Insulin receptor covalent structure

Insulin is released when the animal has just eaten. When insulin binds to the receptors on the surface of a cell it causes cAMP to be converted to 5'-AMP by phosphodiesterase. This removes the cAMP stimulus from cAMP dependent protein kinase which prevents it from phosphorylating all the other enzymes which were mentioned above. Protein phosphatase-1 is also no longer inhibited, allowing the enzyme to remove phosphate groups from phosphorylase kinase, and glycogen phosphorylase. This means that glycogen synthase remains activated and thus glycogen can be synthesised and glycogenesis is initiated. In addition, the binding of insulin causes the activation of insulin sensitive protein phosphatase which removes the phosphate group from glycogen synthase causing it to be activated. Insulin also causes GLUT4 receptors to bring more glucose into the cell. The glucose is converted to glucose-6-phosphate which also activates glycogen synthase, causing glycogenesis to occur. Overall, insulin causes net glycogen synthesis.

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