Veterinary Biotechnology- ICAR JRF/SRF 2024

• Wobble Hypothesis & Inosine: Inosine is a modified purine nucleoside containing the base hypoxanthine, formed by post-transcriptional deamination of adenine in tRNA anticodons.
• Wobble Base Pairing: When present at the wobble position (the first base of the anticodon, $5'$ position), inosine can form stable, non-Watson-Crick hydrogen bonds with three different bases in mRNA codons:
• Uracil (U) (2 hydrogen bonds)
• Cytosine (C) (2 hydrogen bonds)
• Adenine (A) (2 hydrogen bonds)
• It does not pair with Guanine (G) due to severe steric hindrance and electrostatic repulsion between purine ring substituents.

Correct option: (4) U, C, and A,

• Spectrin: A long, flexible, filamentous cytoskeletal heterodimer ($\alpha$ and $\beta$ chains) that forms a two-dimensional hexagonal lattice beneath the erythrocyte plasma membrane, anchored via ankyrin to band 3 and protein 4.1 to glycophorin.
• Hereditary Spherocytosis: Genetic deficiency or structural defect in spectrin (or its anchoring proteins) destabilizes the membrane cytoskeleton, causing erythrocytes to lose their biconcave disc shape and become spherical, rigid spherocytes with increased osmotic fragility that are prematurely destroyed in the spleen (hemolytic anemia).

Correct option: (3) Spectrin.

• Nuclear Lamina: A dense, 10--50 nm fibrous protein meshwork lining the inner surface of the inner nuclear membrane that provides mechanical support to the nuclear envelope and serves as an attachment site for chromatin fibers and nuclear pore complexes.
• Nuclear Lamins: Composed of intermediate filament proteins termed lamins (type V intermediate filaments: lamins A, B, and C).
• Regulation: During mitosis, phosphorylation of nuclear lamins by Cdk1/Cyclin B triggers reversible disassembly of the lamina and nuclear envelope breakdown.

Correct option: (1) _ Nuclear Lamins.