Ahern’s BB 350 at OSU – 12. Membrane Lipids

Ahern’s BB 350 at OSU – 12. Membrane Lipids


>>Happy Monday. Happy day after the exam. How was the exam?>>[INAUDIBLE] >>Great, yeah, and maybe no. I heard, I think, all three. So the exams were just
handed to me by the TA just before I got to
class, so they are graded. I haven’t had a chance to
record them or look at them, so I know nothing about
them at this point. You guys know more
about them than I do. I’m curious for your feedback. I don’t take names, don’t worry. What’d you like or nor like? Yeah?>>[INAUDIBLE] >>OK, wasn’t quite ready
for the Lineweaver-Burk. Thank you. Is that a common
feeling– Lineweaver-Burk? Yeah. Other thoughts? This is the quietest class. They never say anything.>>[INAUDIBLE] >>So–>>[INAUDIBLE]>>So people always talk
about the first part as multiple choice, but
they’re not multiple choice. They’re really true/false. Every statement is a
true/false statement. So you decide if each
statement is true or each statement is
false, and then you decide. But I hear you. So you doubted
yourself on those?>>[INAUDIBLE] >>Well, hopefully,
you guessed well.>>[INAUDIBLE] >>You can’t get negative points. That’s one thing you can’t
get, is negative points. [LAUGHTER] >>So there’s good news there. There are systems
people put in place for penalties for
guessing, in which case it’s possible to
get negative points, but that’s not what I do.>>[INAUDIBLE] >>So what I will do is– shh. I will return the exams in
or after class tomorrow. So I’ll bring them
to class with me, and I will return them at
the end of class tomorrow. Well, we are ready to
move on to our next topic. And we only have one
last thing to finish up on our last topic, which
actually is something that will be of interest
to anyone interested in nutrition and dietetics. And that, actually,
is this batch of coenzymes at the
very end of this. I’m not quite sure
why I put coenzymes here in this scheme of things,
because coenzymes, of course, encompass all areas
of biochemistry. But we do see coenzymes as
being relevant because they play roles with enzymes. So coenzymes play
roles with enzymes, and I want to say a
little bit about them. So what is a coenzyme? A coenzyme is a
molecule that’s not an amino acid that helps an
enzyme to perform a function. So it’s a molecule that’s not an
enzyme that helps an amino acid to perform a function.>>[INAUDIBLE]>>What’d I say?>>[INAUDIBLE]>>It’s not an– blah. You can tell it’s Monday. A coenzyme is a
non-amino acid– it’s not an amino acid– that helps an
enzyme to perform a function. It’s not an amino acid. Non-amino acid. No amino acid. Something other
than an amino acid. Now, coenzymes
are, in many cases, covalently linked to the
enzyme, but not in every case. We’ll see examples of both. Now, coenzymes are of interest
because many of the coenzymes are also known as vitamins. So for example, here’s pyridoxal
phosphate, known as vitamin B6. Here’s thiamine pyrophosphate,
known as vitamin B1. Vitamins, you know from
a nutritional standpoint, are micronutrients that we
have to have in our diet because we need to have the
functions that they provide. So the functions that these
coenzymes– or in this case, these vitamins–
are providing is that of helping an
enzyme to do something. So I’m going to list
a couple of these, and I’ll talk more
about some of them as I get going
further into the term. So one that I always bring up
at the beginning is biotin. Biotin. Biotin is a coenzyme that’s
used by many enzymes. And as we will see,
it’s used to help with the addition of
carboxyl groups to molecules. That is, it helps to put
carboxyl groups onto molecules. That’s what biotin does. And I won’t show
it to you today, but when we talk
about it later, I’ll show you how biotin actually
physically links to the carbon dioxide to allow it
to add as a carboxyl onto a molecule that’s
being carboxylated. A good rule of thumb
is any time you hear an enzyme that has
the name carboxylase in it, then that enzyme very likely
has biotin as a coenzyme. Coenzyme A we’ll
talk about a lot when we talk about the
breakdown of fatty acids. Coenzyme A is a carrier
or a handle for the cell to hold onto– that
is, for the enzyme to hold onto during
the oxidation process. There are two others that I
want to mention here that are relevant for us right now. One is the flavin
coenzymes, and the other are the nicotinomide
