Restriction Enzymes (Edexcel IGCSE Biology: Double Science)

• 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; 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