Video Transcript
Using plasmids to form recombinant
DNA is a crucial part of cloning DNA. In which microorganisms were
plasmids originally discovered?
Let’s look at an example of cloning
the interferon gene in order to answer this question. Interferons are proteins that can
interfere with viral replication. As such, they can be used
effectively as antiviral drugs. They can also be used to treat
certain diseases, such as cancer and multiple sclerosis. In the past, interferon was
extracted from cells, which made it very expensive. These days, a process called DNA
cloning can be used. This makes it possible to make a
copy or clone of the gene for interferon. This process starts with isolating
the gene for interferon and inserting it into a circular piece of bacterial DNA
called a plasmid.
Plasmids were originally discovered
in bacteria and are extrachromosomal pieces of DNA that replicate independently. A single cell can have hundreds of
copies of a single plasmid. In cloning, they’re used to carry
genes that we’re interested in making copies of. So, in this context, they’re
sometimes called vectors or carrier DNA. On the left, you’ll notice that
this construct we’ve made contains DNA from two sources. One is the DNA from the human
interferon gene, and the other is the plasmid DNA from the bacteria. When two sources of DNA are
combined like this, we call it recombinant DNA.
In the final step of the cloning
process, this recombinant DNA can then be transferred into bacterial cells. Here, the bacterial cell can
express this gene to produce the interferon protein. Only one copy of the recombinant
DNA is shown here. But it will replicate in the cell
to make many copies. And there will be even more copies
as the bacteria divide. This will lead to a lot of
interferon production, which can then be extracted and used for medical
purposes. Plasmids are a crucial part of DNA
cloning because they’re used to carry the gene we want to clone. Plasmids were originally discovered
in bacteria.
