BIOSCI 106 Lecture Notes - Lecture 5: Trypsin, Isoleucine, Lysine
6 Sep 2013
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Document Summary
Purines and pyrimidine"s have no dietary requirement, the human body synthesises them itself by use of salvation pathways. Excess dietary nucleic acids my cause gout eg insoluble uric acid. Surplus dietary protein provide amino groups for biosynthesis, surplus carbon skeletons oxidised or otherwise metabolised. Acid denaturation, hydrolysis and pepsin digestion in stomach. Enzymes present in stomach are inactive precursors in pancreatic secretions. Enterokinase on membrane of enterocytes activates trypsinogen. Amino acids and very small peptides absorbed by intestinal cells (brush border) Peptidases break down peptides to amino acids. Active transport from the intestinal lumen into the epithelial cells. Amino acid taken up by cells for protein synthesis or metabolism. A number of protein degradative pathways exist in cells but all involve proteinases. Cellular cytoplasm proteinases are catalysed by calpains or proteasomes. Lysosomal proteinases are called cathepsins, recycle amino acids. Globular protein are digested and absorbed completely as well most fibrous proteins with the exception of a few.
