MCAT Biochemistry Question 91: Answer and Explanation

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Question: 91

1. What role does peptidyl transferase play in protein synthesis?

  • A. It transports the initiator aminoacyl-tRNA complex.
  • B. It helps the ribosome to advance three nucleotides along the mRNA in the 5′ to 3′ direction.
  • C. It holds the protein in its tertiary structure.
  • D. It catalyzes the formation of a peptide bond.

Correct Answer: D

Explanation:

Peptidyl transferase is an enzyme that catalyzes the formation of a peptide bond between the incoming amino acid in the A site and the growing polypeptide chain in the P site. Initiation and elongation factors help transport charged tRNA molecules into the ribosome and advance the ribosome down the mRNA transcript, as in choices (A) and (B). Chaperones maintain a protein’s three-dimensional shape as it is formed, as in choice (C).

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