adenine coenzymes. And you’ll see they’re both
involved in the process of oxidation and reduction. Now, biological
oxidation we’ll talk about in a little bit,
and biological oxidation is a very interesting process. Oxidation that occurs out in the
universe, out in the real world is a relatively
uncontrolled process. You light a piece of paper on
fire, it goes up in flames, and it burns– that’s a
big oxidation that’s going on during that flaming process. If our cells did
oxidation that way, they too, would burn
up very quickly. So cells, being the control
freaks that they are, have ways of controlling
the oxidation that occurs inside of them. And they do this with what
are called electron carriers. Electron carriers. The process of
oxidation, I hope you learned in organic chemistry,
is the loss of electrons. The loss of electrons. If something is losing
electrons, it’s being oxidized. But electrons don’t disappear. Electrons have to go somewhere. And whatever they go to, that
thing that they go to becomes reduced, because reduction
is the opposite of oxidation. And so for anything
that gets oxidized, something else is
getting reduced. One thing losing
electrons, something else gaining electrons. Those electrons
can be problematic. If they are just released willy
nilly, cause a lot of chemistry to go on, a lot of
problems to go on. So cells are control
freaks cells. Cells control the
movement of electrons as a result of oxidation. And they do this with
the electron carriers– the flavin coenzymes and then
nicotinamide adenine coenzymes. You probably have seen the
nicotine adenine coenzymes refer to as NAD or NADH. NAD is the oxidized form. NADH is the reduced form. And that’s a set of
electron carriers. The other set relating
to the flavins are the electron carriers FAD
and FADH2– F as in Frank. And we’ll talk more
about those in just a bit when we talk about
oxidation and reduction So those are coenzymes that
I wanted to point out to you. We will say a little
bit about each of the coenzymes in this
table later in the term, but those are the ones
I wanted to mark up at the start of the process. NAD is the one I referred to
as the nicotinamide coenzyme. You’re not going to have
to memorize that structure, but I’ll just show
you the structure and point out some
cool things about it. You’ll notice that it is a
molecule that has an adenine, it has a ribose, and it has
another ribose down here. They’re joined together
through two phosphates. And this nicotinamide right here
is the electron carrying part of the molecule. This guy right here is
the electron carrying part of the molecule. This shows that nicotinomide
part of the molecule. You can see it, and
again, I’m not asking you to memorize the structure. I’m just showing you this so
you can see what’s happening. You can see what’s
happening here is that we’re going
from an oxidized form, as shown here where we have
two double bonds, over here to a reduced form where
we have– I’m sorry. Let me back up. So we actually start
with this process here, with three double bonds. We’re going over
here to a molecule that has two double bonds. So in doing so, we are adding
electrons to this molecule. So electrons are being
added in this process as we go to the right. When something gets
oxidized in the cell, those electrons, as I
said, have to go somewhere. And one of the most
common places they go is they get added to NAD. NAD is this resonant
structure between these two shown on the left. And when NAD gains
two electrons, it also gains two protons and
becomes what we call NADH, and that’s shown over here. So if I were to ask you of the
nicotinamide molecules, which ones are the oxidized forms,
you would say the NAD pluses. And the reduced
forms are the NADHs. And we’ll say more about
that a little further along. And we’ll save that for later. Well, what I want to do
now is turn our attention to the discussion of
biological membranes. Biological membranes,
because it turns out that membranes are
absolutely essential for cellular identity,
for cellular function. The membrane is the
barrier between what we think of as a cell and
the rest of the universe. So that barrier’s
pretty important. If we don’t have that
barrier, we don’t have a cell. And as we will see, if
we destroy that barrier, we damage that
barrier in some way, we likely will kill what
we think of as the cell. Well, let’s think about what
