Glycogen Metabolism: Insulin Signaling and Summary

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.