Biochemistry- ICAR JRF/SRF 2024

• Features of the Genetic Code:
• Degenerate: Multiple triplet codons specify the same amino acid (61 sense codons code for 20 standard amino acids).
• Non-overlapping: Successive triplets are read independently and sequentially.
• Comma-less (Unpunctuated): There are no internal spacer nucleotides or punctuations between adjacent codons. Reading frame is determined strictly by the initiation codon (AUG).
• Conclusion: Stating that the genetic code has internal punctuations is NOT true (Option 4).

Correct option: (4) Genetic code has internal punctuations to indicate the particular reading frame

• Assertion (A) is True: Euchromatin represents the lightly packed, decondensed form of chromatin (10 nm to 30 nm fiber), whereas heterochromatin remains densely compacted throughout the cell cycle.
• Reason (R) is True & Explains (A): Euchromatin is transcriptionally permissive and active; its uncoiled conformation is required to grant RNA polymerase II, general transcription factors, and chromatin-remodeling complexes physical access to promoter and enhancer elements.
• Conclusion: Both (A) and (R) are true and (R) is the correct explanation of (A).

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)

• Statement (I) is True: $\alpha$-Amanitin (a cyclic octapeptide toxin from death cap mushroom Amanita phalloides) binds tightly to RNA Polymerase II ($K_d \approx 10^{-8}\text{ M}$), blocking translocation and mRNA transcription in eukaryotic cells.
• Statement (II) is True: RNA Polymerase I (synthesizing rRNA) is completely insensitive to $\alpha$-amanitin, and bacterial RNA polymerase is entirely unaffected (as are mitochondrial and chloroplast RNA polymerases).
• Conclusion: Both Statement (I) and Statement (II) are true.

Correct option: (1) Both Statement (I) and Statement (II) are true.