goes into making up a membrane. Our membranes are
made up of something we call a lipid bilayer. A lipid bilayer. You probably learned
that in general biology. I want to spend a little time
talking about those lipid bilayers and the significance
of those lipid bilayers, both for ourselves and also
for the food that we eat. But before I talk about
the membrane structure, I need to provide you with
a bit of an introduction to what lipids
themselves actually are, so let me say a
little bit about that. A lipid, for our
purposes, is a molecule that has at least one
major nonpolar part to it. It has at least one
major nonpolar part. Lipids were first identified in
cells when they extracted cells with organic solvents
and they found that there were certain
substances that were dissolved in those organic substances. And those substances
that were dissolved in those organic solvents
they described as lipids. They described those as lipids. Now, lipids are actually
a little broader than that category, but that
was the original definition. Lipids have a variety
of things, one of which may include, but doesn’t
have to include, fatty acids. Fatty acids. So fatty acids are a kind
of lipid by themselves, and they’re also a component of
bigger lipids, as we will see. So what’s a fatty acid? On the screen you see several
common fatty acids that are found inside of ourselves. Common fatty acids. Palmitic acid is probably
the most common fatty acid that we have in our cells. Palmitic acid has 16
carbons– and though I don’t expect you to memorize
all the various structures or so forth of these,
I will expect you to know that palmitic
is the most common, and I think you should also
know it has 16 carbons. It’s also what we describe
as a saturated fatty acid. You hear about saturated and
polyunsaturated and unsaturated fatty acids. A saturated fatty
acid is one that has no double bonds
between the carbons. You don’t see any double
bonds between the carbons in palmitic acid. Another common saturated
fatty acid is stearic acid. Stearic acid’s just a little
longer than palmitic acid. I didn’t give you the number. If I give you the number,
you would have to kill me. So this way I won’t–
I’ll save my life. The unsaturated fatty
acids are fatty acids that contain at least
one double bond. And a prime example of
unsaturated fatty acids includes oleic acid. Oleic acid is fairly
abundant in olive oil. And oleic acid has
one double bond, as you can see in
the structure here. And what we discover
looking at all of the double bonds within the
naturally-produced fatty acids is that they’re almost always
found in the cis configuration. Naturally-produced fatty
acids are almost always in the cis configuration. We’ll talk about trans
fatty acids and trans fats a little bit later,
but those usually arise as a result of chemical
modification for food purposes. Something that has more
than one unsaturated– that is, more than– start over. Some fatty acid that has
more than one double bond is what we refer to
as polyunsaturated. And you can see several
polyunsaturated fatty acids below, linoleic– that
should be –lenic, linolenic acid, and
arachidonic acid shown there. Linoleic has two
double bonds, linolenic has three double bonds,
and arachidonic acid has four double bonds. They each have important roles. When we talk about
fatty acids, we hear the term
essential fatty acids, just like we hear about
essential amino acids. And when you hear
the word “essential,” it means that it’s something
that we can’t make ourselves and that we have to
have in our diet. To understand what an
essential fatty acid is means that you have to
understand the structure. When we count– when we
look at a fatty acid, I told you, for example, that
palmitic acid had 16 carbons. We can number those carbons
starting at the carboxyl end or starting at the
methyl end, and that’s actually two different
numbering systems that are used. If we start numbering
from the carboxyl end, we use what’s called the
delta numbering system. Yes, I think these terms you
should know– delta numbering system. And if we start the numbering
from the methyl end, we’re referring to the
omega numbering system. >>[INAUDIBLE]>>Yes. If we start numbering
from the carboxyl end, it’s carboxyl number one. That’s the delta
numbering system. And if we number from the
methyl being number one, that’s the omega
numbering system. I’m going to refer
