Proteins Flashcards
(14 cards)
What happens to amino acids after absorption?
they are now in bloodstream
they are transported to the liver for protein synthesis
Where does protein digestion begin?
In the stomach
- pepsin break down proteins into peptides
What is pepsin?
A protease activated in acidic pH that begins protein digestion
Role of pancreatic peptidases
Continue protein digestion in the small intestine
e.g. trypsin, chymotrypsin
Role of brush border peptidases
Final breakdown of peptides into dipeptides & tripeptides
- on the apical membrane of enterocytes
How do dipeptides/tripeptides enter enterocytes?
Through transporter, called PepT1
What happens to dipeptides/tripeptides once inside enterocytes?
Most of them are broken down into smaller constituent amino acids by cytoplasmic peptidases
What is Peptide transporter 1 (PepT1)?
A symporter (also called co-transporter)
- transporting dipeptides/tripeptides from intestinal lumen into enterocytes
- H⁺ moves against conc. gradient into enterocyte, bringing a dipeptide/tripeptide along with it
Common defective amino acid transport disorders
- Hartnup disease
- Cystinuria
- Lysinuric protein intolerance
Consequence of defective amino acid transport
- impaired absorption leading to:
Protein intolerance
Growth retardation
Skeletal & immunological issues
What happens in Hartnup disease?
Defect in neutral amino acid transport (e.g. tryptophan)
What happens in Cystinuria?
Defect in basic and neutral amino acid transport (e.g. lysine, arginine, cystine)
What happens in Lysinuric protein intolerance?
Defect in cationic amino acid transport
Enzymes for protein digestion
Pepsin
Pancreatic peptidases
Brush border peptidases
Cytoplasmic peptisases
