"Chemists and Nobel Prizewinners" tie

(Brady gave it to me),

and we're waiting for the 2015

Nobel Prize in Chemistry to be announced.

And as usual, I have absolutely no idea

who it's going to go to,

which is what makes it really quite fun.

But you'll remember sometimes it goes to...

more to Biology than to Chemistry

because there isn't a Nobel Prize for Biology.

We've already got some chemistry in the Medicine prize,

so Chemistry has been recognized at least a bit already.

So let's see what happens with Chemistry.

[Brady] You going to give us a prediction?

I have absolutely no idea who it will be.

Somebody suggested it might be for

lithium ion batteries, the battery on the mobile phone

that you may be watching this on at the moment,

but... who knows?

It's always the really exciting moment now.

[Göran K. Hansson] (The Royal Swedish) Academy

of Sciences has decided to award the 2015

Nobel Prize in Chemistry jointly to Tomas Lindahl,

Paul Modrich, and Aziz Sancar.

So, I've rushed off and got a DNA model.

I went into the coffee room and asked who'd got one.

The only one I can find is this one, which is a bit dusty,

and, like the damaged DNA in the Nobel Prize,

this one's also damaged.

So, I went back to the coffee room, and got

something a bit more reliable.

These are the spares for the old coffee machine.

Unfortunately we don't use that coffee machine

anymore, so I'm a bit restricted in what I've got

for the model, but it's enough for you to understand.

Just remember: your genetic information,

genetic information of all living things in the world,

are transmitted through DNA.

DNA is a molecule that has two chains linked together.

The linkages between the two chains are what carries

the genetic information, and can be translated

into the making of proteins in your body.

In the Nobel announcement,

the lady who was explaining it said that

each of our bodies has enough DNA

which if it was stretched out would go

to the sun and back from the Earth 250 times.

So there's an awful lot of it.

Each time a cell divides, the DNA has to be

replicated because one pair of chains

has to be made into two pairs of chains,

one for each of the new cells.

When that happens, mistakes can be made,

and the chemistry inside our cells

can also damage the DNA.

And this damage happens very quickly

200 times a day, perhaps, for a given cell,

so if there wasn't a mechanism to repair this damage,

then we'd all die before we were even born.

Now Brady, who is very astute,

says that really what this Nobel Prize is for

is the "DNA Spell Checker." That is, correcting mistakes

rather like a spell checker.

But actually it's better than a spell checker,

because I don't know about your spell checker,

but mine sometimes puts in completely the wrong word

because it misguesses what we've done.

Now, let me try and explain to you,

and before I explain, it's important to realise

that there are lots of different ways

that DNA can be damaged and repaired.

But this is a really high speed explanation,

and we really need to do a proper video about DNA

and that will be coming quite soon, I hope.

But for the moment, what happens with DNA

is that you have two chains

which are indicated by this white piece of plastic,

and inbetween you have so-called "base pairs,"

which, for this, I've just indicated

the things that pair together are either lime green

or dark green.

It's slightly more complicated, but for this that's enough.

Now, the first sort of mistake

is that one of the DNA chains,

the one that's growing, could have the wrong pair.

If we look at this, and this is just a tiny, tiny piece

of the DNA chain, which would go on for miles

in either direction.

So here you have dark green, dark green,

lime, lime, dark, lime, and then here there's a mismatch.

Now if you imagine that the one on this side

is the chain that's growing, that's being synthesised,

the way the spell checking works is that it knows

which one is the good copy, so it can spot the mistake.

It should have been dark green, and it's lime green.

So what happens is that there are enzymes

in the mechanism that chops out the bit that's bad,

and puts in the new one.

You have to imagine that in the cell,

there are lots of these free things swimming around,

so you can always throw one away

and add another one.

It's just like (in theory, at least) on your computer,

there's an infinite supply of letters,

so if you type an "O" instead of an "A,"

you just throw away the O and type another A.

So, the first way

is that you could just chop these things out.

There is another sort of mistake where

there's a chemical reaction that damages

one of these bases and actually, for example,

turns this into something else, which I've done red,

which is, for those of you biochemists,

is usually indicated with the letter "U,"

so this one is one that shouldn't be in DNA at all.

So there is another mechanism,

that was discovered by Tomas Lindahl,

where this is chopped out,

and the right one is put in instead.

The final sort of mechanism is the one which

it causes, or is thought to cause

some sort of skin cancer from the UV light from the sun.

And this is slightly different, where everything is okay

in the completed DNA chain,

and then the UV light comes

(the UV light, I'm showing with this stapler),

and it just staples two of the bases together,

the so-called "thymine."

What it does is the UV light changes one of the

thymine molecules so it reacts with its neighbour.

This only happens where there are two of them

next to each other, and of course

that messes everything up.

But there is a different mechanism

which was discovered by the researchers

in the United States, which chops out these pairs

that are joined together and replaces them

with two more T's, which are not joined together.

Now the importance of all of this is that

it's what keeps us alive.

It's understanding the fundamental mechanisms.

There are other ways that DNA can be damaged,

for example, if you smoke some of the chemicals

that come out in the cigarette smoke

can interact with the DNA and damage the bases,

and there are mechanisms that detect this

and deal with it.

Of course, smoking has not been around very long,

so evolution has not got a special anti-smoking

repair mechanism, but what it has done

is to have a mechanism, a generalized mechanism

to detect things are wrong and weed them out.

Speaking of DNA damage,

I took this out of my colleague's office

while he was giving a lecture; didn't even ask him,

so don't tell him that I actually dropped a piece

and trod on it!

So we'll never repair the damage to this DNA,

but all being well, the mutation won't cause

any serious problem.

...and you can see, I can't read it from here,

but it's about 173 grams.