tRNA tertiary structure — Which statements about the 3D architecture of yeast tRNA (and most tRNAs) are accurate?
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AIt involves extensive base-stacking interactions for stability
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BIts overall 3D fold resembles that of other tRNAs (L-shaped)
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CIt is stabilized largely by non–Watson–Crick (e.g., wobble) base pairs and tertiary contacts
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DAll of the above
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ENone of the above; tRNAs are unfolded in cells
Answer
Correct Answer: All of the above
Explanation
Introduction:tRNAs adopt a conserved tertiary architecture that enables precise positioning in the ribosome during translation. Yeast tRNA was among the first solved RNA 3D structures and serves as a model for tRNA folding principles.
Given Data / Assumptions:
- tRNAs fold into an L-shaped 3D structure from a cloverleaf secondary structure.
- Stacking and noncanonical base pairs contribute substantially to stability.
- Tertiary interactions bridge distant loops and stems.
Concept / Approach:Evaluate each statement against known structural features: base stacking, conserved L-shape across tRNAs, and many non–Watson–Crick interactions (e.g., G•U wobble, base triples) that maintain the compact fold and correct geometry for ribosomal binding.
Step-by-Step Solution:
1) Base stacking between adjacent bases stabilizes helical stems and coaxial stacking.2) Comparative structures show most tRNAs share an L-shaped fold suited for A- and P-site fit.3) Noncanonical pairs and tertiary contacts (e.g., D loop–TψC loop interactions) are crucial for the final 3D shape.Verification / Alternative check:X-ray and cryo-EM data of multiple tRNAs and tRNA–ribosome complexes confirm all three features consistently.
Why Other Options Are Wrong:
e) tRNAs are not unfolded in vivo; they are highly structured for function.Common Pitfalls:Assuming only Watson–Crick pairing matters; overlooking stacking and tertiary contacts in RNA folding.
Final Answer:All of the above.