When DNA forms into little rings outside of living cells, we get plasmids. Plasmids exist everywhere in nature, and are how bacterial cells become resistant to viruses and antibiotics. 

How do bacteria use plasmids to become resistant to viruses and antibiotics?

Basically, when a bacterial cell dies following a battle with a virus or an antibiotic, it leaves behind little bits of DNA- many of which are plasmids- that can tell other bacterial cells how it died. The surviving bacterial cells can then take in those plasmids and incorporate the plasmid DNA into their own DNA, so that they can survive what the other cell didn’t. 

This process is known as cellular transformation. 

How exactly does cellular transformation work?

First, a living bacterial cell must come across a dead bacterial cell that has left behind a few plasmids. The living bacterial cell then reads the DNA from the dead cell and “learns” about what killed the cell, and how to not die from the same thing. If the cell determines that some of the information is useful, it uses various enzymes (AKA Molecular Scissors) to cut open the useful DNA plasmid so it is a string instead of a ring.

Then, the bacterial cell cuts its own DNA open with the same enzymes, and through a series of very complicated DNA-healing steps, can integrate the plasmid DNA into its own DNA. That way, when the transformed living cell comes across the same thing that killed the other cell, it can defend itself from it. 

Many plasmids come equipped with molecular scissors that can chop up DNA and RNA from outside sources, the most notable one being an enzyme called Cas9. Enzymes such as Cas9 can read DNA and RNA that the bacterial cell comes across and takes in from its environment. If a virus attempts to hijack a transformed cell, the cell’s new Cas9 scissors can be used to chop up the viral DNA/RNA, preventing the virus from hijacking the cell. 

Since 2012, scientists have figured out how to make Cas9 cut specific portions of cellular DNA, so that new DNA sequences- made by the scientists themselves- can be incorporated into a cell’s genome, permanently. 

This technique- colloquially known as “CRISPR”, which stands for Clustered Regularly Interspaced Short Palindromic Repeats- has been used to cure genetic conditions such as Sickle Cell Anemia and an unknown metabolic syndrome in a baby named KJ in 2025. 

Indeed, CRISPR has been, is being, and will continue to be used to literally cure genetic conditions!