Question

. Skeletal muscle cells produce glucose carriers (GLUT 4 transporters). Rather then having these transporters continually on their surface, they store them inside vesicles within the cell. During exercise (muscular contraction), these vesicles fuse with the plasma membrane of the cell, inserting the transporters into the membrane. This allows glucose to enter the cell by passive transport. Which of the factors that affect simple diffusion has been altered in this example?

Answer 1

Glucose entry during muscular contraction is mediated through glut 4

It is an example of facilitated diffusion and insulin regulated glucose transporter

Factors affecting simple diffusion has been altered in the above example they are

1). In simple diffusion there is no carrier molecule involved. Because smaller molecules like co2 and o2 diffuse simply. But molecule like glucose is larger and cannot diffuse across the phospholipid bilayer directly hence it needs carrier like glut 4 .

2). Facilitated diffusion has saturation kinetics. There is no increase in diffusion once saturation is reached. But simple diffusion has no saturation. In facilitated diffusion membrane proteins involved in transport is limited , cell needs energy which is taken in the form of glucose during exercise this saturation kinetics limits the excess glucose intake and helps in maintaining blood glucose level also .if saturation is not present all the glucose will be taken up by muscles and blood glucose will decrease causing hypoglycemia. Thus facilitated diffusion helps in overcoming this disadvantage by maintaining saturation.  

3). If the rate of diffusion is slow as in case of simple diffusion, the cells starve during exercise, but it has been overcome by facilitated diffusion where rate of diffusion is faster inspite of saturation point.

4). Simple diffusion has no specificity whereas facilitated diffusion is highly specific, it donot transport cholesterol or fatty acids in the place of glucose .