IGCSE Biology glossary
Plasmid
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Definition
A small circular ring of DNA found in bacterial cells, separate from the main bacterial chromosome. In genetic engineering, plasmids are used as vectors: they are cut open with restriction enzymes, the desired gene is inserted, and the recombinant plasmid is returned to a bacterium.
What to include in an exam answer
Plasmids are found in bacteria. They replicate independently. In genetic engineering, they are the most commonly used vectors. The recombinant plasmid contains the inserted gene.
Example in context
Explain the role of a plasmid in the production of human insulin by bacteria (2 marks): The human insulin gene is inserted into a bacterial plasmid, creating a recombinant plasmid. When this plasmid is taken up by a bacterium, the bacterium reads the insulin gene and produces human insulin.
Related syllabus topic
Biotechnology & genetic modification