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We're going to talk about the anatomy
of the cell membrane.
And believe it or not, understanding the cell membrane
and how substances get across it
is actually one of the most important parts
of not only cytology, the study of cells,
but of anatomy in general.
In this presentation, we're going to focus
on the cell membrane itself, the structure,
in other words, the anatomy,
and then in the next lecture,
we'll actually start to talk about
the exact mechanisms of how substances cross over.
So you may recall that the cell membrane
is a phospholipid bilayer.
And in the word "phospholipid" is "lipid," as in fat or oil.
If you think about, um, film of oil or soap
or soap bubbles and all the swirly,
purple and green colors,
that's what you get in a lipid or an oil.
So a plasma membrane is made up
a lot of the same stuff as soap bubbles.
So that brings us to a mystery to solve
about bubbles.
If plasma membranes are so much like
the substance that they're made of,
is so much like a soap bubble,
can you start to think about some of the ways
that they behave differently than soap bubbles
and how are we going to figure out
how they're structured in order to do that?
So here's some mysteries to solve.
How do we get substances through the soap bubble?
I mean, why don't they just pop?
Here's another one to think about.
Do you remember how many different types of cells
there are?
There's over 200 different types of cells.
Now, can you picture the shapes of cells?
Imagine any specific cells that you can think of,
any specific cell types.
We looked at some red blood cells
and some nerve cells.
Maybe you can picture different types
of muscle cells.
Now, imagine going on a walk or a hike.
Could be in the park or the woods.
What kind of stuff do you run across
on a walk in the woods or the park
that has this similar kinds of shapes
of all the different kinds of cells?
Trees, pine cones, sticks, blades of grass,
even the fluffy tufts of dandelion flowers.
Have you ever seen bubbles shaped like trees
or pine cones or dandelions?
And if not, how could you build cell walls
that are made up of a lot of the same lipid stuff
that soap bubbles are made up of
and still get them to be in all those
different shapes?
There's some things to think about
as we learn about cell membranes
and how they are like soap bubbles
and how they aren't like soap bubbles.
So, we're going to start off talking about
what does a plasma membrane or in other words,
a cell membrane, what does it do,
what is it designed to do,
what are its jobs?
You probably recall the term
selective permeability.
That means that cell wall, excuse me, cell membranes
are able to let some substances through
and keep other substances from crossing.
They are choosy.
They're able to decide what substances
cross over and what substances cannot cross over.
This actually reminds me of--and people will sometimes
use the analogy of walls on a building,
so, um, here we're looking at a cabin,
which actually reminds me of a motorcycle road trip
I took in B.C. and it was absolutely stunning country.
Just beautiful back roads,
all kinds of evergreen trees,
you know, fir and Douglas,
really tall old growth,
just amazing, and there was this little--
what appeared to be a deserted log cabin
on a side of a little back road in a field,
kind of similar to this picture,
although this is not a picture I took of it.
And I saw some kind of rustling in the grass
and so I pulled over and these incredibly cute,
totally adorable, two little black bear cubs
are scampering through the wildflowers
and they're leaping through the flowers
and they look almost comical,
just completely adorable, roly-poly,
and jumpy and sproingy.
And they went over to the cabin
and they were exploring and sniffing around
and then one cub put its paws on the window,
you know, the open, broken old window of the cabin
and then put its paws in and stuck its snout over
and then hopped right in.
And then the other one followed suit
and then they were playing around like this,
you know, hopping in and out of the windows
and going in and out of the doors.
And I was just on my motorcycle by myself,
so, don't worry, I was keeping a good eye out
in case mama bear was around,
because they get pretty fierce
if anybody gets near their cubs, but,
anyway, the point of the story,
why it reminds me of cell membranes
being selectively permeable,
is you have to be careful what you're going to let inside
and outside of the cell.
And in the case of a cell membrane,
it separates the intracellular,
in other words, what's inside the cell
and extracellular,
what is outside of the cell.
And which chemicals are allowed in and out
are very important and hopefully,
from the previous slideshows,
it's starting to sink in why membrane selectivity
is critical to the fluid medium inside the cells.
First and foremost, there's a balancing act
that happens in the body of all kinds of chemical levels
and temperature,
and maintaining certain ranges of chemicals and temperature
in a certain fine-tuned range, despite changes
inside and outside the environment,
is one of the most important concepts in physiology
and hopefully, you will know this term
inside and out and its many applications
in physiology and that is homeostasis.