to both systems. And it’s important that we
have both systems, because they describe different things. And since fatty acids
are different lengths, then that’s a consideration. Mammals, including you and me,
cannot make fatty acids that have double bonds
beyond delta 9. So oleic acid, if we count
them, we have carbon number 1, 2, 3, 4, 5, 6, 7, 8, 9. That is as far out as we
can make a double bond. So oleic acid, we can make. It’s a nonessential
fatty acid, meaning we don’t have to
have it in our diet. Essential fatty acids are
those that we can’t make and that we have to
have in our diet. So if we look at linoleic
or we look at linolenic or we look at
arachidonic, we see that they all have double
bonds past position nine. Here’s linoleic. We have 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12 is the position of
the second double bond. Linoleic acid, we cannot make. We therefore have to
have it in our diet. And linoleic acid is an
essential fatty acid. Linolenic is an
essential fatty acid. Arachidonic is an
essential fatty acid. Now, if we look at the other
numbering scheme, which is the omega numbering
scheme, you’ve heard of omega-3 and
omega-6 fatty acids. So we can tell if we start
numbering from the methyl end what we have. So here is a linoleic
1, 2, 3, 4, 5, 6. Linoleic is an
omega-6 fatty acid. Omega-3s start here– 1, 3, 3. And linolenic–
again, got to get that name changed–
that linolenic is, in fact, an omega-3 fatty acid. Now omega-3s and omega-6s
probably have different bodily functions. Omega-6s are implicated in
some places with respect to inflammation and may
cause some problems. Omega-3s are the ones that
we associate with fish oils and so forth, where people
ascribe various magical effects to them. Arachidonic acid has
its own category, and we’ll talk about that later. Arachidonic acid turns
out to be a precursor of a very interesting
group of molecules called the prostaglandins, and we’ll
talk about them a little bit later. >>[INAUDIBLE]>>Question? There’s a bunch of
saturated fatty acids. When I was a student
taking biochemistry for the first time, I
committed these to memory. I’m not going to make you
commit them to memory, but I’ll tell you what I
used to remember these. And I remembered 12,
14, 16, 18 as LUMPS. Lauric, myristic,
palmitic, stearic. Or you can call them LAMPS,
if you want to, whatever. But I remember the LMPS
was how I remembered those. These are all saturated,
and you can see they differ in size by two carbons. Fatty acids in general will
have even numbers of carbons. There are some exceptions to
that, but for the most part, fatty acids have even
numbers of carbons. And we’ll see why that’s
the case when we learn about their synthesis later. The unsaturated fatty
acids, you’ve already seen most of them
on the other chart, and you can see the
various designations there. You’ll notice that as the
amount of unsaturation goes up, the melting temperature for
that fatty acid goes down. Something that has–
like linolenic that has three unsaturated bonds
has a melting temperature of minus 11 centigrade, whereas
oleic, which only has one, has a melting temperature of 16. And if we compare that
to the saturateds, this with no double bonds,
we see that stearic has a melting point of
71 degrees centigrade. So putting those double
bonds into a fatty acid has a very drastic effect
on the melting temperature. And as we will see, that has
some very important nutritional and other considerations for
organisms that contain them. Why do we care
about fatty acids? Well, we care about fatty
acids for two primary reasons, and there are some
other reasons, as well. But one of the primary
reasons for fatty acids is that they are major
components of fats– not surprisingly,
given their name. A fat is made by combining three
fatty acids with a glycerol. In each case, an ester bond is
made, and the product of that is a fat. I’m not worried that you
know this is tristearin, but I’ll just tell you that
in this case what they did was they took three
different stearic acids and they combined all three
to the hydroxyls of glycerol. Glycerol is this
component at the very top, and the fatty acids, of
course, are down there. And these are ester bonds
that you see right there. There’s the glycerol
part of that. Most fats aren’t
like tristearin. Most fats have a mixture of
saturated and unsaturated fatty acids. Now, a second thing that
