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PLASMIDS, TRANSFORMATION AND ANTIBIOTICSBIS 11 L Theory Section
PlasmidsExtra-chromosomal DNA moleculesSeparate from the chromosomal DNAReplicate independently from the chomosomal DNAUsually circular and double-strandedOccur naturally in bacteriaSometimes can be found in eukaryotes (example, yeast)Chromosomal DNAPlasmid DNA
PlasmidsThe number of plasmids per cell (“copy number”) can vary from zero to thousandsThe size of plasmids can vary from 1 to 200 kilobasepairs (kbp)The ability to replicate independent of the host genome makes them like virusesHowever, the relationship between them and the host is more symbiotic than parasiticAllow host to survive during times of severe stress
TerminologyA plasmid that has integrated into the hosts chromosome is called an “episome”A plasmid that is used in genetic engineering is called a “vector”
Types of PlasmidsDifferent ways to categorize plasmids:Based onConjugation (ability to transfer from one bacteria to another; requires tragenes)Compatibility (related plasmids are often incompatible and cannot exist in the same cell)Function