Question

How can a plasmid be described?

Answer 1

Hint: A plasmid is defined as the extrachromosomal DNA that is present within the cell and is not integrated within the chromosomal DNA and is also capable of replicating independently.

Complete answer:
Plasmids are small, circular double stranded DNA molecules that are majorly present in bacteria but are sometimes also present in certain eukaryotes and archaea. The plasmid DNA is known to comprise an origin of replication by which it carries out independent replication; as a result of which it is also known as replicon.

Plasmids carry at least one gene that is beneficial to the bacteria in which they are residing. These can be antibiotic resistance genes, virulence factors genes that help the bacteria to colonize a host and evade their immune system and also nitrogen fixation genes.

Plasmids are of different types each of which carry out a different function- Fertility F plasmids which comprise of tra genes and are thus capable of conjugation, Resistance or R plasmids which carry genes for antibiotic resistance, Col plasmids which carry genes encoding bacteriocins that can kill other bacteria, Degradative plasmid that helps in the digestion of unusual substance and Virulence plasmids that causes the bacteria to turn pathogenic.

Note: Since the presence of a plasmid provides certain advantages to the bacteria so the plasmids are maintained in the bacteria and after replication each copy of the daughter cell receives a copy of the plasmid. To ensure proper segregation plasmids have partitioning systems that ensure proper segregation with good precision.