What are plasmids?

You plasmids can be defined as small molecules of DNA that are found in bacteria and also in yeast. In this text we will focus on plasmids present in bacteria.

Read too: Bacteria

Characteristics of bacterial plasmids

As stated, plasmids are extrachromosomal circular DNA molecules. They have the cability to replicate independently and usually have few genes. It is noteworthy that in a cell several copies of plasmids can be found and that they are often transferred from one cell to another.

Function of bacterial plasmids

Plasmids usually have genetic information that is not extremely essential for the survival of the bacteria, but they are usually related to some adaptive function for special situations. As an example, we can mention those plasmids that guarantee antibiotic resistance and those that increase the likelihood that a bacterial cell will cause disease.

The plasmid is an extrachromosomal circular DNA
The plasmid is an extrachromosomal circular DNA


Plasmid classification

Plasmids can be classified in different ways, and it is possible to identify, for example, two basic groups:

  • Conjugatives: These plasmids ensure the start of conjugation, a process in which there is an exchange of genetic material between bacteria.

  • Non-conjugatives: These plasmids do not allow the initiation of conjugation.

The conjugation process guarantees the transfer of genes from a donor bacterium to a recipient
The conjugation process guarantees the transfer of genes from a donor bacterium to a recipient

Plasmids can be further classified according to their function in the cell into five groups:

  • Fertility plasmids (F): Promote the beginning of conjugation;

  • Resistance plasmids (R): They guarantee resistance to antibiotics and other substances that can harm the bacteria;

  • Virulence plasmids: They make bacteria capable of causing disease;

  • Col plasmids: They guarantee the production of colicins, which can be lethal to other bacteria;

  • Degradation plasmids: They guarantee the cell the ability to produce degradative enzymes.


By Ma. Vanessa dos Santos

Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/biologia/o-que-sao-plasmideos.htm

Nomenclature of Carboxylic Acids. Carboxylic Acids

Nomenclature of Carboxylic Acids. Carboxylic Acids

Carboxylic acids are those organic compounds that have the carbonyl group attached to a hydroxyl ...

read more
Gay-Lussac volumetric law. Definition of the volumetric law

Gay-Lussac volumetric law. Definition of the volumetric law

Joseph Lous Gay-Lussac (1778-1850) was a scientist who made important studies of gases. He carrie...

read more
France. Characteristics of France

France. Characteristics of France

France or French Republic is a country located on the European continent. The nation has a popula...

read more