Question

The protein-digesting enzyme in the stomach which degrades milk proteins
A. Pepsin
B. Trypsin
C. Ptyalin
D. Rennin

Answer 1

Hint: Digestive enzymes play a key role in breaking down the food we eat. The enzymes speed up biochemical reactions that help to break the carbohydrates, proteins, and fats into sugars, amino acids, and fatty acids respectively.
These small building block substances are easily absorbed in the digestive tract

Complete answer: Pepsin is a proteolytic enzyme that is secreted by the stomach. It helps in protein absorption.
Trypsin plays its key role in the small intestine.
Ptyalin and amylase are present in saliva and help in carbohydrate metabolism.
Rennin is also known as Chymosin. It is a proteolytic enzyme that is secreted by the chief cells of the stomach. It helps to curdle or coagulate milk in the stomach during digestion. This process is mainly seen in small babies.

Additional information: Chymosin is able to convert liquid milk to a semisolid like cottage cheese – that allows the milk to be preserved for a longer period of time in the stomach.
Chymosin secretion is maximal during the first few days after birth and then declines.
Finally, it is replaced by the effect of the secretion of pepsin which is a major gastric protease. Chymosin is secreted in the neonatal stomach of ruminant animals also.
For example cattle, goats, camels, pigs, cats, and rats.
Animals like humans, chimpanzees, and horses have mutations in their Chymosin producing gene that helps not to secrete the enzyme.

So, the correct answer is option D. Rennin.

Note: Pepsin and rennin were thought to be identical in earlier times.
Chymosin is secreted as an inactive proenzyme, prochymosin that is activated on exposure to acid.
The function of Chymosin is similar to pepsin and they are most active in acidic environments.