Discuss zymogens.

ANSWER: Some proteins are synthesized as inactive precursors called zymogens or proenzymes that acquire full activity only upon specific proteolytic cleavage of one or several of their peptide bonds. Zymogen activation by specific proteolysis is an irreversible process. Activation of enzymes and other physiologically important proteins by specific proteolysis is a strategy frequently exploited by biological systems to switch on processes at the appropriate time and place. For instance, insulin, an important metabolic regulator, is generated by proteolytic excision of a specific peptide from proinsulin.