BY5.6 Genetic Engineering

Genetic Engineering

Genetic engineering is already being used to produce GM food crops, insulin for diabetics using GM bacteria, and genetic treatments (gene therapy) for people with genetic disorders like cystic fibrosis.

Proteins are now commonly produced using genetic engineering. For instance, human insulin is now produced by bacteria. This has been achieved by isolating the gene for human insulin, taking this gene and inserting it into bacterial DNA, and growing the bacteria to produce the insulin. This is how it is done:

• The donor DNA is located using a gene probe and "cut out" by a a type of enzyme known as a restriction endonclease, which cuts the DNA at specific base sequences to obtain the gene which then has staggered  "sticky ends".
• The donor DNA then has to be inserted into a vector--in this case, a plasmid (found in bacteria). Bacterial plasmids are obtained by dissolving bacterial cell walls and taking the plasmid.
• The plasmid has to be cut open so that the donor DNA can be put into it. To do this, more restriction endonuclease is used to cut the plasmid open at a specific point, leaving it too with sticky ends.
• The donor DNA must then be inserted into the plasmid. The sticky ends of the plasmid and the sticky ends of the donor DNA will, hopefully, be complementary, so that the donor DNA can be used to complete the loop of plasmid DNA. DNA ligase is used to stick them together.
• The plasmid is now recombinant DNA--DNA containing genes from two arganisms.
• The plasmids need to be in bacteria for the genes to be expressed. Plasmids can be transferred between bacteria in nature, so all the scientists need to do is mix the plasmids with the bacteria and hope that some take the plasmids up.
• Bacteria that are known to have taken up the plasmids are placed in a fermenter and multiply, producing the protein.

Extra notes:

• E. coli is often used for this, as it multiplies quickly--this is also why Meselson and Stahl used it in their experiments with semi conservative replication.
• To ensure that plasmids have taken up by bacteria, the plasmids used will often contain a gene for antibiotic resitance too. Petri dishes with the bacteria on are then covered in an anitbiotic such as ampicillin and only the bacteria which have taken up the plasmid will survive, as they can…