The correct answer is only a. Explanation & Key Takeaways: • In biochemistry, a zymogen also called a proenzyme is an inactive precursor of an enzyme. • A zymogen requires a biochemical change (such as a hydrolysis reaction revealing the active site or changing the configuration to reveal the active site) for it to become an active enzyme. • The biochemical change usually occurs in Golgi bodies, where a specific part of the precursor enzyme is cleaved in order to activate it. • The inactivating piece which is cleaved off can be a peptide unit or can be independently folding domains comprising more than 100 residues. • Although they limit the enzyme's ability, these N-terminal extensions of the enzyme or a “Pro segment” often aid in the stabilization and folding of the enzyme they inhibit. • The pancreas secretes zymogens partly to prevent the enzymes from digesting proteins in the cells in which they are synthesised. • Enzymes like pepsin are created in the form of pepsinogen, an inactive zymogen. • Pepsinogen is activated when chief cells release it into the gastric acid, whose hydrochloric acid partially activates it. • Fungi also secrete digestive enzymes into the environment as zymogens. The external environment has a different pH than inside the fungal cell and this changes the zymogen's structure into an active enzyme. • Another way that enzymes can exist in inactive forms and later be converted to active forms is by activating only when a cofactor, called a coenzyme, is bound. • In this system, the inactive form (the apoenzyme) becomes the active form (the holoenzyme) when the coenzyme binds. • In the duodenum, the pancreatic zymogens, trypsinogen, chymotrypsinogen, proelastase and procarboxypeptidase are converted into active enzymes by enteropeptidase and trypsin. • Chymotrypsinogen, is single polypeptide chain of 245 amino acids residues, is converted to alpha-chymotrypsin, which has three polypeptide chains linked by two of the five disulfide bond present in the primary structure of chymotrypsinogen.