically globular proteins composed of amino acids. Some are RNA-based (ribozymes). They accelerate reactions without being consumed.
– (ii) Substrate specificity: Enzymes bind specific substrates due to the precise geometry and chemical properties of their active sites (e.g., lock-and-key or induced-fit models).
– (iii) Active site: A region on the enzyme where substrate binding and catalysis occur, often with residues like serine, histidine, or aspartate.
– (iv) Cofactor requirement: Some enzymes require non-protein cofactors (e.g., metal ions like Zn²⁺ or organic coenzymes like NAD⁺) for activity.
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Question 1(b):
Answer:
ATP acts as a coenzyme by transferring energy and phosphate groups in enzyme-catalyzed reactions. For example, in hexokinase-catalyzed glucose phosphorylation, ATP donates a phosphate to glucose, forming glucose-6-phosphate and ADP. This role is vital in metabolic pathways like glycolysis.
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Question 1(c):
Answer:
– Thiamine (B₁):
– Role: Coenzyme in decarboxylation (e.g., pyruvate dehydrogenase).
– Deficiency: Beriberi (nerve/heart issues), Wernicke-Korsakoff syndrome.
– Ascorbic acid (Vitamin C):
– Role: Collagen synthesis, antioxidant, iron absorption.
– Deficiency: Scurvy (bleeding gums, poor wound healing).
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Question 1(d):
Answer:
– EDTA: Chelates metal ions, inhibiting metalloproteases and preventing enzyme degradation.
– Triton-X: A detergent that disrupts cell membranes to solubilize membrane-bound enzymes.
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Question 1(e):
Answer:
Ammonium sulphate precipitation is used because:
1. High solubility allows gradual salt addition to precipitate specific proteins.
2. Stabilizes proteins by reducing water activity.
3. Cost-effective and easily scalable.
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Question 1(f):
Answer:
– (i) Dialysis: Separates enzymes from small molecules using a semipermeable membrane.
– (ii) Gel filtration chromatography: Separates proteins by size as they pass through porous beads.
– (iii) Isoelectric focusing: Separates proteins based on their isoelectric point (pI) in a pH gradient.
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Question 3:
Answer:
– (i) Primary structure: Linear sequence of amino acids linked by peptide bonds (e.g., insulin).
– (ii) Helicoidal structure (α-helix): Right-handed coil stabilized by hydrogen bonds (e.g., keratin).
– (iii) Glycolipids: Carbohydrate-attached lipids (e.g., cerebrosides) in cell membranes.
– (iv) Cholesterol: Sterol modulating membrane fluidity and precursor for steroids (e.g., hormones).
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Question 4:
Answer:
DNA structure: Double helix with antiparallel strands (sugar-phosphate backbone), hydrogen-bonded base pairs (A-T, C-G), and major/minor grooves.
– (a) DNA vs RNA:
| Feature | DNA | RNA |
|——————-|———————–|———————–|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, C, G | A, U, C, G |
| Strands | Double-stranded | Single-stranded |
| Stability | More stable | Less stable |
– (b) Fatty acid structures:
– (i) n-Dodecanoate (Laurate): CH₃(CH₂)₁₀COO⁻
– (ii) α-Linolenate (all cis-Δ⁹,¹²,¹⁵): CH₃(CH₂CH=CH)₃(CH₂)₇COO⁻
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Question 5:
Answer:
Functions of essential amino acids (e.g., leucine, lysine):
1. Protein synthesis.
2. Precursors for neurotransmitters (e.g., tryptophan → serotonin).
3. Immune support (e.g., arginine).
4. Energy production (e.g., branched-chain AAs).
5. Enzyme/cofactor synthesis (e.g., histidine → histamine).
– (a) Aromatic AAs structures:
– Phenylalanine: Benzene ring + alanine side chain.
– Tyrosine: Phenol ring + alanine side chain.
– Tryptophan: Indole ring + alanine side chain.
– (b) Carbohydrate classes:
1. Monosaccharides (e.g., glucose).
2. Disaccharides (e.g., sucrose).
3. Polysaccharides (e.g., starch, cellulose).
– (c) Glycosidic bond: Covalent bond linking monosaccharides (e.g., α-1,4 in maltose).