HAZEL SIVE: At this
point during our lecture,
you should understand that
bonds construct molecules.
You should have
had some practice
with representing
molecules and should
be able to draw a
line-angle diagram
or know where the
carbons and the hydrogens
are on a line-angle diagram.
You should be able to recognize
polar and nonpolar molecules.
And you should know
something about recognizing
different types of bonds.
So let's move on to the
second big topic today, which
are the macromolecules.
Macro means big.
And macromolecules just
mean big molecules which
are found prevalently in cells.
There are four major classes
of macromolecules in cells
that we will go through.
They are the lipids,
the carbohydrates,
the nucleic acids,
and the proteins.
And we'll go through
each of the classes now.
They are often polymers.
That is, they are some
kind of joining together
of a monomer, which we
sometimes write as an M.
And a polymer would be M
to the n or n monomer units
joined together to
make the polymer.
Good.
Our first class
of macromolecules
that we're going to
discuss are the lipids.
Lipids do a whole
bunch of things.
They make up the cell membranes
that keep cells intact.
They do things like
insulate seals.
They are part of the whole
signaling circuitry aspect
of cellular function.
And they are also
the way that energy
is stored in our bodies
in a very large extent.
Lipids have certain
key characteristics
that you should know.
They are always nonpolar
or largely nonpolar.
That means they're hydrophobic.
They don't mix with water.
As you know, oil or lipid
and water don't mix.
They may be partly
polar in which case
they get a special name.
And they are called amphipathic.
And those are interesting
because the polar part
of the lipid can
interact with water.
And the nonpolar part will
not interact with water.
They can be long chains
although not usually
polymers in the strict sense.
Or they can be small.
But they have as their key
characteristic this nonpolar
aspect.
And that's the one you
want to focus on if you're
trying to identify a lipid.
Here are some
diagrams of lipids.
You know now from
representing molecules
that all of those zigzag
portions of these molecules
are hydrocarbon chains.
And you can see that
many of these lipids
have got lots of hydrocarbon,
just hydrocarbon,
no other molecules.
But you can see also
that some of them--
and I've circled the
bottom one in blue--
has a polar portion with
lots of oxygens and nitrogens
as well as the nonpolar
portion that makes it a lipid.
You can see some of
these lipids are small.
For example, at the top,
there's cholesterol.
That is a very important
part of the cell membrane.
And that has a particular kind
of structure, lots, again,
of carbons and hydrogens.
And that structure is called
a steroid ring structure.
And so those are your lipids.
Let us move on now
to carbohydrates.
The next major class
of macromolecules
are the carbohydrates.
These do lots of cool things.
They are what gives
you your blood type.
But they also are a way
that energy is taken in.
They're a quick form of energy.
Runners when they're
about to run a marathon
will have carbohydrates
right before because that
is available energy.
They do things
like build the cell
walls of plants and the
exoskeletons of insects
that protect them.
And as we'll talk
about in a little bit,
they are an essential part
of the genes of the DNA.
Carbohydrates can be recognized
by their basic chemical formula
CH2O.
And if you're trying to
recognize whether it's
a carbohydrate, you can count
up the carbons, the hydrogens,
and the oxygens.
And you should be able to tell.
For carbohydrates, we can
usually identify the monomer.
The monomer, the M, would
be the monosaccharides.
These are sugars.
And these will form long
chains that give rise
to the polymers, which are
often starch, glycogen,
or, in plants, cellulose.
And these monomers
are joined together
by a special
covalent bond that's
called a glycosidic bond COC.
Here's a diagram of glucose.
This is called a chair diagram.
And you can see something
about the actual 3D
structure of glucose.
The dark parts of the
molecule are coming out
of the screen towards you.
And the light parts
are going back.
So it's not a flat molecule.
It's actually got some
3D structure to it.
On the bottom of
the slide, you can
see amylopectin, which is a
form of starch where the glucose
monomers are joined together
by the glycosidic bonds
that I have circled.
And that's a
carbohydrate for you.
The monomers of carbohydrates,
or even the polymers,
can exist in isomeric form.
For example, these are the
different forms of glucose.
An isomer is just a
slight rearrangement
of the overall structure
of the molecule.
So glucose can be allotted
a chain, an open chain.
It can be a cyclic molecule in
one form or another form, alpha
or beta forms.
And each of those, each
of the different forms,
can be used to build
polymers of carbohydrates.
Good.
So let us move on now to the
next class of macromolecules.
And this class I would
say is the reason
that we're having this
conversation today.
Nucleic acids and
understanding what they are
and how they function broke open
the field of molecular biology.
And molecular biology is the
common language of biology
that transcends all the
different fields of biology.
And it's because
of nucleic acids
that we have molecular biology.
So let's talk a
little about what
these important
nucleic acids are.
They are the things
that make the genes.
If you think about a gene which
you've undoubtedly heard of,
it is made of the macromolecular
class of nucleic acids.
Nucleic acids are also
required for energy.
They are involved
in the synthesis
of other types of
macromolecules we'll
talk about in a
moment, the proteins.
And they are the things that--
because this is what genes do--
that carry the hereditary
information from cell to cell
from parent to child.
Nucleic acids are made
up of nucleotides.
The nucleotide would
be the monomer.
The polymer is
either DNA or RNA.
The structure of the
nucleotide is stereotypical.
And you should know the
names of the components.
So the nucleotide structure
is comprised of a sugar,
a phosphate, and a base.
And we write it really as
phosphate, sugar, and base.
I'll show you the chemical
structure in a moment.
