What chemical modification occurs to one or more amino acids on a protein after translation?

The correct answer is post-translational modification, which refers to the various chemical modifications that a protein can undergo after it has been synthesized during translation. These modifications can involve the addition of various chemical groups, cleavage of certain peptide bonds, or alterations to the protein's structure.

Post-translational modifications can significantly impact the function, localization, stability, and regulation of proteins within a cell. For instance, common modifications include phosphorylation, glycosylation, acetylation, and methylation. Each of these can alter the activity of the protein or its interactions with other molecules.

While phosphorylation is a type of post-translational modification, it is just one example among many. Proteolytic cleavage, another option, is a specific type of post-translational modification involving the enzymatic cleavage of proteins into smaller peptides or amino acids, which can also occur after translation. Post-transcriptional modifications, on the other hand, occur to RNA molecules prior to translation and do not apply in the context of modifications that take place after a protein is formed.