Plasmids and its typesSijo.A

B.sc.Botany & Biotechnology

Mar ivanios college

Tvm, Kerala

What are plasmids?

Autonomously replicating circular

fragment present in DNA is called

plasmids.

The term plasmid was first introduced

by American molecular biologist Joshua

Lederberg in1952.

An episome is a plasmid capable of

inserting DNA into the host

chromosome.

Because of their ability to transfer DNA

from one bacterium to another, plasmids

are extensively used in recombinant

DNA technology or genetic engineering.

classification

Plasmids can be broadly classified into conjugative plasmids and non-conjugative plasmids.

Conjugative plasmids contain a set of transfer or tra genes which promote sexual conjugation between different cells.

Non-conjugative plasmids are incapable of initiating conjugation, hence they can be transferred only with the assistance of conjugative plasmids.

An intermediate class of plasmids are mobilizable. They promote their conjugation by a helper plasmid.

Based on

function Based on function plasmids are classified

into five.

1) F plasmid(fertility factor)

F plasmid contain tra genes which is responsible for conjugation and result in the expression of sex pili.

F plasmids are actively involved in bacterial conjugation, hence they are called conjugation factors.

2) R plasmid(Resistance factor)

R plasmid contains gene that provide resistance against antibiotics and poisons.

3) Col plasmid(colicinogenic factors)

Col plasmid contains gene that produce some bacterial toxins.(bacteriocin).

Eg: colicin by E.coli, vibriocins by vibriocholerae.

4) metabolic or degradative plasmids

Metabolic or degradative plasmids contain a gene that produce some metabolic enzymes.

They can transmitted through conjugation together with F plasmid.

5) virulente pathogen

They contain gene which turn the bacterium into a pathogen.

Thank you…