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What is the meaning of Plasmid? Concept and Definition of Plasmid


Definition of plasmid


1. Concept of plasmid

Plasmids are molecules of extrachromosomal circular or linear DNA is replicated and transcribed independent of the chromosomal DNA. They are normally present in bacteria, and sometimes in eukaryotic organisms such as yeasts. Their size varies from 1 to 250 kb. The number of plasmids can vary, depending on their type, since a single copy up to a few hundred per cell. The term plasmid was presented for the first time by the American molecular biologist Joshua Lederberg in 1952.1
The molecules of DNA plasmid, adopt a conformation type double helix like DNA of chromosomes, although, by definition, they are out of them. Plasmids found in almost all of the bacteria. Unlike the chromosomal DNA, plasmids do not have associated proteins.
In general, they do not contain essential information, but that they confer benefits to the host defined growth conditions. The most common example is that of plasmids containing a particular antibiotic resistance genes, so that the plasmid will only result in an advantage in the presence of the antibiotic.
There are some integrative plasmid, i.e. which have the ability to be inserted into the bacterial chromosome. These momentarily break the chromosome and are placed in its interior, which automatically cellular machinery also plays the plasmid. When this plasmid has been inserted are given the name of episoma.
Plasmids used in genetic engineering for its ability to reproduce independently of the chromosomal as well as DNA because it is relatively easy to handle and insert new genetic sequences.
Plasmids used in genetic engineering often contain one or two genes that confer antibiotic resistance and allow you to select clone recombinant. There are other methods of selection in addition to resistance to antibiotics, such as those based on fluorescence or proteins that destroy the cells without the use of antibiotics. These new methods of selection of plasmids are often used in biotechnology, due to strong criticism from environmental groups against the possibility of the presence of antibiotics in genetically modified organisms.
Plasmids often contain genes or packages of genes that confer a selective advantage, which gives them the ability to make the bacteria resistant to antibiotics.
Each plasmid contains at least one sequence of DNA that serves as an origin of replication or ORI (a starting point for DNA replication), which enables DNA to be replicated independently of the chromosomal DNA. The majority of bacteria plasmids are circular, but also referred to some linear, which superficially reassembled most of eukaryotic chromosomes.

2. Definition of plasmid

Plasmids, small circular DNA fragments, are present practically in all bacterial cells. They contain from 2 to 30 genes. Some have the ability to merge or go out of the bacterial chromosome.

Episoma to a plasmid incorporated into the bacterial chromosome is called. Plasmids are replicated in similar fashion to the bacterial chromosome. Escherichia coli have been recognized many plasmids, among them the F ("sex factor") and R (resistance to the antibiotic). The F plasmid contains 25 genes, some of which control production of the pilis, "tubes" that "males" (F +), stretching from the surface of bacterial cells to bacterial cells females (F)-.

The image above is modified from http://www.whfreeman.com/life/update/.

The R plasmid confers, cells that possess it, resistance to antibiotics or drugs. An R plasmid can have up to 10 genes that confer resistance.
R plasmids can be transferred to other bacteria of the same species, viruses and even bacteria of different species.
Resistance to antibiotics has been found in causing pathogens of diseases such as: typhoid, meningitis, gonorrhea, and others. They act by providing the information needed to destroy the antibiotic or for cincunvalar the lock which produces the antibiotic in the bacterial metabolic pathway.

3 Meaning of plasmid

He is known as a plasmid with a molecule of deoxyribonucleic acid (DNA) whose replication is independent of the chromosome's DNA. Depending on the cell in question, there may be a single plasmid or up to several hundred.
Plasmids can have identical configuration to the chromosomal DNA (as a double helix) but always found outside the structure and do not have associated proteins. Information that host these molecules usually not essential, although they provide certain qualities to the host under certain conditions.
Typically be that plasmids in bacteria: in fact, the majority of bacteria have these molecules. Plasmid in eukaryotic type bodies have been found, in addition.
Thanks to its capacity of independent reproduction compared the chromosome's DNA, plasmids are used in genetic engineering to select certain clones. Plasmids can be selected for their resistance to some substances such as antibiotics.
According to their function, it is possible to differentiate between different types of plasmids. Resistance plasmids are those who can deal with the action of a poison, an antibiotic, etc. The virulent plasmids, for his part, become bacteria pathogens, while degradativos plasmids help digest substances that are not usual.
It is known as R plasmid to the plasmid of resistance that is part of the bacteria and that can count on up to a dozen genes that provide this capability.
When the plasmid gets integrated by its own action to the DNA of the host chromosome, is called episoma. Cell division occurs, the episoma ends up doubling, and integrate into the basic genetic map of the guest.


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