Insulin Chemistry 11:50, 6 May 2017 (UTC)11:50, 6 May 2017 (UTC)~~ Insulin are hormones that are secreted by the beta cells of pancreas. Beta cells constitutes about 65% of total cells of islets.Amylin is another hormone also secreted by the beta cells of islets,and are often secreted parallel with insulin. Insulin has a molecular weight of about 5808.It is composed of two amino acid chains both chains are connected by disulfide linkage. As insulin is a protein so is synthesized in the ribosome. When the gene for insulin is transcribed into mRNA,the mRNA goes to ribosome that is attached to the endoplasmic reticulum.In the ribosome the mRNA is translated into preproinsulin which is the initial insulin and has a molecular weight of 11500.The preproinsulin is then transported to the endoplasmic reticulum where it is cleaved and results in the formation of proinsulin which has a molecular weight of 9000.The proinsulin has three chains of peptides that are A,B and C.Most of the proinsulin are cleaved in the Golgi apparatus forming insulin which consists of A,B and C chain.The A and B chains are connected by disulfide linkage and the chain peptide called connecting peptide. The insulin and C peptide are packeged into secretory granules in the Golgi apparatus. From Golgi apparatus the insulin packeged with C peptide are secreted and still about 5 to 10 % of secretion is proinsulin means that in total secretion of insulin 5 to 10% are proinsulin that are not cleaved in the Golgi apparatus. These proinsulin and C peptides have almost no insulin activities but C peptides G protein coupled membrane receptor and activates two enzymes systeme,that are endothelial nitric oxide synthase and sodium-potassium ATPase. C peptide levels are also important in isulin treated daibetic patients.Mostly diabetic patients are unable to produce insulin and if daibetic patient is treated with insulin then he/she should have normal insulin levels therefore to know that production of insulin by patient have to find the C peptide as C peptides are produced with the insulin.
By Rahatullah khan MBBS Student at Jianghan University Hubei Province Wuhan city