Ch18.1 - •Turn your CPS clicker on and your cell phone...

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Unformatted text preview: •Turn your CPS clicker on and your cell phone off. •I am switching my ofFce hours to Tuesdays after class beginning next Tuesday. Chapter 18 Metabolism of amino groups and the Urea Cycle Figure 3-5 Pepsin A. is a zymogen. B. requires the action of the hormone gastrin to be active. C. is most active at pH 7.0. D. cleaves proteins completely into free amino acids. The metabolism we have discussed so far has been biosynthetic metabolism (biosynthesis of carbohydrates and lipids) and that will be the primary focus this semester. BUT, one last catabolic pathway you have not studied -- Amino Acid Degradation , which… •can be a signiFcant source of metabolic energy •provides metabolites for other biosynthetic pathways (depending on the needs of the cell/organism) For those of you who love the low carb, high protein diets, amino acid degradation is what you do! Animals degrade amino acids when… • Normal protein turnover (syn. and degrad. of proteins) releases amino acids that are not needed for new protein synthesis • Protein-rich diet is consumed & the ingested amino acids exceed what is needed for protein synthesis (amino acids are not stored for later…must be catabolized) • Carbohydrates are not available (e.g. starvation or untreated diabetes) and proteins are used as fuel First, how are dietary proteins degraded to amino acids and how do these amino acids get to the liver? Dietary protein in stomach secretion of hormone gastrin HCl and pepsinogen secretion HCl -- denatures (unfolds) proteins Pepsinogen -- zymogen of pepsin, which hydrolyzes peptide bonds on amino (N-) side of aromatic amino acids Peptides (low pH) enter small intestine secretion of hormone secretin HCO 3- secretion, neutral pH The zymogens of trypsin, chymotrypsin and carboxypeptidases A and B are secreted from pancreatic cells. Enteropeptidase converts trypsinogen to trypsin, which activates other proteases (these proteases are active at neutral pH). Why are inactive zymogens secreted instead of active proteases? See Figure 18-3 Note trypsin , chymotrypsin and pepsin amino acid specifcities: These enzymes hydrolyze peptides From stomach even Further in small intestine Then short peptides are completely degraded to amino acids by: • Carboxypeptidase A & B- cleave successive C-term. residues • Aminopeptidase- successive N-term....
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This note was uploaded on 02/16/2009 for the course CH 53540 taught by Professor Yin during the Spring '09 term at University of Texas.

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Ch18.1 - •Turn your CPS clicker on and your cell phone...

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