Question

Covalently modified bases are found in

• A. tRNA
• B. hnRNA
• C. snRNA
• D. rRNA

Hint:

tRNA contains unique modified loop regions, including:
- The D-loop (containing dihydrouridine).
- The T\(\Psi\)C loop (containing ribothymidine and pseudouridine).
These modified bases are crucial for its structural identity.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
After transcription, primary RNA transcripts undergo various post-transcriptional modifications, including cleavage, splicing, and covalent modification of specific nucleotide bases.

Step 2: Detailed Explanation:
- tRNA (A): Transfer RNA contains the highest diversity and density of covalently modified bases among all RNA species (accounting for 10--15% of all residues in a tRNA molecule). Examples include pseudouridine (\(\Psi\)), dihydrouridine (D), ribothymidine (T), and methylguanosine (\(\text{m}^7\text{G}\)). These modifications are critical for maintaining tRNA stability and facilitating precise codon-anticodon pairing on the ribosome.
- hnRNA (B), snRNA (C), and rRNA (D): While they undergo some modifications (such as 2'-O-methylation), they do not contain the extensive array of modified bases characteristic of tRNA.

Step 3: Final Answer:
Covalently modified bases are highly characteristic of tRNA molecules, corresponding to option (A).