How to extract DNA from strawberries


Uploaded by GenomeTV on 21.10.2010

Transcript:
Hi, I am Dr. Eric Green. I am the director of the National Human Genome Research Institute,
at the National Institutes of Health. I am here with my wonderful side-kick.
I am Dr. Carla Easter, also at the National Human Genome Research Institute, at the National
Institutes of Health. And I am the education specialist.
And today we're here to --
Isolate strawberry DNA using household things, I guess. Basically, we are going to show you
how to get DNA out of a strawberry.
Okay, great. And why do we pick strawberries?
Well, for me there are many reasons. But first of all they smell really nice. They're very
pretty. The other thing is that they're nice and edible. And their seeds are on the outside
of the strawberry. And I have found that it's very easy to get DNA out of a strawberry.
Although of course, like all living things, they have DNA. We could pick a variety of
different, other things to purify DNA from. We just picked strawberries because it's easy
and they're easy to get.
There we go. So --
Okay.
You ready to start?
Yep. What do we do?
So the first thing we're going to do is take our frozen strawberries, you notice they don't
look like --
And they're a little different than that.
-- those nice strawberries.
Yeah, right.
And we're going to place them in this plastic bag.
And now you can purify DNA from these strawberries or these.
Oh, certainly.
We just picked frozen ones because they're squooshier and mooshier, right?
Yes.
And we're going to --
And you can get them anytime of the year.
Okay. So we're putting them here in the plastic bag.
Yep.
And the reason we're doing that is because the first thing we need to do is bust them
open.
That's right. That's right.
And the reason for that is that the DNA is inside the cells in that strawberry. And we
got that DNA to sort of go into solution, so that we can purify it.
Excellent.
So we do this and I am going to smash them and I am going to point this towards you
--
[laughter]
-- just in case it breaks open, but I know my job here is just to --
-- smash them all up.
Smash them up.
Excellent. So while Dr. Green is smashing, I am going to make what's called a lysis solution.
Lysis?
Lysis.
What does lysis mean?
So lysis means to break open. And the purpose of the lysis solution is to break open the
strawberries cells to get to the DNA, which as Dr. Green said, is inside the strawberries.
And a cell is just basically a bag of living materials and living different kinds of molecules
surrounded by a membrane; sort of think of like Saran wrap, or we could think of it actually
like a water balloon. And we need -- inside instead of water -- there actually is water,
but in there is also DNA. And we're going to use a solution to bust open these cells,
or bust up these teeny, teeny, little, water balloons.
Excellent. So we're going to use household chemicals, as we said, at the beginning. This
is just regular detergent.
Just like for cleaning dishes.
Exactly. Or you could use hand soap or shampoo. Works really well. So two teaspoons of detergent.
We're going to take a half of teaspoon of salt, and then we're going to add half a cup
of water.
Okay.
And I am going to stir this up.
Okay, I think the strawberry puree is --
Is all ready?
-- is ready to go.
Perfect.
So here we go. Detergent and the salt together are just going to bust open those little cells,
those little water balloons. I am going to do this. I know I am not supposed to pound
on it anymore --
That's right.
-- otherwise we actually will get a shower.
There we go.
With soap and all.
So the point is you don't want to create a lot of bubbles as your mixing the lysis solution
around with your strawberry puree.
Otherwise, you just have a bubble bath.
That's right.
Okay, so we're just --
[inaudible]
-- I can hear the water balloons just busting out from the sides.
Can you hear that DNA coming out?
It is and it's saying, “I am free, I am free, I am liberated, I am in the solution
now.”
Excellent.
But now we have all bits and pieces of strawberries mixed in with all this liquid. So that's probably
a little bit too ooky for what we need to do.
Exactly. It would be very hard for us to see the DNA in this mess that we've created.
Right.
So what we're going to do is filter it. And as you can see I am using just a regular coffee
filter. Just one that you would use for making coffee at home in a coffee maker. And --
And it's just going to pull out, separate out the liquid from the strawberry guck. Guck
is technical term we use here in genetics.
That's right, all the time.
So I am going to pour.
Good.
We don't actually need all of it, we just need a good amount, right?
Exactly. And what I am going to do is just fold the edges up, and make just a small little
sac; and this just makes it easier to push the DNA that's in the liquid away from the
big pieces of strawberry. And you want to be gentle. You don't want to squeeze so hard
that you actually break the filter, otherwise --
The guck --
-- the guck will go back in there.
