Nucleic Acids

PAUL ANDERSEN: Hi, It's Mr. Andersen and in this podcast I'm going to talk about nucleic acids.

When I talk to students about nucleic acids, they're confused.

They don't know what they do,

and they don't usually know what they're made up of.

They do know that they're DNA and RNA,

but let's start with what they do.

The biggest job that DNA and RNA have is making the proteins,

the proteins inside the cell. When you look at me,

you're looking at the proteins,

but where are the directions to make those proteins?

Those are found in the DNA.

How do they get to the proteins? Well, they're shuttled out by RNA.

RNA is more of a worker that's making these proteins inside the ribosome.

The first job they have is making proteins.

What's the second thing they do?

Well, they make up our genes and so that's what we

pass on to the next generation. This is my son.

He contains half of the DNA that I do.

I gave him a random half of my DNA and my wife did the same.

He's a combination of me and my wife. Life has just passed

DNA down, generation after generation after generation.

We've never found life on our planet that doesn't have DNA.

That means that we're all connected through this single thread

back to that first universal common ancestor.

But what are they made up of? Those are nucleotides.

These are the building blocks of DNA and the building blocks of RNA.

Let's look specifically at one. This is one nucleotide right here.

A nucleotide is made up of three parts.

We've got a phosphate group that's gonna be pictured right here.

It's an phosphorus in the middle and then oxygen around the outside.

Phosphate groups are really famous in biology.

There are the phosphates that are found in

phospholipids that make the cell membranes of all life.

It's the same phosphate that we're going to find in ATP.

Adenosine triphosphate is the energy source.

In fact, the adenosine triphosphate is

exactly the same adenosine triphosphate that we

add to make DNA and we'll get to that in just a second.

What else do we have? Well, we have a pentose sugar.

Pentose sugar means we have a five-carbon sugar.

In DNA, that's going to be a deoxyribose sugar, and then in RNA,

it's going to be a ribose sugar. Then the most interesting part

of the nucleotide is going to be the nitrogenous base.

It's called a nitrogenous base because it has nitrogen.

Most things in life are made up of carbon,

but there's going to be a lot of nitrogen here in the base of this nucleotide.

This is going to be different in each nucleotide.

Let's take a look at the nucleotides found in DNA.

Basically you have adenine,

cytosine, guanine, and thymine.

We have four different bases,

and therefore we have four different nucleotides.

You can just see, looking at them,

the size is going to be a little different on all four of these.

In RNA, they don't have thymine,

you might know this, but they have uracil.

It's going to look a lot like thymine,

but it's not going to be thymine.

If we're going to now look at all those nucleotides together,

so A, C, G, and T, and that's where the names come from in DNA,

we're talking about these nitrogenous bases or these nucleotides.

And now we've got uracil. Basically, if we put them in order

by their size, we've got two major groups.

We have these ones that have two rings and we call these purines.

This is adenine and this is going to be guanine.

Then we have the pyrimidines, and they're just going to have one ring.

Cytosine, thymine, and uracil are all going to have one ring.

They're going to be smaller.

That'll become really important when we start bonding them together.

Let's talk about bonding.

How do you connect them together?

Well, when we talked about carbohydrates,

there's really only one way to connect carbohydrates.

And when we talk about amino acids,

there's really only one way to connect them.

But especially when we get to DNA,

you can connect nucleotides in two ways.

Let's start with way 1. Way 1, we can put this one right

underneath it. We've got an adenine and guanine,

and then through a dehydration reaction,

we could lose a water right here and we could form

a covalent bond between two nucleotides.

If we were to add another one,

we would add another nucleotide here, we

lose a water, and we're going to make another covalent bond.

We can attach them together like that. That's what RNA is.

RNA is a number of nucleotides simply in a row and

they're connected with covalent bonds between each one.

There's another way, however,

when we get DNA, that we can bond them.

Let's say we have these two nucleotides, adenine and guanine.

How can I attach this thymine right here?

Well, basically I can turn it upside down and it's

going to form hydrogen bonds here between the adenine and thymine.

You've probably heard this before,

that adenine will always bond to thymine

and guanine will always bond to cytosine.

That's why; there's going to be interactions between the oxygen,

nitrogen, and the hydrogen and make these hydrogen bonds

that are going to connect the two. When you're looking at DNA—

let's switch to this next slide. When you're looking at DNA,

that's what's being connected right here in the middle.

That's going to be those hydrogen bonds between the nitrogenous

bases on either side. And so why do we have DNA?

Well, we think life started with RNA because it contains a message.

But over time, we kind of had two RNAs wrap around each other

and we eventually had DNA. There's more to it than that,

but DNA is going to be a more stable structure.

We're going to have these hydrogen bonds here,

and then we're gonna have hydrogen bonds

between different backbones of the DNA as well.

What are the backbones of DNA really made up of?

It's just a sugar attached to a phosphate to a sugar to a

phosphate to a sugar. What are some differences between

DNA on the right and RNA on the left?

Well, the first one would be the uracil versus the thymine.

That's going to be a different nitrogenous base.

DNA is going to be a double helix and RNA is going to be a single helix.

Then in life, DNA is going to be found in the nucleus, and

RNA is going to be found pretty much everywhere that we need it.

If you're confused on how we go from DNA to proteins,

or if you're really interested in the whole secret of life,

I'll put a little link to a video I made that

talks you through how we go from DNA to proteins.

But the last thing I wanted to leave you with is how important they are.

If you're interested in RNA and if you're interested in science

and video games, then you may want to check this out.

This is Eterna. Eterna is a video game.

I think it's centered at Stanford University.

Basically what they're doing is they're letting people on

the internet build sections of RNA.

Basically, you build sections of RNA.

They have competitions each week and basically the

winners each week, they will make your RNA.

They'll actually synthesize and make your section of RNA.

Then they'll see how it does. I'm going to launch the video game

and talk you through the first level. If you're interested

in RNA or making things real in biochemistry,

you may want to give this a shot. Here's level 1.

Basically it's a tutorial, so I

can click on "Next" and it'll talk me through what I'm going to do.

You're going to build your own RNA. Let me click on the next one.

RNA is made up of four bases. Hopefully you know what that means now.

Yellow base is adenine, guanine, uracil, and cytosine.

As a warm-up drill, let's convert all the bases to guanine.

Let me click here to start. Basically what you can do is go down here.

I'm going get my mutate and I'm going to mutate this to guanine.

I love the music in here, the little sound effects.

Nice. So I cleared level 1. Then you can go to the next puzzle

and we keep just going through. Basically on this one,

what you can do is they will attract each other.

For example, they're going to say that adenine and

uracil are going to come together and

the guanine and cytosine are going to come together.

Basically what you do is you get to play around with pairing these.

I'm going to stop playing a video game in front of you, but give it a look.

It's a really cool idea. People competing to make RNA

and then they're actually building it in the real world.

That's nucleic acids, incredibly important, and I hope that's helpful.