Cambridge O Level Biology · Syllabus 5090 · Human Nutrition
Protease
What is Protease?
A digestive enzyme that breaks down protein into amino acids. Protease produced in the stomach works best in the acidic conditions created by hydrochloric acid, while protease produced by the pancreas works best in the alkaline conditions of the small intestine.
This definition is part of the Human Nutrition chapter in Cambridge O Level Biology.
Common mistakes with Protease
- “Protease digests protein into fatty acids.” Why it is wrong Fatty acids come from lipid, not protein. Protein is built from amino acids, so amino acids are what it breaks down into. Write instead "Protease breaks protein into amino acids. Lipase breaks lipid into fatty acids and glycerol."
- “Hydrochloric acid digests the protein in the stomach.” Why it is wrong Acid is not a catalyst and is not an enzyme. It creates the conditions in which the stomach's protease works, and it kills many ingested microorganisms. Write instead "Hydrochloric acid provides the acidic conditions the stomach protease needs, and kills many ingested microorganisms. The protease does the digesting."
Questions students ask about Protease
Why does the stomach need a different protease from the small intestine?
Because an enzyme's shape depends on the pH around it. The stomach is strongly acidic and the small intestine is alkaline, so an enzyme with an acidic optimum would be denatured in the intestine, and one with an alkaline optimum would be denatured in the stomach. Making two proteases with two optima is the only way to digest protein in both regions.