Question

Consider the following and choose the correct answer Assertion [A]: Peptide bond formation occurs at the P site of the ribosome. Reason [R]: Peptidyl transferase activity is an intrinsic property of rRNA. The correct answer is

• A. Both [A] and [R] are true and [R] is the correct explanation of [A]
• B. Both [A] and [R] are true and [R] is not the correct explanation of [A]
• C. [A] is true, but [R] is false
• D. [A] is false, but [R] is true

Hint:

Ribosomal sites: \[ \boxed{ \begin{aligned} \text{A site} &\rightarrow \text{Entry of aminoacyl-tRNA} \text{P site} &\rightarrow \text{Holds peptidyl-tRNA} \text{E site} &\rightarrow \text{Exit of deacylated tRNA} \end{aligned} } \] Peptidyl transferase activity is an intrinsic property of \[ \boxed{\text{rRNA (Ribozyme).}} \]

Answer 1

The Correct Option is D

Step 1: Examine the assertion. Peptide bond formation occurs at the \[ \boxed{\text{Peptidyl Transferase Center (PTC)}} \] of the large ribosomal subunit. During elongation, the aminoacyl-tRNA enters the \[ \boxed{\text{A site}} \] and the growing peptide attached to the tRNA at the P site is transferred to the amino acid in the A site. Hence, peptide bond formation is associated with the \[ \boxed{\text{A site and the Peptidyl Transferase Center,}} \] not the P site alone. Therefore, \[ \boxed{\text{Assertion [A] is false}.} \]

Step 2: Examine the reason. The peptidyl transferase activity of the ribosome is catalyzed by \[ \boxed{23\mathrm{S}\ \text{rRNA}} \] in prokaryotes (or \(28\mathrm{S}\) rRNA in eukaryotes), demonstrating that the ribosome acts as a ribozyme. Hence, \[ \boxed{\text{Reason [R] is true}.} \]

Step 3: Establish the relationship. Since the assertion is false but the reason is true, \[ \boxed{(D)} \] is the correct answer.