Genetic Engineering (AQA GCSE Biology): Revision Note

Genetic engineering: Basics

• 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’

Plant genetic engineering

• 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

Bacteria genetic engineering

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)

Diagram of the use of restriction enzymes

Use this image

• 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

Diagram of how a recombinant plasmid is created and used

Use this image

• 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 genetic engineering

Advantages and disadvantages of GM crops

Advantages:

• Reduced use of chemicals such as herbicides and pesticides – better for the environment

• Cheaper / less time-consuming for farmers

• Increased yields from the crops as they are not competing with weeds for resources or suffering from pest damage

Disadvantages:

• Increased costs of seeds – companies that make GM seeds charge more for them to cover the cost of developing them

• This can mean smaller, poorer farmers cannot compete with larger farms

• Increased dependency on certain chemicals, such as the herbicides that crops are resistant to – often made by the same companies that produce the seed and more expensive to buy

• Risk of inserted genes being transferred to wild plants by pollination which could reduce the usefulness of the GM crop (eg if weeds also gain the gene that makes them resistant to herbicide)

• Reduced biodiversity as there are fewer plant species when herbicides have been used – this can impact insects and insect-eating birds

• Some research has shown that plants that have had genes inserted into them do not grow as well as non-GM plants

GM crops

• 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, e.g. ‘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

Curing diseases with genetic engineering

• 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

The process of genetic engineering

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