any newcomer who joins a molecular
biology lab will undoubtedly be asked to
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 heretics I know plasmic
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
it Latin for it in nature plasmids often
contain genes that provide a competitive
advantage giving its host bacterium and
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
resistant 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 change 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
[Music]
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 bacteria 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 to catch our newest
videos subscribe to the add gene YouTube
channel and visit blog at gene org for
more plasmid info
[Music]