The next three subjects

The next three subjects - The genes encoded by a plasmid...

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The next three subjects: plasmids, bacteriophages, and transposons will show that the genetic make-up of a cell can be subject to changes in addition to those processes we talked about that lead to mutations and rearrangements. Plasmids: naturally occurring extrachromosomal nucleic acids capable of independent replication in the cell (contain origins of replication ) The overwhelming majority: circular, double-stranded DNA molecules Plasmids could be found in most bacterial species , but also in some eukaryotes including yeast, some protozoa, and some plants. We will restrict our discussion to plasmids found in bacteria. The size of bacterial plasmids ranges from a few kb to more than 500 kb, or from encoding one or two genes to several hundred genes.
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Unformatted text preview: The genes encoded by a plasmid often provide an additional advantage for the host cell like allowing it to grow in otherwise hostile environments. Examples are genes that confer resistance to antibiotics or to heavy metals, such as mercury and lead. In the absence of selective pressure plasmids are usually dispensable to the host cell or can even be regarded as a burden because resources must be spent in replicating them. Some bacterial plasmids have the ability to transfer themselves from one cell to another, thus spreading horizontally in a population. (Vertical spreading would be through growth and cell division.) The ability can go even so far that some plasmids transfer themselves from one bacterial species to another....
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