Production of insulin
- as an
example of the medical use of genetic engineering in GM biotechnology
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Production of insulin
- as an
example of the medical use of genetic engineering in biotechnology
The principles of genetic
engineering are illustrated by the production of insulin from bacteria
Genetic engineering is essentially
the process of transferring a useful gene from one organism to
In this case, bacteria are
genetically engineered to make human insulin.
The procedure uses a genetically
engineered bacterium Escherichia coli and the fungus, yeast.
The insulin hormone is identical to
that produced in the human body by the pancreas.
1. An appropriate host bacteria is selected that
will give a good yield of insulin (or any other desired product).
2. The bacterial plasmids are extracted from
the bacteria - the plasmid acts as the vector for the insulin gene.
3. The vector plasmid DNA is cut by
the same restriction enzymes - these enzymes recognise specific sequences
of DNA and cut the DNA at these points - each end is capable of bonding
with other DNA sections - hence the lovely phrase 'sticky ends' - which
is are unpaired bases.
4. The human gene responsible for insulin
production (or other genes coding for something else) is cut from the human chromosomal DNA with
the same restriction enzymes - it is derived from pancreatic DNA
- this cut out section of DNA also has 'sticky ends'.
5. From the two splits, you get reactive sites
on the ends (described as 'sticky') which are short tails of
unpaired bases that are complementary to each other - hence they
will be able to link together.
Enzymes (ligases) are then added and used to
('splice') the insulin gene (or other desired) into the bacterial plasmid DNA,
forming the recombinant DNA.
In other words the DNA ligase enzymes 'glue' the 'sticky'
together to reform a complete plasmid ring - this is known as
6. The modified plasmid vectors containing the
new DNA are inserted back into
the host transgenic bacteria cells.
7. The cloned bacteria rapidly reproduce when grown
in a fermenter under highly controlled conditions - in doing so they use the inserted gene to make the protein
you want e.g. in this case, the protein hormone molecule insulin.
8. The insulin (or other product) can be produced in bulk and extracted-harvested
and purified and the separated waste
bacterial cells destroyed.
BUT, still one more complication!
Unfortunately, not all the host cells
will have been modified correctly e.g. a faulty vector transfer.
Therefore in the final stage, you have to
be able to select and identify the individual host cells that
have successfully incorporated the desired gene.
Antibiotic resistance gene markers are
used to identify the correctly modified host cells.
A marker gene coding for antibiotic
resistance is inserted into the vector plasmid at the same
time as the gene for the desired characteristic.
The host bacteria are grown in a special
vessel containing antibiotics.
Only the bacteria containing the marker gene
will be able to survive and reproduce, because the antibiotics will
kill the rest of the cells that were not genetically modified
Working two genes in tandem! Clever stuff!
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