Plasmids are the extra chromosomal structures in the cells of bacteria which have the ability to self replicate. They do not combine with the genetic material of the host cell but stay independently. They are genetically modified and are used in the recombinant DNA technology. They are able of carrying 20 genes at a time.


Plasmids are usually made up of double stranded non-chromosomal DNA, but in some cases they are circular. They make their structure circular by combining the two ends of the double stranded DNA together. These ends are combined through covalent bonds.


1) The main function of plasmids is to carry antibiotic resistant genes and spread them in the whole human or animal body. In this way many diseases of humans and animals can be treated.

2) The other function of plasmids is to carry those genes which are involved in metabolic activities and are helpful in digesting the pollutants from the environment.

3) They are also capable of producing antibacterial proteins.

4) Plasmids re also able to carry the genes which are concerned with increasing the pathogenicity of bacteria which cause diseases like anthrax and tetanus.

There are five types of plasmids which are used for different purposes.

1) Resistance-® Plasmids:-
This type of plasmids is involved in the bacterial conjugation. They usually carry those genes which code for the resistance of antibiotics or poisons. They also code for those genes which are responsible for the production of conjugation pili. The main role of conjugation pili is to transfer the R plasmid from a donor bacterium to the recipient bacterium. This is how the other bacteria also become antibiotic resistant.

2) Degradative plasmids:-
This type of plasmids is capable of degrading or digesting the dead organic matter from dead animals or plants. They use this organic matter in the process of biosynthesis and make energy and recycle them.

3) Fertility Plasmids:-
These plasmids carry the tra-genes which are used in the process of conjugation. They are helpful in transferring the genetic material between bacteria.

4) Col Plasmids:-
The plasmids of this type produce such antibiotics which are involved in killing the other harmful strains of bacteria by staying in the host bacterial cell. The antibiotics are also called as colicin.

5) Virulence Plasmids:-
As the name shows, these plasmids have the ability to transform bacteria into a pathogen. So they are responsible for carrying the genes which cause diseases.

Plasmids in Gene Therapy:-

Plasmids have a significant role in gene therapy. They are mostly used for the insertion of therapeutic genes in the human body to fight against diseases. They are easy to manipulate and their replication in the bacterial cell is easy. They have the ability to efficiently target the cells which are defected and trigger the therapeutic genes in them. There are no harmful effects of plasmids like the viral vectors.

Plasmids in Recombinant DNA technology:-

Recombinant DNA technology makes use of plasmids for many purposes. For the drug delivery, this technology makes use of the plasmids to insert the desired drug into the body. They are also involved in causing antibiotic resistance and are used to kill harmful bacteria from the body. Recombinant DNA technology applied plasmids for the first time on the human body for the insertion of human insulin. It gave very efficient results. The other application of plasmids is the insertion of human growth hormone in the mammalian cells of animals.

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