Generate an image that explains this Insulin is a peptide hormone that consists

generate an image that explains this Insulin is a peptide hormone that consists of two longitudinal chains, una cadena A (21 amino acids) y una cadena B (30 amino acids). Dos enlaces disulfuro unen la cadena A a la cadena B y un tercer puente disulfuro se localiza en la cadena A. Insulin synthesis is directed by a gene on chromosome 11, miembro de una superfamilia de genes que codifican factores de crecimiento relacionados. mRNA directs ribosomal synthesis of preproinsulin, containing four peptides: a signal peptide, las cadenas A y B de la insulina, and a linker peptide (C peptide). The signal peptide is cleaved at a very early stage of the biosynthetic process (while the peptide chains are still being assembled), lo que da proinsulina (fig. 9-27). Up Next, proinsulin is transported to the endoplasmic reticulum, donde, with the linker peptide still attached, disulfide bridges form to give rise to a "folded" form of insulin. Proinsulin is packaged into secretory granules in the Golgi apparatus.. Durante este proceso de empaquetado, proteases cleave the linker peptide, con lo que se produce insulina. Insulin and the cleaved linker peptide are packaged together in secretory granules and when the b cell is stimulated, son liberados en cantidades equimolares a la sangre. Secretion of the linker peptide (C peptide) is the basis of a test of b cell function in people with type I diabetes mellitus receiving exogenous insulin injections. (En estas personas, serum insulin concentrations do not reflect endogenous secretory rates.) Insulin is metabolized in the liver and kidney by enzymes that break disulfide bonds.. Se liberan las cadenas A y B, ahora inactivas, y se excretan por la orina.

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