Protein Digestion

Question 1

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

Answer 1

stomach

note: digestion begins here due to acid conditions and pepsin

Question 2

____ cells secrete HCl

Answer 2

parietal

Question 3

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

Answer 3

parietal

Question 4

In the stomach, Cl- is exchanged for what?

Answer 4

HCO3-

Question 5

The pH of gastric juice is about ___

Answer 5

2

Question 6

Pepsinogen and HCl secretion is stimulated by ___ and ____

Answer 6

histamine; gastrin

Question 7

Pepsinogen is the zymogen of pepsin, secreted by ____ cells

Answer 7

chief

Question 8

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

Answer 8

46; 5

Question 9

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

Answer 9

False; pepsins are stable and active at acidic pH

Question 10

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

Answer 10

carboxyl; aspartate

Question 11

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

Answer 11

large peptide fragments

Question 12

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

Answer 12

1. CCK

2. Secretin

Question 13

CCK and Secretin stimulate secretion from ____

Answer 13

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

Question 14

CCK stimulates intestinal mucosal epithelial cells to secrete ____

Answer 14

enteropeptidase

Question 15

What does enteropeptidase do?

Answer 15

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

Question 16

Trypsin further activates more _____

Answer 16

trypsinogen

Question 17

____ is an endoprotease, and a carboxyl protease

Answer 17

pepsin

Question 18

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

Answer 18

trypsin, chymotrypsin, and elastase

Question 19

Carboxypeptidases A and B are metalloproteases requiring ___

Answer 19

zinc

Question 20

What are the products of intraluminal protein digestion?

Answer 20

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

Question 21

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

Answer 21

1. endopeptidases
2. aminopeptidases
3. dipeptidases

“EAD”

Question 22

Brush border protein digestive enzymes produce what?

Answer 22

Free AA and di- and tri-peptides

Question 23

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

Answer 23

Na+ or H+ (active transport)

Question 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

Answer 24

blood