ID #2165

In class you gave the example of insulin giving a signal to the cell. The cell then picked up the insulin by recognizing it with its transmembrane proteins in the plasma membrane. The insulin was then taken away to get degraded. My question is, is the signal the insulin was giving just, "degrade me" or did it give another signal and it is just getting degraded regardless.

It is unlikely that the cell would create a molecule whose sole purpose it was to go somewhere else just to be degraded, so it's safe to assume that the body released insulin from the pancreas for a reason. This isn't a physiology class, so this won't be on the exam, but insulin is a hormone that is critical to regulating blood glucose levels. There's a "right" amount of glucose in the blood, to be delivered to tissues (especially the brain) for fuel. Too little, and the body needs to signal tissues which store glucose as glycogen to release some of it. To much, and the body needs to signal tissues to take more glucose into cells and store it for later. Insulin is a signaling molecule that tells the body that it needs to increase the number of glucose transporters in the membranes of cells like liver cells and take more glucose out of the bloodstream. That's why I used a liver cell as my example in class, and used insulin as an example of a molecule that might need to be removed from the extracellular space. Hopefully now you can see why this molecule (the insulin molecule itself) needs to be removed. As soon as it is recognized, the cell responds by taking in more glucose. If the insulin is not removed, the cell will continue responding, meaning too much glucose would be taken out of the bloodstream, which is not any more acceptable than having too much (in fact, it's probably worse).

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