Plasmids are extra-chromosomal DNA molecules found in bacteria that can replicate independently of chromosomal DNA. They vary in size but are usually between 1,000 to 25,000 base pairs. Plasmids are not essential for bacterial survival but can contain genes that allow bacteria to survive better in adverse environments or compete with other microbes. There are several classes of plasmids including F-plasmids for conjugation, R-plasmids for antibiotic resistance, Col-plasmids for bacteriocin production, and virulence plasmids that make bacteria pathogenic. Bacteria can exchange plasmids through conjugation, transformation, or transduction. Plasmids are useful tools in molecular biology and

1. PlasmidsPlasmids

2. What is plasmid
• Plasmid is an extra chromosomal DNA molecule which
is capable of replicating independently from the
chromosomal DNA.

3. • They are found in numbers ranging from one per cell to
hundreds per cell (this is called "copy number").

4. • plasmids are not essential for the survival of
bacteria.
• but they may encode a wide variety of genetic
determinants, which permit their bacterial hosts
to survive better in an adverse environment or to
compete better with other microorganisms
occupying the same ecological environment.

5. • Plasmids vary in size, but most are between
1,000 to 25,000 base pairs.
• can be found in Bacteria and Eukarya.

6. Types of plasmids
There are five main classes :
1- Fertility- F-plasmids
They are capable of conjugation (transfer of genetic
material between bacteria ).
2- Resistance- R-plasmids
which contain genes that can build a resistance against
antibiotics or heavy–metal.

7. 3- Col-plasmids
which contain genes that code for bacteriocins, that can
kill other bacteria.
4- Degradative plasmids
which enable the digestion of unusual substances.
5- Virulence plasmids
which turn the bacterium into a pathogen.

8. Plasmid Exchange
• Bacteria can exchange or transfer plasmid between
other bacteria in three different ways.
• In every case the source cells of the plasmid are called
the
–DONORS-
and the cells that receive the plasmid are called the
–-RECIPIENTS-

9. The three forms of bacterial DNA exchange
are :
1) CONJUGATION
This process involves one bacterium making a copy of a
plasmid, and transferring that copy to another bacterium.

10. 2) TRANSFORMATION
This is the process in which a recipient cell takes up plasmid
DNA from the environment (such as DNA released from a dead
organism.

11. 3) TRANSDUCTION
This process involves the transfer of plasmid DNA from one
cell to another by a bacteriophage.

12. Conformations of plasmids
Plasmid DNA may appear
in different conformations,
like, coiled, Supercoiled,
circular and linear, which
(for a given size) run at
different speeds in a gel
during electrophoresis:
Supercoiled

13. Plasmid DNA extraction
Plasmid DNA can easily be purified away from
the rest of the genome. For their use as vectors
and for molecular cloning .
In recent times many commercial kits have been
created to perform plasmid extraction at various
scales . which are:
• minipreps
• medipreps
• maxipreps

14. Visualization of plasmid
• plasmid can be visualized on a gel after staining
with:
Ethidium bromide
and viewing the fluorescence pattern under an
ultraviolet light.

15. (-)
Large molecules
Small molecules
(+)
gel electrophoresis of plasmid

16. • Plasmids are extremely valuable tools in the fields of
molecular biology and genetics, specifically in the area of
genetic engineering where they are commonly used to
multiply (make many copies of ) particular genes .
• Plasmids in this conditions are called vectors .
Applications of plasmids

17. They play a critical role in :
 gene cloning, recombinant protein production (e.g., of
human insulin).

18.  In gene therapy research.

19. • Many plasmids are commercially available for such uses.