Q.28 Hydrolysis of a peptide involves cleavage of the bond between the atoms
(A) N and C𝛼
(B) C and O
(C) C𝛼 and C
(D) N and C

Hydrolysis of a peptide breaks the bond between the peptide nitrogen and the carbonyl carbon, so the correct option is (D) N and C. This bond is the actual peptide bond (amide bond) that links two amino acids in a polypeptide chain.​

Question and Correct Answer

Question:
Hydrolysis of a peptide involves cleavage of the bond between the atoms:
(A) N and Cα
(B) C and O
(C) Cα and C
(D) N and C

Correct Answer:
(D) N and C

During peptide hydrolysis, water adds across the peptide bond (an amide bond) between the carbonyl carbon of one amino acid and the nitrogen of the next, breaking the C–N linkage and yielding a carboxyl group and an amino group.​

Brief Concept: What Is a Peptide Bond?

• A peptide bond is an amide bond formed between the carboxyl carbon of one amino acid and the amino nitrogen of another.​

• This bond is written as $-\mathrm{CO}-\mathrm{NH}-$ and connects the C (carbonyl carbon) of one residue to the N (amide nitrogen) of the next, forming the peptide backbone.​

• Hydrolysis is the reverse of peptide bond formation: water splits the C–N bond, giving back an –COOH (or –COO⁻) and –NH₂ (or –NH₃⁺) group.​

Explanation of Each Option

Option (A) N and Cα

• Cα (alpha carbon) is the central carbon of an amino acid to which the amino group, carboxyl group, hydrogen, and side chain (R group) are attached.​

• The bond between N and Cα is not the peptide bond; instead, it is part of the amino acid backbone adjacent to the peptide bond and is not the bond hydrolyzed during peptide bond cleavage.​

• Therefore, option (A) is incorrect.

Option (B) C and O

• The C–O bond here refers to the carbonyl C=O bond of the amide group, which is not what is broken in normal peptide hydrolysis.​

• In hydrolysis, the carbonyl carbon remains bonded to oxygen; water attacks the carbonyl carbon and ultimately cleaves the C–N bond, not the C–O bond.​

• Therefore, option (B) is incorrect.

Option (C) Cα and C

• The bond between Cα and the carbonyl carbon (C) is part of the amino acid skeleton and remains intact during typical peptide bond hydrolysis.​

• Hydrolysis separates amino acids at the peptide (amide) linkage between carbonyl carbon and nitrogen, not between Cα and the carbonyl carbon.​

• Therefore, option (C) is incorrect.

Option (D) N and C ✔️

• The peptide bond is specifically the amide bond between the carbonyl carbon (C) of one amino acid and the amide nitrogen (N) of the next amino acid.​

• During hydrolysis, water adds across this C–N bond: the hydroxyl group attaches to the carbonyl carbon (forming a carboxyl group) and a proton attaches to the nitrogen (forming an amino group), effectively cleaving the N–C bond.​

• Hence, option (D) is correct because hydrolysis of a peptide involves cleavage of the bond between N and C.

Key Takeaways for Exams

• Peptide bond = C (carbonyl carbon) – N (amide nitrogen).​

• Hydrolysis of peptide bond = cleavage of the C–N bond using water, regenerating free amino and carboxyl groups.​

• Bonds involving Cα (N–Cα or Cα–C) are not hydrolyzed in simple peptide bond cleavage; they belong to the amino acid backbone, not the peptide linkage itself.​