Question

Ribozyme is:

• A. \(23S\) rRNA
• B. \(28S\) rRNA
• C. \(18S\) rRNA
• D. \(5.8S\) rRNA

Hint:

Remember: \[ 23S \ \text{rRNA} \rightarrow \text{Peptidyl transferase activity} \] Therefore: \[ 23S \ \text{rRNA} = \text{Ribozyme} \]

Answer 1

The Correct Option is A

Concept: A ribozyme is an RNA molecule that functions as a biological catalyst. Normally, enzymes are proteins, but certain RNA molecules can also catalyze biochemical reactions. Such catalytic RNA molecules are known as ribozymes.

Step 1: Understanding the term ribozyme.
The word ribozyme is derived from: \[ \text{RNA} + \text{Enzyme} \] Hence, a ribozyme is an RNA molecule having enzymatic activity.

Step 2: Identifying the catalytic RNA in ribosomes.
In prokaryotic ribosomes:

• The small subunit is \(30S\)
• The large subunit is \(50S\)

The \(50S\) large subunit contains: \[ 23S \ \text{rRNA} \]

Step 3: Function of \(23S\) rRNA.
During protein synthesis, peptide bonds are formed between amino acids. The catalytic activity responsible for peptide bond formation is called: \[ \text{Peptidyl Transferase Activity} \] This activity is performed by: \[ 23S \ \text{rRNA} \] and not by proteins. Thus, \(23S\) rRNA acts as an enzyme and is therefore called a ribozyme.

Step 4: Eliminating incorrect options.

• \(28S\) rRNA is present in eukaryotic ribosomes but is not commonly referred to in standard NCERT context as the ribozyme.
• \(18S\) rRNA forms part of the small subunit and mainly helps in mRNA binding.
• \(5.8S\) rRNA has structural functions.

Hence, the correct answer is: \[ 23S \ \text{rRNA} \]