And we can abbreviate
this as PSB.
The sugar is a five-carbon
sugar called ribose
or it might be or deoxyribose.
And the bases are adenine,
guanine, cytosine,
and thymine--
A, G, C, or T.
Now, let's make a little
notation here on the side.
There are two kinds
of nucleic acid--
DNA or RNA.
In DNA, these are the basis.
In RNA, the T is replaced
by something called uracil.
Otherwise, the
bases are the same.
And so in RNA,
there is U and not
T. And a notation
about the sugar--
in DNA, the sugar
is deoxyribose.
And in RNA, the sugar is ribose.
Let's look at a
slide to give you
a better sense of
nucleic acid's structure.
Here's a diagram
of a nucleotide.
This is a particular nucleotide.
Doesn't matter what right now.
You can see the phosphate
group highly electronegative
there, phosphate
with four oxygens
covalently bonded to one
of the sugar carbons.
It's called a 5 prime carbon
and will become important
in a little moment.
And those other 4 prime, 3
prime, 2 prime, and 1 prime
are the carbons of the sugar.
And you can see that there are
a couple of hydroxyls here.
That 3 prime hydroxyl
is really important.
And we'll talk more
about it in a moment.
And then the other part
there is the base, which
is joined to one of the
carbons of the sugar, the 1
prime carbon of the sugar.
Here are the bases
of the nucleic acid--
adenine, guanine,
cytosine, thymine.
And you can see at
the top uracil, which
is really similar to
thymine except it is lacking
this methyl group right here.
The bases can be divided
into two separate types
of structure.
On the left of the
slide are the purines,
which have got two carbon rings.
And on the right
are the pyrimidines,
which have just got
one carbon ring.
Good.
We're going to come back to
nucleic acids in a moment
when I tell you something
special about them.
But in the meantime, I want to
talk about the last major class
of macromolecules.
And those are the proteins.
All of these classes
of macromolecules
are really interesting and
unbelievably important.
And there is no life without
any of the four classes
that I'm telling you about.
The proteins are
particularly cool.
They do everything.
The only thing that
they don't quite do
is to carry hereditary
information from cell
to cell from parent to child.
They participate in that.
But they are not
actually the information
that is transmitted
through the genes.
Proteins, however-- and
you can see on this slide--
contribute to the
structure of the cell.
They are involved
as enzymes, which
are the catalysts of the cell.
We'll talk a bit about
in another lecture.
They give you a
whole body structure.
They are the reason that
you are standing up.
It is because of the structure
of the proteins and the things
that they build.
And really, anything you
can think about in life,
the proteins are involved in.
Proteins are made up
of a monomer called
an amino acid or an amino acid.
This would be the monomer.
In the nucleic acids, there
are four different types
of bases, four
different types that
can contribute to the
nucleotides in the amino acids
or amino acids.
There are about 20
different amino acids that
are essential for human life.
And there are lots more that are
found in other places in life.
But there are 20 common ones
that we can think about.
A protein is an
amino acid polymer.
And it can be little
proteins and big proteins.
In just the same way,
as we'll discuss,
there can be small nucleic acid
polymers and large nucleic acid
polymers.
The structure of
the amino acid is
built around something
called the alpha carbon.
And I'll draw the
chemical formula
because it's the easiest
way to think about it.
If this is the alpha
carbon, it has on one
end a carboxyl group.
Has on the other end an amino
group and a hydrogen, and then
there is this thing called R.
R is a side group.
And it's the side group
that gives the amino acid
its character.
R can be polar or nonpolar.
It can be charged or uncharged.
And the R is really what gives
the amino acids their name.
We can think about
the amino acids,
or we can write the amino
acids in three different ways.
We can write, for example, the
full name of the amino acid,
for example, valine.
Or we can abbreviate
it Val, three letters,
or we can use the
one letter code V.
Here's a diagram of an
amino acid with the R group
as I told you about.
And you can see that
the charges on the amino
and the carboxyl groups can
be differentially distributed
to the way that I've
drawn them on the board.
And here are the
structures of the whole set
of common amino acids.
You don't need to
know each of these.
But you should be able to look
at these particular structures
and say, oh, this looks like it
would be a charged amino acid
or an uncharged.
This would be
polar or not polar.
So let's review a moment
recognizing macromolecules
and how you would tell
these four classes apart
because that's one of
the things I'd like
you to get out of this class.
The lipids-- look for something
nonpolar, hydrophobic,
lots of hydrocarbon.
May have a little polar
bit, but really most of it
should be nonpolar hydrocarbon.
The carbohydrates-- look
for the CH2O formula.
And they are always
polar because they've
got a lot of oxygen
groups and hydroxyl groups
there, which are polar groups.
Proteins-- look for
the alpha carbon.
I've ringed it here.
And you should find
next to the alpha carbon
there should be an amino group.
On the other side, there
should be a carboxyl group,
and then there should be
something else sticking out,
which would be your R
group, your side group.
And finally, the nucleic acids--
complicated.
The way to start is look
for a phosphate group.
If you can find a phosphate
group, it may be an amino acid.
If you can find a phosphate
group attached to a sugar,
and you know sugars
have got CH2O formulas,
then you are on the right track.
And then if you see
something that's
got a bunch of nitrogens
and some oxygens
and either one or two
rings attached to it,
that's probably the base.
You can make these assignations.
You can recognize
these macromolecules
using a set of rules, using a
set of ways to recognize them.
And I would like you now to
go to your next assignment
where you're going to do
some practice of recognizing
macromolecules.
