00:01 Now I wanna spend a little bit time talking about how we reverse all the process. 00:06 So a reversal of the process happens with another hormone. 00:09 And that another hormone is one that we all have heard about and that's insulin. 00:13 Insulin as we will see has the effect of countering the entire epinephrine glucagon system. 00:19 Now insulin stimulates an enzyme called phosphatase that I have mentioned earlier. 00:23 And what phosphatase does is it removes phosphates from the glycogen enzymes. 00:28 This favors glycogen synthesis; because, it was additional phosphate to the glycogen synthase that inactivated it. So removing the phosphate will activate it. 00:38 Conversely we take the phosphate off of glycogen phosphorylase and we will have the effect of reducing its activity. 00:46 Insulin also stimulates the uptake of glucose by cells and this is important; because, blood glucose can be hazardous for the body. So getting glucose out of the blood and into the cells is important. 00:58 In this figure we can see a little bit of the results of insulin action on cells. 01:02 We see in yellow that insulin binds to a receptor of its own called the insulin receptor. 01:07 That binding to the insulin receptor, stimulates several things to happen. Now, as I noted, the liver cells, one of the things that happens, is that they are stimulated to take up glucose from the blood stream. 01:18 The body treats glucose like it's a poison. 01:21 In some ways it may well be a poison; because, people who have trouble maintain their blood glucose levels have many problems. We know for example the issues associated with diabetes. 01:32 So maintaining proper glucose levels is important and insulin plays a role in that process. 01:38 We see insulin stimulates the movement of a protein called glucose transporter-4 to the cell surface and so that green dimer that you see on the cell surface has moved there as a result of the insulin action. 01:52 The glucose is brought into the cell when that happens and you can see the glucose concentration increasing. 01:58 Couple of things can happen with that. Glucose in the cell, again, the cell is now gonna treat it like it is a poison. 02:04 The cell deals with that glucose in two ways. 02:07 One is it reduces the free glucose concentration by making glycogen. 02:12 That takes glucose away out of the free system and makes glycogen and glycogen is not a problem. 02:18 In addition glycolysis is favored by the breakdown of glucose so that also has the effect of reducing the glucose concentration. 02:26 Now the by product of glycolysis in breaking down glucose is you make a lot of pyruvate. 02:32 If you are not getting plenty of exercise what happens is a lot of pyruvate gets converted into acetyl-CoA, and acetyl-CoA goes to fatty and you can probably figure out where that's headed. 02:44 So when glucose levels are high insulin decreases glucose concentration by favoring glycogen synthesis, as I noted, and by inhibiting glycogen breakdown. 02:56 So when glucose is needed, epinephrine does its job and stimulates the release of glucose from glycogen. 03:02 And when glucose is abundant, insulin stimulates the dephosphorylation of those same enzymes to use the glucose in either glycogen or glycolysis. 03:11 So maintaining sugar balance in the body is an essential function. 03:16 And in this lecture we have seen how glycogen metabolism is managed to help the body to manage its own glucose needs. 03:23 With these manage needs done properly, the body functions having glucose when necessary and being able to store glucose when there is an excess.
The lecture Glycogen Metabolism: Insulin Signaling and Summary by Kevin Ahern, PhD is from the course Carbohydrate Metabolism.
Which of the following statements about insulin is NOT true?
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