fatty acid– oh, gesundheit. Before I talk about
the second thing that they’re important for,
talk about what we do with fats. Of course, fats, as everybody
knows, very important energy storage in our body. Fats can store energy
at a higher density than anything else that we have
in our body for storing energy. Fats, per carbon, can store
a lot more energy than sugar. A lot more energy
than amino acids. So fats are very good
at energy storage. And the energy of fats is
realized by breaking a fat down into glycerol and the
fatty acids comprising it. That’s how we get the energy,
because the fatty acids are then taken and
oxidized in a cycle that we we’ll talk about
later, called beta oxidation. And that oxidation process
that oxidizes fatty acids produces a lot of energy. A lot of energy. The second category of molecules
that’s very important for us with respect to fatty acids
are the membrane lipids, and there are two
groups of those. The main group R is the
glycerophospholipids. I need to explain them to you. Glycerophospholipids. That’ll be in the highlights. I won’t spell it here for you. You’ll also hear them called
phosphoglycerides– same thing. I tend to call them
glycerophospholipids, but you’re welcome to call
them phosphoglycerides. Now, how do we get– or
what is a phosphoglyceride? A phosphoglyceride looks
very much like a fat. It has one major difference. So a phosphoglyceride
or a glycerophospholipid has the same backbone of
glycerol that a fat does. It also has two of the
three fatty acids esterified to it that a fat does. But at position number three,
instead of a fatty acid, it has a phosphate. Now, this really dramatically
changes the chemistry of this fat or fatty acid. It drastically
changes the chemistry. Whereas the fat had three fatty
acids linked to a glycerol, the fat was very, very nonpolar. In fact, fats are
so nonpolar we have specialized cells
called adipocytes that store fat for us. And fats are so
nonpolar that when they go moving through
our bloodstream, we have to package
them up in complexes so that they can move in
the aqueous environment of the blood. So fats are very,
very, very nonpolar. You put a phosphate on
there, and now you’ve really changed its chemistry. What you’ve done is you’ve
made a part of the molecule be very polar,
because it’s ionized. Phosphatidic acid ionizes–
the phosphate ionizes at physiological pH, and the
fatty acids just sit there. Well, the fatty
acids are long things that are sticking
out far to the right. They usually have a
structure like you see here where carbon number 1 is
saturated and carbon number 2 is unsaturated. It’s a very common structure
for a glycerophospholipid. Carbon number 1 a saturated
fatty acid, carbon number 2 an unsaturated fatty acid. Carbon number 3, of
course, has a phosphate. If we have just a
phosphate on there, we call the molecule
phosphatidic acid, as you see on the left. That phosphate however, can
be attached to other things. And when we do that, we
create a class of molecules called phosphatides. Phosphatides. P-H-O-S-P-H-A-T-I-D-E-S. So if I attach, for example,
a serine to the phosphate, I would call this
overall compound on the right phosphatidylserine. Phosphatidyl, and
then whatever’s attached to the phosphate
gives the rest of the name. If I attach ethanolamine,
I would call it phosphatidylethanolamine. If I attach choline,
phosphatidylcholine, et cetera. Now, this change in the
chemistry that I noted means that one portion of
the molecule is very polar, another portion of the
molecule is very nonpolar. And molecules that have
this property and that have this structure
that you see here, when you put them in
an aqueous environment, will do something
really, really cool. They will organize
themselves all by themselves in a lipid bilayer. It doesn’t take anything more. It’s built into their chemistry. They will make a lipid bilayer. Let’s take a look
at a lipid bilayer. This is what a lipid
bilayer looks like. You can see there’s
two layers of these. There’s a polar portion that’s
shown by that head there, and there’s a nonpolar portion
shown by these tails in here. It forms a bilayer
because what it’s doing is it’s trying
to orient itself so that the nonpolar
portions are avoiding water, whereas the polar heads
are in contact with water. And it doesn’t take
too much imagination to see how the membrane around
