2. The term plasmid was first introduced by the American molecular biologist
Joshua Lederberg in 1952.
He was an American molecular biologist known for his work in genetics,
artificial intelligence, and space exploration
He won the 1958 Nobel Prize in Physiology
or Medicine for discovering that bacteria can
mate and exchange genes. He shared the prize
with Edward L. Tatum and George Beadle who
won for their work with genetics.
3. WHAT IS PLASMID ?
• Like other organisms, bacteria use double-stranded DNA as their
genetic material. However, bacteria organize their DNA differently
to more complex organisms.
• In addition to the chromosome, bacteria often contain plasmids –
extra -chromosomal hereditary determinant
4. • Plasmids are small double-stranded DNA molecules, usually
circular that can exist independently of host chromosomes and are
present in many bacteria (they are also present in some yeasts and
• They have their own replication origins and are autonomously
replicating and stably inherited .
• A replicon is a DNA molecule or sequence that has a replication
origin and is capable of being replicated. Plasmids and bacterial
chromosomes are separate replicons.
• Plasmids have relatively few genes, generally less than 30. Their
genetic information is not essential to the host, and bacteria that lack
them usually function normally.
5. TYPES OF PLASMIDS
1.on the basis of function
• Fertility Plasmids ( F PLASMID )
– carry the fertility genes (tra-genes) for conjugation, the transfer of
genetic information between two cells.
• Resistance Plasmids (R PLASMID )
– Contain genes that can build resistance to antibiotics or poisons.
• Col Plasmids
– contain genes that encode for the antibacterial polypeptides called
bacteriocins, a protein that kills other strains of bacteria. The col
proteins of E. coli are encoded by proteins such as Col E1.
6. • Degradative Plasmids
– Allows to digest unusual substances.
• Virulence Plasmids
– Turn bacterium into a pathogen
an episome is a plasmid of bacteria or viral DNA that can integrate itself
into the chromosomal DNA of the host organism . For this reason, it can
stay intact for a long time, be duplicated with every cell division of the
host, and become a basic part of its genetic makeup.
7. 2.BY THEIR ABILITY TO TRANSFER TO
• Conjugative plasmids
‘tra’ ( -sexual transfer of
genetic material), which perform the complex process of conjugation, the
transfer of plasmids to another bacterium.
• Non-conjugative plasmids
are incapable of initiating conjugation, hence they can only be transferred
with the assistance of conjugative plasmids.
• Intermediate classes of plasmids
are mobilizable, and carry only a subset of the genes required for transfer.
They can parasitize a conjugative plasmid, transferring at high frequency only
in its presence. Plasmids are now being used to manipulate DNA and may
possibly be a tool for curing many diseases.
CONSISTS OF :
An origin of replication .
Multiple cloning sites( a
polylinker to clone the gene
of interest) .
An antibiotic resistance
gene ( Selectable marker).
The size of plasmids varies
from 1 to over 400 kilobase
9. Plasmid – a vector
A vector is a DNA molecule used to carry genes from
organism to organism.
Plasmids have 3 key parts. They have an origin of
replication, a selectable marker gene, and a cloning site.
The origin of replication is used to indicate where DNA
replication is to begin. The selectable marker gene is used
to distinguish cells containing the plasmid from cells that
’ contain it. The cloning site is a site in the plasmid
where the DNA is inserted.
11. • Plasmids are first type of cloning vector
developed.These are used as vector to clone DNA in
bacteria. Engineered plasmids can be used to clone
genetic material of up to 10,000 base pairs.
• Examples :
14. Plasmids in genetic
• In genetic engineering, plasmids provides a versatile tool
that are used to make copies of particular genes. This is
done by inserting the gene to be replicated into the
plasmid, then inserting the plasmids into bacteria by a
“T ”. N
exposed to antibiotics that destroy bacteria without the
plasmid. These bacteria are then grown in large amounts
with their new genes.
16. • One more key use of plasmids is to make large amounts
of proteins. In this case, researchers grow bacteria containing a
plasmid harboring the gene of interest. Just as the bacteria
produce proteins to confer its antibiotic resistance; it can also be
induced to produce large amounts of proteins from the inserted
gene. This is a cheap and easy way of mass-producing a gene or
the protein it then codes for, for example, insulin or even
antibiotics. Though, a plasmid can only contain inserts of about 1–
10 kbp. To clone longer lengths of DNA, cosmids ( type of
hybrid plasmid), bacterial artificial chromosomes or yeast artificial
chromosomes could be used.
19. DNA VACCINES
• Plasmid DNA (pDNA) is the base for promising DNA vaccines and gene
therapies against many infectious, acquired, and genetic diseases, including
HIV-AIDS, Malaria, and different types of cancer, enteric pathogens, and
• Compared to conventional vaccines, DNA vaccines have many advantages
such as high stability, not being infectious, focusing the immune response to
only those antigens desired for immunization and long-term persistence of the
• Especially in developing countries, where conventional effective vaccines are
often unavailable or too expensive, there is a need for both new and improved
vaccines. Therefore the demand of pDNA is expected to rise significantly in
the near future.
• How plasmid DNA vaccines works in the treatment of
- The human tumor representing antigens like carcinoembryonic antigens
(CEA) , melanoma-associated antigens are frequently expressed by human
tumor cell. The genes coding for tumor antigens (Ag) has enabled the design
of antigen-specific cancer vaccines based on plasmid DNA .
- A DNA vaccine is composed of a plasmid DNA that encodes the antigen of
interest under the control of a mammalian promoter and can be easily
produced in the bacteria .
- DNA vaccines can be introduced into the skin (intradermally), subcutaneum
or to the muscle by one of several delivery methods which further generates
the efficient immune response in the body against the cancer cells.