tRNA selection on the ribosome — basis of accuracy How do ribosomes select the correct transfer RNAs (tRNAs) during translation?

Introduction:
Translation fidelity depends on accurate matching of mRNA codons with tRNA anticodons. The ribosome’s decoding center in the small subunit monitors base pairing geometry and employs kinetic proofreading to ensure that only cognate tRNAs are accepted for peptide bond formation.

Given Data / Assumptions:

• Incoming aminoacyl-tRNAs are delivered to the A site by elongation factors (EF-Tu in bacteria, eEF1A in eukaryotes).
• Codon–anticodon base pairing is evaluated by the ribosome’s decoding center.
• Correct pairing accelerates GTP hydrolysis and accommodation; incorrect pairing promotes rejection.

Concept / Approach:

The ribosome discriminates based on the physical fit of Watson–Crick pairs and induced-fit conformational changes, not on tRNA abundance or amino acid identity. Aminoacyl-tRNA synthetases ensure the correct amino acid is attached to a given tRNA before delivery to the ribosome.

Step-by-Step Solution:

Verification / Alternative check:

Structural studies show rRNA nucleotides monitoring minor groove geometry; kinetic analyses reveal multi-step selection and proofreading that favor cognate tRNAs by orders of magnitude.

Why Other Options Are Wrong:

Option A reverses the order; ribosomes bind mRNA first. Options C and D misstate selection logic; abundance influences availability but not decoding accuracy. Option E is incorrect; the ribosome does not sense amino acid side chains to select tRNAs.

Common Pitfalls:

Confusing aminoacyl-tRNA synthetase specificity (charging) with ribosomal decoding specificity.

Final Answer:

Solely on the basis of codon–anticodon pairing geometry within the decoding center, assisted by kinetic proofreading