Uses of Recombinant DNA Technology (AQA A Level Biology): Revision Note

Uses of recombinant DNA technology

• DNA that has been altered by introducing nucleotides from another source is called recombinant DNA (rDNA)

• If the organism contains nucleotides from a different species, it is called a transgenic organism

• Any organism that has introduced genetic material is a genetically modified organism (GMO)

• Recombinant DNA has been used to produce recombinant proteins (RP), thus, recombinant proteins are manipulated forms of the original protein

Producing recombinant proteins

• Recombinant proteins are generated using microorganisms such as bacteria, yeast, or animal cells in culture. They are used for research purposes and treatments (e.g. diabetes, cancer, infectious diseases, haemophilia)

• Most recombinant human proteins are produced using eukaryotic cells (e.g. yeast or animal cells in culture) rather than using prokaryotic cells, as eukaryotic cells will carry out the post-translational modification (due to the presence of the Golgi Apparatus and/or enzymes) that is required to produce a suitable human protein

• The advantages of genetic engineering organisms to produce recombinant human proteins:

  • More cost-effective to produce large volumes (i.e. there is an unlimited availability)

  • Simpler (when using prokaryotic cells)

  • Faster to produce many proteins

  • Reliable supply available

  • The proteins are engineered to be identical to human proteins or have beneficial modifications

  • It can solve the issue for people who have moral, ethical, or religious concerns against using cow or pork-produced proteins

Example: Insulin

• Insulin was the first recombinant human protein to be approved for use in diabetes treatment

• Bacterial plasmids are modified to include the human insulin gene

  • Restriction endonucleases are used to cut open plasmids, and DNA ligase is used to splice the plasmid and human DNA together

• These recombinant plasmids are then inserted into Escherichia coli by transformation

• Once the transgenic bacteria are identified (by the markers), they are isolated, purified and placed into fermenters that provide optimal conditions

• The transgenic bacteria multiply by binary fission, and express the human protein - insulin, which is eventually extracted and purified

• The advantages for scientists to use recombinant insulin are:

  • It is identical to human insulin, unless modified to have different properties (e.g. act faster, which is useful for taking immediately after a meal or to act more slowly)

  • There is a reliable supply available to meet demand (no need to depend on the availability of meat stock)

  • Fewer ethical, moral or religious concerns (proteins are not extracted from cows or pigs)

  • Fewer rejection problems, side effects, or allergic reactions

  • Cheaper to produce in large volumes

  • It is useful for people who have animal insulin tolerance

Example: Factor VIII

• Factor VIII is a blood-clotting protein that haemophiliacs cannot produce

• Kidney and ovary cells from hamsters have been genetically modified to produce Factor VIII

• Hamster cells constantly express Factor VIII, which can then be extracted and purified, and used as an injectable treatment for haemophilia

• The advantages for scientists to use recombinant Factor VIII:

  • Fewer ethical, moral or religious concerns (proteins are not extracted from human blood)

  • Less risk of transmitting infection (e.g. HIV) or disease

  • Greater production rate

Gene therapy in medicine

• The use of gene therapy in medicine is becoming more common

• Gene therapy involves using various mechanisms to alter a person’s genetic material to treat or cure diseases

• As scientists gain a better understanding of the human genome and therefore the location of genes that cause genetic disorders, the possibilities of gene therapy being able to replace a faulty gene, inactivate a faulty gene or insert a new gene are growing

• Gene therapy is being used in medicine for introducing corrected copies of genes into patients with genetic diseases (e.g. cystic fibrosis, haemophilia, severe combined immunodeficiency)

• Currently, all gene therapies have targeted and been tested on somatic (body)

  • Changes in genetic material are targeted to specific cells and so will not be inherited by future generations (as somatic gene therapy does not target the gametes)

• Often, the effects of changing the somatic cells are short-lived

• There are two types of somatic gene therapy:

  • Ex vivo – the new gene is inserted via a virus vector into the cell outside the body

    • Blood or bone marrow cells are extracted and exposed to the virus, which inserts the gene into these cells. These cells are then grown in the laboratory and returned to the person by injection into a vein

  • In vivo – the new gene is inserted via a vector into cells inside the body

• There is the potential for new genetic material to be inserted into germ cells

  • This is illegal in humans, as any changes made to the genetic material of germ cells are potentially permanent and could therefore be inherited by future generations

Example: Severe combined immunodeficiency (SCID)

