Question

Explain the digestion of proteins in the digestive system of humans.

Answer 1

Hint: Various enzymes are needed for the digestion of proteins in the human body. The digestion of protein starts in the stomach where the pH is low enough for the action of the enzyme Pepsin.

Complete answer:
Proteins are the macromolecules that are broken down into amino acids during digestion and are then absorbed in the blood. Pepsin is secreted as pepsinogen by the chief cells of the stomach. Pepsinogen is activated to pepsin by gastric H+. The optimum pH for pepsin to digest proteins is between 1 and 3. Here the proteins are broken down into peptide bonds.
The remaining digestion takes place in the duodenum of the small intestine where the pancreatic juice contains proteases which include trypsin, chymotrypsin, elastase, carboxypeptidase A, and carboxypeptidase B. These are secreted in inactive forms that are activated in the small intestine as follows:
1. Trypsinogen is activated to trypsin by an enzyme known as enterokinase.
2. Chymotrypsinogen, proelastase, and procarboxypeptidase A and B are then converted to their active forms. (Even trypsinogen is converted to more trypsin by trypsin)
3. After their digestive work is complete, the pancreatic proteases degrade each other and are absorbed along with dietary proteins.
Digestive products of protein can be absorbed as amino acids, dipeptides, and tripeptides.

Note:
There are two types of peptidase:
- Endopeptidase enzymes degrade proteins by hydrolyzing interior peptide bonds.
-Exopeptidase is an enzyme that hydrolyzes one amino acid at a time from the C-terminus of proteins and peptides.
When the pH is >5, pepsin is denatured. Thus, in the intestine, as ${HCO_3}^-$ ion is secreted in pancreatic fluids, duodenal pH increases and pepsin is inactivated.