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PLASMIDS, SANDHYA A 191822016 - Coggle Diagram
PLASMIDS
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PROPERTIES
They are not essential and they usually do not encode essential genes. However, the plasmid genes may give the bacterium a selective advantage
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They exist as supercoiled (closed circle), nicked (open circle) and linear. Though supercoiled in most bacteria, they are linear in some species.
Plasmids are extrachromosomal, double stranded, autonomously replicating nucleic acid molecules that are distinct from the chromosome.
They replicate independently of chromosome and are maintained in daughter cells. The proteins needed for plasmid replication may be plasmid or chromosomally encoded.
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TRANSMISSION
Self-transmissible or conjugative plasmids carry genes needed to provide all functions for their transfer. These plasmids tend to be large. Many plasmids are incapable of selftransmission but can be transferred at high frequency from cells that carry a self-transmissible plasmid.
Plasmid DNA sequences can be transmitted among bacteria by transformation, transduction, or conjugation. Since plasmids replicate independently, recombination is not required for inheritance of traits
DNA exchange occurs in nature by transfer of certain plasmids, called conjugative plasmids from donor cells to recipient cells
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Moreover, many conjugative plasmids carry multiple antibiotic resistance genes.
APPLICATION
Production of useful substances (hormones, enzymes, antigens for vaccines, etc.)
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DEFINITION
A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently.
Episomes:
Sometimes F factor plasmid gets integrated into bacterial chromosome. Such plasmids are called episomes. Such cells are Hfr, i.e. high frequency of recombination
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