Insulin Biosynthesis Secretion and Action

Presentation notes on Insulin Biosynthesis, Insulin Secretion, Insulin Role in Human Body & Insulin Functions in Diabetes  for Medical & Biology Students in ppt / pdf / word / .doc format

INSULIN BIOSYNTHESIS, SECRETION AND ACTION :

Biosynthesis :

Insulin produced in the beta cells is initially synthesized as a 86 amino acid precursors polypeptide, preproinsulin. Subsequent proteolytic processing give rise to proinsulin. Proinsulin generates the C peptide and the A and B chains of insulin which are connected by disulfide bonds. The mature insulin molecule and C peptide are stored together and cosecreted from secretory granules in the beta cells.

     

Secretion:

Glucose is the key regulator of insulin secretion by the pancreatic beta cell, although amino acids, ketones various nutrients, gastrointestinal peptides and neurotransmitters also influence insulin secretion. Glucose stimulation of insulin secretion begins with its transport into the beta cell by the GLUT 2 glucose transporter. Glucose phosphorylaton by glucokinase is the rate limiting step that controls glucose regulated insulin secretion. Further metabolism of glucose phosphate generates ATP which inhibits the activity of an ATP sensitive K+ channel which induces beta cell membrane depolarization and insulin secretion.

Action :

Once insulin is secreted into the portal venous system , ~50% is degraded by the liver. Unextracted insulin enters the systemic circulation where it binds to receptors in target sites leading to receptor autophosphorylation and the recruitment of intracellular signaling molecules such as insulin receptor substrates (IRS). These and other adaptor proteins initiate translocation of GLUT 4 to the cell surface an attempt that is crucial for glucose uptake by skeletal muscle and fat.

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