MCQ Physiology Answer 5

The correct answer is D
Explanation

Protease enzymes are potentially dangerous because they can break down other enzymes (including themselves!) and other proteins in cells. To prevent this they are synthesised in the RER of their secretory cells as inactive forms, called zymogens. These are quite safe inside cells, and the enzymes are only activated in the lumen of the intestine when they are required.

Pepsin is synthesised as inactive pepsinogen, and activated by the acid in the stomach

Rennin is synthesised as inactive prorennin, and activated by pepsin in the stomach
The pancreatic exopeptidases are activated by specific enzymes in the duodenum
The membrane-bound peptidase enzymes do not have this problem since they are fixed, so cannot come into contact with cell proteins.

The lining of mucus between the stomach wall and the food also protects the cells from the protease enzymes once they are activated

Category: Physiology MCQs