Structure and Functions of Collagen and Insulin.

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Structure and Functions of Collagen and Insulin

Insulin is a polypeptide hormone produced by cells in the islets of Langerhans in the pancreas. Insulin decreases the levels of glucose in the blood and regulates the metabolism of glucose, fats and proteins. In order to meet the demand for insulin needed by diabetics, the hormone is mass-produced with the aid of genetically engineered bacteria, but can also be taken from pigs and cattles.

The structures of insulin and proinsulin are given below. Proinsulin is a single polypeptide chain of 86 amino acids that permits correct alignment of three pairs of disulfide bonds.


The C-peptide of proinsulin is depicted as open circles.

Insulin is derived from proinsulin by cleavage of the C-peptide structure at the dipeptides Arg-Arg and Lys-Arg. Insulin is composed of an A chain of 21 amino acids and a B chain of 30 amino acids, the chains being held together by two disulfide bonds. A third disulfide bond is present within the A chain.

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Insulin is an anabolic signal. The binding of the hormone to its receptor initiates a series of events within the cells that results in the increased uptake of glucose into the cells, where it is converted into metabolic energy or stored as glycogen and fat. Insulin stimulates many metabolic reactions following receptor binding:

  • stimulates glucose transport
  • stimulates amino acid transport
  • increases glycogen synthase activity
  • increases the rate of general protein synthesis
  • depresses lipolysis and protein degradation

Insulin is catabolized primarily in the liver and kidney. An insulin-specific protease and ...

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