Question

In the stomach, curdling of milk is due to the action of
A. Pepin
B. Rennin
C. HCl
D. Renin

Answer 1

Hint: Curdling of milk is the coagulation of milk protein, which is carried out by the help of specific enzymes present in the stomach and secreted to digest the milk and its protein component. Such enzymes, which digest the milk, are released from a specific type of gastric cell.

Complete answer:
Rennin is the enzyme which performs curdling or coagulation of milk in the stomach. Rennin is also known as Chymosin, it is a proteolytic enzyme, which is synthesized by the chief cell in the stomach. Chymosin is an inactive proenzyme, which converts into active form under the influence of acid or pH.

In the small intestine part is called duodenum which secretes chymotrypsin which acts on the milk protein and shows curdling of milk in the small intestine.

Hence, the correct answer is option (B).

Additional information:
> Option A:
Pepsin is the proteolytic enzyme which breaks the larger polypeptide protein molecule into smaller ones. This enzyme is secreted by the chief cells of the stomach. Pepsin secreted as proenzyme by chief cells but later converted into an active form by the action of HCl of the stomach, to degrade the protein molecule.

> Option C:
HCl (Hydrochloric acid) is secreted in the stomach by stomach lining cells called a parietal cell. HCl helps to digest the food and kill the harmful microbes, which enter with food. HCl is also necessary to activate the various enzymes and provide optimum pH to optimize the activity of Enzyme in the stomach.

Note: Pepsin and rennin both are secreted by a chief cell of the stomach and released in the form of proenzyme. But pepsin does not act on the milk protein called casein only digest by the rennin enzyme. Rennin is secreted in the child while in adult chymotrypsin secreted in the small intestine to digest milk protein.