Protein Digestion Flashcards Preview

Biochem > Protein Digestion > Flashcards

Flashcards in Protein Digestion Deck (24):
1

Unlike carbs and lipids, digestion of proteins does not start until reaching the _____

stomach

note: digestion begins here due to acid conditions and pepsin

2

____ cells secrete HCl

parietal

3

K+, H+ exchanging ATPase is specific to ____ cells

parietal

4

In the stomach, Cl- is exchanged for what?

HCO3-

5

The pH of gastric juice is about ___

2

6

Pepsinogen and HCl secretion is stimulated by ___ and ____

histamine; gastrin

7

Pepsinogen is the zymogen of pepsin, secreted by ____ cells

chief

8

Pepsinogen is activated to pepsin by removal of ___ AA from the N-terminus, with auto-activation at a pH

46; 5

9

True or false? Pepsins are unstable and inactive at acidic pH

False; pepsins are stable and active at acidic pH

10

Pepsins are ____ peptidases that contain two _____ residues at the active site

carboxyl; aspartate

11

Pepsin begins proteolysis in the stomach. The product is mainly what?

large peptide fragments

12

The presence of AA, oligopeptides, and polypeptides in the duodenum stimulates secretion of what two things from intestinal endocrine cells?

1. CCK
2. Secretin

13

CCK and Secretin stimulate secretion from ____

Pancreas (trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidases A and B, other digestive enzymes)

14

CCK stimulates intestinal mucosal epithelial cells to secrete ____

enteropeptidase

15

What does enteropeptidase do?

activates trypsinogen to trypsin (removal of a hexapeptide from N-terminus)

16

Trypsin further activates more _____

trypsinogen

17

____ is an endoprotease, and a carboxyl protease

pepsin

18

____, ____, and ____ are endoproteases, and serine proteases

trypsin, chymotrypsin, and elastase

19

Carboxypeptidases A and B are metalloproteases requiring ___

zinc

20

What are the products of intraluminal protein digestion?

Free AA (40%)
Small peptides of 2-8 residues (60%)

21

What 3 protein digestive enzymes are found in the intestinal cell brush border?

1. endopeptidases
2. aminopeptidases
3. dipeptidases

"EAD"

22

Brush border protein digestive enzymes produce what?

Free AA and di- and tri-peptides

23

The transport of di- and ti-peptides is usually dependent on ___ or ____

Na+ or H+ (active transport)

24

The intestinal epithelial cells contain intracellular dipeptidases and tripeptidases. These peptidases complete the breakdown to AAs which are transported to the ____ from the epithelial cells

blood