1. Buccal Digestion: Buccal does not contain any protein digesting enzymes. Mucin present in saliva makes the food slippery.
2. Digestion in the stomach
(i) Inactive pepsinogen is converted to active pepsin under the influence of HCl. Pepsin breaks down proteins into proteases and peptones.
(ii) Gelatinase enzyme breaks down gelatin to produce peptones and polypeptides.
3. Digestion in the pancreatic juice of the small intestine
(i) Inactive trypsinogen is converted to active trypsin under the action of enterokinase enzyme. Trypsin converts peptone into dipeptides and polypeptides.
(ii) Inactive chymotrypsinogen is converted to active chymotrypsin with the help of trypsin enzyme. Chymotrypsin breaks down milk casein into paracasein.
(iii) Elastase enzyme breaks down elastin into peptides.
(iv) Peptides are produced from collagen by the action of collagenase enzyme.
4. Digestion in the intestinal juice of the small intestine
(i) Amino peptidase enzyme breaks down polypeptides into amino acids.
(ii) Prolidase enzyme cleaves the peptide into proline.
(iii) Dipeptides and amino acids are produced from tripeptides under the action of tripeptidase enzyme.
(iv) Dipeptidase enzyme breaks down dipeptide into amino acids.
Protein is a complex biochemical substance. It is complex, insoluble and non-absorbable for the organism. It is of no benefit to the organism. Proteins are digested and converted into amino acids by the action of various enzymes. Amino acids are simple, soluble and absorbable by the body. Our body cells absorb amino acids. Later amino acids combine to form proteins. These proteins make up our body.