9.1 Glucose Transport

Question 1

How is glucose entry in the cell determined?

Answer 1

• driven by concentration and is independent of sodium, unlike absorption from the digestive tract

Question 2

What’re the 4 glucose transporters, and which ones are most significant?

Answer 2

• GLUT 1 through GLUT 4.
• GLUT 2 and GLUT 4 are the most significant of these because they are located only in specific cells and are highly regulated.

Question 3

GLUT 2

Answer 3

• a low-affinity transporter in hepatocytes and pancreatic cells
• captures the excess glucose primarily for storage
• When the glucose concentration drops below the Km for the transporter, much of the remainder bypasses the liver and enters the peripheral circulation
• the liver will pick up excess glucose and store it preferentially after a meal, when blood glucose levels are high.

Question 4

What serves as the glucose sensor for insulin release?

Answer 4

• In the β-islet cells of the pancreas, GLUT 2, along with the glycolytic enzyme glucokinase

Question 5

GLUT 4

Answer 5

• in adipose tissue and muscle and responds to the glucose
  concentration in blood
• Insulin stimulates the movement of additional GLUT 4 transporters to the membrane by a mechanism involving exocytosis

Question 6

How does the Km of GLUT 4 being close to normal glucose levels in blood affect uptake of glucose?

Answer 6

B/c GLUT4 concentration is close to glucose concentration so anything over, won’t be able to bind to GLUT-4. So must increase # of GLUT-4 transporters

Question 7

How does insulin affect # of GLUT 4 transporters?

Answer 7

• Decreased insulin decreases GLUT 4
• Increased insulin increases GLUT 4

Question 8

How do muscles store excess glucose?

Answer 8

• As glycogen

Question 9

How does adipose tissue store glucose?

Answer 9

• Uses form dihydroxyacetone phosphate (DHAP), which is converted to glycerol phosphate to store incoming fatty acids as triacylglycerols