17. During protein synthesis, tRNAs are NOT involved in
(a) Charging (b) Initiation
(c) Elongation (d) Termination
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Protein synthesis, or translation, is a core process in molecular biology where cells build proteins using mRNA, ribosomes, and tRNAs. A common MCQ asks: During protein synthesis, tRNAs are NOT involved in (a) Charging (b) Initiation (c) Elongation (d) Termination. This question tests understanding of tRNA functions across translation stages.
The correct answer is (d) Termination. tRNAs play essential roles in charging, initiation, and elongation but have no direct involvement in termination. Below, we break down each option with clear explanations, highlighting tRNA’s precise roles in the protein synthesis stages.
What is Charging in Protein Synthesis?
Charging, also called aminoacyl-tRNA formation, happens before translation begins. Aminoacyl-tRNA synthetases attach specific amino acids to their matching tRNAs, forming aminoacyl-tRNAs.
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tRNAs are directly involved here as the acceptor molecules.
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This step ensures tRNAs carry the correct amino acids to the ribosome, matching the mRNA codon via anticodon pairing.
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Without charging, translation can’t proceed accurately.
tRNAs are central to this preparatory phase, making (a) incorrect.
tRNA’s Role in Initiation of Translation
Initiation assembles the ribosome on mRNA to start protein building. In prokaryotes, the initiator tRNA (tRNA^fMet with N-formylmethionine) binds the start codon (AUG) at the P-site. Eukaryotes use tRNA^iMet similarly.
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tRNAs are essential for initiation, delivering the first amino acid.
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Initiation factors (like IF1-3 in prokaryotes or eIFs in eukaryotes) help position the initiator tRNA.
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This sets up the reading frame for elongation.
Thus, (b) is wrong—tRNAs kick off the process.
How tRNAs Drive Elongation
Elongation builds the polypeptide chain through repeated cycles. Aminoacyl-tRNAs enter the A-site, matching mRNA codons.
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tRNAs are critically involved, shuttling amino acids for peptide bond formation via peptidyl transferase.
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EF-Tu (prokaryotes) or eEF1A (eukaryotes) deliver tRNAs; EF-G or eEF2 translocates them.
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After bond formation, deacylated tRNA exits the E-site, and the process repeats.
Elongation relies heavily on tRNAs, ruling out (c).
Why tRNAs Skip Termination
Termination occurs when a stop codon (UAA, UAG, UGA) enters the A-site. Release factors (RF1/RF2 in prokaryotes or eRF1 in eukaryotes) recognize these codons and trigger polypeptide release.
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tRNAs are NOT involved; no tRNA anticodon binds stop codons.
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RF3 and ribosome recycling factor (RRF) aid disassembly, but tRNAs play no role.
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This prevents erroneous amino acid addition at the end.
This makes (d) the right choice—tRNAs are absent from termination.
Key Takeaways on tRNA Functions in Translation
| Stage | tRNA Involvement | Key Players Besides tRNA |
|---|---|---|
| Charging | Yes (amino acid attachment) | Aminoacyl-tRNA synthetases |
| Initiation | Yes (start codon binding) | Initiation factors, fMet-tRNA |
| Elongation | Yes (amino acid delivery) | Elongation factors (EF-Tu, EF-G) |
| Termination | No | Release factors (RF1/2), RRF |
Understanding tRNAs are NOT involved in termination clarifies translation’s modular nature. This MCQ often appears in exams like NEET, CSIR NET, or biotech courses, emphasizing tRNA’s specificity.
Master these protein synthesis stages for better grades in molecular biology or biochemistry. For more MCQs on tRNA functions or translation process, explore our biotech resources.
