7.4

• Recombinant DNA

  Includes DNA from more than one organism
• 2 different ways in Isolation of the gene

  1. Cut out a section of DNA with the gene of interest with restriction endonuclease enzyme

  2. Use reverse transcriptase enzymes to make DNA from mRNA
• Recombinant DNA

  1. Isolation of the gene

  2.Cut plasmid with the same restriction endonuclease enzyme to leave complementary sticky ends

  3. Join plasmid and gene with DNA ligase to form recombinant DNA

  4. Reincorporate plasmid into host nucleus
• Effective vectors

  • Target the right cells
  • Incorporate the gene into the host genome
  • Have no adverse side effects
• Gene markers

  Used to show where a foreign gene has been inserted (fluorescence and antibiotic resistance combined with replica plating)
• Transgenic plants

  Plants which contain genetic material from an unrelated organism
• Genetic modification using Agrobacterium tumefaciens

  1. Ti plasmid (transfers bacterial genetic information directly to plant DNA) extracted

  2. Bacterial genes are inserted into plasmid via genetic modification

  3. Plasmid is returned to the bacterium

  4. Plant is infected with the bacterium

  5. Plant grows a crown gall. The cells of the crown gall contain the inserted gene

  6. These cells can be isolated and cultured to grow whole new transgenic plants
• Uses of transgenic plants

  • Flood resistance
  • Pesticide production
  • Herbicide resistance
  • Changing the nutrient value of plants (e.g. replacing linoleic acid with oleic acid in soya beans)
• Give ways in which recombinant DNA can be inserted into other cells

  • Virus vector
  • Gene guns
• What are ‘knockout mice’ and how are they useful?

  Mice with one or more genes silenced. Can be used to investigate gene function, or create animal models of disease to allow research and testing of treatment
• Recombinant DNA technology


  The transfer of DNA fragments from one organism to another
• Recombinant DNA technology works because the genetic code is universal, and therefore transcription and translation occur by the same mechanism and result in the same amino acid sequence across organisms
• Using reverse transcriptase to produce DNA fragments

  1. mRNA complementary to the target gene is used as a template

  2. Free nucleotides match up to their base pairs

  3. Reverse transcriptase forms the sugar-phosphate backbone

  4. Creates cDNA (complementary DNA)
• Using enzymes to produce DNA fragments

  1. Restriction endonucleases (RE) cut DNA at specific sequences

  2. Different REs cut at different points, but one RE will always cut at the same sequence

  3. Using particular REs allows you to cut out a certain gene of interest
• Ways to insert recombinant DNA into other cells


  • Virus vectors
  • Gene guns
• Inserting a DNA fragment into a vector

  1. A plasmid (circular DNA from a virus) is used as the vector, and is cut using the same restriction enzymes as the DNA, so that the ends are complementary

  2. DNA ligase joins the fragment and plasmid together
• Inserting a vector into a host cell

  1. Known as cell transformation

  2. The host cells (bacteria) are mixed with the vectors in an ice-cold solution

  3. Then heat shocked to encourage the cells to take up the vectors

  4. The cells can then be grown and the DNA fragment will be cloned
• Gene guns


  Microscopic gold pellets are coated with copies of the DNA fragment, which are then propelled at high speed into cells
• Identifying recombinant cells


  1. Marker genes can be inserted into plasmids at the same time as DNA fragments e.g. antibiotic resistance genes

  2. The transformed cells are then placed on a plate with antibiotics, so only the ones that successfully took up the vector will grow
• Knockout mice


  • Mice with one or more genes silenced
  • Can be used to investigate gene function, or create animal models of disease to allow research and testing of treatments
• Transgenic plants


  Genetically modified plants, which contain genetic material from an unrelated organism
• Producing transgenic plants


  1. Plasmid extracted from bacterium, gene inserted, and then returned

  2. Plant is then infected with the bacteria

  3. This will produce a gall, containing cells that contain the inserted gene

  4. These cells can be used to grow a whole new plant
• Genetically modified plant


  • Soya beans
  • Linoleic acid (polyunsaturated) is replaced by oleic acid (monounsaturated)
  • This is oxidised less easily and so prolongs shelf life, as well as being healthier
• Advantages of the widespread use of genetic modification

  • Improve nutritional value of foods
  • Greater crop yields
  • Less need for pesticides
  • Reduces need for land clearing
• Disadvantages of the widespread use of genetic modification

  • Reduced biodiversity
  • Unknown effects on health
  • Cross-pollination could result in herbicide-resistant weeds
  • May increases costs for farmers