3. Bacterial Plasmids in Nature
1-Occur naturally in bacteria and usually
carry genes that are useful but not
essential to survival: e.g. genes which
make bacteria resistant to antibiotics.
2-Plasmids are released by dead bacteria
and absorbed by those still living thus
genetic information is exchanged (sexual
reproduction?).
4. Bacterial Plasmids in Nature
3-Some plasmids even contain
genes that build a transfer tube
between bacteria.
4-There can be as many as
several hundred copies of a
single plasmid in each bacteria.
5. FUNCTIONS OF PLASMIDS
1-the main function is to carry antibiotic resistance genes
2-carry genes involved in metabolic activities and digesting pollutants
3-producing antibacterial proteins
4-carry genes which are concerned with increasing pathogenicity of
bacteria
5- using in cloning process in humans
6. Classifications of plasmids
1-conjugative plasmids :
Conjugative plasmids contain a set of transfer or
tra genes which promote sexual conjugation
between different cells
2-non-conjugative plasmids:
Non-conjugative plasmids are incapable of
initiating conjugation, hence they can be
transferred only with the assistance of
conjugative plasmids.
7. TYPES OF PLASMIDS ACCORDING TO FUNCTIONS
1-Fertility F-plasmids, which contain transfer or tra genes. They are capable
of conjugation and result in the expression of sex pilli.
2-Resistance (R) plasmids, which contain genes that provide resistance
against antibiotics or poisons. Historically known as R-factors, before the
nature of plasmids was understood.
3-Col plasmids, which contain genes that code for bacteriocins, proteins that
can kill other bacteria.
4-Degradative plasmids, which enable the digestion of unusual substances,
e.g. toluene and salicylic acid.
5- Virulence plasmids, which turn the bacterium into a pathogen
8. Plasmid Structure
1- Plasmids only need an “origin or
replication” and a “useful” gene to be
considered complete.
2-Molecular biologists have been able to
“insert” custom built restriction sites into
many plasmids so they can be used to
“insert” DNA fragments from other genes
into them and thus have a way to
propagate those DNA pieces.
9. Plasmids can be manipulated easily in the laboratory
1-Plasmids can be collected from bacteria.
2-Restriction enzymes can be purified and used to identify and cut out specific
sequences of DNA along with the plasmid vector.
3-Ligase (enzyme) can be purified and used to “glue” pieces of DNA together.
4-Bacteria can be transformed by taking in plasmids given to them
10. How to produce human insulin from bacteria and become a
multimillionaire
1-Isolate plasmid DNA from bacteria and
insulin gene from human.
2-Cut both DNAs with the same
restriction enzyme.
3-Mix the DNA together with ligase.
4-Insert the new DNA into bacteria
(transformation).
5-Use antibiotics to kill any bacteria
without the plasmid.
6-Grow bacteria and harvest the insulin.
Insulin
Purification
Insulin gene
Human DNA
