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- [Voiceover] There are several
different organic molecules

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you'll find within living organisms.

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Carbon is probably one of
the more important ones.

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I mean, the others are very
important, don't get me wrong,

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but carbon, you a lot of
times have heard of humans

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as a carbon-based life form.

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Pretty much carbon is the building block

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of all living things.

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It's about 18% of our body weight.

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I mean, don't memorize the number.

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Depending on the book,
it'll be 16, it'll be 20.

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It's a range.

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But these macromolecules,
these components, these pieces,

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well, carbon is incorporated
to building larger molecules,

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things like carbohydrates,
lipids, proteins, nucleic acids.

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Well, all these larger macromolecules

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have to somehow be made, put together.

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One way is dehydration synthesis.

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And look at the second term, synthesis.

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Well, synthesis means to build or make.

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Dehydration, remove water.

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So the case of dehydration synthesis,

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it's removing basically a
water molecule to form a bond.

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You'll end up removing two
hydrogen and one oxygen ions.

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What happens, though, is
you need energy to do this.

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Energy is required to break the bonds

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and release the water molecule.

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So you build from the small
subunits to the larger subunits

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to eventually the macromolecules,

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things like proteins, lipids,
nucleic acids, carbohydrates.

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But you don't always want to build.

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Sometimes you wanna break
them down, release energy.

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One way the body obtains
energy for the cells is

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to break down chemical bonds.

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The term hydrolysis, well,
you have hydro and then lysis.

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Hydro is water, lysis is cut or break.

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So hydrolysis means you can
add water to break a bond.

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When you add water to break this bond,

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you're releasing energy.

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So pretty much dehydration synthesis

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is the reverse of hydrolysis.

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Hydrolysis breaks down,
dehydration synthesis builds up.

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So what you're looking
at here is the rough idea

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of how hydrolysis and
dehydration synthesis work.

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If you start in the top right,

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notice there is a highlighted
H, then a non-highlighted O

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then another OH on their side.

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What ends up happening is
if you take that molecule

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plus the one in the
top left, you get again

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a highlighted OH now and another OH.

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By putting energy in the right side

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you add energy in and you
take out a water molecule.

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You form a bond between
these two molecules.

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But if now you add water
back in to the left side

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hydrolysis, you add water back in,

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it breaks a bond releasing energy.

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So it all depends on
you trying to build up

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larger molecules or
break them down smaller.

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Dehydration synthesis builds them up

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and then hydrolysis breaks them down.

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So let's look at
carbohydrates to start with.

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You might have heard of carbohydrates as

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a fast energy source,
something that you want

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to eat right before a sporting event

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to get some high energy.

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Well the general formula is

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C subscript n H2O subscript n.

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What that basically means is if there are

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six carbon so C subscript six

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there are also six H2O equivalents,

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so the Ns are the same.

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So you have for every one carbon you have

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two hydrogens, to one oxygen.

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Now you have smaller
types of carbohydrates

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called monosaccharides, you
might have heard of them

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or their simpler term
called simple sugars.

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Mono means one, saccharides a ring.

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So simple sugars are one ring.

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Things like glucose, very
common sugar in your body.

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Fructose, galactose, ribose, deoxyribose,

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and those last two ribose and deoxyribose.

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Deoxyribose is found in DNA,

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ribose, RNA.

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Well if you take these monosaccharides

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and start putting them
together and building

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larger and larger, you
can make monosaccharides

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linking together to make disaccharides,

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di just means two.

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So you take two
monosaccharides they go through

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dehydration synthesis, hold
that water molecule out,

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then you get a disaccharide

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two monosaccharides bound together.

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You can keep adding
more and more and more,

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monosaccharides onto its chain.

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Just every one you add has to

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go through dehydration synthesis.

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So sucrose, you may heard of that,

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that's glucose and fructose put together.

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Maltose, is two glucose
molecules put together.

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And lactose, glucose and
galactose put together.

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Where do you find lactose anyway?

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Yeah it's in dairy, milks,
cheeses, ice creams, yogurts.

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So for instance if
someone's lactose intolerant

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the problem is they
cannot take that lactose

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disaccharide and very easily break it down

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into glucose and galactose.

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They're either missing or
they don't have enough of

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the enzyme that breaks down lactose.

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If you're curious the enzyme
is called lactase by the way.

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Just switch the O to an
A, lactase is the enzyme

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that breaks down lactose.

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So here is your ribose and deoxyribose

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so they're both pretty much the same.

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Five-carbon monosaccharides
the difference comes

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into play though when you start looking

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at the number of oxygens.

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Deoxy means you've lost an oxygen.

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So look towards the bottom
right of deoxyribose.

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You'll see the bottom line has OH

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then next to it just an H.

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But in ribose both the
bottom ones are OHs,

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there's your difference.

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To show a little more of how
things are coming together

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or breaking apart, glucose plus fructose

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go through dehydration synthesis,

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take that water molecule out,

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form a bond you get sucrose.

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Now don't worry about
memorizing all these formulas

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it's not that important.

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What's more important is knowing

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glucose and fructose are monosaccharides,

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sucrose disaccharide.

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Carbohydrates are ring shaped,
or roughly ring shaped.

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They have this one to two one ratio.

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You're not gonna have to draw out sucrose,

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or draw out glucose, or draw out fructose.

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Polysaccharides, well we went through

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monosaccharides, one ring.

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Disaccharides, two rings.

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Now polysaccharides have many rings.

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I put thousands together
here but it could be

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hundreds it could be thousands,

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it could just keep going, going.

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These are huge groupings
of monosaccharides

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all bonded together.

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Starch is a perfect example
of a polysaccharide.

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Starch is how a lot of
plants will store energy.

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The plants will take the
individual monosaccharides

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and then to start to bind
them together to make starch.

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Glycogen is how us as
animals store energy,

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it's one way at least.

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Glycogen is just a whole series, a mess,

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of glucose molecules bound together.

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Now the reason it's stored energy is

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every bond contains energy.

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So anytime you break a
bond you release energy.

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The glucose molecule also contains energy.

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Cellulose another polysaccharide,

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it's indigestible you cannot digest it.

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You can chew it up as much as you want,

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it still comes out as cellulose.

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This is more of a structural
support for plants.

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So as a plant-based polysaccharide
get a structural support

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something us as humans cannot break down.

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So here's what you're seeing with the

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dehydration synthesis the
formation of glycogen.

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One glucose, second
glucose, they go through

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dehydration synthesis to form

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the longer chain of glycogen.

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Each one of those monosaccharides,

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each one of those individual rings,

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was bound to the next via
dehydration synthesis.