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Short answer
A plasmid vector is a plasmid that has been engineered in the lab to carry foreign DNA into a cell. “Plasmid” names what the molecule is, a small circular DNA that copies itself independently of the host chromosome. “Vector” names the job it does, which is to carry a DNA insert. Every plasmid vector is a plasmid; not every vector is a plasmid.
Definition and scope
The NHGRI Genetics Glossary defines a plasmid as “a small circular DNA molecule found in bacteria and some other microscopic organisms,” and notes that scientists use recombinant DNA methods to splice genes they want to study into a plasmid. When the plasmid copies itself, it also makes copies of the inserted gene.
Addgene’s “Plasmids 101” describes plasmids as small circular pieces of DNA that replicate independently from the host’s chromosomal DNA and are mainly found in bacteria. It adds that plasmids made in the lab are often called “vectors” or “constructs”: they are artificial and designed to carry foreign DNA into another cell.
Plasmid vs vector
The two words answer different questions. A plasmid is a type of molecule, while a vector is a role. A plasmid becomes a plasmid vector when it is designed to carry an insert. Other carriers also exist; for example, viral vectors deliver a transgene using a virus, which is covered in viral vector types and how each delivers a transgene. Addgene’s own list of plasmid types includes viral plasmids, which shows the categories overlap rather than exclude each other.
How a plasmid vector is used in practice
Addgene states that a lab-created plasmid has, at a minimum, three elements: an origin of replication, a selection marker and a cloning site. The sections below say what each one is and what to look for when reading a vector’s documentation.
Checklist: the three minimum elements
| Element | What Addgene says it is | What to look for in a vector description |
|---|---|---|
| Origin of replication | A DNA sequence that starts replication by recruiting replication machinery proteins; it controls the host range and copy number of the plasmid. | That the origin is named, since it determines which hosts the plasmid can replicate in. |
| Selection marker | Typically an antibiotic resistance gene that allows selection of bacteria that contain the plasmid. | Which marker is present, so the matching selection can be planned. |
| Multiple cloning site (MCS) | A short DNA segment containing several restriction sites for easy insertion of DNA. | That the cloning site is documented, because it is where the insert goes. |
To read these features on a diagram, see how to read a plasmid map. For the workflow that puts an insert into a vector and a vector into a host, see gene cloning, restriction enzyme digest setup and Gibson assembly.
Types of plasmid vectors
Addgene lists these types of plasmids used in the lab:
- Cloning plasmids
- Expression plasmids
- Gene knock-down plasmids
- Reporter plasmids
- Viral plasmids
- Genome engineering plasmids
A plasmid used as a cloning vector, in the sense of “plasmid as cloning vector”, is the first type in that list: its job is to hold and copy an insert. The other types add features for what the insert should then do in the cell.
Where it matters for labs and supply decisions
Because the origin of replication controls host range and copy number, and the selection marker sets how plasmid-containing bacteria are selected, those two features link a vector to the host cells and selective media a lab needs. Hosts are discussed in competent cells. When a vector is received or specified, confirm its three elements against its documentation before ordering the host strain or the selection reagent that goes with it.
Common misunderstandings
“Plasmid and vector are synonyms”
They overlap in lab usage, since Addgene notes lab plasmids are called vectors, but the terms are not interchangeable in general. A vector is any carrier; a plasmid is one kind.
“A vector is a virus”
A vector can be viral, but a plasmid vector is a circular DNA molecule, not a virus. Viral plasmids are one of the plasmid types Addgene lists.
“Any plasmid is a vector”
Plasmids occur naturally in bacteria. NHGRI describes them as found in bacteria and some other microscopic organisms. The term vector applies to those engineered to carry foreign DNA.
FAQ
What is a plasmid vector?
A plasmid designed in the lab to carry foreign DNA into a cell, typically with an origin of replication, a selection marker and a cloning site.
What is the difference between a plasmid and a vector?
A plasmid is a small circular DNA molecule that replicates independently of the host chromosome. A vector is any carrier of foreign DNA, and engineered plasmids are one kind of vector.
Can a plasmid be used as a cloning vector?
Yes. Addgene lists cloning plasmids among the plasmid types used in the lab, and the multiple cloning site is where the insert is added.
Sources
- NHGRI, Talking Glossary of Genomic and Genetic Terms: Plasmid (checked 2026-10-29).
- Addgene blog: Plasmids 101: What is a plasmid? (checked 2026-10-29).
