Final answer:
Phosphorylation is an example of a post-translational modification of a polypeptide.
Step-by-step explanation:
An example of a post-translational modification of a polypeptide is phosphorylation. Phosphorylation is the addition of a phosphate group to specific amino acids in a protein chain after it has been translated from mRNA. This modification can alter the function, activity, or localization of the protein, and it plays a crucial role in many cellular processes. For example, phosphorylation of proteins can regulate enzyme activity, signal transduction pathways, and gene expression.