- Alright, so in a previous video
I talked about how cyclic Monosaccharides
like this green cyclic Glucose can react with Alcohols,
like this pink Alcohol,
to form Acetals and Ketals.
And I believe that I mentioned that
sometimes the Alcohol comes in and is reduced,
is actually another Carbohydrate.
So let me kind of draw this in here.
And it makes sense because
what you see with Carbohydrates is that
they're choke-full of Hydroxides,
they're choke-full of these OH groups,
and so, really they can function really similarly
to Alcohols and reactions,
and when this happens,
the individual Monosaccharides are linked together
to make an Acetal,
and we call this linkage a Glycosidic Linkage.
So this is a Glycosidic Linkage.
Now, when two Monosaccharides are linked together
in this fashion by Glycosidic Linkages
we call the product a Disaccharide.
Disaccharide.
And we have "Di" which means two,
and "saccharide" which means sugar,
so sugar...
So, two Monosaccharides linked together
they're called a Disaccharide.
Now with Disaccharides, most commonly the Glycosidic Linkage
forms between the anomeric carbon, or C1,
so remember this is the anomeric carbon, the C1,
so over in our Glycoside here, be right here,
just the same, we got a C1 of the first Sugar,
and the C4 of the second Sugar.
So, right here would be C4,
and it's just the same over here so,
right here we have C4, and that's the second Sugar.
So we call this a 1,4 Glycosidic Linkage.
And then just like we could have further break down
our Monosccharides into Alpha and Beta
based off the orientation of
the anomeric Hydroxide group,
we can more specifically call the 1,4 Linkage
an Alpha or a Beta Linkage,
again, based off what is now the orientation of
the OR group on the anomeric carbon.
So same rules apply,
if the group is cis with respect to the sixth carbon
it's Beta,
and of course if it's trans it would be an Alpha Linkage.
So, in this case, our OR group, which--
Our OR group is this whole Carbohydrate
is cis with respect to the sixth carbon,
so we have a Beta 1,4 Glycosidic Linkage.
And if that bit of naming confused you a little bit
I went over that in greater detail in a different video,
but what I wanna confused on here
are some of the common Disaccharides,
so let me clear some space, let me give us some room.
I'm gonna go and fade in a drawing
that I did a little bit ago to save just a bit of time,
and what we have here is a Disaccharide,
you see two Carbohydrates,
two Monosaccharides linked together,
and this one happens to be Lactose
which you might be familiar with.
So, Lactose.
And Lactose happens to be,
really the principal Disaccharide found in milk
and that's actually true for both human milk
and for cow milk,
and unlike really most Disaccharides
Lactose isn't really appreciably sweet.
It consists of one Galactose,
so this one right here is Galactose,
and one Glucose Carbohydrate,
and their bound together by a 1,4 Glycoside Bond
just like we saw before.
So we've got the one and a four,
and this is a Glycoside Bond,
and this one happens to be in a Beta orientation,
so Lactose is a Disaccharide made of
Galactose and Glucose joined together by
a Beta 1,4 Glycoside Bond.
Now, next step we have Maltose,
so let me write that in here, we've got Maltose.
And Maltose is, again, a Disaccharide
but this time it's made of two individual Glocuse units,
so we got a Glucose right here
and we've got a Glucose right here
and they're bound together similarly
by a 1,4 Glycoside.
So we've got the one carbon right here,
that's this one,
and we've got the four carbon over here,
so this is again a 1,4 Glycosidic Linkage,
but as opposed to Lactose, up here
this one is actually Alpha,
you can see that this OR group, the second Carbohydrate
which is functioning as the OR group
is in a trans position with respect to the
first Carbohydrate's sixth carbon over here,
so this is an Alpha 1,4 Glycosidic Linkage unit,
binds together two Glucose units.
So that's Maltose, another pretty common Disaccharide.
And then last but not least,
let me pull in here for you, Sucrose.
And Sucrose is actually probably
the most common Disaccharide in all of nature
and you deal with it quite frequently unimagined
because Sucrose is the principal Disaccharide
of table sugar, which comes from sugar cane.
So Sucrose is actually quite sweet
but it's different substantially so
from Maltose and Lactose,
and I wanna point out a couple of the key differences.
So, in Lactose and Maltose, both of these appear,
you have two pyranoses,
remember pyranoses are six-membered Carbohydrate rings,
I went over that in a previous video,
but we have two six-membered rings
bound together by this Glycoside,
and in Sucrose that's different,
we've got a six-membered Glucose right here,
this is Glucose,
bound to a five-membered or a furanose Fructose,
so we've got Fructose right here.
So, Fructose...
And what happens is,
you have both of the Carbohydrates
linked together by their anomeric carbons,
so right here we've got two anomeric carbons
linked together.
