Question

All relevant enzymes, including their inactive (precursor) and active forms, where they are released from, activated by, and their specific role in protein digestion In describing absorption, be sure to include the process through the final digestive product entering the blood stream.

Answer 1

Ans

Digestion of proteins-

1.In stomach- Gastric glands secrete gastric juice containing mucus, HCl, two proenzymes- pepsinogen and prorenin.

Pepsinogen is a inactive form which is converted into active form called pepsin.

pepsin hydrolyses large molecules of proteins into smaller molecules of proteoses and peptides in acidic medium of pH 2.

prorenin is a inactive form activated by HCl into active form renin.

renin ​​​​​​​hydrolyses soluble milk protein casein into paracasein and whey proteins. Paracasein is spontaneously precipitated in presence of calcium as insoluble calcium paracaseinate,forming solid curd. The curd stays in stomach for a longer period for proper action of pepsin which converts calcium paracaseinate into peptones.

2.In small intestine-

Pancreatic juice is released from pancreas on stimulation by secretin and cholecystokinin that enters small intestine. This juice contains trypsinogen,chymotrypsinogen and procarboxypeptidase, and several other enzymes.

• Trypsinogen is activated to trypsin by enterokinase present in intestinal juice. Trypsin breaks proteins into peptides.
• Chymotrypsinogen is activated to chymotrypsin by trypsin.Chymotrypsin splits proteins into peptides and also clots milk in an alkaline medium by hydrolysing casein to paracasein and whey proteins.
• Procarboxypeptidase is activated to carboxypeptidase by trypsin. This enzyme separate individual amino acids adjacent to the free terminal carboxyl group of the peptides, reducing them to dipeptides. It thus produces amino acids and dipeptides.

intestinal juice contains aminopeptidase, dipeptidase,enterokinase etc. Aminopeptidase separate individual amino acids adjacent to the free terminal amino group of the peptides reducing them to dipeptides. Dipeptidase splits dipeptides into amino acids.

Absorption- absorption of amino acids from intestine to blood occurs by active transport utilising energy from ATP. Amino acids are carried by hepatic portal vein to the liver for metabolism.