8.17 Drug Production from Genetically Modified Organisms

• 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