Homeo-what?
Basically, just keeping the chemical levels,
the temperature levels, the pH,
in a certain range despite the changing environment.
You may remember that there's not only so many
chemicals sloshing about,
that it's just like the levels of chemicals
in a pool.
But one thing that's different from a pool
is the cell, being a living organism,
it actually is carrying on lots and lots and lots of different
chemical activities and all those activities
are called metabolic activities.
And all of those create waste products.
So of course, you're having to handle those waste products.
So just like you have the changes coming
from the outside, you also have the changes coming on
from the inside, like the metabolic activities
creating waste.
And to go back to the analogy of the pool,
you wouldn't want to swim in a pool of pee,
just like the cells wouldn't want to be full
of metabolic waste like uric acid
or urea.
This reminds me of swimming in public pools.
Have you ever gone swimming during the times
where there's lots of babies and toddlers?
It's kind of like Russian roulette.
One day, or one minute, it's like all sunny
and sunshine and happiness,
and then the next minute you hear the scary shark music.
And then the lifeguard yells, "Evacuate!"
And they have to clear it out and go fishing for poop.
"Everybody out of the pool,"
and they're fishing for poop
and dumping in chemicals, lots of chlorine,
nobody can go in the pool for a while.
So, um, that is homeostasis in a public pool.
Scary.
But okay, so this is what gets inside and outside
of the cell is huge,
it's critical to the cell's not only ability to live,
also to be healthy.
But also for it to carry on
its many, many, many, many functions.
So with over 200 different kinds of cells,
they're not just like these little round
soap bubbles floating around, just generic cells,
but they all have specific jobs to do.
Think about any specific jobs you can think
that cells have to do,
and a lot of those specific jobs
are gonna actually involve the cell membrane.
So the cell membrane is cool and critical
not just to decide what gets in and out of it,
but actually because it has to do a lot with specific
functioning of the cells, too.
For example, communication.
Now this, um, works with a lot of
the communication systems in the body.
For example, uh, the nervous system.
Using nerve cells to conduct electrochemical signals.
Both the electrical part of the signal conduction,
which is, you know, like, uh,
kind of like a flash of lightning,
or it's like knocking down a long pile of Dominoes
and the cascade reaction and the quick sending
of the signal, the electric part
carries out on the cell membrane,
through the cell membrane,
and because of the cell membrane.
It is an active part and reason of why
that electrical signal happens.
So it's not just like a passive, you know, envelope.
And then at the end of the nerve cell,
it has to, um, spray out little, uh, vesicles,
little--secrete little vesicles
that have chemicals in it to send signals.
And that ability to send those chemicals
out of the cell, that also is very much
relying on how the cell membrane
does its job.
There's communication between, um,
so not just the nerve cells themselves,
but the communication of all different kinds
of cells relies on the plasma membrane.
For example, when hormones, which are chemicals
that send signals, when those hormones
go floating around in the body,
cells have to be able to understand or translate
what those messages mean.
And so in order to receive those messages
and interpret the messages,
that is also relying on the cell membrane.
So there's special little proteins
in the cell membrane that have to do with
receiving those signals, those chemical signals.
And there's other ways, too, and we'll see this
as we study each system of the body.
And another function that the membrane--
cell membrane serves is also as
sort of identity markers, so that the organism
and its every cell is--has a way
of identifying itself as the body's own cells.
So for example, if you had foreign substances
like bacteria, viruses,
fungi enter the organism,
they, uh, in most cases, are not going to have
the same little identity markers.
Now, some of them come up with, you know, tricky mechanisms
of trying to imitate those identity markers
so that your body doesn't recognize them
as invading substances,
but what your body tries to do is have
these little proteins on the surface
of your cell membrane that are like little flags,
you know, they're like, um, countries
with their own flags saying, "Okay, this is, you know,
this is Sweden," and you know, each one has its own flag.
And many people know of the blood typing system
that uses A, B, and O,
that has to do with those markers.
So, uh, it's important to understand
that the cell membrane is semi-permeable,
phospholipid bilayer,
and we're going to take a look at the actual
structure of this:
the substances that actually create this
and their chemical properties, because the next thing
we're going to learn is how substances
actually cross this membrane and these--
the way that substances cross is very much dependent
on the anatomical structure.
