Question

In the following process of digestion, the enzymes at location 'X' and 'Y' are respectively proteins $\underrightarrow X$ proteoses and peptones $\underrightarrow Y$ dipeptides.
a. Chymotrypsin and pepsin
b. Pepsin and trypsin
c. Ptyalin and pepsin
d. Trypsin and di-peptidase

Answer 1

Hint: The enzyme at location 'X', is the main digestive enzyme and it is the component of gastric juice released by the gastric glands of the stomach. The enzyme at location 'Y', is the enzyme that is a part of pancreatic juice released by the pancreas. Both of these enzymes function in the digestion of proteins.

Complete answer:
Protein digestion starts in the stomach. When the food reaches the stomach, the pepsinogen (an inactive form of pepsin) gets activated by the $HCl$ present in the gastric juice. Here the proteins get broken down into smaller pieces like proteases and peptones.

From the stomach when these proteases and peptones reach the intestine, they present an enzyme called trypsinogen (inactive form of trypsin) which gets activated by the action of an enzyme called enterokinase. In the intestine due to the action of trypsin enzyme these proteins get further broken down into polypeptides.

Thus the whole process occurs like this:
Proteins \[\xrightarrow{{Pep\sin }}\] Proteoses and Peptones \[\xrightarrow{{Tryp\sin }}\] Dipeptide

The optimum pH for the activity of pepsin enzyme is acidic i.e. $1.8$ , whereas the optimum pH for the activity of trypsin is alkaline i.e. $7.5 - 8$
Both of these enzymes are proteolytic but they are different.

Hence, the correct answer is option (B).

Note: So overall, the protein digestion starts from the stomach where the pepsin enzyme breaks down the protein into peptones and proteases. Then both of these small chain proteins reach the intestine where the trypsin enzyme further hydrolyze them into the dipeptides. The end product of protein digestion is an amino acid.