Vectors, Inserts, and Host Systems
The Cloning Vehicle
What a vector must do
A cloning vector needs an origin of replication, a selectable marker, and one or more cloning sites. These features allow the DNA construct to persist, be selected, and receive the insert.
Major vector types
Plasmids
- Small circular DNA molecules
- Easy to manipulate and widely used for routine cloning
Bacteriophage and cosmids
- Can carry larger inserts
- Useful for larger DNA libraries
Insert design
Successful cloning often depends on choosing the correct insert boundaries, preserving reading frames when needed, and avoiding internal restriction sites that conflict with vector construction.
Host systems
Most routine cloning uses bacterial hosts such as because they grow quickly and are easy to select and screen. Some applications use yeast, insect, or mammalian cells when the biological context requires eukaryotic processing.
Which feature is essential for a plasmid vector to be maintained inside a bacterial host?
An origin of replication allows the plasmid to be copied as the host cell divides.
Correct answer: An origin of replication
Why might a researcher choose a BAC instead of a standard plasmid?
BACs are used when insert size exceeds typical plasmid capacity.
Correct answer: Because a BAC can carry much larger DNA inserts than a standard plasmid.
Vector components