Genetic Engineering


[MUSIC PLAYING] Hey there. You may be wondering
what you’re doing at the front of a
bioengineering lab, and why a total stranger is
talking to you right now. But I’m here to talk about
some of the awesome experiments that Herbert Boyer and Stanley
Cohen did in the 1970s. You might be thinking to
yourself, uh– the ’70s? Isn’t that like, when
the dinosaurs lived? Boring. Well, have you ever
gotten a vaccine or eaten groceries
from a grocery store? That’s all thanks to
some of the experiments that these two lab
pals did in the ’70s, where they took enzymes
that cut DNA, and were able to enter these pieces
into new bacterial DNA. They pioneered the field
of genetic engineering. And thanks to all the
work that they did, we have medications for people
with diabetes and heart attack victims. You know what? Why don’t you guys
just follow me inside. So the first thing that
Cohen and Boyer did was they took DNA from a frog
and cut it up into pieces. I should probably
explain to you guys what’s going on in this tube. Here’s some DNA from the frog. It encodes certain traits that
affect how the frog develops, how it survives, how it looks. Now there’s a piece of DNA
in this genome whose job is to encode for certain proteins
that the frog uses to survive. We’re going to cut this piece
out using a restriction enzyme. This is the thing
that Boyer discovered. It’s kind of like
a pair of scissors. By cutting the DNA
at specific points, we can get different pieces. Now there are tons of different
kinds of restriction enzymes, and they all cut in
different places in DNA. Our enzyme that we’re using
today is called EcoR1. Now this piece of DNA
has more than one spot that EcoR1 can cut, as
shown by the dotted lines. So we’re going to end up
with other pieces of DNA in addition to the
one we actually want. Now that’s actually
OK, because we’re going to deal with
that problem later. What’s going on the tube is
we’re literally just cutting up our piece of DNA,
just like this. Now here’s a tube
full of plasma. It’s basically a
circular ring of DNA that can exist in bacteria. And it basically encodes
for certain traits that affect how bacteria
look, or act, or survive. Now to add our DNA from the
frog DNA to our bacterial DNA, we need to cut the
plasmid open too. So we’ve got to add
our EcoR1 scissors, and they’re going
to cut at this site. You let this reaction proceed,
letting all the ingredients– the plasmids, the restriction
enzyme, and some water and buffers to hang out together
until all the plasmids are cut like this. Now we need to add the
DNA pieces from the frog and allow them the pieces
to join our cut plasmids. Here’s what’s going
on in the tube now. I’ve got pieces of frog DNA. And I’ve got cut
plasmids, like this. I need to add this
guy into this plasmid. And the way I’m going to do
that is by adding an enzyme called DNA ligase. This enzyme kind
of acts like tape, and it fixes the DNA
insert into the plasmid. Now another important
thing about the plasmid itself is that it
carries a marker that makes it resistant to a certain
kind of antibiotic called tetracycline. This will come in
handy in a little bit. After a little while, we’ll have
a couple types of DNA going on. This is the one that we want. It’s plasmid, and it has
the purple frog DNA insert. But we’ll also get
things like this. We’ll get plasmids that had
other parts of the frog’s genome inserted into it. And we’ll also get
plasmids that just close back up on themselves. So now that we have
these new plasmids, we’ve gotta stick them
into some bacteria. Here we’re gonna
take some E. coli. As you can see, it already
has some DNA in it. The important thing
about these guys is that they’ll
actually die if you add the tetracycline
antibiotic, which we talked about earlier, to them. What Boyer and Cohen did to get
the plasmids inside of these E. coli is that they cooled all
the cells down, and then quickly heated them up, creating little
holes in the cell membrane. Then the plasmids could slip
through and get into the cell. These are the kind of
bacteria that we have now. Bacteria that got the
plasmid we wanted. These are the guys we wanted. But we’ll also get bacteria
that got the plasmids that we didn’t want. Say, this one with the
wrong piece of DNA, or this one with just a plain
plasmid without any frog DNA. And more than likely, we’ll get
ones that just didn’t pick up any of the plasmids. Now what I’m going to do
next is plate these cells on some tetracycline
agar plates, which is basically
some fancy jello that has antibiotic in it. So these guys won’t
be able to grow. But these guys will. I’ve plated the E. coli
that we transformed with our new plasmids
onto this plate, which has tetracycline in it. We’re going to let this
sit in the incubator overnight and allow
our bacteria to grow. And we’ll check on it
again in the morning. Alright. So as you can tell,
we’ve definitely got some colonies that grew
on our plate overnight. So now the problem
that we have is we need to be able to
distinguish the bacteria that got these plasmids
from the ones that got these plasmids, which don’t
have our frog DNA in them. So what we’re going to do
is use the same techniques that we did at the very
beginning of this experiment, and extract the plasmids
from all these bacteria. Then we’re going to use the
same restriction enzymes and cut up these plasmids. You might be able to notice
that our frog purple insert is a different size than the pink
that comes from the background frog DNA. So what we can use is
something called a gel box, and use a technique called
gel electrophoresis. And what it’s
going to do is it’s going to separate our
different pieces of DNA out. And from this
experiment, we’ll be able to tell the plasmids
that took up the frog DNA from the ones that didn’t,
or s the ones that just closed up on themselves. Thanks to these cloning
techniques that me and my buddy developed, the field of genetic
engineering was pioneered. Things like insulin are
being made these days using these very
same techniques. Well, that’s all I’ve
got time for today, guys. Thanks for stopping by. Hopefully you have a
better appreciation for some of the
cloning techniques you saw today, and just
have a better understanding of genetic engineering. See you guys later. [MUSIC PLAYING]

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