<P> Once the tyrosine kinase is activated in the insulin receptor, it triggers the activation of the docking proteins, also called IRS (1 - 4) that are important in the signaling pathway, and then the activation of the PI - 3k </P> <P> The two enzymes Mitogen - activated Protein Kinase (MAP - Kinase) and Phosphatidylinositol - 3 - Kinase (PI - 3K, Phosphoinositide 3 - kinase) are responsible for expressing the mitogenic and metabolic actions of Insulin, respectively . </P> <P> The activation of MAP - Kinase leads to completion of mitogenic functions like cell growth and gene expression . </P> <P> The activation of PI - 3K leads to crucial metabolic functions such as synthesis of lipids, proteins and glycogen . It also leads to cell survival and cell proliferation . Most importantly, the PI - 3K pathway is responsible for the distribution of glucose for important cell functions. The activation of PI - 3K leads to the activation of PKB (AKT) that induces the impact of insulin on the liver . For example, the suppression of hepatic glucose synthesis and the activation glycogen synthesis . Hence, PKB possesses a crucial role in the linkage of the glucose transporter (GLUT4) to the insulin signaling pathway . The activated GLUT4 will translocate to the cell membrane and promotes the transportation of glucose into the intracellular medium . </P>

Where do most of the steps of a signal transduction pathway occur