Just like coffee grounds that would just get in your coffee.
Exactly. Okay, does that look good?
Looks good.
Perfect.
Alright so this is basically the material that was in the cells of the strawberry.
[assent]
And it has lots and lots and lots of different kinds of chemicals in there, because all the
contents of a strawberry cell. But the good news is that a lot of DNA should be there
because strawberries have a lot of DNA.
Yep.
And so we need to get the DNA out of solution because it's now dissolved --
Right.
-- in the detergent.
So we're going to do what's called, “precipitation.”
Okay. Precipitation.
Precipitation.
So, it's going to rain?
It's going to rain.
Okay.
Basically.
All right.
So when you think about precipitation in this case, hopefully, if we've done this right
the DNA will fall out of solution. We'll actually get to see the DNA start to form. Just as
the rain comes out of the clouds or the snow, we'll see DNA start to form in our solution
here.
Or in science, or in particular in chemistry, when you talk about precipitation, it's often
about something that's in solution becoming solid again, or becoming material that you
could then see, and then manipulate not in a liquid form. And so we're going to try to
get the DNA to come out of solution.
Excellent.
So to do that, what do we do?
We're going to use just regular rubbing alcohol. Just any old rubbing alcohol that you would
buy at any old drugstore.
Right. Okay.
And this is not the alcohol you drink.
Nope, certainly not. And we're just going
to pour an equal amount, right --
[assent] That's right.
-- to the strawberry juice, if you will. So I'll just carefully pour. Stop about there.
Perfect.
And what you immediately see, of course, is almost like two different layers forming.
Exactly. So you can see two different, sort of, phases. So you have all that red stuff
that's at the bottom, and then we've got something that's forming up here in the top.
Slimy, gunky, gross. Almost like snot --
[laughter]
-- or a cotton ball. Sort of cotton ball in liquid.
Excellent.
It's interesting is that the redness of the strawberry is not, and the upper layer, it's
in the lower layer. And so what's the gunky, slimy, stuff.
I don't know.
I think it's the DNA.
[laughter] What do you think it is?
I remember in medical school --
[inaudible]
-- you know in medical school -- we started with strawberries and we learned
strawberry medicine. And here we go.
Awesome.
So, yeah. So you can sort of see the DNA precipitating --
Precipitating.
-- coming out of solution into a solid form, and there's a lot of it.
Awesome.
So you can see that nicely. So I guess we can use something and we just happen to here
a popsicle sticks --
[assent]
-- a little bit notched to go in. And we can just touch it. And very easily pick it up.
Looks like just a --
That's awesome.
-- big, old, slimy, wad of strawberry DNA.
That's awesome.
Now that you have it, you have it separated. This is purifying DNA. And actually what's
amazing is that is has no red with it at all. It's just totally white, which is exactly
what DNA should be. What could you do with this after you've done it?
So I always tell the students when I am doing this in the classroom that, first of all this
is extremely dirty, so if we were going to do any sort of experimentation we would want
to clean it up. But one of the things you could do is actually analyze this DNA. So
just as you would watch CSI or any of those other forensic shows, this is the same way
they would isolate DNA from skin, or from blood, or anything just using different chemicals.
So the opportunity would be to now analyze it and sort of figure out what is it? Where's
it from?
Now so this of course is strawberry DNA, but in hospitals increasingly now we're purifying
DNA from blood, or form scrapes from inside of your cheek and doing all sorts of medical
tests. And that, in many ways, is the future of medicine. Is looking at humans' DNA and
trying to figure out thing about it that may be relevant for your health. Now for students
at home who actually do this, can they same this DNA?
Of course.
How would they do that?
Actually you can put it into a sealed container and put it in the refrigerator and it would
stay for a long time.
Like a zip-lock bag or --
Like a zip-lock bag --
--something like that --
-- or a small tube --
--little container.
-- as long as you could seal it up.
Okay. So if they want to do this at home. What do they -- how do they get instructions
--
So if you wanted to do this --
-- to figure out how to do it?
-- you can visit our website and just go and look at the instructions and do exactly what
Dr. Green and I did here and isolate your own strawberry DNA.
And we have point-by-point, tell them exactly what to do --
Exactly.
Those instructions are on our website. Well, that's great. Okay. So this was wonderful.
Thanks for helping me do this.
Thank you.
And I hope everybody enjoyed it.