hapter Amino Acid Oxidation and the Production of urea
Chapter 18 Amino Acid Oxidation and the Production of Urea
I. The surplus amino acids in animals can be completely oxidizer or converted to other storable fuels Amino acids in excess(from diet protein turnover can neither -be stored, nor excreted, but oxidized to release energy or converted to fatty acids or glucose Animals also utilize amino acid for energy generation during starvation or in diabetes mellitus Microorganisms can also use amino acids as an energy source when the supply is in excess Plants almost never use amino acids as an energy source(neither fatty acids)
1. The surplus amino acids in animals can be completely oxidized or converted to other storable fuels • Amino acids in excess (from diet, protein turnover) can neither be stored, nor excreted, but oxidized to release energy or converted to fatty acids or glucose. • Animals also utilize amino acid for energy generation during starvation or in diabetes mellitus. • Microorganisms can also use amino acids as an energy source when the supply is in excess. • Plants almost never use amino acids as an energy source (neither fatty acids)
2. Dietary proteins are digested into amino acids in the gastrointestinal ract Pepsin cleaves polypeptides into smaller peptides in stomach(N-terminal side ofY, F, W residues) Trypsin( C-terminal side of K, R) and chymotrypsin (C-terminal side of F, W, and Y)further cleave the peptides in small intestine Carboxypeptidase and aminopeptidase cleave the small peptides into amino acids. which are then absorbed and eventually delivered to liver
2. Dietary proteins are digested into amino acids in the gastrointestinal tract • Pepsin cleaves polypeptides into smaller peptides in stomach (N-terminal side of Y, F, W residues). • Trypsin (C-terminal side of K, R) and chymotrypsin (C-terminal side of F, W, and Y) further cleave the peptides in small intestine. • Carboxypeptidase and aminopeptidase cleave the small peptides into amino acids, which are then absorbed and eventually delivered to liver
stomach lining Parietal cells (secrete HCD (secrete pepsinogen) Stomach Gastric mucosa (secretes gastrin) Pancreas ancreatic d Exocrine cells of pancreas Zy coll ct and exopeptidase Villi of small intestine Small Vill Intestine Intestinal (absorbs amino
Pepsin Chymotrypsin,trypsin, and exopeptidases Amino acids
3. The amino groups and carbon skeletons of amino acids, take separate but interconnected path ways The amino group is reused or excreted, as ammonia urea(via the urea cycle) or uric acid The carbon skeletons(a-keto acids) generally find their way to the citric acid cycle for further oxidation or conversion. The degradation of the carbon skeletons may be very complicated but similar to that of fatty acids in some cases
3. The amino groups and carbon skeletons of amino acids take separate but interconnected pathways • The amino group is reused or excreted, as ammonia, urea (via the urea cycle) or uric acid. • The carbon skeletons (a-keto acids) generally find their way to the citric acid cycle for further oxidation or conversion. • The degradation of the carbon skeletons may be very complicated but similar to that of fatty acids in some cases