Question

Describe the process of digestion in human beings.

Answer 1

Digestion of proteins in humans:

There is no digestion of protein in the oral cavity because protein digestive enzymes are absent in the saliva.

(a) Digestion of protein in the stomach: Gastric juice contains HCI and two proenzymes, pepsinogen and prorenin. HCI maintains a pH of 2-3.7 and kills bacteria and other pathogens. Gastric juice mixes with food until it becomes a semi-solid mass called Chyme. Proenzymes become activated as below:

Pepsinogen \[\ce{->[HCl][2-3.7 pH]}\] Pepsin
Prorennin \[\ce{->[HCl]}\] Rennin

These enzymes act as follows:
Casein \[\ce{->[Rennin][(Milk protein)]}\] Paracasein
Paracasein + Ca → Calcium Paracasinate (Curd)
Calcium paracaseinate \[\ce{->[Pepsin]}\] Peptones
Protein \[\ce{->[Pepsin]}\] Peotone

(b) Digestion of protein the small intestine Action of pancreatic juice. It contains proenzymes trypsinogen, chymotrypsinogen, and procarboxy peptidase.

Trypsinogen \[\ce{->[Enterokinase][of interstinal juice]}\] Trypsin
Chymotrypsinogen \[\ce{->[Trypsin]}\] Chymotrypsin
Procarboxypeptidase \[\ce{->[Trypsin]}\] Carbody - peptidase
Peptones \[\ce{->[Trypsin]}\] Peptides
Peptones \[\ce{->[Chymotrypsin]}\] Peptides
Peptides \[\ce{->[Carboxypeptidase]}\] Smaller peptides + Amino acid

The action of intestinal juice. Intestinal juice contains endokinase, aminopeptidase, and dipeptidase. Actions of these enzymes are summarized below:

Peptides \[\ce{->[Aminopeptidase]}\] Smaller peptides + Amino acid
Peptides \[\ce{->[Dipeptidase]}\] Amino acid