Question

42. Which is correct about the peptide elongation by ribosome? Select one: a. Addition of a new amino acid is achieved by peptide transfer from the A site tRNA to the P site URNA. b. Translation is not affected by the cellular availability of GTP. O c. Peptide bond formation is catalyzed by enzymatic proteins in ribosome. O d. The peptide bond is formed by a nucleophilic attack of the A-site NH2- onto the P-site -COOH. O e. None of these

Answer 1

42. Option D

(In case D is not right, than E will be correct)

First option is incorrect because during the process of translation, peptide transfer occurs from P site to A site.

Second option is incorrect because GTP is required during elongation and termination of translation.

Third option is incorrect because peptide bond formation occurs with the help of RNA-based enzymes which are present in the ribosome.

Fourth option is correct because peptide Bond formation occurs by the nucleophilic attack of A site NH2 onto ester of carbonyl group of P site amino acid.

43. All of these

DNA polymerase is the enzyme which is responsible for the elongation of DNA during DNA replication. It cannot initiate DNA synthesis on its own and requires a free hydroxyl group. This free hydroxyl group is provided by an RNA primer which is synthesized by primase enzyme at 3' end of parental DNA molecule. The primer provides a frre hydroxyl group at 3' end.

Not only inside living system, but DNA replication in vitro also requires a primer which provides a free hydroxyl group. During PCR primer pair is added during the type of annealing and primer binds to 3' end of single stranded template DNA.

44. C

First option is correct because tryptophan Operon is a repressible type of Operon. In the presence of tryptophan in the external medium the Operon is switched off.

Second Option is correct because whenever the tryptophan levels are low in the medium ribosome stalls leading to the formation of attenuator which is a structure formed by internal base pairing of messenger RNA.

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