PLASMIDS
Table of contents
Introduction
Physical nature and copy number
Plasmid incompatibility
Types of plasmid
Replication of plasmid
Plasmid curing
Plasmid as cloning vector
Introduction
Plasmids are the genetic elements that occur in bacterial cell in addition
to bacterial chromosome.
These are extra chromosomal DNA found in bacterial cytoplasm that
replicate seperately from chromosome.
The existence of plasmid in bacterial cytoplasm was revealed by
Lederberg in 1952 while working on conjugation process in bacteria.
Lederberg coined the term plasmid to refer to transmissible genetic
elements that were transferred from one bacterial cell to another.
Mostly thousands of plasmids are known of which naturally occurring
plasmids are isolated from bacterial cells.
Besides this, many artificially modified plasmids have also been
developed which are used as vector in genetic engineering.
, Physical nature and copy number
They are small, double stranded DNA molecule generally, circular in
nature.
Naturally occurring plasmids vary in size from approximately 1Kb to more
than 1 MB (Mega Base).
A typical plasmid DNA is considered to be less than 5% the size of
bacterial chromosome.
Most of the plasmid isolated from bacterial cell exist in supercoiled
configuration which is most compact form of DNA existing within the cell.
Plasmid Incompatibility
A common feature of plasmid is the plasmid Incompatibility.
It is a condition where a plasmid is transferred to a new bacterial cell that
already possess another plasmid.
The second plasmid is not accommodated and is lost in subsequent
replication.
The two plasmids which cannot exist together in a cell is called
incompatible plasmid.
Various incompatibility groups of plasmid have been recognised in
bacteria.
Types of Plasmid
Various types of plasmid naturally occur in bacterial cell and the most
favoured classification of plasmid is based on their function encoded by
their own genes.
1. F Plasmid - F stands for fertility and the F plasmid is very well
characterized plasmid.
Table of contents
Introduction
Physical nature and copy number
Plasmid incompatibility
Types of plasmid
Replication of plasmid
Plasmid curing
Plasmid as cloning vector
Introduction
Plasmids are the genetic elements that occur in bacterial cell in addition
to bacterial chromosome.
These are extra chromosomal DNA found in bacterial cytoplasm that
replicate seperately from chromosome.
The existence of plasmid in bacterial cytoplasm was revealed by
Lederberg in 1952 while working on conjugation process in bacteria.
Lederberg coined the term plasmid to refer to transmissible genetic
elements that were transferred from one bacterial cell to another.
Mostly thousands of plasmids are known of which naturally occurring
plasmids are isolated from bacterial cells.
Besides this, many artificially modified plasmids have also been
developed which are used as vector in genetic engineering.
, Physical nature and copy number
They are small, double stranded DNA molecule generally, circular in
nature.
Naturally occurring plasmids vary in size from approximately 1Kb to more
than 1 MB (Mega Base).
A typical plasmid DNA is considered to be less than 5% the size of
bacterial chromosome.
Most of the plasmid isolated from bacterial cell exist in supercoiled
configuration which is most compact form of DNA existing within the cell.
Plasmid Incompatibility
A common feature of plasmid is the plasmid Incompatibility.
It is a condition where a plasmid is transferred to a new bacterial cell that
already possess another plasmid.
The second plasmid is not accommodated and is lost in subsequent
replication.
The two plasmids which cannot exist together in a cell is called
incompatible plasmid.
Various incompatibility groups of plasmid have been recognised in
bacteria.
Types of Plasmid
Various types of plasmid naturally occur in bacterial cell and the most
favoured classification of plasmid is based on their function encoded by
their own genes.
1. F Plasmid - F stands for fertility and the F plasmid is very well
characterized plasmid.
