7.4 gene technology

• what is recombinant DNA technology?

  • identify gene
  • make copies
  • transfer copies of DNA from one organism to another
• why does recombinant DNA technology occur?

  • genetic code is universal
  • transcription and translation can occur in same mechanism
  • produce same amino acid sequence
  • in all organisms
• how is reverse transcriptase used to produced DNA fragments?

  • mRNA thats complimentary to target gene used as template
  • mixed with free nucleotides that join via complimentary base pairing + reverse transcriptase
  • form phosphate sugar backbone
  • form cDNA (complimentary DNA)
• How is recombinant DNA produced?

  • plasmid cut with restriction enzyme
  • target gene removed by cutting with same restriction enzyme
  • target gene spliced into open plasmid via DNA ligase (forms phosphodiester bond between plasmid + gene)
  • fragments joined via DNA ligase (covalently)
  • forms hybrid vector + other products
• how do restriction enzymes work?

  • active site complimentary to DNA recognition sequence
  • hydrolyses DNA to leave blunt and sticky ends
  • target genes are cut with same restriction enzyme so complimentary base pairing can occur
• sticky ends = unpaired bases at the end

  blunt ends = no unpaired bases at the end
• how is recombinant DNA inserted into other cells?

  • virus vectors
  • gene guns
• how do you identify recombinant cells?

  • use plasmid vector with antibiotic resistant gene
  • vector contains 2 marker genes:
  • marker gene 1 = identify if cell has taken up plasmid or not. cells with plasmid gain antibiotic resistance
  • grown on medium, non recombinant cells will die
  • marker gene 2 = identify if cell has taken up hybrid vector.
  • foreign DNA in marker gene 2. cells with hybrid gene cant make this DNA
  • cell with hybrid vector not resistant. so will die
  • ampicillin test on replica plate
  • colonies that grow on first plate but not on replica (ampicillin) plate are recombinant.
• how are viruses used as vectors?

  • in latency
  • nucleic acid inserted into DNA of host cell
• how are gene guns used as vectors?

  • air pressure used
  • fires heavy metal particles
  • with the target gene on into cells.
• what do you do to allow bacteria to take up recombinant dna?

  • soak in ice cold calcium chloride
  • heat shock of 42 degrees for 2 mins
• what are knockout mice? what are they used for?


  • mice with one gene silenced
  • similar gene is inserted so the original is impossible to read
  • used to understand gene function
  • to test for treatments
• how are knockout mice formed?

  using embryonic stem cells...

  • DNA sequence changed to inactivate gene
  • mutant gene injected in embryo
  • resulting offspring will have cells with mutant gene or normal genes
  • sperm cell with mutant genes are isolated
  • male mice bred with normal female. producing heterozygous children
  • heterozygotes bred together to produce homozygous recessive mice with mutant gene.
• how can plants be genetically modified?

  using agrobacterium tumefaciens...

  • Ti plasmid removed from bacterium
  • T-DNA cut with restriction enzyme
  • foreign DNA cut with the same restriction enzyme
  • foreign DNA inserted into T-DNA of plasmid
  • plasmid reinserted into bacterium. and inserted into chromosome of plant cell
  • plant cell grown on culture
  • plant generated from clone and all cells contain foreign gene
• GM soya plants

  • resistant to herbicides
  • resistant to fungus pathogen
  • resistant to droughts
  • produces less linoleic acid
  • produces more oleic acid
• how does linoleic and oleic acid affect GM soya plants?

  linoleic acid

  • polyunsaturated
  • oxidises soya bean - doesnt last as long

  oleic acid

  • monounsaturated - healthier
  • not easily oxidised - lasts longer
• benefits of recombinant gene technology?

  • medicines can be produced without animal harm
  • improved agriculture - less pesticides used
  • GM crops can grow on previous unsuitable soil
  • improved nutritional quality
• risks of recombinant gene technology?

  • modified organism - unforeseen genetic effects and disease
  • ecosystems - unforeseen effect on food web
  • biodiversity - reduces genetic diversity due to selective breeding
  • human society - could be taking away other country income
  • farmers - wont be able to afford benefits of GM crops