Question

Referring to peptide bond formation in amino acids, the equilibrium lies on the side of hydrolysis, but peptide bonds and kinetically stable. Explain this ( I don't get what they mean by this)

Answer 1

Proteins are polymers of amino acids linked together by peptide bonds. A peptide bond is a type of amide bond formed between the alpha amino group of an amino acid and the alpha carboxyl group of the penultimate amino acid.

NH₂-R₁-COOH + NH₂-R₂-COOH -------> NH₂-R₁-CO-NH-R₂-COOH + H2O

The equilibrium of the above reaction lies on the reactants side. So, peptide bond formation is an endergonic reaction (requires energy). However, peptide bonds are kinetically quite stable. This is because of the slow rate of hydrolysis. The peptide bond is stable as it exhibits resonance. It is a rigid planar covalent bond.

Peptide bonds are so stable that their half-life in a free solution is 1000 years. peptide bond cleavage requires special enzymes known as proteases.