Applications of recombinant DNA technologyAQA A-Level Biology: Revision notes
Section 1
What recombinant DNA technology does
Recombinant DNA is DNA formed by combining genetic material from two different sources, usually different species. A gene is cut out, placed in a vector (such as a plasmid, a virus or a liposome) and delivered into a host cell, which then makes the protein it codes for. The organism that carries the foreign gene is transgenic.
This works across species because the genetic code is universal: the same triplet codes for the same amino acid in every organism. Bacteria cannot remove introns, so the gene transferred is usually a copy without introns.
Say that the genetic code is universal: that is the reason a human gene works in a bacterium.
Section 2
Applications in medicine
Genetically modified bacteria, yeast or mammalian cells grown in fermenters make human proteins: insulin for diabetes, clotting factor VIII for haemophilia, growth hormone and some vaccines.
Compared with extracting these from animals or donated blood, the products are identical to the human protein, so there is less risk of immune responses or infection, the supply is large and reliable, and animals are not used.
Section 3
Applications in agriculture and industry
Agriculture: genes are transferred into crops to give herbicide resistance, insect resistance (for example a toxin gene from Bacillus thuringiensis), drought tolerance or added nutrients (for example vitamin A in rice). Benefits include higher and more reliable yields and less spraying with pesticide.
Industry: modified microorganisms make enzymes for detergents and food processing, such as chymosin for cheese making, and can make materials and fuels.
Section 4
Gene therapy
Gene therapy aims to treat a genetic disorder, usually caused by a faulty recessive allele, by inserting a functional allele into the patient's cells using a vector such as a harmless virus or liposome. The cells then make the missing protein. It is an application of recombinant DNA technology to human cells.
Somatic gene therapy targets body cells (for example bone marrow stem cells in SCID) and is not passed on to children. Germ-line therapy would alter eggs, sperm or embryos, so changes would be inherited; this raises serious ethical concerns and is not allowed in the UK.
Problems: the allele may insert in the wrong place and cause cancer, the vector may cause an immune response, the effect may not last in dividing cells, and treatment is costly.
Gene therapy does not repair or remove the faulty allele. It adds a working copy.
Section 6
Balancing humanitarian benefits and opposition
Humanitarian view: GM crops can reduce famine and malnutrition, and recombinant drugs and gene therapy can save lives.
Opposition: environmentalists worry about gene flow to wild relatives, herbicide-resistant weeds, monocultures and loss of biodiversity. Anti-globalisation activists object to multinationals controlling seed and drug supplies and to the dependence this creates.
In an evaluation, give a point on each side, then a justified judgement: for example, benefits outweigh risks if products are affordable, well tested and regulated. When interpreting data, quote the figures and compare them.
End a six-mark evaluation with a conclusion that is reasoned, not just a restatement.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Applications of recombinant DNA technology
- A pharmaceutical company produces human insulin by inserting the human insulin gene into plasmids, which are then taken up by bacteria grown in large fermenters. Before this technology, insulin for people with diabetes was extracted from the pancreases of pigs and cattle.Suggest two advantages of producing human insulin using recombinant bacteria instead of extracting it from pigs.2 marks
- A seed company has produced soya plants containing a gene from a bacterium that makes them resistant to a broad-spectrum herbicide. Farmers can spray the herbicide over whole fields to kill weeds without harming the soya crop. Most of the farmers buying the seed run large commercial farms.Suggest two reasons why some environmental groups oppose the use of this herbicide-resistant soya.2 marks
- A child is diagnosed with severe combined immunodeficiency (SCID), caused by a recessive allele that means the enzyme adenosine deaminase is not made, so white blood cells die. In a clinical trial, bone marrow stem cells are removed from each child, a functional allele is inserted into them using a viral vector, and the cells are returned to the child's blood. In the trial, 18 of 20 children recovered a working immune system within three years, but 2 children developed leukaemia because the vector inserted the allele next to a gene controlling cell division.Describe how gene therapy is used to treat a condition caused by a faulty recessive allele.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).