Question

Ribozyme is:

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

Hint:

The ribosome is essentially a ribozyme-based enzyme complex, not a protein enzyme system.

Answer 1

The Correct Option is A

Concept: The discovery of ribozymes revolutionized molecular biology because it challenged the long-standing “protein-only enzyme hypothesis.” Ribozymes are RNA molecules capable of catalyzing biochemical reactions without the involvement of proteins. This showed that RNA can act both as genetic material and as a catalyst, supporting the RNA world hypothesis of early life evolution.

Step 1: Using ribosome structure to understand catalytic RNA location.
Ribosomes are ribonucleoprotein complexes composed of rRNA and proteins. However, experimental evidence shows that proteins are not directly responsible for peptide bond formation. Instead, rRNA carries out the catalytic function. In prokaryotic ribosomes: - 30S small subunit → decoding - 50S large subunit → catalysis

Step 2: Using peptidyl transferase activity as evidence of ribozyme function.
The key reaction in translation is peptide bond formation between amino acids. This reaction is catalyzed by the peptidyl transferase center, which is composed entirely of rRNA. Therefore, ribosomal RNA acts as an enzyme. This proves that RNA is not only informational but also functional.

Step 3: Using identification of 23S rRNA as the catalytic component.
In prokaryotes, the 23S rRNA located in the 50S ribosomal subunit performs the peptidyl transferase activity. This makes it the best and classical example of a ribozyme. Other rRNAs like 16S or 5.8S are structural or functional in decoding but not catalytic. Final Understanding: Ribozymes represent a fundamental shift in biology, showing that RNA can function as both information carrier and catalyst.