Plasmid
Molecular Biology · Microbiology · Biotechnology
Say it: PLAZ-mid
A plasmid is a small, usually circular DNA molecule that copies itself independently of the main chromosome, found mostly in bacteria.
Also: plasmids
Definition
What is a plasmid?
Plasmids are extra pieces of DNA that exist alongside the main chromosome, most often in bacteria but also in archaea, yeasts and some other organisms. They are usually circular and double-stranded, carry relatively few genes and have their own origin of replication, so they are copied independently of the chromosome. A single cell may hold one copy or many.
Plasmid genes are rarely needed for everyday survival, but they can give the host a real advantage, such as resistance to antibiotics, the ability to make toxins or the means to break down unusual nutrients. Many plasmids can move from one bacterium to another, sometimes between species, which is a major reason antibiotic resistance spreads so quickly.
In the lab, plasmids are the standard vectors for cloning. Scientists cut a plasmid and a gene of interest with the same restriction enzyme, join them with DNA ligase and introduce the recombinant plasmid into bacteria, which copy the gene each time they divide. An antibiotic resistance gene carried on the plasmid lets researchers pick out the cells that took it up. The geneticist Joshua Lederberg coined the word in 1952.
Word parts
Where does the word “plasmid” come from?
- plasm-
- something formed or moldedGreek plasma
- -id
- a body or particlesuffix used in biology
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Related
Terms that go with it
- BacteriumA bacterium is a single-celled prokaryote with no nucleus, found in almost every habitat on Earth, including in and on the human body.
- Antibiotic resistanceAntibiotic resistance is the ability of bacteria to survive and multiply despite an antibiotic that once killed them or stopped their growth.
- Molecular cloningMolecular cloning is a set of laboratory methods for inserting a specific DNA fragment into a vector and copying it many times inside host cells.
- Recombinant DNARecombinant DNA is DNA made in the laboratory by joining pieces of DNA from different sources, often different species, into one molecule.
- Restriction enzymeA restriction enzyme is a bacterial protein that cuts DNA at a specific short sequence, making it a basic tool for cutting and joining DNA.
- Genetic engineeringGenetic engineering is the direct change of an organism's DNA using laboratory techniques, to add, remove or alter genes and give it new traits.
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Written for biofideX in plain words, after checking these references:
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