Insulin Structure & Function

Function

Insulin is made by the pancreatic islet beta cells in response to elevated blood glucoselevels. Insulin signals cells that the body is in the "fed" state, and that it should take up glucose from the blood and make other appropriate response. For example, in the liver glycogen synthesis is turned on, which provides a supply of glucose when the blood glucose levels fall under fasting conditions. Insulin also increases fat synthesis in adipocytes. In type 1 diabetes, the pancreatic cells do not release insulin, resulting in high blood sugar levels and increased fat metabolism. Consequently, there is "spillover" of glucose into the urine, and weight loss due to the loss of body fat stores.

Structure

Insulin is composed of two different types of peptide chains. has 21 amino acids and has 30 amino acids. Both chains contain but no beta strands. There are 3 conserved which help keep the two chains together. Insulin can also form in solution due to the hydrogen bonding between the B chains (shown as white lines). The dimers can further interact to form due to interaction between hydrophobic surfaces. This the hydrophobic (gray) and polar (purple) parts of an insulin monomer at a pH of 7. Indeed "fast acting" insulin is produced by switching the last two amino acids, which reduces the formation of the hexameric insulin.