The Process of Genetic Modification (Edexcel IGCSE Biology: Double Science)

• Genetic modification involves the transfer of a gene or section of DNA from one organism into the DNA of another organism
• To begin this process, first the gene that is to be inserted is located in the original organism
• Restriction enzymes are used to cut the required gene out of the DNA
  • Different types of restriction enzymes cut the DNA in different locations (they target different sequences of DNA). This means that specific enzymes can be selected that will cut out the required piece of DNA
• Cutting DNA with restriction enzymes results in pieces of DNA with ‘sticky ends’
  • Sticky ends are short sections of single-stranded DNA; they are 'sticky' because they will pair together with another sticky end that contains complementary bases
• A bacterial plasmid is cut by the same restriction enzyme
  • This ensures that the base pairs of the two sticky ends are complementary to each other, meaning that they will 'stick' together

Restriction enzymes cut DNA strands at specific sequences to form ‘sticky ends’

• The plasmid and the isolated gene are joined together by DNA ligase enzyme
  • If two pieces of DNA have complementary sticky ends, DNA ligase will link them to form a single, unbroken molecule of DNA

• Plasmids and viruses can act as vectors for genetic engineering
  • They take up pieces of DNA and then insert this recombinant DNA into other cells
• Viruses transfer DNA into human cells or bacteria
• Plasmids transfer DNA into bacteria or yeast

DNA ligase is used to join two separate pieces of DNA together

• 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 genetically engineered bacteria can be placed in a fermenter to reproduce quickly in controlled conditions and make large quantities of the human protein