What does post-translational modification NOT involve?

The correct answer is the formation of peptide bonds. Post-translational modification refers to the various chemical modifications that occur to proteins after their synthesis (translation) on ribosomes. This process can include a wide range of modifications such as the addition or removal of functional groups, covalent modifications like phosphorylation, glycosylation, and ubiquitination, as well as the binding of cofactors or ligands.

Formation of peptide bonds, however, takes place during the translation process and is not part of the modifications that occur afterward. Peptide bonds link amino acids together to form a polypeptide chain, while post-translational modifications modify this already-formed protein. Thus, post-translational modifications do not involve the creation of peptide bonds but rather alter the structure and function of the protein that has already been synthesized.