design...

construct...

or modify a plasmid.

But what exactly is a plasmid, and why is it so useful in the lab?

At their most basic level, plasmids are small circular pieces

of DNA that replicate independently from the host from a seminal DNA compared to

the millions or billions of bases that make up the entire genome plasmids

typically contain a couple thousand at most.

They're relatively small, stable,

and easy to manipulate

So where do plasmids come from?

In nature they're found in microbes, like bacteria.

In the 1940s scientists, began noticing

that there are heritable cytoplasmic factors that could be transferred between cells.

But there was no consensus on what they were or what to call them

It wasn't until 1952 that Nobel laureate Joshua Lederberg coined the term plasmid

a combination of the words cytoplasm and id (Latin for "it").

In nature plasmids often contain genes that provide a competitive advantage,

giving its host bacterium an ability that it didn't have before

These benefits include antibiotic resistance,

the wherewithal to survive in harsh environments,

and even the ability to wage war to gain an environmental advantage.

But plasmids aren't just useful to bacteria.

because they're incredibly easy to manipulate,

they've also made themselves indispensable to

life scientists and bioengineers.

Plasmids created in the lab are known as

constructs or vectors.

To understand what plasmids can do let's break down its

parts using a plasmid map.

All plasmids contain an origin of replication, or Ori.

It tells the plasmid where to begin replication.

Plasmids often contain genes that are advantageous for survival.

One of the most common naturally occurring,

types of genes is antibiotic resistance.

When used in the lab, antibiotic

resistance genes allow scientists to separate out cells that contain plasmids

from those that don't.

The wonderful thing about plasmids is that they can be

easily engineered and can introduce foreign DNA into cells through electroporation,

or other methods.

Many plasmids are designed so scientists can

insert genes they want to be expressed in organisms.

One way to do this is through restriction sites.

Restriction enzymes recognize these sites and cut

out the present gene like molecular scissors.

Then a different gene can be inserted into the site.

Often these restriction sites are located in what's

called a multiple cloning site,

a short segment of DNA that contains several restriction sites.

This adds flexibility to the cloning process.

How is the inserted gene expressed?

A promoter site which is upstream of the inserted gene on the plasmid,

acts as a green light that allows gene transcription

RNA polymerase binds to the promoter moving along the strand.

As it moves along the strand, it creates a new strand of mRNA, expressing the gene.

The plasmid cloning process is very versatile so there's a whole array of genes that

scientists can introduce into the cell

for example if you wanted to track a specific species of bacteria in a

population you could insert a GFP expressing gene into a plasmid and

transform it into your bacterium.

Your cells will fluoresce making, them easier to find.

Or if you're trying to study the effect of a specific protein on a phenotype,

you could insert the gene of interest into the plasmid.

Move this into a cell,

and look for changes in the cell

We hope you enjoyed this video in our Plasmids 101 series.

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and visit blog.addgene.org for more plasmid info