All language subtitles for high energy molecule 9

B. A high energy molecule.

I'm not going to go into the chemical details here,

but I'm going to briefly sketch.

That is an adenosine molecule, which we'll come to know about.

And off this adenosine molecule, I'm

going to take the phosphate groups that we were just

talking about.

Negative, negative, negative, negative, negative.

That molecule there, hydrophobic or hydrophilic?

Hydrophilic.

It's very negative, right?

Good, that's not the part I care about.

The part I care about is, you have three phosphate groups.

They're all negative.

What do negatives like to do?

Repel.

Do you think those three negatives

are very happy being covalently bonded to each other?

No, they're straining at the bit there.

They'd love to get away from each other.

Right?

In other words, if I could free them up,

if I could break that bond, I would release energy.

It turns out that we can very simply understand here

that that is a great way to store energy,

and a lot of energy, to use it later on a reaction.

By sticking three negatives together, I can store energy.

And the cell has figured this out

and it uses that molecule as an energy currency.

An energy store to run reactions.

When it needs energy, it resorts to adenosine

with three phosphates, or adenosine triphosphate.

Or, amongst friends, ATP.

There you go.

Last example.

And then we'll quit.

I just want to bring us back to glycolysis and Buchner

and sugars.

Let's just talk for a moment about sugars.

We'll see more about sugars a little bit later in the course.

But let's talk about carbohydrates.

Carbohydrates have the following structure.

They have a certain number of carbons.

I'm going to do a carbohydrate here

that has six carbons on it.

Every carbon except one carbon has a hydroxyl group on it,

but they can go in different ways and different places

and all that here on the carbon.

I'm drawing this one this way.

Just hydrogens there.

Except this guy here, or one other one somewhere.

We have a carbonyl.

C double bond O. And if you do the arithmetic, this thing

here-- H, H, I'm bored drawing these Hs,

and you're going to get bored drawing them,

and we're not going to draw them usually as you'll find out--

has this formula CH2O six times.

That is C6H12O6.

If a sugar has six carbons, we call it a hexose,

because hex means six.

If it has five carbons, we call it pentose,

because pent means five.

If it's got three carbons, we'll call it a triose,

because tri means three.

Anyway these are just different names

for different kinds of sugars.

And amongst the hexoses are things like glucose,

the very important sugar.

In fact, the sugar that yeast needs here

in growing this glucose.

Now I'm not going to go into a lot of detail,

but I'm going to mention that this linear chain is not

the usual way that glucose will be found.

Glucose will spontaneously make itself

into a nice little chair.

And the structure glucose is usually running around

in looks like this.

One of the carbons is up here.

Then as we chase the carbon chain, carbon, carbon, carbon,

oxygen here.

And depending on the sugar, whether these

hydroxyl groups are up, or down, or vary.

And you get this nice thing.

And this can be a very reactive group.

This monosaccharide, single sugar molecule,

they can form together by dehydration synthesis

to make two-- a disaccharide.

And I'm going to forget all the chemical structure here,

and I'm just going to draw you a hexagon here.

And say they might bond together like that.

And then they could continue to bond together like that.

Or they could bond together in many, many other combinations.

Sugars are kind of very permissive.

You could bond them this way, and that way, and this way.

And depending on how you bond them, you get very different

shapes.

You can make long, linear chains that

nuzzle up against each other.

You can make chains that don't nuzzle up each other.

You can make branched structures.

And let's just bring up some examples of this.

We can put them together here.

You get starch molecules.

Put them together in a different way,

up, down, up, down, up, down.

You get cellulose molecules.

You put it together in branched ways,

you get what's called glycogen. The way

you store sugars in your liver.

And, in particular, if we take the way

of doing this where those chains lineup just perfectly,

look what happens.

If this lines up just perfectly you

could make hydrogen bonds across, and across, and across,

within and across.

And those fibers can be so powerfully strong that you get

cellulose that holds up trees.

Pretty impressive.

And at the same time, by just bonding in a different way,

you get the glycogen, which is stored

in a completely non-structured, non-rigid way in your liver.

So what's the take home message?

What we've said is life is understandable at a chemical

level.

We didn't need Vitalism to explain life.

We've got a limited set of forces.

We've got covalent bonds, strong covalent bonds.

We have hydrogen bonds.

We've got ionic bonds.

We've got Van Der Waals forces holding up our gecko.

We've got hydrophobic forces, which aren't really forces.

They're just the exclusion of things that are breaking up

happy hydrogen bonds.

And together we can explain by understanding

the structure of a molecule.

We can understand how membranes form spontaneously,

how energy might be stored in a molecule, how trees might stand

up by very large numbers of hydrogen bonds between chains

of sugars holding themselves up.

At this level, biochemistry helps

us understand those things that once seemed magic about life.

Next time, we're going to move forward

to the most interesting molecule of all.

Those molecules that Buchner purified from his yeast juice.

The proteins that can carry out those magical transformations.

So that's for next time.

All right, back again with a question.

We got questions for you on carbohydrates and on ATP.