A plasmid is a tiny, extrachromosomal DNA molecule within a cell that is physically segregated from chromosomal DNA and can replicate alone. They are generally found as small circular, double-stranded DNA molecules in bacteria. Plasmids are occasionally present in archaea and eukaryotic organisms. In nature, plasmids often carry genes that boost the survival of the organism and bestow selective advantage such as antibiotic resistance. Plasmids are usually very tiny and include only additional genes that may be useful in certain circumstances. Artificial plasmids are widely utilized as vectors in molecular cloning, serving to ride the replication of recombinant DNA progressions within host organisms.
Properties and Characteristics of Plasmids
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In order for plasmids to replicate unassisted within a cell, they must acquire a stretch of DNA that can work as an origin of replication. The self-replicating unit, the plasmid, is named a replicon.
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Plasmids often carry at least one gene. Many of the genes carried by a plasmid are effective for the host cells. For instance, encouraging the host cell to survive in an environment that would contrarily be fatal or restrictive for growth.
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Plasmids can provide bacteria with the capacity to fix nitrogen. Some plasmids have no noticeable effect on the phenotype of the host cell or its usefulness to the host cells cannot be assumed, and these plasmids are labeled as cryptic plasmids.
Do All Bacteria Have Plasmids?
Yes, Plasmids naturally exist in all bacterial cells. Each bacterial cell has its own plasmid, that is transmitted during a process of conjugation. These plasmids have a great benefit to the bacterial cell as they deliver DNA containing identifiable antibiotic resistance gene sequences which would lead to the production of antibiotic resistance determinants.
In some cases, bacteria need to pick up a new plasmid from the environment, as they readily lose them during the antibiotic resistance and during the process of conjugation, as one of the daughter cells may not receive the plasmid.
Here are a Few Important Functions of Plasmids in a Bacterial Cell:
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It helps in their survival by producing toxins.
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Facilitate the process of replication in bacteria.
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Few plasmids contain genes that help in food digestion.
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The R plasmids help a bacterial cell by defending against environmental factors such as antibiotics, poison, etc.
Role of Plasmids in Bacterial Cell
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Plasmids Support Bacteria to Survive Stress: Plasmids contain just a few genes, but they make a big difference to their bacterium. The genes are usually not important for the bacterium’s day-to-day survival. Instead, they help the bacterium to withstand occasional stressful situations. For instance, many plasmids contain genes that make the host bacterium immune to an antibiotic. Other plasmids comprise genes that enable the host to digest unusual materials or to kill other kinds of bacteria.
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Plasmids Make Themselves Indispensable: Keeping a plasmid is hard work for a bacterial cell because replicating DNA uses up energy. However, by preserving its bacterial host from stress-related death, a plasmid maximizes its opportunities of being kept around. Under stressful conditions, bacteria with the plasmid will live longer and have more chances to pass on the plasmid to daughter cells or other bacterias. Bacteria without the plasmid are less inclined to survive and reproduce.
Did You Know?
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A plasmid is a DNA molecule that is separate from the chromosomal DNA and that can replicate (copy itself) independently.
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The term plasmid was mainly introduced by the American molecular biologist Joshua Lederberg in the year 1952.
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Plasmid length varies from 1 to over 1,000 kilobase pairs.
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Plasmids can be found in all three main domains – Archaea, Bacteria, and Eukarya.
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Unlike viruses, plasmids are “naked” DNA and do not encode genes essential to cover the genetic material for transfer to a new host.
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Plasmids are transferable genetic components, or “replicons”, capable of independent self-copying in a suitable host.
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Plasmids are double-stranded and, in many cases, circular.
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Plasmids mostly occur naturally in bacteria but are sometimes found in eukaryotic organisms.
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The number of identical plasmids within a single cell can vary from one to thousands.
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Plasmids are often correlated with conjugation, a means of horizontal gene transfer.
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Plasmids also can provide bacteria with a capacity to fix elemental nitrogen or to degrade complicated organic compounds.