Physiology of Finfish and Shellfish (2+1)

4.3.2.9 Protein Metabolism

Proteins contain carbon, hydrogen, oxygen, nitrogen and sometimes other atoms,which are arranged as strands of amino acids . They form the cellular structural elements are biochemical catalysts and are important regulators of gene expression. Nitrogen is essential to the formation of twenty different amino acids, the building blocks of all body cells. Amino acids are characterized by the presence of a terminal carboxyl group and an amino group in the alpha position and they are connected by peptide bonds.

Protein anabolism is the process by which protein are formed from amino acids (anabolic amino acid synthesis). Protein catabolism is the process by which proteins are broken down to their amino acids. This is also called proteolysis.

Digestion breaks protein down to amino acids. If amino acids are in excess of the body's biological requirements, they are metabolized to glycogen or fat and subsequently used for energy metabolism. If amino acids are to be used for energy their carbon skeletons (A carbon skeleton is a linkage or chain of carbon atoms) are converted to acetylcoenzyme A (acetyl CoA), after deamination which enters the Krebs cycle for oxidation producing ATP. The final products of protein catabolism include carbon dioxide, water, ATP, urea and ammonia.