a cell could automatically form. That’s actually
what’s happening here. We could think of this as
the outside of the cell, and the portion here
inside of the cell. But in both cases, the outer
portion and the inner portion are bathed in water. And it’s the water that
helps to hold this structure into a lipid bilayer. So that’s a very
cool thing that’s built into the chemistry of
the glycerophospholipids. There’s another
group of compounds that are– at first glance,
look– actually, let me show you this. There’s the
phosphatidyl compounds. So I said there’s
phosphatidylcholine. There’s the phosphatidyl
part, there’s the phosphate, there’s choline attached to it. No, you don’t need to
know the structure. Phosphatidylethanolamine,
phosphatidylserine. Some of these get
exotic, as you can see. Now, the other
class of molecules that is of interest
to us are what are known as the sphingolipids. The sphingolipids. I’ll talk about the
waxes and other things in a minute, but
the sphingolipids. Sphingolipids at first
glance, as I said, look different than the
glycerophospholipids, but they’re really
not that different. And in fact, when we
look at a lipid bilayer, we discover that they have
both glycerophospholipids and they have sphingolipids. So the chemistry
that I said was built into the
glycerophospholipids is also built into the sphingolipids. Now, the sphingolipids tend to
be a little bit more exotic, and I’m going to show
you something with them in a minute. But suffice it to say that their
chemistry is not significantly different than that of
the glycerophospholipids, even though they may
look very different. The sphingolipids get their
name from the fact they resemble a compound called sphingosine. We make sphingolipids lipids,
not with glycerol– there’s no glycerol in a sphingolipid. Instead, we make sphingolipids
by combining palmitic acid with serine, the amino acid. Palmitic acid with serine. To that mixed
compound– and we’re not going to worry about
the structure of it. To that mixed compound, we
can attach another fatty acid. And when we do that, we create
a molecule called a ceramide. So a ceramide we would
think of as something that has palmitic acid, serine,
and another fatty acid linked to it. Depending on what else we
attach to this molecule, we can create a
variety of things. If we attach to this
molecule a phosphocholine, we make a very interesting
molecule called sphingomyelin. Sphingomyelin. Sphingomyelin is found
abundantly in nerve tissue. It helps to line the myelin
sheath of nerve cells. The myelin sheath,
S-H-E-A-T-H, of nerve cells. We discover that
sphingolipids are very common in brain tissue. Very, very common
in brain tissue. And sphingolipids can have
some very exotic things attached to them. Sphingomyelin is a very
unusual sphingolipid in that it actually contains phosphate. Most sphingolipids do
not contain phosphate. That’s one way they differ
from glycerophospholipids. Most sphingolipids
don’t contain phosphate. Instead, what most sphingolipids
will have is down here on the bottom. Instead of having
phosphocholine, they’ll have a sugar attached. They’ll have a sugar attached. If they have one
sugar attached, we will call them a cerebroside. One sugar means
it’s a cerebroside. If there’s a complex of
several sugars that are added– and these can get quite hairy. If there’s a complex of several
sugars added at this point, we call it a ganglioside. So I’m going to repeat that. A sphingolipid that
has a phosphocholine is sphingomyelin,
a sphingolipid that has a simple sugar
attached is a cerebroside, and a sphingolipid that has
a complex of sugars attached is known as a ganglioside. You’re getting a lot
of nomenclature here. I didn’t cover the waxes. Everybody knows
what wax is, right? I got too much in
my ears, which means I either can’t hear very well,
or I’ve got something– yuck. Right? Waxes are very,
very, very nonpolar. They are made by esterifying
a long-chain alcohol to a long-chain fatty acid. Meaning that in
the middle, that’s the only place of any
polarity in this molecule, and it’s so insignificant
that waxes are extraordinarily insoluble in water,
which is why you put wax on your car, et cetera. Extraordinarily insoluble. Waxes, of course,
are also lipids. I said if I make a sphingolipid
and I put a sugar on it, I make a cerebroside–
there is a cerebroside. In this case, it has
