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Competent host and inserting recombinant DNA sheet
3-mark answer frame

Describe the methods used to introduce recombinant DNA into host cells.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Say why a method is needed. DNA is hydrophilic and cannot pass through cell membranes.
  2. 2 · Explain competence in bacteria. Treat with a divalent cation such as calcium; keep with recombinant DNA on ice, heat shock at 42°C, then back on ice.
  3. 3 · Describe micro-injection. Recombinant DNA is injected straight into the nucleus of an animal cell.
  4. 4 · Describe biolistics. Plant cells are bombarded with gold or tungsten micro-particles coated with DNA.
  5. 5 · Describe disarmed pathogens. Harmless Agrobacterium or retroviruses deliver the recombinant DNA when they infect the cell.
  6. 6 · Close in one line. So the method is chosen to suit the host: bacterium, plant or animal.

Scoring tip: Write '42°C' and 'on ice' for the heat shock, and name gold or tungsten for biolistics.