NUTR 3000 - Protein Digestion

in monogastrics, protein digestion begins in the

stomach

pepsin is a

protease

What does pepsin do?

hydrolyzes proteins in acid conditions

When secreted, pepsin is in what form

inactive form, pepsinogen

How is pepsinogen activated to pepsin

HCl rains down from the fundus (top of stomach)

pepsinogen is secreted from

the stomach wall

pepsin breaks down protein chains of amino acids into

smaller peptides

in the first few days after birth, some young animals will secrete a second protein protein digesting enzyme. These animals are

calves, lambs, pigs, cats, and rats

in the first few days after birth, some young animals will secrete a second protein protein digesting enzyme. its active form is known as ________________________ while the inactive form is _____________

rennin or chymosin, prochymosin

Prochymosin is also activated by

HCL in the stomach

Prochymosin (and pepsin if animal doesn't have prochymosin) helps to clot

casein, a high percentage of milk consumed

Renin secretion drops after

the first few days after birth

Why is it imoirtant for casein to clot?

clotting slows down the rate of passage, allowing it to be digested. Half the milk's protein is still in the stomach/abomasum 12 h after a meal. If milk didn't clot, it would pass to quickly through the tract. Important when designing milk replacers

The chyme in the stomach moves to the

SI

The pancreas secretes three inactive enzymes bound for the SI called

trypsinogen, chymotrypsinogen, procarboxypeptidase

What triggers the pancreas to secrete enzymes?

CCK

Pancreatic enzymes are sent to the

duodenum of the SI

The inactive proteases of the pancreas are activated in the

intestinal lumen

Enteropeptidase activates

trypsinogen to trypsin

trypsin activates

chymotrypsinogen to chymotrypsin

and

procarboxypeptidase to carboxypeptidase

other than proteases, the pancreas also secretes

bicarbonate

pancreatic bicarbonate is released into the SI in order to

neutralize stomach chyme pH

The two kinds of proteases (peptidases)

endopeptidases (inside)

Exopeptidases (outside)

Endopeptidases break protein chains in the

middle, where they have specific target sites

Examples of endopeptidases

pepsin, trypsin, chymotrypsin

Exopeptidases take amino acids from the

ends of protein chains

Some exopeptidases are secreted by the

pancreas and mucosa of SI

examples of exopeptidases

aminopeptidase and carboxypeptidase

Aminopeptidase hydrolyzes the ________ peptide bond at the ______-terminus end of proteins and peptides

first, N

Carboxypeptidase hydrolyzes the ______ peptide bond at the ______-terminus of proteins and peptides

first, C (carboxyl end)

Individual amino acids, oligopeptides and some peptides, are absorbed by the

SI mucosa of the jejunum and the ileum

Absorption of AAs in the SI mucosa is

active via carrier pumps (requires energy

__ forms of AA are preferentially absorbed to ___ forms

L, D

In the SI, there is __________ for absorption between AAs

competition

L and D AAs

OH on right =D

OH on left = L

Animal proteins have what configuration of AAs

L

Bacterial polypeptides may contain

D configuration AA

Why are proteinases inactive when secreted

to protect organs from digestion

After absorption, AAs can be used for

protein synthesis

enzyme, hormone, metabolite syntheses

deamination/transamination