Question

1. Discuss the importance of amino acid (a.a.) oxidation in biochemistry metabolism.
2. Outline the digestion and absorption of proteins (include enzymes involved).
3. Indicate the pathology of ammonia toxicity in the body.

Answer 1

a) Metabolic uses of amino acids includes building blocks for protein synthesis, source of energy, precurors of neurotransmitters and hormones and precursors of nucleotides and hemes.

b) Digestion of proteins starts from mouth where the large pieces breaks into smaller ones which moves through esophagus to stomach. The stomach then releases gastric juices containing hydrochloric acid enzymes like pepsin which initiates the breakdown of protein. The strong contractions of stomach converts the partially digested proteins into a more uniform mixture called chyme. Then the stomach empties the chyme into small intestine where majority of protein digestion takes place. The pancreas also releases pancreatic juice and two major enzymes trypsin and chymotrypsin which further breaks down the protein fragments. During digestion the proteins are broken down into amino acids and dipeptides for easy absorption.

In the lower part of the small intestine amino acids are transported from intestinal lumen to blood through intestinal cells. The movement of amino acids require a lot of energy in the form of ATP and special transport proteins. After this the amino acids are transported to the liver. Since amino-acids also contains nitrogen, so liver converts it into urea, which is transported to kidney and excreted in the urine. With this process the excess nitrogen is easily transported out of the body. Also urea is easily soluble in water.

C) Ammonia is a waste product which forms during digestion of proteins and excess of ammonia is very harmful for human body. It can cause several complications like renal failure, severe liver diseases, chicken pox, decreased blood flow to the liver, complications in urea cycle and several others.