glucose attached. Here are some gangliosides,
and I told you they can get hairy–
that’s hairy. Memorize that structure
for the next exam, guys. [LAUGHTER] (FALSETTO) Hahaha. OK. [LAUGHTER] The last of the lipids
that I want to talk about are the steroids. Steroids are molecules that
are derived from cholesterol. We think of steroid hormones. But steroids are
just molecules that are derived from cholesterol. One of the reasons our body
makes cholesterol and needs cholesterol is because
it uses cholesterol to make other important
things in our body. They include steroids
and they include bile acids, which are
important for our digestion that we’ll talk about. The basic structure
of cholesterol looks like what you see here. And the specific
structure of cholesterol looks like what you
see on the right. No, I’m not going
to ask you to draw the structure of cholesterol. But cholesterol is
another compound that’s found in membranes, as well. Now, cholesterol does not
form lipid bilayers by itself. It doesn’t do it. But what cholesterol
will do is it will fit into a lipid bilayer
that has already formed. So one of the reasons
that we make cholesterol is because cholesterol is
important for our membranes. It’s an important
component of our membranes. I’m going to spend
some time talking in just a couple of minutes
about membrane fluidity– the fluid nature of membranes. And cholesterol plays a role,
not in making them more fluid, but in making them more
fluid over a wider range. Cholesterol by itself
doesn’t make them more fluid, but cholesterol can extend the
range over which a membrane is fluid, as we will see. Well, let’s talk about
that lipid bilayer, and then we’ll talk a
little bit about fluidity. I showed you this
figure earlier, and you can see up
here that we have these different plus and minus
signs, et cetera, et cetera. That might be a little
confusing to you, but suffice it to say that what
we attach that phosphate could be a molecule that’s
negatively charged, or we can attach a molecule
to that phosphate that’s positively charged. And so this is
reflecting that, as we can see on the surface of
these cells, or these layers. I should also point
out that I said that if you take
glycerophospholipids and sphingolipids and
you mix them with water, they will spontaneously
form this structure all by themselves. This actually is
used in some methods of getting things into cells. Let’s imagine– actually, I
may have a figure for that. Hold on. Let’s imagine that we have
a drug that we would like to get into a
cell, but this drug doesn’t get across the
cell membrane very well. We’re going to see the cell
membrane is a very, very good barrier against most
things getting into it, and so if we want to
get a drug into a cell, we’ve got to use some
tricks sometimes. One of tricks involves the
use of glycerophospholipids and sphingolipids. How does it work? If I take a mixture of
glycerophospholipids and sphingolipids and water and
I shake it up, what’ll happen is the lipid bilayer
will spontaneously form. It’ll form cell-like
structure, just like you saw in that
figure that I showed you. Fine and dandy. Who cares? Well, who cares is this. Let’s imagine I’ve got this
drug I want to get into a cell. So I take that drug and I
put it into the mixture that has the glycerophospholipids,
the sphingolipids, and the water. Everybody with me? I shake it up, and
when the lipid bilayer forms these
cellular-like structures, they’re going to contain
some of that drug. Well, I’ve made something that’s
a membrane that looks exactly like the cell membrane. If I make that membrane
fuse with the cell membrane, guess what it’s going to
deliver into the cell? The drug that’s
inside of itself. Consequently, this
technique can be used to introduce things into cells. It’s mostly used in a laboratory
environment, not in a person, as such, although there are
places where you could do that. But as a result of this,
we can get this into cells. These structures that
I just described to you are called liposomes. A liposome is an artificial,
cell-like structure made by mixing
glycerophospholipids and sphingolipids with water. A liposome. Yes?>>[INAUDIBLE]>>So say what part? What a liposome is, or? Yeah. So a liposome is a
cellular-like lipid bilayer that’s made by mixing
glycerophospholipids, sphingolipids, and water. I’ll slow down. Everybody can
catch their breath.>>[INAUDIBLE]>>What’s that? You’re ready for a joke? Let’s see, I told you
