Fish Nutrition and Feed Technology- ICAR JRF/SRF 2024

• Protein Architecture: Proteins are polymers of amino acids organized into primary, secondary, tertiary, and quaternary conformations.
• Chemical Bonds Stabilizing Protein Structures:
• Primary Structure: Linear chains of amino acids linked covalently by peptide bonds (amide linkages formed between $\alpha$-amino and $\alpha$-carboxyl groups).
• Secondary & Tertiary Structure: Folding is stabilized by hydrogen bonds, ionic interactions (salt bridges), hydrophobic interactions, and van der Waals forces.
• Disulfide Bridges: Covalent cross-links formed between the sulfhydryl ($-SH$) groups of cysteine residues provide structural stability to the tertiary and quaternary structures.
• nalysis:
• All statements describing peptide bonds, cross-linking by sulfhydryl and hydrogen bonds, and van der Waals interactions accurately define the forces holding complex protein structures together. Hence, Option 4 is correct.

• Omega-3 ($\text{n-3}$) Fatty Acids: $\omega-3$ denotes a class of polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond three carbon atoms away from the terminal methyl group (omega carbon).
• Nutritional Significance in Aquaculture:
• Key marine fish EFAs include Eicosapentaenoic acid (EPA, 20:5n-3) and Docosahexaenoic acid (DHA, 22:6n-3), as well as their precursor $\alpha$-Linolenic acid (ALA, 18:3n-3).
• They are critical structural components of cellular membranes, ensuring membrane fluidity at low temperatures, and serve as precursors for anti-inflammatory eicosanoids.
• nalysis:
• (Fatty acid): Correct. $\omega-3$ is a vital polyunsaturated fatty acid.
• (Amino acid): Incorrect. Amino acids contain amine and carboxyl groups attached to an $\alpha$-carbon.
• (Mineral): Incorrect. Minerals are inorganic elemental nutrients.

Correct option: (1) Fatty acid

• Essential Amino Acids (EAAs) for Fish: Fish cannot synthesize 10 amino acids de novo or at rates sufficient to support normal growth, making dietary inclusion mandatory:

$$\text{PVT TIM HALL} \rightarrow \text{Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine}$$

• nalysis:
• (Tryptophan): Correct. Tryptophan is an aromatic essential amino acid necessary for protein synthesis, serotonin biosynthesis, and prevention of spinal deformities (scoliosis/lordosis).
• (Proline): Incorrect. Proline is a non-essential cyclic amino acid.
• (Alanine): Incorrect. Alanine is a non-essential amino acid synthesized from pyruvate via transamination.
• (Monosaccharide): Incorrect. A monosaccharide is a simple sugar, not an amino acid.

Correct option: (1) Tryptophan