Question

Matters of stability. Proteins are quite stable. The lifetime of a peptide bond in aqueous solution is nearly 1000 years. However, the free energy of hydrolysis of proteins is negative and quite large. How can you account for the stability of the peptide bond in light of the fact that hydrolysis releases considerable energy?

Answer 1

Proteins are heteropolymers of amino acids linked together by peptide bonds. The peptide bond is non-polar, planar and exhibits resonance (Partial double bond nature). The peptide bond is highly stable. The formation of a peptide from amino acids requires energy as the entropy decreases. However, peptide bond hydrolysis releases energy (Exothermic reaction).

This can be explained as follows.
The high stability of the peptide bond is due to the high energy barrier to break it. However, once the activation energy is reached, the product will have lesser energy as compared to the substrates. hence, it becomes an exergonic reaction. The high stability of the peptide bond is due to its high activation energy barrier.