about the crunch bird. All right, I’ve got
a genie joke for you. So there’s this guy walking
along, and he looks down and there’s this old, dusty
looking vase that’s there, and it’s got a cork in it. And he pulls the cork
out, and of course, out pops this magic genie. And the genie says, oh,
master you have freed me. You have freed me. I will grant you three wishes. You know the story, right? And he says, OK. He says– he sits and he thinks. He says, I want to be rich
beyond my wildest dreams. Poof. The genie hands him
this certificate that says he has a billion
dollars in a Swiss bank account. Pretty good deal. Pretty good deal. What’s your second
wish, oh master? He says, well, I want to be
a really powerful person. Poof. He gets a certificate
that says he’s the president of General
Motors– Apple Computer, make him whatever you want. I don’t care. Wow. The genie says, and yes,
oh, master, the third wish? Ans he says, well, let’s see. I’ve got money. I’ve got power. He says, I want every
woman to love me. Poof. He turns into a
box of chocolates. [LAUGHTER] Bad. Bordering on a sexist joke. I gotta not do that, OK. [LAUGHTER] All right. But it’s kind of cute. Nobody was harmed in the
telling of that joke, I hope. Let’s finish today
with a cool thing relating to nutrition
that you can relate to, and then I’ve got
a song for you. Cool thing relating to nutrition
relates to membrane fluidity. If I say “fluidity,” what’s
the term fluidity mean to you? Like a fluid. And fluids are liquid
and they flow, right? And if I said like a solid,
you would say not so fluid. Doesn’t move very well. If we think about the
membrane lipid bilayers that I’ve been
showing to you, it turns out that their
fluidity is very important for their function. We need the lipid bilayer to
be fluid at the temperature at which we live. That’s important. We need our lipid bilayer
to be fluid and functional at the temperature
at which we live. Well, we live– our body
maintains temperature pretty well, 98.6 degrees. We maintain that pretty well. Our cell membranes don’t
have to be too varied. Maybe a little bit
different in the skin than they are inside
of us, et cetera, but they don’t vary much. And what affects the
fluidity of a membrane? Well, it turns out that
the melting temperature of the fatty acids
in the membrane– in the glycerophospholipids
and in the sphingolipids– the melting temperature of those
fatty acids has a big effect. Organisms that live
in a cold environment, like fish in the
ocean, have to have lipid membranes that are
different than the lipid membranes that we have. They’re in a lot colder
place, unless they’re very tropical fish or
something, but they’re in much colder
environment than we are, and they don’t want their
lipid bilayers to freeze. So consequently, if we
look at fish membranes and we compare the fatty acid
composition of fish membranes to our membranes, we
discover, not surprisingly, that fish membranes
have fatty acids that are very unsaturated. This is why people eat fish oil. Fish are abundant in
unsaturated fatty acids, and they have this abundance of
unsaturated fatty acids because of the need to keep
their membranes fluid in the cold
environment of the ocean. Fish oil is very abundant
in omega-3 fatty acids, for example. And omega-3 fatty
acids, as I said, is what people ascribe these
great magical properties, and so forth. I promised I would
finish with that. Any questions about that
before we sing a song? You guys just
finished an exam, so I have a song about taking an exam
that maybe you can relate to. And it’s to an old Beatles tune,
so you may not know the tune, but bear with me as
I try to sing it. It’s called “Student
Nightmares.” (SINGING) I answered
three B, but then I thought it might be C.
Or was the false true? I can’t undo. It makes me blue. It asked me to list all the
enzymes that regulate fat. As I wrote them down, I
discovered I didn’t know jack. I oughta give thanks, scoring
some points, filling in blanks. I squirmed in my seat, feeling
the heat, shuffling my feet. Professor then told me there
wasn’t a chance I would pass, so I started crying and fell
through a big pane of glass. I suffered no harm, because
I awoke to my alarm. Oh, nothing compares to deadly
scares of student nightmares. OK, guys, see you tomorrow.

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