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Genetically Engineered Insulin
For many years insulin has been taken from pigs and cows for use by humans with
diabetes. It was taken from the pancreas of the animals when they were slaughtered
for food and purified. However, this was time consuming and posed risks to the
humans using it, any diseases that the animals had could be potentially passed on to
humans via the insulin. There is a slight chemical difference between animal and human
insulin so a few patients had allergic reactions to it caused by the immune system
recognizing the `foreign invader'.
Insulin is now made by genetically engineered microbes. This enables human insulin to be
made in large commercial quantities and then purified for human use.
Making Human Insulin
The amino acid sequence for insulin was found in 1995 using the Human Genome Project.
To genetically engineer human insulin the gene for insulin is identified
and then cut out of the human DNA using a restriction enzyme
(which leaves sticky ends on the gene).
A plasmid (a ring of bacterial DNA) is taken out of bacteria and is also
cut using restriction enzymes (which leaves sticky ends on the
plasmid). The insulin gene is annealed (joined) into the plasmid (using
the sticky ends) and is sealed in place using another enzyme called
The plasmid is then inserted back into the bacterium.
The genetically engineered bacteria is then put into a clean
fermentation vessel with a supply of nutrients and is allowed to grow
(divide and reproduce).
The insulin is then harvested and purified for human use.