These videos are quite complex but help tie together a number of VCE Biology 3&4 topics. They show how insulin stimulates glucose transport into the cell in response to an increase in blood sugar. Topics include homeostasis, signal transduction, hormones, exocytosis and membrane transport proteins.
When the amount of sugar in the blood gets too high it’s lowered, and when it gets too low it’s raised. This is called a negative feedback loop and it helps keep the sugar level fairly constant. Insulin is a hormone that is produced in response to raised blood glucose and helps lower it.
Insulin is a protein hormone so it can’t get across the cell membrane. So its message(“blood sugar is up”) is passed across the cell membrane by another protein which sits in the cell membrane – a signal transduction protein.
GLUT4 is a membrane transport protein that transports glucose from the blood into fat and muscle tissues by facilitated diffusion. When it’s not needed it’s kept inside the cell in vesicles. Because it’s a membrane-bound protein it sits in the membranes of these vesicles.
The message from insulin causes a series of reactions including causing these vesicles to fuse to the cell membrane by exocytosis. The GLUT4 molecules are now sitting in the cell membrane, so glucose can diffuse across them from the blood into the cell.