Now, that's different that Maltose and Lactose,
so for example right here is the anomeric carbon
of both Maltose and Lactose,
it's over here, that's the C4 that's bound,
so these are both linked together
by their anomeric carbons,
and what happens is you have
two Acetals that are formed,
so we've got an Acetal right there,
and remember an Acetal is when a carbon
is linked to an OR group over here,
and an OR group over here,
and then you have a second Acetal
at the Fructose's anomeric carbon.
And so with Maltose, and the same thing with Lactose,
you have Hemiacetals that are formed,
so you've got an Acetal right here
and then you've got a Hemiacetal over
kind of on the tail, on the second Glucose,
that's a Hemi, a Hemiacetal.
And then you can look at
and it's the exact same thing for Lactose,
but what happens here is,
remember that with a Hemiacetal you can add on
a second OH group to form another Acetal,
a Hemiacetal can be further reduced into an Acetal,
but once you have an Acetal
you can't further reduce it,
so that makes Sucrose a non-reducing Sugar
and then Lactose and Maltose are both reducing Sugars.
And so, Lactose, Maltose and Sucrose are probably
the three most common Disaccharides
and they give a good basis for Disaccharides.
And then, really, Polysaccharides
are just an extension of these thoughts.
So let me clear some space.
And for those reducing Sugars like Maltose and Lactose
that are let with a Hemiacetal group at the end,
we can keep adding Sugar groups on to the chain,
that's kind of this reducing characteristic,
they can keep growing which ends up making
more Acetal groups but always leaving
a Hemiacetal group on the end.
So I've kind of pre-drawn an, another drawing here,
let me make a little bit more room for it.
And that's what I've shown you,
I've shown just kind of the addition,
a couple additions of extra Carbohydrates
onto Disaccharides.
So both of these have three Carbohydrates,
and you could keep going,
but that's what makes them Polysaccharides.
So, this first one that I drew in
is a Polysaccharide called Cellulose,
and Cellulose is found in the cell walls
of really nearly all plants,
and it gives support and structure
to wood and to plant stems,
and really cotton is essentially just pure Cellulose.
But Cellulose is a Polysaccharide made of
repeating Glucose units that are joined together
by Beta 1,4 Glycosidic Bonds.
So all of these are Beta 1,4 Glycosidic Linkages.
And, really this, it forms an unbranched,
just kind of straight chain,
and that's the Polysaccharide Cellulose.
Now, down here I have another Polysaccharide
which is also super common,
and this is Starch.
And you can see that, really this is made of
repeating again, repeating Glucose units here.
The difference is that these Linkages are Alpha,
still 1,4.
So still 1,4 Linkages but these are Alpha units.
And really the functional difference here
is that as humans we have the enzyme
to break down these Alpha 1,4 Linkages
and we can use Starch which, again,
is found in a lot of plant products
as a source of energy
'cause we can break these down into Glucose
to undergo cellular respiration,
but we lack the enzyme
to break down the Beta 1,4 Glycosidic Linkages of Glucose.
So we can't appreciably use Cellulose as an energy source.
And then, one last...
Excuse me, one last Polysaccharide
that I wanna show you
is really very similar to Starch,
I'm gonna use the Starch as a little basis here,
but if you kind of branch off of the Starch
every once in a while on the C6 carbon,
so that's the C6 carbon right here.
And you add on another Glucose,
so I'll stop there,
this is another, another Glucose.
You can keep going with Alpha 1,4--
Yeah, excuse me, Alpha 1,4 Linkages again,
and you can form essentially just branches, branches.
So this one would go here,
and then you can maybe down the line here
have another one.
And so these are, these are mostly Alpha 1,4 Linkages,
every once in a while you get an Alpha 1,6 Linkage
thrown in there which creates some significant branching.
And so, if it's highly branched, we call it Glycogen,
and that's a little bit,
a little bit down of a concept
but essentially that's what Glycogen is,
it's a major Polysaccharide made of Alpha 1,4 Linkages with,
that are heavily branched
by this Alpha 1,4--
1,6, excuse me, breaks.
But Glycogen, it's significance for us,
it's principally as a source of storage of energy.
So we can build Glycogen stores in our body
and it creates a really functional store of Glucose
because with all these branches we have
a lot of tails of Glucose
that can be chopped off pretty quickly to get
a fast Glucose source.
So, that's probably a good start
for Polysaccharides as well,
we've got Cellulose which is Beta 1,4 Linkages
of Glucose in a straight chain.
We've got Starch which is essentially
kind of a chain of Alpha 1,4 Linkages of Glucose.
And then we've got Glycogen which is
really, really similar to Starch,
except that there are Alpha 1,6 Linkage breaks in here
that enable a form kind of chains of this Polysaccharide.