by Microbiology Doctor-dr
Plasmids- Definition, Properties, Structure, Types, Functions, Examples
What are Plasmids?
- Plasmids are double-stranded, self-replicating additional chromosomal structures found in a wide range of bacteria.
- Joshua Lederberg created the word "plasmid" in 1952.
- Plasmids are useful genetic tools for introducing, manipulating, or deleting certain genes from the host cell.
Plasmid Characteristics
- Extra chromosomal DNA fragments may be found in the cell.
- They're made up of two strands. The linear plasmids seen in bacteria such as Streptomyces spp. and Borrelia spp. are exceptions.
- They have the ability to multiply on their own.
- The lack of a plasmid in a cell has no effect on its function, whereas the presence of a plasmid is typically helpful.
- Sex factors, conjugants, extrachromosomal replicons, and transfer factors are all terms for plasmids.
- The copy number refers to how many copies of the plasmid are present in the bacterial cell. Tiny plasmids are usually found in huge quantities, whereas giant plasmids are found in small numbers.
- The ability of two distinct plasmids to live in the same bacterial cell is referred to as plasmid compatibility.
Plasmids' Structure
1. There are some necessary ingredients in every plasmid. The following are some of them:
- OR stands for origin of replication, and it refers to the point in the strand where the replication process starts. This is an A=T rich area in plasmids because it is simpler to separate the strands during replication.
- Selectable marker site - This area contains antimicrobial resistance genes that may be used to identify and select bacteria that carry plasmids.
- This is where the transcriptional machinery is loaded in the promoter region.
- The primer binding site is a short single-strand DNA sequence that is used in DNA amplification and sequencing.
- Multiple cloning sites — This site comprises a number of sequences that restriction enzymes may bind to and break the double-stranded structure.
2. The plasmid's size ranges from 2 to 200 kb.
3. It is the cell's extrachromosomal element that is not essential for the cell's growth and development.
4. The TRA gene, which is the transferred gene and is required for plasmid transfer from one cell to another, is found in the majority of plasmids.
Plasmid structure
Plasmid Transfer
Conjugation is the process of transferring plasmids:
- A donor cell and a recipient cell are involved in the conjugation process.
- The donor cells generate a pilus, which binds to the receiving cell and forms a conjugation bridge.
- From the donor to the recipient cell, one copy of the plasmid is transmitted.
The other methods by which the plasmids can be transferred are transduction and bacterial transformation.
Conjugation
Types of Plasmids
Plasmids may be divided into two categories based on the presence of the TRA gene:
1. Conjugative plasmids - these plasmids are typically found in bacteria and include the TRA (transfer) gene.
2. Non-conjugative plasmids are those that do not include the TRA genes.
Plasmids may be categorized into the following kinds based on their functions:
1. F Plasmids (Fertility plasmids)
- F Plasmids are a kind of plasmid that may be found in (Fertility plasmids)
- They carry the TRA genes and may therefore be passed from one cell to the next.
- They have the ability to multiply inside the bacterial cell.
- They trigger the formation of a pilus, a lengthy protein-rich structure that aids in cell-cell communication.
- It also includes a sequence that causes incompatibility.
2. plasmid R (Resistance plasmids)
- These plasmids carry and transfer antimicrobial resistance genes from one cell to the next.
- Antibiotic resistance genes protect bacteria against antibiotics used in human treatment as well as antibiotics found naturally in the environment.
- These plasmids are generally huge in size and have a low number of copies in the cell.
3. Col Plasmids (Colicin plasmids)
- Col Plasmids are a kind of plasmid that may be found in (Colicin plasmids)
- Bacteriocin-producing plasmids are known as bacteriocinogenic plasmids.
- These proteins have the capacity to kill bacteria without Col plasmids, which are closely related.
- In E. coli, these plasmids have been found.
4. Degradative Plasmids
- These plasmids can digest uncommon chemicals including toluene, camphor, and salicylic acid, among others.
- The presence of these plasmids in the organism allows diverse drugs and substances to be broken down.
5. Virulence Plasmids
- These plasmids generate virulence factors, which allow bacteria to infect other cells. Bactria with virulence plasmids may infect cells from plants, animals, and humans.
- The Ti plasmid, for example, is a virulence plasmid found in the Agrobacterium tumefaciens bacteria that causes crown gall disease in plants.
Functions and Applications of Plasmids
- Because of their ability to include a gene and reproduce inside the cell, plasmids may be employed as vectors to introduce a specific gene into other species.
- Antibiotic resistance genes are carried by them, making them an essential element in bacteria.
- Degradative plasmids can be employed to break down environmentally hazardous industrial compounds.
- Plasmids are also employed in gene therapy since they are simple to control.
- Plasmids are employed in medicine administration and hormone synthesis in other cells because they are good vectors (a vehicle/factor that is used to transmit a gene from one organism to another).
- Horizontal gene transfer is facilitated by plasmids.
Plasmid Examples:
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Plasmid Examples
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Plasmid Examples
