Biotechnology is the manipulation of biological systems to manufacture important foods, drugs, biopolymers and other materials. This is illustrated below by the production of the protein human insulin in bacterial culture:
 

	1. Small circles of DNA exist in bacteria, known as plasmids. These are modified to include the piece of human DNA containing instructions for making proinsulin. Proinsulin is the precursor for insulin.
	2. The plasmid is then inserted into Eschericia coli (E. coli) bacteria, which can now produce human proinsulin.
	3. The bacteria multiplies and produces large quantities of human proinsulin in a fermentor.
	4. Bacteria are then killed by heat sterilization, leaving behind the proinsulin.
	5. Proinsulin is enzymatically cleaved to produce human insulin. Enzymatic cleavage is the slicing of a molecule by a protein.
	6. The solution is centrifuged to remove cell matter and purified by liquid chromatography and crystallization.

 
Insulin is a hormone produced by the pancreas, and is essential for the regulation of glucose in the body. The pancreas of a diabetes patient has lost the ability to produce insulin. Prior to the development of the above biotechnology process in the 1980's, only animal insulin (usually from slaughtered pigs) was available to diabetics in limited quantities.