Correct option is A
Explanation of the correct answer:
In the process of peptide bond formation, the nucleophile is typically the nitrogen of the amine group of the amino acid. Here's why (1) is the correct answer:
During protein synthesis, the peptide bond is formed between the carboxyl group of one amino acid and the amine group of the next. Normally, the ribosome catalyzes the reaction where the nitrogen of the amine group (from the incoming amino acid) attacks the carbonyl carbon of the carboxyl group of the growing polypeptide chain, resulting in the formation of a peptide bond and the release of water.
In the case where protein synthesis occurs in reverse direction (C-terminal to N-terminal), this same mechanism applies, but the sequence of adding amino acids would start from the C-terminal end. However, the nucleophilic attack remains from the nitrogen atom of the amine group of the incoming amino acid onto the carbonyl carbon of the previous amino acid’s carboxyl group.
Information Booster:
Peptide Bond Formation: The process of peptide bond formation involves a nucleophilic attack where the amine nitrogen of the incoming amino acid attacks the carbonyl carbon of the preceding amino acid. This is true in all organisms regardless of the direction of protein synthesis.
Additional Information about Incorrect Options:
Option 2: The carbon of the carboxyl group does not act as the nucleophile in peptide bond formation. Instead, the nitrogen of the amine group serves as the nucleophile that attacks the carbonyl carbon.
Option 3: The oxygen of the carboxyl group is not the nucleophile; it is the electrophile in this reaction, as the carbonyl carbon (attached to the oxygen) is attacked by the amine group.
Option 4: The alpha-carbon (Cα) does not directly participate in the nucleophilic attack during peptide bond formation. It is part of the backbone of the amino acid, but not the atom involved in forming the peptide bond.
