What must occur for protein translation to begin?
A water molecule must be added to the protein chain.
A peptide bond must form between subunits of mRNA.
The amino acid Cys must be picked up by tRNA.
The codon AUG must be identified.
The Correct Answer and Explanation is :
The correct answer is: “The codon AUG must be identified.”
Explanation:
Protein translation is the process by which the genetic information encoded in mRNA is used to synthesize proteins. It occurs in the ribosomes, the cellular machinery that facilitates the translation of mRNA into a polypeptide chain.
The initiation of translation begins with the recognition of the start codon on the mRNA strand. In almost all organisms, the start codon is AUG, which codes for the amino acid methionine (Met). The AUG codon plays a critical role because it signals the ribosome where to begin assembling the protein.
The process starts when the small ribosomal subunit binds to the mRNA and scans along it until it identifies the AUG codon. Once the AUG codon is identified, a transfer RNA (tRNA) molecule carrying methionine (the amino acid that AUG codes for) pairs with this codon. This pairing occurs via the tRNA’s anticodon, which is complementary to the AUG sequence.
Once the AUG codon has been recognized and the methionine-tRNA is in place, the large ribosomal subunit joins to form a complete ribosome. This initiates the elongation phase, where amino acids are sequentially added to the growing polypeptide chain according to the codon sequence on the mRNA.
Other choices in the question represent later steps or unrelated processes:
- A water molecule added: This happens at the end of translation during termination, not initiation.
- Peptide bond formation: This occurs as amino acids are added during elongation, not to start translation.
- Cys picked up by tRNA: While tRNAs do carry specific amino acids, methionine (not cysteine) is the first amino acid used to start translation.
Thus, the identification of the AUG start codon is essential for the translation process to begin.