So once again, when the insulin primary messenger, a peptide hormone, moves into its cavity that is created by the two alpha subunits the closure of the two alpha chains causes the two beta chains to move closer together and this leads to crossfosphorylation as shown here and here. That basically changes the confirmation of those beta subunits and that activates those beta subunits. So we see the binding of the insulin on one side of that receptor activates it on the other side and so that signal can basically be transduced passed down from the outside to the inside of that cell. Now, what actually happens when these two regions are phosphorylated? So this beta submune and the other beta submune well, remember, what the tyrosine protein kinase does is it phosphorylates. It attaches a phosphoryl group onto tyrosine residues and some of these tyrosine residues that are phosphorylated actually begin to act as attachment points for other proteins namely an important protein known as IRS which stands for insulin receptor substrate.