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Plasmids
By: Brye, Hannah,
and Jen
What are plasmids?
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Genetic structure in a cell that
can independently replicate
chromosomes
It is typically a small circular DNA
strand in the cytoplasm of a
bacterium
Used mainly in the manipulation
of genes
Plasmids can be found in all
three major domains, Archaea,
Bacteria and Eukarya.
Importance of Plasmids
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Easy to work with
Self-replicating
Stable
Functional in many species and can be useful for a diverse set of applications
Plasmids play a very important role in genetic engineering, particularly in gene cloning. When
genes are cloned, the process usually takes place within bacteria. In order to get the gene that is to
be cloned into the bacteria, a vector is necessary. A plasmid is what is used as the vector, as it can
pass easily from one cell to another.
Biotechnology
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Plasmids have been key to the development of molecular biotechnology.
They act as delivery vehicles, or vectors, to introduce foreign DNA into bacteria.
Using plasmids for DNA delivery began in the 1970s when DNA from other organisms was first
‘cut and pasted’ into specific sites within the plasmid DNA. The modified plasmids were then
reintroduced into bacteria.
Decades after their first use, plasmids are still crucial laboratory tools in biotechnology
Scientists can force bacteria to keep them. Virtually all plasmids that are used to deliver DNA
contain genes for antibiotic resistance. Once bacteria have been treated with a plasmid,
scientists grow them in the presence of antibiotic. Only those cells that contain the plasmid will
survive, grow and reproduce. The others will be killed by the antibiotic.
They are copied independently. Plasmids can be copied numerous times, regardless of
whether the bacterial host is replicating its own DNA, and every time a plasmid vector is
replicated, so is the introduced DNA that it contains.
They are circular. DNA that is circular is well suited to incorporate extra DNA sequences. That’s
because it can be cut open without falling apart, then snap back together once new DNA has
been incorporated.
Major steps involved
Steps in cloning a gene:
1.
2.
3.
4.
5.
Plasmid DNA is isolated
DNA containing the gene of interest is isolated
Plasmid DNA is treated with a restriction enzyme that cuts in one place,
opening the circle
DNA with the target gene is treated with the same enzyme and many
fragments are produced
Plasmid and target DNA are mixed and associated with each other
Applications in the medical field and Usage
Strategies utilizing plasmid DNA have been used for non-treatable
neurological disorders, such as Parkinson disease (PD), Alzheimer disease
(AD), and multiple sclerosis (MS).
Because of their ability to move genes from cell to cell, plasmids have become
resourceful tools for both research and biotechnology. In the laboratory,
researchers use plasmids to carry marker genes, allowing them to trace the
plasmid’s inheritance across host cells. Transferred or cloned genes are used
to produce a variety of important medical, agricultural, or environmental
products that can be economically used by humans.
Unknowns
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Naturally occurring stable elements which are found in bacteria, fungi and
even bacteria of some plants
Composed of dna or rna, single or double stranded, linear or circular
Exist and replicate independently of the chromosome in which they are
found
Not required by their host cell for survival
Subgrouped into 5 main types based on their function
R plasmids: carry genes encoding resistance to antibiotics
Col plasmids: confer on their host for the ability to produce antibacterial
polypeptides called bacteriocins that are often lethal to closely related or
other bacteria
Unknown continued
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The col proteins of E. coli are encoded by plasmids such as ColE1.
F plasmids contain the F or fertility system required for conjugation (the
transfer of genetic information between two cells).
These are also known as episomes because, under some circumstances,
they can integrate into the host chromosome and thereby promote the
transfer of chromosomal DNA between bacterial cells.
Degradative or catabolic plasmids allow a host bacterium to metabolize
normally undegradable or difficult compounds such as various pesticides.
Finally, virulence plasmids confer pathogenicity on a host organism by the
production of toxins or other virulence factors.
Cool Facts
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Plasmid size varies from 1 to over 1,000 kilobase
pairs (kbp)
The number of identical plasmids within a single cell
can range from one to thousands
Extremely effective cloning vector
Plasmids may carry genes that provide resistance to
naturally occurring antibiotics in a competitive
environmental niche
Ethical/ Moral issues
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Depends on what the plasmid contains, some have origins of replication which mean they
can replicate independently of the cell nucleus, they can contain genes that confer a selective
advantage
There's always controversy over the subject of cloning
Some people believe that there should only be one of each individual
Many scientists believe that it is “playing God”
Some believe it is unnatural
Video
https://www.youtube.com/watch?v=GNMJBMtKKWU
Referencing
https://www.addgene.org/mol-bio-reference/plasmid-background/
https://www.ncbi.nlm.nih.gov/pubmed/22023479
http://www.encyclopedia.com/science-and-technology/biology-and-genetics/genetics-and-genetic-en
gineering/plasmid
http://www.wisegeek.com/what-are-plasmids.htm
http://www.encyclopedia.com/science-and-technology/biology-and-genetics/genetics-and-genetic-en
gineering/plasmid
http://biotechlearn.org.nz/themes/bacteria_in_biotech/bacterial_dna_the_role_of_plasmids