genes into other organisms for expression
the required DNA fragment in plasmids in bacterial cells is
fine for producing large quantities of some proteins artificially.
The bacteria Escherichia coli is being used in this
way to produce vast quantities of human insulin.
bacteria are not capable of producing all human and plant
proteins. This is because bacteria make proteins in a different
way to us. Also many human gene products are altered or changed
in the cell after they are synthesised by the addition of
carbohydrates. Bacterial cells can not carry out these modifications.
is far better and efficient to produce some gene products
in animal and plant cells. Neither of these cells have plasmids
so other methods have to be used to put the cloned gene into
the cells and help them insert themselves into the hosts DNA.
Vectors used for Inserting genes into Humans
are little oil droplets that have recombinant plasmids in
them. The droplets have sugar particles on their surface,
which act as cell receptors and allow the liposomes to enter
the human cells. However, very few of the plasmids reach the
nucleus so the gene is often not expressed in a large enough
usually cause disease by entering cells and attaching to the
chromosomes of the host and taking the cell over. Scientists
are able to remove part of the viruses own DNA to make it
harmless and insert the cloned gene they want to put into
the cells. As the virus enters the cells the recombinant gene
combines with the human chromosomes and is expressed.
the viruses used so far have made some patients ill and the
transferred gene has proved to be unstable and continuous
virus treatment is required.
Vectors used to Insert genes into Plants
The bacteria Agrobacterium tumefaciens is used to transfer
recombinant plasmids into plant cells. The plasmids used are
usually Ti plasmids. These cause plants to develop growths
or tumours on their shoots and are naturally found in Agrobacterium.
the Agrobacterium infects plant leaf cells grown in culture
the recombinant plasmid attaches the new gene to the plant
chromosomes. These plasmid genes cause the plant cells to
divide rapidly and make a mass of identical cells or a callus.
These cells can then be grown into whole new plants that can
be tested for the presence of the new gene property.
A more commonly used method is Ballistics.
special gun is used to fire minute gold pellets coated with
DNA into the plant tissue/nucleus.
Vectors used to Insert genes into animal cells.
Much recent genetic research has centred on ensuring the recombinant
gene is inserted into every gene of an animal for life. This
is done by placing the gene directly in the to the zygote
or egg cell using a syringe (a microinjection) and then placing
the new recombinant zygote back into the mothers womb. See