IGCSE Biology glossary
Restriction enzyme
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Definition
An enzyme that cuts DNA at specific base sequences, producing fragments with either blunt or sticky ends. In genetic engineering, restriction enzymes are used to cut out a desired gene from donor DNA and to cut open a plasmid vector at a corresponding site.
What to include in an exam answer
The same restriction enzyme must be used to cut both the donor DNA and the plasmid, so the sticky ends are complementary and can be joined. This is a key step in genetic engineering.
Example in context
Explain why the same restriction enzyme is used to cut both the donor DNA and the plasmid (2 marks): Using the same restriction enzyme produces complementary sticky ends on both the gene and the plasmid. This allows the gene to be inserted into the plasmid and joined by ligase.
Related syllabus topic
Biotechnology & genetic modification