What is the effect of insulin on glucose uptake into cells?

• A. Increases glucose uptake into cells via GLUT-4 transporters
• B. Decreases glucose uptake
• C. Converts glucose to glycogen in the brain
• D. Inhibits glucose transport into muscle cells

Answer: (A)

Insulin increases glucose uptake into muscle and fat cells by promoting the movement of GLUT-4 transporters to the cell membrane. When insulin binds its receptor, a signaling cascade triggers GLUT-4-containing vesicles to fuse with the plasma membrane, allowing more glucose to enter the cell from the bloodstream. Brain uptake of glucose is largely insulin-independent, using GLUT-1 and GLUT-3 transporters that are always present on the cell surface, so insulin does not drive glucose into brain cells in the same way. The glucose that enters these cells can then be used for energy or stored as glycogen or fat, which is why insulin helps lower blood glucose levels after a meal.