HRR: digestion/absorption of carbs and protein

Question 1

What are the forms of starch?

Answer 1

Amylose and amylopectin

Question 2

Describe amylose.

Answer 2

Linear storage polysaccharide

Question 3

What linkages are found in amylose?

Answer 3

a-1,4

Question 4

Describe amylopectin.

Answer 4

Branched storage polysaccharide

Question 5

What linkages are found in amylopectin?

Answer 5

a-1,4 and a-1,6

Question 6

Describe glycogen.

Answer 6

Heavily branched storage polysaccharide

Question 7

Where is glycogen found?

Answer 7

Muscle and liver

Question 8

What linkages are found in glycogen?

Answer 8

a-1,4 and a-1,6

Question 9

What is the difference between amylopectin and glycogen?

Answer 9

Glycogen is way more branched

Question 10

Describe cellulose.

Answer 10

Storage polysaccharide found in plants

Question 11

What linkages are in cellulose?

Answer 11

B-1,4

Question 12

Describe sucrose.

Answer 12

Disaccharide consisting of glucose and fructose

Question 13

Describe lactose.

Answer 13

Disaccharide consisting of glucose and galactose

Question 14

Describe trehalose.

Answer 14

Disaccharide consisting of glucose with a-1,1 links

Question 15

Where is there the most absorption of monosaccharides?

Answer 15

Duodenum and upper jejunum

Question 16

Where does carb digestion start?

Answer 16

In the mouth with salivary a-amylase

Question 17

Describe the digestion of carbs.

Answer 17

1. Partial digestion by salivary amylase
2. Further digestion via pancreatic a-amylase in the small intestine
3. Conversion of disaccharides and oligosaccharides by brush border enzymes in the small intestine
4. Absorption into enterocytes and export into the bloodstream

Question 18

What is the intraluminal hydrolysis phase?

Answer 18

The process of breaking down complex carbohydrates to oligosaccharides and disaccharides. The process is mediated by salivary and pancreatic a-amylase that hydrolyze a-1,4 links

Question 19

What can amylase NOT cleave?

Answer 19

Terminal a-1,4 links, a-1,6 links, and a-1,4 links immediately next to a-1,6

Question 20

Pancreatic amylase is stimulated by…

Answer 20

Cholecystokinin

Question 21

What is the membrane digestion phase?

Answer 21

Digestion of partially broken-down carbohydrates in the brush border of the small intestine via hydrolases

Question 22

What are the 3 big disaccharidases found in the brush border of the small intestine?

Answer 22

Glucoamylase, sucrase-isomaltase, and lactase

Question 23

What links can glucoamylase break?

Answer 23

Terminal a-1,4 links; can break down maltose, maltotriose, and limit dextrin

Question 24

What are the final products of glucoamylase?

Answer 24

Glucose and shortened limit dextrin

Question 25

What links can sucrase-isomaltase break?

Answer 25

Terminal a-1,4, a-1,6

Question 26

What are the final products of sucrase-isomaltase?

Answer 26

Glucose

Question 27

What links can sucrase itself break?

Answer 27

a-1,2

Question 28

What is the final product of sucrase breaking down sucrose?

Answer 28

Glucose and fructose

Question 29

What links can lactase break?

Answer 29

B-1,4

Question 30

What are the final products of lactase?

Answer 30

Galactose and glucose

Question 31

Describe the SGLT1 transporter.

Answer 31

Takes galactose and glucose out of lumen and into enterocytes, but requires Na to be brought in as well

Question 32

How do we balance osmolarity from SGLT1 transporter?

Answer 32

An Na-K pump on the basolateral membrane removes sodium from the enterocyte and brings in potassium to correct salt balance and create a gradient for Na to allow SGLT1 to continue functioning

Question 33

Describe the GLUT5 transporter.

Answer 33

Takes fructose out of lumen and into enterocytes in the small intestine

Question 34

Describe the GLUT2 transporter.

Answer 34

Allows glucose, galactose, and fructose to exit enterocytes and enter the interstitial space

Question 35

Describe lactose intolerance.

Answer 35

Primary deficiency of lactase production or secondary to intestinal injury from something like infection

Question 36

What causes symptoms from lactose intolerance?

Answer 36

The lactose is converted by bacteria into lactic acid, methane, and hydrogen gas. The osmotic effect of these in the lumen of the bowel causes bloating, nausea, abdominal pain, etc due to drawing in more water

Question 37

Where does digestion of protein begin?

Answer 37

In the stomach by pepsin

Question 38

Describe the digestion of proteins.

Answer 38

1. Digestion begins in the stomach by pepsin 2. Pancreatic proteases continue to break down proteins in the small intestine 3. Oligopeptides get digested by brush-border enzymes into di and tripeptides and amino acids 4. Di and tripeptides are absorbed into enterocytes 5. Di and tripeptides are converted into amino acids within enterocytes, then exported into the blood

Question 39

How does pepsin work?

Answer 39

Cleaves bonds at the carboxyl ends of aromatic or acidic amino acid residues

Question 40

What does enterokinase do?

Answer 40

Convert trypsinogen to trypsin

Question 41

Describe the function of trypsin.

Answer 41

Once trypsin is activated by enterokinase, it sets off a cascade and activates the other pancreatic proenzymes, including more trypsin

Question 42

What are endopeptidases?

Answer 42

Those that prefer cleaving in the central parts of the molecule vs terminal links. They’re very specific in terms of where and what they like to cut

Question 43

What are the endopeptidases?

Answer 43

Trypsin, chymotrypsin, elastase, pepsin

Question 44

What are exopeptidases?

Answer 44

They like to cut towards the outside/terminal ends of molecules

Question 45

What are the exopeptidases?

Answer 45

Aminopeptidases and carboxypeptidases

Question 46

How are amino acids brought into enterocytes?

Answer 46

A lot of them require sodium-dependent transporters, but some are sodium-independent

Question 47

How are di and tripeptides taken into enterocytes?

Answer 47

Proton-dependent pepT1 transporter

Question 48

How do amino acids exit enterocytes?

Answer 48

Sodium-independent amino acid transporters

Question 49

Describe the role of NHE3 in enterocytes.

Answer 49

Di and tripeptides need a proton to be taken into the cell via pepT1. In order to maintain a proton gradient, NHE3 puts protons back into the lumen in exchange for sodium. The sodium will be balanced out by Na-K pump on basolateral membrane

Question 50

Describe the B0AT1 transporter.

Answer 50

It delivers neutral amino acids into enterocytes, such as tryptophan and phenylalanine

Question 51

What is hartnup disease?

Answer 51

Defective B0AT1 transporter causes an inability to absorb neutral amino acids like tryptophan. An inability to bring in tryptophan means we do not have the precursor for niacinamide and cannot make NAD and NADP. This leads to pellagra

Question 52

What are the signs of pellagra?

Answer 52

Dermatitis, dementia, diarrhea