• Genetic engineering is a technique used to deliberately modify a specific characteristic of an organism
  • The technique involves?removing a gene?that codes for a desired characteristic from?one organism?and?transferring?the gene?into another?organism where the?desired gene is then?expressed
• The genetically engineered organism is said to contain?recombinant DNA?and will be a?genetically modified organism?(GMO)
• Micro-organisms, plants and animals have been genetically engineered to produce proteins used in medicine

Genetically modified micro-organisms

• Restriction enzymes?are used to?remove?the gene coding for a desired protein from an organism's genome
  • The protein coded for here will be responsible for the?characteristic desired?in the GMO e.g. the ability to produce insulin
• Many?copies?of the gene are made using the?polymerase chain reaction, or?PCR
  • The enzyme?DNA polymerase?is used to join free?nucleotides?into new strands of DNA that are complementary to the original strand
• These copies are?inserted into?small loops of DNA called?plasmids,?which then?transfer the copies?into micro-organisms
  • The plasmids are said to be DNA?vectors
  • The enzyme DNA ligase catalyses the joining of the desired gene to the plasmid vector
• The genetically modified micro-organisms are?grown in large fermenters?containing nutrients, enabling them?to?multiply?and produce?large quantities?of the new protein
• The protein can be?isolated?and?purified?before being packaged and distributed
  • Human insulin?and?human blood clotting factors?are examples of medicinal proteins produced by genetically modified bacteria

The human insulin gene can be inserted into bacterial plasmid vectors which are then transferred into bacterial cells

Genetically modified plants

• A similar process can be used to insert desired genes from other organisms into plant cells
• After the gene is inserted into a plasmid and then transferred to a bacterial cell, the bacteria can be used to?infect plant cells;?the bacterium acts as a?vector?for?introducing the gene into the plant DNA
  • Note that this isn't the only method of introducing new genes into plant cells
    • Another method involves a 'gene gun'; tiny pellets are coated with the desired DNA and then fired into the plant cells
• The gene is transferred from the bacterial cell?into the plant cell nucleus, after which the?plant cell is stimulated to multiply and grow into an?adult plant
  • Each cell?of the plant?contains a copy?of the gene coding for the desired protein
• The protein can now be?purified?from the plant tissues, or the plant can be?eaten?to deliver the drug
  • Human insulin?and a?cholera vaccine?are examples of drugs produced by modified plants

Genetically modified animals

• The gene that codes for the desired protein is injected into the?nucleus of a?zygote
• The zygote is?implanted?into the uterus of a surrogate animal where it develops into an?adult?animal
  • Every cell?of this genetically modified animal will?contain a copy?of the gene coding for the desired protein
• The protein can be?purified?from?e.g. the milk?of the animal
  • Human blood clotting proteins?can be produced from the milk of genetically modified animals

• While GMOs can be used for medical benefit, there is still?much concern about the potential impacts?of changing the genes of organisms, as well as the?ethics of genetically modifying animals
  • These concerns are often amplified when the GMOs are?crop plants destined for human consumption

Risks and Benefits of Genetic Engineering Table