Lecture 12 Prtotien Metabolism
CCeaated: 2013-08-12 11:30 AM Updaated: 2013-09-28 9:53 PM
Humans can only synthesize about 10 of the 20 amino acids (the
simpler non-essential amino acids).
In animals, proteases present in stomach and intestines cleave the
peptide bond to yield amino acids and small oligopeptides.
Carbon skeletons of all twenty amino acids are derived from just 7
3 glycolytic pathway intermediates:
2 pentose phosphate pathway intermediates:
2-citrate cycle intermadiates:
Can make any amino acid out of these 7 intermediates.
The duodenum secretes a protease called enteropeptidase, which
activates several proteolytic enzyme precursors (zymogen) released
from the pancreas.
One of the pancreatic zymogen is trypsinogen which is cleaved to
form the endopeptidase trypsin
Trypsin cleaves numerous pancreatic zymogens, including
chymotrypsinogen, proelastase and procarboxypepetidases A
and B, as well as, trypsinogen itself to amplify the proteolytic cascade.
amino acids can be generated by degradation of cellular protein which
has 2 pathways:
1. An ATP-independent process that occurs inside vesicles called
2. ATP-dependent process that targets specific proteins for
degradation in Proteasomes if they have a Ubiquitin molecule/ tag covalently attached to lysine residue
Ubiquitin is a 76 amino acid protein found in all eukaryotic cells that
is specifically attached to proteins by ubiquitin ligating enzymes.
The proteins are cleaved by endo and exo-proteases/peptidases to
individual amino acids
Most amino acids are de-aminated first by a process called
transamination. Transferring the amino group to an α-ketoacid. To
yield an α-keto acid of the original amino acid and a new
a-ketoglutarate is the main amino acid acceptor and yields
glutamate and a keto acid
Glutamate’s amino group can be transfer