Week 3: Carbohydrate digestion & absorption

Question 1

Enzyme specific for sucrose

Answer 1

Sucrase

Question 2

Amylase is made in?

Answer 2

Pancreas and secreted into the duodenum

Question 3

Where is sucrase located?

Answer 3

doubled-headed membrane bound epithelial brush border of the intestines

Question 4

Describe the sucrose structural configuration

Answer 4

doubled headed membrane-bound enzyme with 2 domains

• Sucrase domain
• Isomaltase domain

Question 5

Function of isomaltase domain of the sucrase enzyme

Answer 5

isomaltase can digest α 1, 6 - glycosidic linkages to unbranch starch and allow amylase to continue digesting α 1, 4 glycosidic linkages

Question 6

What is sucrose?

Answer 6

disaccharide

fructose-glucose

Question 7

What is lactose?

Answer 7

Disaccharide

galactose-glucose

Question 8

Lactase structure

Answer 8

membrane-bound with a single active domain that digests lactose

Question 9

Describe the enzymatic consequences of lactose intolerance

Answer 9

inactivated lactase gene makes some people less able to digest lactose

bacteria can digest the lactose into galactose and glucose monomers and ferment it into lactate which produces gas and bloating, and because lactate and lactate can bind water we have an increase in water retention in the colon which increases the chance of having watery diarrhea

Also the increased gas and bloating and water retention lead to increased colonc motility which is the effect of lactose intolerance

Question 10

SGLT AKA

Answer 10

Sodium-Glucose Transporter

Question 11

SGLT-1 transporter function transport type

Answer 11

• Form of secondary active transport (is coupled to primary active transport Na+K+ antiporter to build a gradient for SGLT 1) (Na+ out and K+ in)
• glucose and sodium symporter into the cytosol of the cell

Question 12

galactose transporter

Answer 12

Uses SGLT-1 because their structures are so similar

Question 13

Fructose transporter

Answer 13

GLUT-5 transporter

Question 14

GLUT-5 transporter transports

Answer 14

*only fructose*

was a misnomer when discovered was thought to transport glucose

Question 15

GLUT-5 transporter mechanism of transport

Answer 15

facilitated diffusion by using fructose concentration gradient

Question 16

What happens to the glucose that is transported into an enterocyte?

Answer 16

Some of the glucose is metabolized to make ATP for cellular processes

The bulk of the glucose that entered the cell exits the cell via GLUT-2 into the blood

Question 17

GLUT-2 transport mechanism

Answer 17

Facilitated diffusion using a greater concentration in the enterocyte vs the blood

Question 18

GLUT-2 transports?

Answer 18

Glucose and fructose

Question 19

Glucose structure

Answer 19

6 C ring

Question 20

Fructose structure

Answer 20

5 C ring

Question 21

What is rehydration therapy?

Answer 21

implicated in cholera, cholera toxin keeps Cl- channel open which pulls water into the lumen of the intestine causing watery diarrhea

So rehydration therapy is ingesting glucose and Na+ (Gatorade)

By adding a lot of glucose and Na+ water will follow the glucose transport into the blood