Edexcel IGCSE Biology: Double Science 复习笔记 5.3.2 Genetic Engineering: Insulin

Edexcel IGCSE Biology: Double Science 复习笔记 5.3.2 Genetic Engineering: Insulin

Manufacturing Insulin


  • The gene for human insulin can be inserted into bacteria which then produce human insulin which can be collected and purified for medical use to treat people with diabetes



Genetic modification of bacteria to produce human insulin

  • 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)
  • 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
  • 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
  • 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