Protein and carb digestion

Question 1

three major dietary carbohydrates

Answer 1

cellulose (dietary fiber, undigested in humans). Starch (amylopectin and amylose glucose polymers). Disaccharides (sucrose=glucose+fructose, lactose=glucose+galactose)

Question 2

salivary alpha amylase: what does it do? what does it produce? Does it fxn in stomach?

Answer 2

hydrolysis of internal alpha 1,4 linkages (not alpha-1,6 or terminal alpha-1,4). Produces maltos, maltotriose, alpha dextrins. inactivated by gastric acid

Question 3

Pancreatic alpha amylase: what does it do?

Answer 3

targets are same as salivary amylase.

Question 4

where are most oligosaccharides broken down? by what and what secretes them? What are some examples?

Answer 4

brush border of upper jejunum. Enzymes secreted by enterocyte. Lactase, sucrase, maltase, alpha-dextrinase (debranches alpha-dextrins by cleaving alpha-1,6 branch points)

Question 5

Mech of monosaccharide absorption for glucose and galactose? For sucrose?

Answer 5

SGLT (sodium dependent glucose transporter). Requires basolateral Na/K ATPase to create gradient then 2 Na brought in with each glucose.

For fructose you use GLUT5. Does not require Na. Goes through a carrier down its concentration gradient (facilitated diffusion)

Question 6

How do the monosaccharides leave enterocyte

Answer 6

glucose and fructose both go out down their conc gradient via the GLUT2 carrier

Question 7

three phases of protein digestion

Answer 7

gastric, pancreatic, intestinal (depending on source of peptidases)

Question 8

what happens in gastric phase of protein digestion

Answer 8

acid denatures proteins, pepsin starts to break peptides down

Question 9

Can you absorb di and tri peptides? how about di and tri saccharides?

Answer 9

yes (although most are absorbed as AAs); no

Question 10

enteropeptidase: what secretes is and by what signal? Fxn?

Answer 10

intestinal mucosal epithelial cells upon CCK stimulation. Converts trysinogen to trypsin which then converts the other propeptidases

Question 11

at what pH are the pancreatic peptidases active?

Answer 11

Neutral. They require bicarb secretion to neutralize stomach acid

Question 12

How are most AAs absorbed?

How are peptides absorbed?

Answer 12

Na dependent mechanism.

Probably by a single transporter and are then degraded intracellularly. (very few peptides make it out basolateral side)

Question 13

Is there ever intact protein absorption?

Answer 13

infants can absorb intact proteins. Important for immunity (mother’s Ig).

In adults, M cells absorb whole proteins (for immune purposes, not dietary)