RNA Biology—Modified (Unusual) Bases Among the following RNA types, which commonly contains numerous modified or unusual bases as a normal feature of its structure?

Introduction / Context:
Post-transcriptional RNA modifications diversify nucleotide chemistry and influence structure and function. While several RNAs carry modifications, transfer RNA (tRNA) is particularly rich in unusual bases (e.g., pseudouridine, dihydrouridine, inosine, queuosine) that are essential for folding, decoding, and stability.

Given Data / Assumptions:

• tRNAs require precise 3D structure for aminoacylation and codon recognition.
• Enzymatic modifications occur after transcription.
• Other RNAs (rRNA, snRNA) do contain modifications, but the density and diversity are greatest in tRNA.

Concept / Approach:
Choose the RNA species with the highest frequency and diversity of modified bases. tRNA anticodon wobble modifications tune decoding; body modifications stabilize the L-shaped fold. mRNA generally contains far fewer modifications (though m6A and others exist) and hnRNA is a precursor to mRNA with limited base modifications compared to tRNA.

Step-by-Step Solution:

Verification / Alternative check:
tRNA modification maps across organisms consistently show extensive chemical diversity relative to other RNAs.

Why Other Options Are Wrong:

• mRNA/hnRNA: relatively sparse base modifications; capped at the 5' end and polyadenylated at 3' but not heavily base-modified like tRNA.
• rRNA/snRNA: do have modifications (e.g., 2'-O-methyl, pseudouridine), but not as numerous per molecule as tRNA.

Common Pitfalls:
Conflating cap and tail structures with base modifications; caps and poly(A) are not base substitutions within the RNA chain.

Final Answer:
tRNA