Question

The main digestive function of enterokinase is
(a) Conversion of pepsinogen into pepsin
(b) Conversion of trypsinogen into trypsin
(c) Conversion of trypsin and trypsinogen
(d) Stimulation of the gastric glands to secrete gastric juices

Answer 1

Hint: Pancreatic juice is composed of two products to proper digestion and they are digestive enzymes and bicarbonate. The 3 enzyme groups which are used to make macromolecules to absorbable substances are proteases, pancreatic lipase, and amylase.

Complete answer:
The protein digestion is due to the pancreatic proteases and several proteases are synthesized in the pancreas but the two major pancreatic proteases are trypsin and chymotrypsin, which are synthesized and packaged into vesicles as the inactive proenzymes trypsinogen and chymotrypsinogen. These proteases are secreted into the lumen of the small intestine.
Packaging of an inactive precursor is a way for the cells to safely handle these enzymes as proteases are rather dangerous enzymes to have in cells.
Trypsinogen and chymotrypsinogen must be converted into their active forms to digest proteins after getting released into the lumen of the small intestine. Enterokinase is embedded in the intestinal mucosa and trypsinogen is activated by this enzyme to trypsin.
Once trypsin is formed it activates chymotrypsinogen to chymotrypsin, procarboxypeptidase to carboxypeptidase, and additional molecules of trypsinogen and this result in the explosive appearance of active protease once the secretions of pancreases reach the small intestine.
So, the correct answer is ‘Conversion of trypsinogen into trypsin’.

Note: Proteins are digested into peptides and smaller peptides by trypsin and chymotrypsin, but they are not able to digest proteins or peptides to single amino acids. The final digestion of peptides into amino acids is mainly because of peptidases on the surface of small intestinal epithelial cells even if some of the proteases from the pancreas like carboxypeptidase have the ability to make peptides to amino acids.