Genetic Modification

• Genetic modification - changing the genetic material of an organism by removing, changing or inserting individual genes from another organism

  • the organism receiving the genetic material is said to be ‘genetically modified’, or is described as a ‘transgenic organism’
• Recombinant DNA - the DNA of the organism that now contains DNA from another organism
• The gene for human insulin has been inserted into bacteria which then produce human insulin which can be collected and purified for medical use for diabetics
• 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
• 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, 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
• The process of genetic modification using bacterial production of human protein (1)

  • The gene that is to be inserted is located in the original organism (for example, this could be the gene for human insulin)
  • 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)
  • The plasmid and the isolated gene are joined together by DNA ligase enzyme
• The process of genetic modification using bacterial production of human protein (2)

  • If two pieces of DNA have matching sticky ends (because they have been cut by thesame restriction enzyme), DNA ligase will link them to form a single, unbroken molecule of DNA
  • The genetically engineered plasmid is 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 gene and make the human protein
• The process of genetic modification using bacterial production of human protein (3)

  • The genetically engineered bacteria can be placed in a fermenter to reproduce quickly in controlled conditions and make large quantities of the human protein
• The process of genetic modification using bacterial production of human protein

  A) double-stranded DNA

  B) restriction enzyme

  C) sticky ends

  D) plasmid

  E) gene

  F) inserted

  G) plasmid vector

  H) restriction enzyme

  I) sticky ends

  J) DNA ligase

  K) recombinant plasmid

  L) recombinant plasmid

  M) bacterial cell

  
• Restriction enzymes - used to isolate the required gene, leaving it with ‘sticky ends’ (a short section of unpaired bases)
• Bacteria are extremely useful for genetic engineering purposes because:

  • They contain the same genetic code as the organisms we are taking the genes from, meaning they can easily ‘read’ it and produce the same proteins
  • There are no ethical concerns over their manipulation and growth (unlike if animals were used, as they can feel pain and distress)
  • The presence of plasmids in bacteria, separate from the main bacterial chromosome, makes them easy to remove and manipulate to insert genes into them and then place back inside the bacterial cells
• Genetic Modification Advantages:

  • Reduced use of chemicals such as herbicides and pesticides - better for the environment, cheaper and less time-consuming for farmers
  • Increased yields from the crops as they are not competing with weeds for resources or suffering from pest damage
• Genetic Modification Disadvantages (1):

  • Increased costs of seeds - companies that make GM seeds charge more for them to cover the cost of developing them which can mean smaller, poorer farmers cannot compete with larger farms
  • Increased dependency on certain chemicals such as the herbicides that crops are resistant to are 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 e.g. if weeds also gain the gene it will make them resistant to herbicide
• Genetic Modification Disadvantages (2):

  • Reduced biodiversity as there are fewer plant species when herbicides have been used - 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
• What does the ligase enzyme do?


  Joins DNA fragments
• What are the steps of genetic modification?

  1. Isolate the insulin gene from human DNA using restriction enzymes, forming sticky ends.
  2. Use the same restriction enzymes to cut open a bacterial plasmid, forming complementary sticky ends. 
  3. Insert the the insulin gene into the plasmid using the enzyme DNA ligase, to form a recombinant plasmid.
  4. Insert the recombinant plasmid into the host bacteria. 
  5. Let the bacteria divide and then produce the insulin protein.