Figure 1: Structure of Human Insulin.(http://rst.gsfc.nasa.gov/Sect20/A12.html)
The biologically active circulating form of insulin is a monomer, which consists of two chains, an A chain with 21 amino acids and a B chain of 30 amino acids. (in humans). The A and B chains are linked by two disulfide bridges, A7-B7 and A20-B19. The A chain also contains an intra-chain disulfide bridge connecting A6 and A11. Insulin is produced and stored in the body as a hexamer. It is far more stable and non-reactive than the monomer form. The structure of insulin is well preserved in vertebrate animals, with slight variations in structure. Cow insulin differs from human insulin in only three amino acid residues, and pig insulin differs in only one. (Mayer, Zhang and DiMarchi)
Insulin functions to control blood glucose concentration. When released it stimulates cells in the liver, muscle and adipose tissue to take up glucose from the blood and store it as glycogen in the liver and muscle tissue. This also functions to stop the use of lipids as an energy source. When insulin is absent, glucose is not taken up by the body and lipids instead will be mobilized to the liver as an energy source. Insulin has also been shown to have effects on the brain such as improving cognition. Once in the brain, insulin enhances both learning and memory. (Soria, Tuduri, Gonzalez, Martin, and Nadal 52-60)
References:
De Meyts, Pierre. "Insulin and its Receptor: Structure, Function and Evolution." BioEssays 26.12 (2004): n. pag. Web. 11 Oct 2010.
Mayer, John P., Faming Zhang, and Richard D. DiMarchi. "Insulin Structure and Function." Peptide Science 88.5 (2007): n. pag. Web. 11 Oct 2010.
Soria, Bernat, Eva Tuduri, Alejandro Gonzalez, Franz Martin, and Angel Nadal. "Pancreatic Islet Cells: a Model for Calcium-dependent Peptide Release." HFSP Journal 4.2 (2010): 52-60. Web. 11 Oct 2010.
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