Question

Milk protein is acted upon by a gastric enzyme
(a)Casein
(b)Rennin
(c)Pepsin
(d)Caseinogen

Answer 1

Hint: Another name for the proteolytic gastric enzyme that acts upon the milk proteins is chymosin. It digests milk by curdling or coagulating it in the stomach. It is found in young mammals as their primary diet includes milk.

Complete answer:
Milk protein is acted upon by a gastric enzyme known as rennin which digests these milk proteins called caseinogen. It is also known as chymosin and is activated by the HCl present in the stomach where it is converted from inactive prorenin to rennin. It converts the milk protein caseinogen to casein and finally to calcium paracasein thus causing curdling. Coagulation or curdling of milk is very important or else the milk would rapidly pass out from the stomach without proper digestion. The enzyme chymosin is used commercially for cheesemaking which is extracted from the stomachs of young calves.

Additional Information: Let us know more about this enzyme rennin.
- Rennin is secreted in maximum quantity after a few days from birth but its production decreases rapidly with time.
-This is because milk consumption decreases as the infant grows older.
-Now, the enzyme rennin is replaced by pepsin which is able to digest all types of proteins entering through food.
-The major protein present in milk is casein which is further of 4 types known as alpha-s1, alpha-s2, beta, and kappa.
-All these proteins are coagulated by chymosin as it coagulates them with the calcium ions present in the milk.
So, the correct option is ‘Rennin’.

Note: -Rennin should not be confused with renin which is a hormone released by the kidney to regulate blood sodium levels and blood pressure.
-Pepsin is also a proteolytic gastric enzyme that breaks proteins into smaller peptides.
-Pepsin is produced by the chief cells that line the wall of the stomach and it is one of the most important enzymes required for digesting proteins in food.