Multiple Choice
Which enzyme in the ribosome catalyzes the formation of the peptide bond during protein synthesis?
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4. Protein Structure
Peptide Bond
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Which functional groups of two amino acids (aa1 and aa2) are directly involved in the formation of a peptide bond between aa1–aa2?
A
The amino group of aa1 and the carboxyl group of aa2
B
The side chains (R groups) of both aa1 and aa2
C
The carboxyl group of aa1 and the amino group of aa2
D
The alpha carbon atoms of both aa1 and aa2
Verified step by step guidance1
Step 1: Understand the concept of a peptide bond. A peptide bond is a covalent bond formed between two amino acids during a condensation reaction, where a molecule of water is released.
Step 2: Identify the functional groups involved in the formation of a peptide bond. Amino acids have two key functional groups: an amino group (-NH₂) and a carboxyl group (-COOH). These groups are located on the backbone of the amino acid, not the side chains (R groups).
Step 3: Determine the interaction between the amino group and carboxyl group. During peptide bond formation, the carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another amino acid. This reaction results in the formation of an amide bond (-CONH-) and the release of a water molecule (H₂O).
Step 4: Clarify the directionality of the reaction. The carboxyl group of the first amino acid (aa1) and the amino group of the second amino acid (aa2) are directly involved in the bond formation. This establishes the N-terminus (free amino group) and C-terminus (free carboxyl group) of the resulting peptide.
Step 5: Exclude other options. The side chains (R groups) of amino acids are not involved in peptide bond formation, nor are the alpha carbon atoms directly involved. The correct answer is: 'The carboxyl group of aa1 and the amino group of aa2.'
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