Protein Digestion- Lecture 10/19/21 Flashcards
Sources of Amino acids
- Body breakdown (3/4)
- Digestion of dietary protein (1/4)
Pepsin
Cleaves proteins and produces peptides
Protein enzymes in the duodenum
- Trypsin
- Chymotrypsin
- elastase
- Carboxypeptidase A and B
Cholecystokinin
CCK, stimulates the gallbladder to contract and the pancreas to release juices
Enteropeptidase
Cleaves trypsinogen to form trypsin in intestinal lumen
Trypsin autoactivity
Once enteropeptidase forms active trypsin, it can cleave trypsinogen to form more trypsin
Trypsin activating mechanisms (4)
- Autoactivity
- Chymotrypsinogen->Chymotrypsin
- Proelastase-> elastase
- Procarboxypeptidase-> carboxypeptidase
Trypsin inhibitor
Binds to trypsin so tightly it cannot cleave, present only in the pancreas
Aminopeptidase
On the brush border, cleaves oligopeptides into amino acids
Amino acid absorption
Active transport using a sodium symporter
SLC7A9
Transporter of Cystine in the kidney, Cystine is the least soluble amino acid conjugate, causes kidney stones (also transports lysine)
Cathepsins
Lysosomal proteases that degrade proteins taken in by the cell
The ubiquitin/proteosome pathway
The major pathway for the degradation of intracellular proteins (eg. muscle)
Difference in half lives for proteins
Structural proteins tend to have a long half life, regulated enzymes tend to be very short
Internal protein ubiquitination signals (3)
- N-end rule
- Pest sequences
- Destruction boxes
