The number of  $\mathrm{C}=\mathrm{O}$  groups present in a tripeptide Asp – Glu – Lys is _____

The number of C=O groups present in a tripeptide Asp–Glu–Lys is 5.

Explanation

• Each amino acid (Aspartic acid, Glutamic acid, Lysine) contains one main carboxyl group (−COOH), with Asp and Glu having an extra side chain carboxyl group.
• When these amino acids form a tripeptide, two peptide bonds are created, each contributing a C=O group.
• Lysine only contributes one carboxyl (from backbone), Asp and Glu each have side chain carboxyls in addition to the backbone group and peptide bonds.

Breakdown:

• Asp (α-carboxyl + side chain carboxyl): 2 C=O
• Glu (α-carboxyl + side chain carboxyl): 2 C=O
• Lys (α-carboxyl only): 1 C=O
• Two peptide bonds: Each formed between the α-amino and α-carboxyl groups, but the C=O of the carboxyl group remains in the backbone (not the side chain).

Total = 5 C=O groups