Summary
Small circular DNA molecules in bacteria that often carry genes for antibiotic resistance.
In depth
Plasmids replicate independently, ranging from 1 to hundreds of kilobases. R plasmids carry resistance genes, F plasmids encode conjugation. They are used as cloning vectors.
Plasmids can carry virulence, metabolism and resistance genes. Incompatibility groups prevent coexistence of related plasmids. Cells may carry several.
Example: the Ti plasmid in Agrobacterium causes crown gall.
Plasmids are usually circular, double-stranded DNA with an origin of replication; copy number varies from one to hundreds. Incompatibility groups define plasmids that cannot be kept together. Besides resistance, they may carry genes for toxins, metabolism of unusual compounds (such as toluene) or symbiosis (the Ti plasmid of Agrobacterium causes crown gall in plants).
As cloning vectors they have an origin, a selectable marker and a multiple cloning site, and are introduced by transformation. Plasmids are also used for DNA vaccines and CRISPR delivery. Curing removes them using agents like acridine dyes.
Example: the pUC19 plasmid carries ampicillin resistance and lacZ for blue-white screening.
Frequently asked questions
What is Plasmids?
Small circular DNA molecules in bacteria that often carry genes for antibiotic resistance.
Which area of biology covers Plasmids, and how advanced is it?
Plasmids is one of the 54 topics in Microbiology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Bacteria, Bacterial Genetics, Conjugation.
Can you give an example of Plasmids?
Ampicillin resistance on pUC plasmids is used as a selectable marker.
What should I learn before Plasmids?
Work through the Beginner topics in Microbiology first, such as Microorganisms, Bacteria, Archaea, then return to Plasmids. Intermediate topics assume the Beginner vocabulary.
What topics are related to Plasmids?
The closest topics to Plasmids are Bacteria, Bacterial Genetics, Conjugation, Quorum Sensing. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Plasmids?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Plasmids. To practise the whole of Microbiology, use the Microbiology quiz.
How is Plasmids different from Bacteria?
Plasmids: Small circular DNA molecules in bacteria that often carry genes for antibiotic resistance. Bacteria: Single-celled prokaryotes found everywhere, vital for nutrient cycling, digestion and some disease. Read both side by side and note what each one explains.
How should I study Plasmids step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Bacteria and explain the difference aloud. Finally, take the Microbiology quiz and come back to this page for any question you miss.