Editing Beta cell (section)

== Insulin synthesis ==
Beta cells are the only site of insulin synthesis in mammals.<ref>{{cite journal | vauthors = Boland BB, Brown C, Alarcon C, Demozay D, Grimsby JS, Rhodes CJ | title = β-Cell Control of Insulin Production During Starvation-Refeeding in Male Rats | journal = Endocrinology | volume = 159 | issue = 2 | pages = 895–906 | date = February 2018 | pmid = 29244064 | pmc = 5776497 | doi = 10.1210/en.2017-03120 }}</ref> As glucose stimulates insulin secretion, it simultaneously increases proinsulin biosynthesis through translational control and enhanced gene transcription.<ref name="Boland_2017" /><ref>{{cite journal | vauthors = Andrali SS, Sampley ML, Vanderford NL, Ozcan S | title = Glucose regulation of insulin gene expression in pancreatic beta-cells | journal = The Biochemical Journal | volume = 415 | issue = 1 | pages = 1–10 | date = October 2008 | pmid = 18778246 | doi = 10.1042/BJ20081029 }}</ref>

The [[Insulin|insulin gene]] is first transcribed into mRNA and translated into preproinsulin.<ref name="Boland_2017" /> After translation, the preproinsulin precursor contains an N-terminal signal peptide that allows translocation into the [[Endoplasmic reticulum|rough endoplasmic reticulum]] (RER).<ref name="Fu_2013">{{cite journal | vauthors = Fu Z, Gilbert ER, Liu D | title = Regulation of insulin synthesis and secretion and pancreatic Beta-cell dysfunction in diabetes | journal = Current Diabetes Reviews | volume = 9 | issue = 1 | pages = 25–53 | date = January 2013 | pmid = 22974359 | pmc = 3934755 | doi = 10.2174/157339913804143225 }}</ref> Inside the RER, the signal peptide is cleaved to form proinsulin.<ref name="Fu_2013" /> Then, folding of proinsulin occurs forming three disulfide bonds.<ref name="Fu_2013" /> Subsequent to protein folding, proinsulin is transported to the Golgi apparatus and enters immature insulin granules where proinsulin is cleaved to form insulin and [[C-peptide]].<ref name="Fu_2013" /> After maturation, these secretory vesicles hold insulin, C-peptide, and amylin until calcium triggers [[exocytosis]] of the granule contents.<ref name="Boland_2017" />

Through translational processing, insulin is encoded as a 110 amino acid precursor but is secreted as a 51 amino acid protein.<ref name="Fu_2013" />