Plasmid Topics

• plasmid dna
• dna restriction
• horizontal gene transfer
• restriction digests
• restriction digest
• eukaryotic organisms
• gel electrophoresis
• molecular cloning
• conjugative plasmid
• antibiotic resistance
• miniprep
• organic compounds
• micrometre
• selective advantage
• micrograms
• microbes
• high frequency
• fragments
• vectors
• bacteria

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Plasmid, Plasmid

Plasmids usually occur naturally in bacteria, but are sometimes found in eukaryotic organisms (e.g., the 2-micrometre-ring in Saccharomyces cerevisiae ).

Plasmids can be found in all three major domains, Archea, Bacteria and Eukarya.

Rather, plasmids provide a mechanism for horizontal gene transfer within a population of microbes and typically provide a selective advantage under a given environmental state. Plasmids may carry genes that provide resistance to naturally occurring antibiotics in a competitive environmental niche, or alternatively the proteins produced may act as toxins under similar circumstances. Plasmids also can provide bacteria with an ability to fix elemental nitrogen or to degrade calcitrant organic compounds which provide an advantage under conditions of nutrient deprivation.

In this case, researchers grow bacteria containing a plasmid harboring the gene of interest. Just as the bacteria produces proteins to confer its antibiotic resistance, it can also be induced to produce large amounts of proteins from the inserted gene.

They can 'parasitize' a conjugative plasmid, transferring at high frequency only in its presence. Plasmids are now being used to manipulate DNA and may possibly be a tool for curing many diseases.

For their use as vectors, and for molecular cloning, plasmids often need to be isolated.

The yield is a small amount of impure plasmid DNA, which is sufficient for analysis by restriction digest and for some cloning techniques.

Essentially this is a scaled-up miniprep followed by additional purification. This results in relatively large amounts (several micrograms) of very pure plasmid DNA.

Restriction digests are frequently used to analyse purified plasmids. These enzymes specifically break the DNA at certain short sequences. The resulting linear fragments form 'bands' after gel electrophoresis. It is possible to purify certain fragments by cutting the bands out of the gel and dissolving the gel to release the DNA fragments.

These programmes record the DNA sequence of plasmid vectors, help to predict cut sites of restriction enzymes, and to plan manipulations. Examples of software packages that handle plasmid maps are Lasergene, GeneConstructionKit, and Vector NTI.

Source: Wikipedia > Plasmid