Physiologic Effects of Insulin :: essays research papers

Stand on a streetcorner and ask people if they know what insulin is, and many will reply, "Doesntit have something to do with blood sugar?" Indeed, that is correct, hardly such a response is a bit likesaying "Mozart? Wasnt he some kind of a musician?" Insulin is a key sham in the control of intermediary metabolism. It has profound effectson both carbohydrate and lipid metabolism, and significant influences on protein andmineral metabolism. Consequently, derangements in insulin signalling have widespread anddevastating effects on many organs and tissues. The Insulin Receptor and Mechanism of ActionLike the receptors for other protein hormones, the receptor for insulin is embedded in the plasmamembrane. The insulin receptor is composed of two alpha subunits and two betasubunits linked by disulfide bonds. The alpha chains are entirely extracellular and houseinsulin binding domains, bandage the linked beta chains penetrate through the plasma membrane. The insulin re ceptor is a tyrosine kinase. In otherwords, it functions as an enzyme that transfersphosphate groups from ATP to tyrosine residues onintracellular target proteins. Binding of insulin to thealpha subunits causes the beta subunits to phosphorylatethemselves (autophosphorylation), thus activating thecatalytic activity of the receptor. The activated receptorthen phosphorylates a number of intracellular proteins,which in turn alters their activity, thereby generating abiological response. Several intracellular proteins have been identified asphosphorylation substrates for the insulin receptor, the best-studied of which is insulinreceptor substrate 1 or IRS-1. When IRS-1 is activated by phosphorylation, a lot of thingshappen. Among other things, IRS-1 serves as a type of docking center for recruitment andactivation of other enzymes that ultimately mediate insulins effects. A to a greater extent detailed look atthese processes is presented in the section on Insulin Signal Transduction. Ins ulin and Carbohydrate MetabolismGlucose is liberated from dietary carbohydrate such as stiffen or sucrose by hydrolysis within thesmall intestine, and is then absorbed into the blood. Elevated concentrations of glucose inblood energize release of insulin, and insulin acts on cells thoughout the body tostimulate uptake, utilization and storage of glucose. The effects of insulin on glucosemetabolism vary depending on the target tissue. Two important effects are Insulin facilitates entry of glucose into muscle, adipose and some(prenominal) other tissues.The only mechanism by which cells can take up glucose is by facilitated diffusion througha family of hexose transporters. In many tissues - muscle macrocosm a prime example - themajor transporter used for uptake of glucose (called GLUT4) is made available in theplasma membrane through the action of insulin.