B2.045 Prework 1 Biological Differences of GLUT Isoforms

Question 1

how do GLUT 1-4 and GLUT 5,7 differ?

Answer 1

GLUT 1-4 stereo-selective for glucose

GLUT 5,7 stereo-selective for fructose

Question 2

characterize GLUT 1-4

Answer 2

passive, facilitated diffusion requires sugar gradient

bi-directional transport

Question 3

how does GLUT appear to function?

Answer 3

alternating conformations between cytoplasmic and extracellular facing modes

Question 4

why do we think GLUT has alternating conformations?

Answer 4

alternative drugs can block the two different protein sites

Question 5

how do the 12 GLUT isoforms differ?

Answer 5

substrate specificity
substrate Km
tissue distribution
regulation

Question 6

where is GLUT2 located?

Answer 6

liver, islets, kidney, small intestine

Question 7

why is the GLUT2 Km so high compared to normal circulating glucose in the small intestine? (17 mM vs. 5 mM)

Answer 7

this makes GLUT2 more useful in the fasting state and prevents the channel from running backwards from blood into cell

Question 8

what is the function of GLUT2 in the pancreas?

Answer 8

15-25% activity
can sense changes in blood glucose with a 1:1 correlation
respond with insulin release