Question

​​​​​​please answer all the following using insulin as the hormone! thank you

• 1. Name the hormone and describe its chemical nature

  2. Name the gland that produces that hormone

  3. Mention the function of the hormone

  4. Say if it acts in an endocrine/paracrine/autocrine manner

  5. Explain if the hormone has a nuclear or membrane receptor

  6. Explain the feedback mechanisms that operate to control the hormone production

Answer 1

Insulin is a hormone produced by the pancreas by beta cells of Langerhans.

The chemical formula of human insulin is C₂₅₇H₃₈₃N₆₅O₇₇S₆ made up of 51 amino acids with molecular mass 5808 Da.Initially, Insulin is formed of three chains (A, B, and peptide C) in its inactive forms. Later the peptide C is removed to make the insulin working. Chain A consists of 21 amino acids and chain B has 30 amino acids. The chains A and B have inter-disulfide links at A7-B7and A20-B19. The chain A has an intrachain disulfide link at A6-11.

Insulin has a very important role in metabolism. It acts in an endocrine manner being secreted into the bloodstream by the pancreas and regulates the blood sugar level.

Insulin receptor (IR) a transmembrane receptor associated with tyrosine kinase which gets activated upon binding of insulin.

Insulin is released in response to an increased blood glucose level. When glucose reaches the pancreatic cells it is converted to glucose-6-phosphate to make ATP. Due to increased ATP concentration, the sodium channels close and membrane depolarized and ultimately calcium channels to open and an influx of calcium ions leads to the release of insulin stored in insulin vesicles.

Insulin increases the absorption of glucose by cells by activating the GLUT transporters (glucose transporters) on the cells. On the other hand when glucose levels are low in blood the alpha cells in the pancreas secrets another hormone glucagon which has reverse effects of insulin. Glucagon increases blood sugar level by increasing glycogen conversion to glucose (glycogenolysis). Another molecule GABA (γ-aminobutyric acid ) is released with insulin by beta cells that inhibit glucagon synthesis from alpha cells of the pancreas.