• Severe combined immunodeficiency (SCID) is caused by a lack of adenosine deaminase (ADA), an enzyme essential for immune function. Without it, children are highly vulnerable to infections and often must live in isolation; children born with SCID are sometimes called “bubble babies” because they must be kept in extremely sterile environments to avoid infections

• To treat SCID, scientists have used ex vivo somatic gene therapy. During this therapy, a virus transfers a normal allele for ADA into T-lymphocytes removed from the patient and the cells are then returned via an injection

• This is not a permanent cure as the T-lymphocytes are replaced by the body over time, and therefore the patient requires regular transfusions to keep their immune system functioning

Social & ethical considerations associated with gene therapy

• Potential for side effects that could cause death

  • E.g. Leukemia-like cancer (T-cell leukemia) has occurred in some children after retroviral gene therapy

• Whether germline gene therapy should be allowed

  • It could be a cure for a disease, or it could create long-term side effects

• The commercial viability for pharmaceutical companies

  • If it is a rare disease, the relatively small number of patients may not mean that the companies will make a profit

• The expense of treatments as multiple injections of the genes, may be required if the somatic cells are short-lived (e.g. severe combined immunodeficiency)

  • This may make the cost of gene therapy accessible to a limited number of people

• People may become less accepting of disabilities as they become less common

• The right to determine which genes can be altered and which cannot (e.g. should people be allowed to enhance intelligence or height?)

• Another method of enhancing sporting performances unfairly through gene doping

  • Genes are altered to give an unfair advantage e.g. to provide a source of erythropoietin

Genetic engineering in agriculture

• The main purpose of genetically engineering plants and animals is to meet the global demand for food

• Crop plants have been genetically modified to be:

  • resistant to herbicides – increases productivity / yield

  • resistant to pests – increases productivity / yield

  • enriched in vitamins – increases the nutritional value

• Farmed animals have been genetically modified to grow faster

  • It is rarer for animals to be modified for food production due to ethical concerns associated with this practice

• The benefits of using genetic engineering rather than the more traditional selective breeding techniques to solve the global demand for food are:

  • organisms with the desired characteristics are produced more quickly

  • all organisms will contain the desired characteristic (there is no chance that a recessive allele may arise in the population)

  • the desired characteristic may come from a different species / kingdom

Example: Insect resistance in cotton

• Cotton has been genetically modified with a gene for the Bt toxin, which is taken from the bacterium Bacillus thuringiensis

• Cotton plants modified with the Bt toxin gene produce an insecticide

• When an insect ingests parts of the cotton plant, the alkaline conditions in their guts activate the toxin (the toxin is harmless to vertebrates as their stomach is highly acidic), killing the insect

• Different strains of thuringiensis produce different toxins, which are toxic to different insect species

• Insect populations have developed resistance to the genes for Bt toxin, reducing its effectiveness as a means of protecting crops

Social and ethical implications associated with GMOs in agriculture

• There is less of a debate in using microorganisms for the production of medicines, antibiotics and enzymes compared to the use of genetically modified organisms (GMOs) for food production

• The use of GMOs in food production has been proposed as a solution to feeding the increasing world population, the decreasing arable land and decreasing the impact on the environment; however concerns such as the development of resistance in insects and weeds and the costs of seeds have meant that some countries are not allowing GMOs to be grown

• Ethical implications of using GMOs in food production:

  • The lack of long-term research on the effects on human health – should GM food be consumed if it is unknown whether it will cause allergies or be toxic over time (although there has been no evidence to suggest this would occur to date)

  • Making choices for others:

    • Without appropriate labelling the consumer cannot make an informed decision about the consumption of GM foods

    • Pollen from the GM crop may contaminate nearby non-GM crops that have been certified as organic

    • Reducing the biodiversity for future generations

• Social implications of growing GMOs for food:

  • Whether the crops are safe for human consumption and for the surrounding environment

  • GM crops may become weeds or invade the natural habitats bordering the farmland

  • The development of resistance for the introduced genes in the wild populations

  • Potential ecological effects (e.g. harm to non-targeted species like the Monarch butterflies)

  • Cost to farmers (new seed needs to purchase each year)

  • The ability to provide enriched foods to those suffering from deficiencies (e.g. Golden Rice) and therefore decrease diseases

  • Reduced impact on the environment due to there being less need to spray pesticides

  • Reduction in biodiversity, which could affect food webs

  • The herbicides that are used on the GM crops could leave toxic residues