Insulin receptor. Molecular model of the insulin receptor molecule (brown, orange, blue, grey and mauve) bound to an insulin molecule (red and yellow). Both the surface structure (blobs) and secondary structure (ribbons) of the receptor are shown. The insulin receptor is a transmembrane protein, that is it spans the cellular membrane (yellow and cream). Binding of insulin to the extracellular part of the protein activates a number of changes inside the cell that lead to the uptake of glucose, the synthesis of glycogen and fatty acids and glycolysis, the production of energy from glucose.