So we're going to kind of break it down
and look at the different elements here,
so first of all, starting off basic,
semi-permeable means that some things can get through,
and phospholipid refers to, uh,
these molecules that have fats in them.
They have a phosphate side and a lipid side.
and this is going to--
and these arrange themselves in a bilayer.
Which "bi" means two.
So it's a double layer, like two sheets put together.
And these parallel sheets of phospholipids
actually are self-arranging or they arrange themselves,
and we'll take a look at the fluid mosaic model next
and see how that-- how they can actually
move around.
But looking at this diagram here,
the little circles are the, um,
phosphate part of the lipid,
or the phosphate segment,
and then like a ball if it was--
and then there's two little, like, legs
or antennas on the ball and that's the lipid segment.
And having these two different chemical sides,
it ends up that there's a, um, charged or polar side
and that would be the phosphate side,
which is then water-loving because it's charged,
and then the, um, water-hating
or hydro-phobic side that is, um, non-charged,
the lipid side.
Let's--
So--and these phospholipids, this is the part
of the membrane that is like the soap bubble.
But you can see in the diagram
and in this particular diagram, it's in pink and purple,
there are all these things inside the phospholipids
and these are mostly proteins.
So there's a bunch of proteins embedded within
the, um, the lipids and we'll take a look
at what these different proteins do
and how they're structured
in just a minute, but let's--
Let's actually talk about this in terms
of the fluid mosaic model.
So...
The cartoon-like diagram we just looked at
might give a rather static impression
or if people use analogies like, um,
walls of a building or something,
you might think of the cell membrane
being sort of rigid.
But cell membranes in animals
are not made up of walls like in plants.
In plants, the cells actually do have walls
and it's basically because plants don't have
their own little skeletons, and so each little cell
having more of a firm wall structure
actually provides more of the--
more of the skeleton of the plant.
But a fluid mosaic model of the cell membrane
is basically looking at the different parts
of the membrane and how it actually
moves around a lot.
So the phospholipid part that's like a soap bubble
and it has a consistency of oil,
those little phospholipids are self-orienting
because there's a-- a positive char--
there's a charged side and a non-charged side.
If any of them get poked around or disrupted or moved,
they can kind of jostle around or even float around,
and they'll reorganize themselves.
So if a couple of them get knocked out of place
or nicked out of place,
because of the part that's charged
and not charged, they'll reorient themselves.
But within that, they can actually move around,
and if they were cut they would actually
re-seal themselves.
And within the soap bubbly, kind of phospholipid part
are little rafts that are like lily pads.
And these lily pads add more structure
and stability to the membrane
and also provide areas so that materials
can travel through the membrane
and make it more stable and make channels
to go through.
So some of the materials that are in the little
lily pad rafts or lipid rafts,
there's a lot of, um, well, the first thing you see
on the list says phospholipids
and that might actually be confusing
because didn't we just talk about the phospholipids
making up the fluid part?
Well yes, it's true, and this might be
more chemistry than you want,
as much of--a lot of what I said might be.
So for this next little teeny bit,
you can just go, "La-la-la-la,
I'm not listening to you."
But so the little balls with the little legs on them,
little phosphate heads and then
the little lipid tails,
if you want to make them more fluid and moveable
versus more close together,
there's a way you can do that chemically,
and basically it's to make it saturated
or not saturated.
Um, it has to do with li--
how many of the little molecules are--
remember when we talked about that rule of eight,
and if those electron pairs are all--
if the electron shells are all full,
how they're more stable and more happy,
and if they're not full,
then they get a little irritable.
They get unstable, they're looking desperately
for something to connect with.
Well, a lot of what the body is made up of
is carbon, and so, when you talk about things
like fats being saturated or unsaturated,
um, has to do with how many of the little connections
that could be made with carbon
are made with carbon, and if there's any of them
not made, and anyway,
you don't need to remember which is which,
but basically saturated versus unsaturated
is whether or not you have all the little
carbon connections made and that can determine
whether these little phospholipids
basically have a kink in their tail.
So whether they're, you know, like the little person
with their legs standing out
or a person with their legs standing straight,
and that would determine--
I think that one's more like a space alien,
but anyway, that'll determine whether they're spaced
further apart or held closer together.
