Here is an animation showing how adrenaline changes glycogen synthesis in the cell. Note how the trimeric G-protein changes from the inactive (GDP-bound) to active (GTP-bound) state. When PKA binds cAMP, the catalytic subunit is released and it activates phosphorylase kinase and glycogen phosphorylase and inactivates glycogen synthase. This changes the cell from the default state of synthesizing glycogen from glucose to breaking down glycogen to produce glucose.

For an awesome animation of the same process prepared by one of the students in 442, check out this link. You can view this on your browser if you have a PC and you install the Flash player, or you can view this as a Quick time movie on a Mac or PC. Check it out!