Protein Digestion and Absorption Flashcards
Can proteins be absorbed?
No, they must be broken down into free amino acids, di-peptides, or tri-peptides
How are proteins digested in the stomach?
HCl (from parietal cells) converts pepsinogen (from chief cells) into pepsin. Pepsin hydrolyzes peptide bonds, particularly between aromatic amino acids
How are proteins digested in the small intestine?
proteolytic enzymes are secreted from the pancreas. they are divided into two categories endopeptidases and exopeptidases
What do endopeptidases do?
Hydrolyze internal peptide bonds. Specific endopeptidases include trypsin, chymotrypsin, and proelastase
What do exopeptidases do?
catalyze the hydrolysis of peptide bonds at the C- or N-termus. Specific exopeptidases include Carboxypeptidase A and Carboxypeptidase B
What are the membrane-bound proteolytic enzymes in the intestine?
Enterokinase, Aminopeptidase, and Dipeptidase
How are free amino acids transported?
via transporters with the co-transport of Na
How are di- and tri-peptides tranpsorter?
By Pept-1 with the cotransport of H
On average, every 1%-unit reduction in dietary CP will result in an ________ reduction in nitrogen excretion
8% reduction
When amino acids are catabolized what happens to the amino N group?
it is released as ammonia, which binds to urea (mammals) or uric acid (birds).
What are the different amino acid groups?
- Nonpolar (aliphatic)
- Polar, uncharged
- Aromatic
- Positively charged
- Negatively charged
What amino acids fall under nonpolar?
LIV GAP
Leu, Ile, Val, Gly, Ala, Pro
What amino acids fall under polar, uncharged?
SCAT MG
Ser, Cys, Asp, Thr, Met, Gln
What amino acids fall under aromatic?
PTT
Phe, Trp, Tyr
What amino acids fall under postively charged?
LAH
Lys, Arg, His
