Insulin is produced by beta cells of islets of Langerhans.
It is produced from the pro hormone, ‘preproinsulin’ in endoplasmic reticulum. A portion of the structure is cleaved off and the remaining portion is folded with the help of C-peptide to form ‘proinsulin’
The C-peptide portion is then removed to form Insulin
This active Insulin is transported via Golgi apparatus to cytoplasmic granules for exocytosis into plasma
Insulin then binds with its receptor on Insulin sensitive cells
Insulin receptor is a tetramer consisting of 2 alpha & 2 beta units.
Insulin binds to the alpha unit on the cell membrane, while the beta unit, which spans the cell membrane activates tyrosine kinase and the second messenger system
This activates cytoplasmic vesicles containing transport molecules
The vesicles fuse with the cell membrane to incorporate the transport molecules into the cell membrane, which facilitate the transport of glucose into the cell.
MNEMO> MECHANISM OF ACTION: INSULIN Vs GLUCAGON
Insulin binding to the receptor activates an intracellular second-messenger system via tyrosine kinase.
Glucagon binding to its receptor activates a G-protein second-messenger system via adenylyl cyclase.
“Insulin is TricKy”
“Glucagon is ACcurate”