SUBMITTED BY

SWADHA GUPTA

CUG/2014/1065

1st sem M.Sc. Life

sciences

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.

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

• 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

other fungi).

• 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.

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.

• Degradative Plasmids

– Allows to digest unusual substances.

• Virulence Plasmids

– Turn bacterium into a pathogen

• EPISOMES

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.

2.BY THEIR ABILITY TO TRANSFER TO

OTHER BACTERIA

• 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.

PLASMID

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

pairs (kbp).

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.

• 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 :

pBR322 plasmid

pUC18 plasmid

Plasmids in genetic

engineering

• 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.

• 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.

Various applications

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

influenza.

• 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

vaccine protection.

• 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.

references

• Lancing M. Prescott – Microbiology

• http://www.innovateus.net

• http://www.ncbi.nlm.nih.gov/

• https://www.newworldencyclopedia.org

• Structural biochemistry .docx plasmid

Thank you !!

Question

• How plasmid DNA vaccines works in the treatment of

cancer?

- 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.