PLASMIDS EXPLAINED

Plasmids are small circular pieces of DNA with the ability to replicate separately from the host DNA. Typically plasmids contain at most a couple thousands of base pairs which is significantly less than the rest of the genome. Plasmids are small, stable and easy to manipulate. Plasmids exist inside microbes such as bacteria.

The usefulness of plasmids lie in that they can be used as vectors in the lab, meaning that we can utilize them to introduce foreign DNA into cells through electroporation or other methods. As for the bacteria themselves, plasmids often contain genes that give the bacteria a competitive advantage to allow for survival in extreme conditions.

Let us take a look at how plasmids work and why they can be so useful in the lab:

1. The first thing we find on this map of the plasmid is the ORI or “Origin of Replication”. From here replication of the plasmid begins.
2. Following the ORI we find a selectable marker. The selectable marker allows for differentiation of bacteria in which the engineered plasmid has been successfully inserted. One often utilized selectable marker is the gene for antibiotic resistance which also often occurs in nature. As the name suggests this makes the bacteria resistant against antibiotics allowing for a simple screening process where all bacteria not containing the engineered plasmid simply die.
3. The gene which we wish to express inside the cell can be inserted in between two restriction sites which are located in what’s called a multiple cloning site, which is a short segment of DNA containing several restriction sites. These restriction sites make it easier to insert the gene of interest at this location.
4. The promoter located before the first restriction site ensures that this inserted gene gets expressed.

By manipulating plasmids and inserting new genes of interest we create a so called recombinant plasmid.