Insulin is peptide a hormone found in the body, created by the beta cells of the pancreas. The hormone allows the body to use glucose from carbohydrates in the food eaten for energy, or to store it for later use. Insulin stops the blood sugar from getting too high or too low as a result, which can result in hyper/hypoglycemia.
The body needs sugar for energy, but sugar can not travel to cells directly. When blood sugars rise in the body after eating, the pancreas is sent signals to release insulin into the bloodstream. If the body has more sugar than it needs, it will be stored in the liver and released as the body needs more energy, whether that is between meals or when the body is stressed.
In the liver and skeletal muscles, glucose is stored as glycogen, and in fat cells, it is stored as triglycerides. When the control of insulin levels fails, a person can develop diabetes.
The Effect Of Insulin On Glucose Uptake And Metabolism
● Insulin binds to its receptor
● Protein activation cascades are started
● Glycogen synthesis begins
● Includes translocation of Glut-4 transporter to the plasma membrane and influx of glucose
Insulin has two modes of action on the body - an excitatory one and an inhibitory one. Insulin stimulates glucose uptake and lipid synthesis; it inhibits the breakdown of lipids, proteins and glycogen, and inhibits the glucose pathway (gluconeogenesis) and production of ketone bodies (ketogenesis).
The Structure Of Insulin
● Human insulin consists of 51AA in two chains connected by 2 disulfide bridges. This is a single gene product that is cleaved into 2 chains during post translational modification.
● T1/2-5-10 minutes, degraded by glutathione-insulin transhydrogenase which cleaves the disulfide links.
● Bovine insulin differs by 3AA, while pork insulin differs by 1AA.
● A complex with ZN2+ ions stores insulin.
Regulation Of Insulin
The production of insulin is regulated using several steps along the synthesis pathway. This is as follows:
● At transcription from the insulin gene
● In MRNA stability
● At the MRNA translation
● In the post translational modifications
Glucose levels are controlled by insulin so that the rate of glucose production by the liver is equal to the rate of use by the cells. In a healthy individual, the role of insulin is to keep a steady blood glucose level by ensuring release from the liver is sufficient.
If there is a lack of insulin in the liver, the liver releases glucose into the bloodstream faster than the tissues can metabolize.
Mechanism Of Action
Insulin acts on specific receptors located on the cell membrane of almost every cell, but the density will depend on the type of cell. For example, liver and fat cells are richer than other kinds of cells. The insulin receptor is a receptor tyrosine kinase, otherwise known as RTK, which is a heterotetrameric glycoprotein consisting of 2 extracellular α and 2 transmembrane B subunits linked together by disulfide bonds, orienting across the cell membrane as a heterodimer. The A subunits carry insulin binding sites, while the B subunits have tyrosine kinase activity.