GLUT1, found in the plasma membrane of erythrocytes, is a classic example of a uniporrer.

a. Design a set of experiments to prove that GLUT1 is indeed a glucose-specific uniporter rather than a galactoseor mannose-specific uniporrer.

b. Glucose is a 6-carbon sugar while ribose is a 5-carbon sugar. Despite this smaller size, ribose is not efficiently transported by GLUTl. How can this be explained?

c. A drop in blood sugar from 5 mM to 2.8 mM or below can cause confusion and fainting. Calculate the effect of this drop on glucose transport into cells expressing GLUT1.

d. How do liver and muscle cells maximize glucose uptake without changing v_max"'?

e. Tumor cells expressing GLUT1 often have a higher V_max for glucose transport than do normal cells of the same type. How could these cells increase the Y_max?

f. Fat and muscle cells modulate the V_max for glucose uptake in response to insulin signaling. How?