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SEM : SEMESTER - III SUB : MICROBIAL GENETICS CLASS : II- M. Sc MICROBIOLOGY
PRINCE SHRI VENKATESHWARA ARTS AND SCIENCE COLLEGE GOWRIVAKKAM, CHENNAI- 600073.
Faculty : Dr. S. Gayathri Devi Topic : Structure of Plasmids Aim : Outline the utility of plasmids
DEPARTMENT OF MICROBIOLOGY
There are three important structure that make up a plasmid,
The ORI is the place where DNA replication begins, enabling a plasmid to reproduce itself as it must to survive within cells.
Selectable markers are often antibiotic resistance genes ; bacteria that have been subjected to a procedure to introduce foreign DNA are grown on a medium containing an antibiotic, and those bacterial colonies that can grow have successfully taken up and expressed the introduced genetic material.
Plasmids almost always carry at least one gene.
Many of the genes carried by a plasmid are beneficial for the host cells, for example: enabling thehost cell to survive in an environment that would otherwise be lethal or restrictive for growth.
Some of these genes encode traits for antibiotic resistance or resistance to heavy metal, while othersmay produce virulence factors that enable a bacterium to colonize a host and overcome its defences, or have specific metabolic functions that allow the bacterium to utilize a particular nutrient, including the ability to degrade recalcitrant or toxic organic compounds.
Plasmids can also provide bacteria with the ability to fix nitrogen.
Some plasmids, have no observable effect on the phenotype of the host cell or its benefit to the hostcells cannot be determined, and these plasmids are called cryptic plasmids.
Fertility F-plasmids , which contain tra genes. They are capable of conjugation and result in the expression of sex pilli. Resistance plasmids , which contain genes that provide resistance against antibiotics or poisons. Col plasmids , which contain genes that code for bacterial toxins(colicins) that can kill other bacteria. Degradative plasmids , which enable the digestion of unusual substances, e.g. toluene and salicylic acid. Virulence plasmids , which turn the bacterium into a pathogen, e.g. Ti plasmid.
Plasmids are the most-commonly used bacterial cloning vectors.
Protein production
Gene therapy
