QS Study

Digestion of Protein

Protein is one of the most vital substances in our body. Our muscles, hair, eyes, organs, and many hormones and enzymes are mainly made out of protein. The body requires proteins, and principally the necessary amino acids contained in them. Two stages are involved in the digestion of proteins: the first occurs in the stomach and the other in the in the duodenum, the first part of the small intestine.

  1. In the mouth – No digestion occurs because there are no enzymes in the mouth for protein digestion. Once the food reaches your stomach, it encounters a harshly acidic environment.
  2. In the stomach: Here digestion begins; protein is conversed into peptone by pepsin with the help of HCl.

Protein → (Pepsin) ↑↓ (HCl) → Peptone

  1. In the intestine: Influence of pancreatic enzymes. Most of the protein digestion occurs in the upper GIT (Duodenum) under the influence of proteolytic enzymes of the pancreas.

Protein/Peptone → Trypsin, chymotrypsin → Polypeptide.

Polypetide → Carboxyl polypeptides → Amino acid.

Influence of enterocytes

Enterocytes have 2 types of enzymes on their brush border-

  1. Aminopolypeptidase
  2. Several dipeptidases

These split remaining large polypeptides into amino acids, dipeptides or tripeptides. Inside the cytosol of enterocytes, other peptidases break down virtually all the dipeptides and tripeptides into amino acids.

Fig: Digestion of protein

The end product of protein digestion

Amino acid → 90%;

Others are the peptide, polypeptide.