Insulin production

In humans, the gene for insulin is located on the
short arm of chromosome 11 in region 1, band
5.5. With 1430 base pairs, it is a small gene. It
consists of a signal sequence (L, leader) and two
exons. The gene is expressed exclusively in !-
cells of the islands of Langerhans of the pancreas.
A !-cell-specific enhancer is located at
the 5! end of the gene, and a variable number of
tandem repeats (VNTR) are located further upstream.
The primary transcript is spliced to produce
the mRNA template for preproinsulin. The
signal peptide (24 amino acids) is removed, and
the B chain and A chain are joined by two disulfide
bridges. Proper binding and three-dimensional
structuring require the presence of a connecting
peptide (C peptide). The complete insulin
molecule consists of an A chain of 21
amino acids and a B chain of 30 amino acids. The
signal peptide of the insulin molecule is required
for secretion.