Molecular structure of glucose | Macromolecules | Biology | Khan Academy

What I wanted to do in this video is familiarize ourselves with one of the most important molecules in biology

And that is Glucose

sometimes referred to as Dextrose

and the term Dextrose comes from the fact

that the form of Glucose typically

Typically found in nature if you form a solution of it, it's going to polarize light to the right and Dextre means

Right

But the more typical term glucose this literally means sweet in greek if you ask a greek friend to say sweet

it sounds like Lucas or I'm not saying it perfectly, but it sounds a lot like a glucose

And that's because that's where the word comes from and it is super important because it is it is it is how

energy [is] stored and transferred in biological systems in fact right [now] when if someone were to talk about your blood your blood sugar

they're talking about the glucose content, so when people talk about blood

blood sugar they're talking about your they're talking about your glucose content the whole process of photosynthesis

this is all about plants using harnessing the [sun's] energy and

storing that energy in the form of glucose when we talk about when we talk about things like

respiration in our in our cells cellular respiration

that's all about taking glucose and using it to full and to create atp's which are the molecular currency of energy

Inside of our body, so these are in credit is an incredibly important molecule

We can start wreaking chains of glucose to form Glycogen to form

Starches this along with another similar another simple sugar fructose you can use to form our table sugar

But even glucose by itself is sweet so let's get familiar with it as a molecule

so immediately

When you look at this is it kind of drawn as a as an open chain we see that we have one two three

Actually, let me number these we have one two

three four five six carbons, so

chemical formula would be C

sub six a subscript of six we have how many hydrogen's

How many hydrogen's we have we have 1 2 3 4 5 6 7 8 9 10 11 12 hydrogen's?

C6H12 and then we have how many oxygens do we have?

Have one two three four five six oxygens

Six oxygens, so you might notice we have six carbons and then the ratio for every one oxygen

We have two hydrogen's which is really the ratio of Hydrogen's to oxygens in

Water and if we want to really if we really want to if we add obviously here

We don't have just two hydrogen's and one oxygen

We have 12 hydrogen's and six oxygens, but it's really good to even just familiarize yourselves with what are the different parts here

So we see on the number one carbon it is part of a carbonyl group

when a carbon is bonded to

double bonded to an oxygen like that. That's a carbonyl

Carbonyl

carbonyL group and in fact because this carbon

it's double bonded to an oxygen, but then it's other bonds are I guess you could say a

Carbon chain right over here and then but this other bond right here is a hydrogen

we would call this an aldehyde we would call this an

aldehyde group and it makes Al

Aldehyde and it would officially make the entire molecule an aldehyde if you contain an aldehyde group

You are an aldehyde, so glucose

and when it's written when it's drawn as a straight chain or it's a straight chain form it would be considered an aldehyde and then

Of course it has all these hydroxyl groups on them, and these hydroxyl groups these O-H groups over here

That would officially make glucose also it would officially make it an alcohol, and it's neat to keep in mind

How the structure is so you have six carbons?

One of them is part of this aldehyde group

It's part of this carbonyl right over here

And then the other five are each bonded to a hydroxyl and what I've oriented it this way

four of the hydroxyls are on the right-hand side and the one on the three carbon is on the left-hand side and

all of the other carbon bonds are with

hydrogen carbon likes to form four covalent bonds every one of these six carbons has formed four covalent bonds

And so you would fill up all the rest once you've accounted for this carbonyl here

And you've accounted for all of these hydroxyls everything else is going to be hydrogen

Now this is when you've drawn when you've drawn glucose just as a straight chain

but many times you will see it in its cyclical form

It's neat to kind of think of how do you go from this form to this form over here?

And so what I've drawn here is this exact same this exact open chain

But I've started to I've started to bend it a little bit and just to be able to keep track of things let's renumber

The carbons, so this is the carbon. That's part of the carbonyl group

So it's carbon one and then we number up from there two three

four five

And then that is the number six carbon the reason why I've made these this bond over here nice and fat is

To show that it's it's kind of closer to us

It's popping out of the page and as we go from the the second carbon of the first carbon

We're going back into the page when we go from the third carbon to the fourth Carbon

We are going we are going back into the page right over here, so this big fat bond. This is

between Carbon three and Carbon two, that's this

That's this right over here and this going from two to one

That's this bond

And I'll draw it a little bit kind of going in and then this bond is

This bond right over here and so it take a second pause the video if you need but try to orient yourself to orient yourself

Imagine we're going to take this to the right like this to bring it over here

And then we're going to rotate we're going to rotate this end and bend it up backwards like that

To get to this form C six is now bent all the way up is now rotated all the way up there

We've bent we've bent this chain and the whole reason is is because this will typically react the hydroxyl group

This is it

This is the the most typical form of glucose you will see when you see in a sick little form there's actually other forms that

You can have but the oxygen that forms a hydroxyl group on the fifth carbon

it can it can attack it can attack the the

The number one carbon that forms this carbonyl group

And that's because oxygen we've talked a lot about it is very electronegative likes to hog electrons

So this carbon is partially positive and so you could take one of the lone pairs

You could take one of this oxygen right over here. It's going to have two lone pairs

Let me just draw them as neatly as I can that's one lone pair, and then this is another lone pair right over here

so this oxygen

can

Form a bond with this carbon when we learn organic chemistry and more depth, we'd call that a nucleophilic attack

it sounds very fancy. Just the fact that these are drawn to each other this has a partially positive charge this guy has a

lone pairs of electrons that can be used to form bonds with things and so when that when those electrons form this bond or

Bond to this carbon that's going to be this bond

this Bond right

over here

And then this carbon can let go this carbon can let go of the electrons in

One of these let me do this in a more obvious color

and in the double bond right [over] here it could let go of one of the bonds the electrons in one of the bonds and

then that can be taken back by the oxygen or even better that can be used by that oxygen to capture a

Hydrogen proton in the solution and actually probably part of a

Hydronium Molecule

But let me just draw it this way

this would just be used to capture a

Hydrogen proton that would just be a hydrogen a hydrogen atom without its electron. It's just a hydrogen ion

It would just be a hydrogen proton and that would form this bond

That would form this bond right over here and let me let me just be very clear this carbon this carbon right over here is

This carbon right over there this oxygen this oxygen is

This oxygen is that oxygen right over there, and so hopefully you see how it forms a cyclone. You're probably saying Oh, wait wait

don't we have a little hydrogen attached here

isn't the way I've drawn it looks like there's an extra hydrogen over here, and then that would leave this guy with a

Positive charge we leave with a positive charge, but you can imagine we're in a solution of water then hey

I have some I have another water molecule right over here

And you know these things are all bouncing around and interacting in different ways

But it could use let me do that in the right color it could use

So that's oxygen it could use one of its lone pairs instead of this you know this will become positive temporarily

But then it can use it can do it can use one of its lone pairs to grab just the hydrogen proton which would allow

Which will allow this character to take its to take its

Electrons to take these electrons back and turn into this character and just be neutral and then this this guy

Would have gained so we have a proton going into the solution you have hi

But we took a proton from [the] solution

We took a proton we gave a proton to the solution

And so you could end up with this so the whole reason I did

This is [just] so when you see it in biology class or chemistry class you're not intimidated by it in fact

This is something that's really valuable to get very very familiar [with] because you're going to see

Glucose and other sugars in many many many different molecules

throughout your academic career