Genetic Engineering (AQA GCSE Biology: Combined Science)

• Genetic engineering is changing the genetic material of an organism by removing or altering genes within that organism, or by inserting genes from another organism
• The organism receiving the genetic material is said to be ‘genetically modified’, or is described as a ‘transgenic organism’
• The DNA of the organism that now contains DNA from another organism as well is known as ‘recombinant DNA’

• Genetically modified plants are plants that have had foreign DNA inserted into their genome
• This is usually done to improve food production in some way
• For example:
  • Tomatoes have been genetically modified to make them grow larger fruit
  • Wild rice has been genetically modified to produce beta carotene (needed by humans to make vitamin A)
  • Crop plants have been genetically modified to be resistant to diseases or resistant to certain herbicides

Genetic modification of bacteria to produce human insulin

• The gene for human insulin has been inserted into bacteria which then produce human insulin which can be collected and purified for medical use to treat people with diabetes
• The gene that is to be inserted is located in the original organism – the gene for insulin production is located within a human chromosome
• Restriction enzymes are used to isolate or ‘cut out’ the human insulin gene, leaving it with ‘sticky ends’ (a short section of unpaired bases)
• A bacterial plasmid is cut by the same restriction enzyme leaving it with corresponding sticky ends (plasmids are circles of DNA found inside bacterial cells)

Restriction enzymes cut DNA strands at specific sequences to form ‘sticky ends’

• The plasmid and the isolated human insulin gene are joined together by DNA ligase enzyme
  • If two pieces of DNA have matching sticky ends (because they have been cut by the same restriction enzyme), DNA ligase will link them to form a single, unbroken molecule of DNA

• The genetically engineered (recombinant) plasmid is inserted into a bacterial cell

DNA ligase is used to join two separate pieces of DNA together – the recombinant plasmid is then inserted into a bacterial cell

• When the bacteria reproduce the plasmids are copied as well and so a recombinant plasmid can quickly be spread as the bacteria multiply and they will then all express the human insulin gene and make the human insulin protein
• The genetically engineered bacteria can be placed in a fermenter to reproduce quickly in controlled conditions and make large quantities of the human protein

Advantages & disadvantages of GM crops table

• Crops can be genetically modified (they are known as GM crops)
• Crop plants, such as wheat and maize, have been genetically modified to contain a gene from a bacterium that produces a poison that kills insects, making them resistant to insect pests such as caterpillars. This can improve crop yields
• Crop plants have also been genetically modified to make them resistant to certain herbicides (chemicals that kill plants), meaning that when the herbicide is sprayed on the crop it only kills weeds and does not affect the crop plant
• Some crops have been genetically modified to produce additional vitamins and improved nutritional value, eg. ‘golden rice’ contains genes from another plant and a bacterium which make the rice grains produce a chemical that is turned into vitamin A in the human body, which could help prevent deficiency diseases in certain areas of the world
• Some have been genetically modified to be drought-resistant (to grow better in very dry conditions). This can also improve crop yields
• Concerns about GM crops include the effect on populations of wildflowers and insects
• Some people feel the effects of eating GM crops on human health have not been fully explored

• Modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders
• As these inherited genetic diseases are caused by faulty genes, it may be possible to treat these by inserting working versions of these genes into people with the genetic disease
• This is called gene therapy

Higher tier only

• The main steps in the process of genetic engineering:
  • Enzymes are used to isolate (cut out) the required gene
  • This gene is inserted into a vector
  • The vector is usually a bacterial plasmid (a piece of circular DNA found inside bacterial cells) or a virus
  • The vector is used to insert the gene into the required cells of the target organism
  • Genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics