DNA cloning and recombinant DNA | Biomolecules | MCAT | Khan Academy

- [Voiceover] Let's talk a
little bit about DNA Cloning.

Which is all about making identical copies

of a piece of DNA.

And usually it's a piece of DNA

that codes for something we care about,

it is a gene that will
express itself as a protein

that we think is useful in some way.

Now you might have also
heard the term cloning

in terms of the Clone Wars in Star Wars

or Dolly the sheep

and that is a related idea.

If you're cloning an animal
or an organism, like a sheep,

well then you are creating an animal

that has the exact genetic
material as the original animal.

But when we talk about
cloning and DNA cloning

we're talking about something
a little bit simpler.

Although, as we'll see, it's
still quite fascinating.

It's identical copies of a piece of DNA.

So how do we do that?

Well let's say that this is a
strand of DNA right over here

and I'm just drawing it as a long,

but this is a double-stranded,

and I'll just write it down,

this is double stranded.

I don't want to have to take the trouble

of keep drawing the multiple strands.

Actually, let me just draw,

let me just try to draw the two strands

just so we remind ourselves.

So there we go.

This is the double-stranded DNA

and let's say that this part of this DNA

has a gene that we want to clone.

We wanna make copies of
this right over here.

So gene to clone.

Gene to clone.

Well, the first thing we wanna do

is we wanna cut this gene out some how.

And the way we do that

is using restriction enzymes.

And there's a bunch of
restriction enzymes,

and I personally find it fascinating

that we as a civilization
have gotten to the point

that we can find and
identify these enzymes

and we know at what points
of DNA that they can cut.

They recognize specific sequences

and then we can figure out

well which restriction
enzyme should we use

to cut out different pieces of DNA,

but we have gotten to that
point as a civilization.

So we use restriction enzymes.

We might use one restriction enzyme,

Let me use a different color here,

that latches on right over here

and identifies the genetic
sequence right over here

and cuts right in the right place.

So that might be a restriction
enzyme right over there

and then you might use
another restriction enzyme

that identifies with the
sequence at the other side

that we wanna cut.

So let me label these.

These, those things right over there

those are restriction enzymes.

Restriction enzymes.

And so now you would have,

after you applied the restriction enzymes,

you will have just that gene.

You might have a little bit
left over on either side

but essentially you have cut out the gene.

You've used the restriction
enzymes to cut out your gene

and then what you wanna
do is you wanna paste it

into what we'll call a plasmid.

And a plasmid is a piece
of genetic material

that sits outside of chromosomes

but it can reproduce along,

or I guess we can say can replicate

along with the machinery of the,

the genetic machinery of the organism.

Or it can even express itself

just like the genes of the organism

that are in the chromosomes,
express themselves.

So then so this is where we cut,

let me write this,

we cut out the gene

and then we wanna paste it

then we wanna paste it into a plasmid.

And plasmids tend to be circular DNA

so we will paste it into a plasmid.

And in order for them to fit

there's oftentimes these
overhangs over here.

So you might have an overhang over there,

you might have an overhang over there.

And so the plasmid that we're placing in

might have complimentary base
pairs over the overhangs,

which will allow it easier,

it will become easier for
them to react with each other

if they have these overhangs.

So let me, we're pasting
it into the plasmid.

And this is amazing

because obviously DNA,

this isn't stuff that we can, you know,

manipulate with our hands

the way that we would copy
and paste things with tape.

You're making these solutions

and you're applying the
restriction enzymes.

The restriction enzymes are just in mass

cutting these things.

They're bumping in just the right way

to cause this reaction to happen

then you're taking those genes

and you're putting them with the plasmids

that happen to have the
right sequences at their ends

so that they match up

and then you also put in
a bunch of DNA ligase.

DNA ligase,

to connect the backbones

right over here.

And we also saw DNA ligase
when we studied replication.

So that is DNA ligase,

which you can think of
it as helping to do,

helping to do the pasting.

And so now we have this plasmid

and we want to insert it into an organism

that can make the copies for us.

And an organism that's typically used,

or a type of organism is bacteria
and E. coli in particular,

and so what we could do is,

we could, let's say that we have a bunch,

let's say you have a vial right over here.

You have a vial and it
has a solution in it

with a bunch of E. Coli.

A bunch of E. coli.

And you actually wouldn't
be able to see it visually

but there is E. coli in that solution.

And then you would put your plasmids,

which would be even harder to see,

in that solution and
somehow we want the E. coli,

we want the bacteria
to take up the plasmid.

And the technique that's typically done

is giving some type of
a shock to the system

that makes the bacteria
take up the plasmids.

And the typical shock is a heat shock.

And this isn't fully understood

how the heat shock works

but it does

and so people have been
using this for some time.

So if you have a bacteria,

you have a bacteria right over here,

it has its existing DNA,

so this is its existing genetic material

right over there, let me label this.

This is the bacteria.

You put it in the presence of our plasmids

so you put it in the
presence of our plasmid

and you apply the heat shock

and some of that bacteria is
going to take in the plasmid.

It's going to take in the plasmid.

And so just like that,
it's going to take it,

it's going to take it in.

And so what you then do

is you place the solution
that has your bacteria,

some of which will have
taken up the plasmid,

and you put it

and then you try to grow
the bacteria on a plate.

So let me draw that.

So let me draw,

so here we have a plate

to grow our bacteria on,

and it has nutrients right over here

that bacteria can grow on.

It has nutrients.

It has nutrients, and so you could say,

okay well put this here

and then a bunch of
bacteria will just grow.

So you would see things like this,

which would be many, many,
many cells of bacteria,

there would be colonies of bacteria.

You could just let them grow

but there's a problem here.

Because I mentioned some of the bacteria

will take up the plasmids

and some won't.

And so you won't know,

hey when this bacteria,

when it keeps replicating
it might form one of these,

it might form one of these colonies.

So this is a colony that you like.

So this one is a good colony,

put a checkmark there.

But maybe this colony is
formed by an initial bacteria

or a set of bacteria that
did not take up the plasmid

so it won't contain the
actual gene in question.

So you don't want that one.

So how do you select for the bacteria

that actually took up the plasmid?

Well, what you do is

besides the gene that you care about

that you want to make copies of,

you also place a gene

for antibiotic resistance

in your plasmid.

So now you have a gene for
antibiotic resistance here,

and so only the bacteria,

and I think it's amazing
that we as humanity

are able to do these types of things,

but now only the bacteria
that have taken up the plasmid

will have that antibiotic resistance.

And so what you do is in your nutrients

you grew nutrients plus antibiotics,

plus an antibiotic.

Antibiotic, and so this one will survive

'cause it has that resistance.

It has that gene that allows
it to not be susceptible

to the antibiotics.

But these are not going to survive.

They're not even going to happen.

They're not even going to grow

because there's antibiotics mixed in

with those nutrients.

And so this is a pretty cool thing.

You started with the gene
that you cared about,

you cut and pasted it into our plasmid.

Let me write the labels down,

into our plasmid that
also contained a gene

that gave antibiotic resistance

to any bacteria that takes up the plasmid.

You put these plasmids in
the presence of the bacteria

or you provide some type of a shock,

maybe a heat shock, so that
some of the bacteria takes it up

and then the bacteria starts reproducing.

And as it reproduces it also
is reproducing the plasmids

and because it has this
antibiotic resistance

it is going to grow on this
nutrient antibiotic mixture

and the other bacteria that
did not take up the plasmids

are not going to grow.

And so just like that you can take this,

you can take this colony right over here,

and put it into another solution

or continue to grow it

and you will have multiple
copies of that gene

that are inside of that bacteria.

Now the next question,

and I'm over simplifying
things fairly dramatically

is well you now have a bunch of bacteria

that have a bunch of copies of that gene,

how do you make use of it?

Well, the bacteria themselves,

let's say that gene is for
something you want to manufacture

say insulin for diabetics,

well you could actually use
that bacteria's machinery,

we used its reproductive machinery

to keep replicating the
genetic information,

but you can also use its
productive machinery,

I guess you could say,

it's going to express its existing DNA

but it can also express the
genes that are on the plasmid.

And in fact that's what
would give the bacteria

its antibiotic resistance

but if this gene was say for insulin,

well then the bacteria will
produce a bunch of insulin,

a bunch of insulin molecules,

which you might be able
to use in some way.

And I'm not going to
go into all the details

of how you will get the insulin out

and how you could make use of it,

but needless to say,

it's pretty cool that we
can even get to this point.