Which of the following best describes the formation of the peptide bond between
ID: 197951 • Letter: W
Question
Which of the following best describes the formation of the peptide bond between adjacent amino acids?
a. The carboxy end of the amino acid in the P site makes a nucleophilic attack on the ester linkage between the amino acid in the A site (the end of the polypeptide chain) and its tRNA
b. The amino end of the amino acid in the P site makes a nucleophilic attack on the ester linkage between the amino acid in the A site (the end of the polypeptide chain) and its tRNA
c. The carboxy end of the amino acid in the A site makes a nucleophilic attack on the ester linkage between the amino acid in the P site (the end of the polypeptide chain) and its tRNA
d. The amino end of the amino acid in the A site makes a nucleophilic attack on the ester linkage between the amino acid at the end of the polypeptide chain and the tRNA in the P site.
How does the cell know when to stop adding amino acids to a growing polypeptide chain?
a. The translation machinery reaches the end of the mRNA
b. Proteins called release factors recognize stop codons, aiding in the dissociation of the polypeptide chain from the ribosome
c. tRNA’s recognize stop codons and bind a modified amino acid that cannot form a peptide bond
Explanation / Answer
Answer.
1). d. The amino end of the amino acid in the A site makes a nucleophilic attack on the ester linkage between the amino acid at the end of the polypeptide chain and the tRNA in the P site.
Explanation.
The -amino group of aminoacyl-tRNA in the A site attacks the carbonyl carbon of the pept-tRNA in the P site to produce a new, one amino acid longer pept-tRNA in the A site and a deacylated tRNA in the P site.
2).
b. Proteins called release factors recognize stop codons, aiding in the dissociation of the polypeptide chain from the ribosome
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