Plasmid
Definition
A small, circular, double-stranded DNA molecule that replicates autonomously inside a bacterial cell. Used as a cloning vector when equipped with a selectable antibiotic-resistance marker, an origin of replication, and a multiple cloning site.
- Structure
- Small, circular, double-stranded DNA
- Replication
- Autonomous, independent of the host chromosome
- Cloning vector requirements
- Selectable marker, origin of replication, multiple cloning site
- Host organism
- Typically bacteria
Common questions
Why is an antibiotic-resistance marker included on a cloning plasmid?+
Growing transformed bacteria on antibiotic-containing media kills cells that failed to take up the plasmid, so only cells carrying the vector and its marker survive, giving a simple way to select for successfully modified bacteria.
What role does the multiple cloning site play in plasmid-based cloning?+
It provides a cluster of unique restriction enzyme cut sites close together, letting researchers cut the plasmid open at a convenient location and insert a foreign DNA fragment without disrupting the plasmid's replication or marker genes.
Related terms
- Bacterial Artificial Chromosome (BAC)
- An F-plasmid-derived cloning vector capable of carrying 100-300 kb inserts stably in E. coli at one copy per cell. The Human Genome...
- Blue-White Screening (Alpha-Complementation)
- A colony selection method for pUC-family vectors in which intact lacZ-alpha produces functional beta-galactosidase that cleaves X-gal to a blue indigo product....
- Multiple Cloning Site (MCS)
- A short stretch of synthetic DNA containing a cluster of unique restriction sites, engineered into cloning vectors such as pUC19 and pBlueScript...
- RFLP (Restriction Fragment Length Polymorphism)
- The first DNA profiling method used in forensic casework, developed by Alec Jeffreys in 1984. Restriction enzymes cut DNA at specific sequences,...
- Sticky End (Cohesive End)
- A single-stranded overhang generated when two cuts on opposite strands of a DNA duplex are offset rather than directly opposite each other....
- Type II Restriction Endonuclease
- A bacterial enzyme that cleaves double-stranded DNA at a specific palindromic recognition sequence, generating fragments whose ends reflect the exact geometry of...