And I am certainly not going to make you
memorize that, but again, sometimes I give you more detail
than I will test you on because, um,
while you may sometimes just want the simplest version
of information to memorize possible,
sometimes it's actually useful to understand
the chemical composition in a little bit greater depth
because then you could actually form a picture in your head
of what's going on.
And then some of the other things
in the little lily pad rafts are cholesterol
and sphingolipids.
It's not very often you get to say "sphingolipids."
So I encourage you to take this opportunity.
You're among friends.
The cholesterol.
People often think of cholesterol
as just a bad thing.
Cholesterol is actually necessary in your cell membranes
and other places in your body.
Just like there's good fats.
But one thing these sphingolipid, cholesterol
part of the lily pads do is they basically,
they're like--
they're like quilt-like patches,
like patches in a quilt.
And they happen to hold stuff together more,
so they have a more stable structure.
Like lily pads floating in water,
they would be like the lily pads.
But aside from just holding stuff together,
they can do something else really cool
and they can actually hold the proteins in place.
So inside a lily pad, we could have one of these
gorgeous flowers and pretend the flower--
I can't draw flowers.
Definitely can't draw flowers with my little marker here.
But pretending that one of these beautiful flowers
was inside the lily pad and that was a protein,
then they can do cool stuff
like be little channels or gateways.
And there are actually stems going down here
from the bottom of the lily pad.
Just like when Thumbelina gets deserted
on the lily pad, I think it's by a dragonfly,
and then the fish are so sad for her
that they go and they start nibbling--
I can't draw a fish, either.
You'll just have to imagine fish.
And the fish are all sad for Thumbelina.
So then they nibble.
And this right here in the body.
Since I'm just telling a story of Thumbelina here.
This stem of the lily pad
would be going through the membrane of the cell
and this would be a channel
where proteins could get through.
But in the story of Thumbelina,
she gets deserted on this lily pad,
you may recall, by a dragonfly, I think,
and I guess it depends on who tells the tale,
and the fish are sad for her,
because Thumbelina is so awesome.
And so they nibble at the stem
and free her and then she gets to take this awesome
water rafting trip, whitewater rafting trip
down the river on lily pads.
It's pretty cool.
Let's take a look at a nice animation
of the fluid mosaic model,
because a lot of times, when you look at these diagrams
and textbooks and all
just limited by the two-dimensional nature
of paper, there's only so much of a picture
that you can get of what this actually looks like
or how it actually works in the body.
And this little animation, I think, is pretty cool.
Just to give you a little bit of a feeling of what
the phospholipid bilayer is really like.
So here, something bumps into it.
It is actually very flexible,
and even when these little phospholipids get knocked
out of place, because they're positive or, excuse me,
they're charged and non-charged sides,
they'll scoot right back in line.
Oh, no, I'm getting seasick!
But it's like that, they move around,
and what this animation does not show
is that they not only go up and down like waves,
but they can actually float around and orient--
you know, move around left and right and squish about.
Now we're seeing some protein channels,
some lily pads letting stuff float through,
and we'll talk in the next segment,
the next lecture, about how this happens,
but there's little protein channels
those green, little lily pads can move about.
Here comes one floating now in a sea of phospholipids.
What does limit it from actually just floating about all the time
are the cholesterols which anchor
as well as there are also proteins that anchor.
So, there are some things anchoring it in there.
All right, so, let's watch another super quick video
that's gonna tell you some real basics
about the cell membrane.
Hi, my name is Mary Poffenroth,
and I'm an adjunct professor of biology.
And today, we're gonna be talking
about the plasma membrane.
The plasma membrane separates the internal environment
from the external environment.
It kind of acts like border control,
controlling what comes in and what goes out of the cell.
The plasma membrane is made up of mostly proteins
and special lipids called phospholipids.
These phospholipids arrange in a double layer,
or bilayer, arrangement.
The top and the bottom of this bilayer arrangement
are water-loving, or hydrophilic,
and the inside of the tails
is going to be water-hating, or hydrophobic.
Think of it kind of like an Oreo cookie
where the round, chocolaty cookies
are going to be hydrophilic, or water-loving,
and that creamy center, that's gonna be water-hating.
So, let's think about it for a second.
Why would a cell want the edges
that touch the outside as well as the inside
of the cell to be water-loving?
Let's use humans as an example.
Humans, like most creatures on this planet,
are mostly made of water.
Now, you wouldn't want a cell
floating around in a bunch of water
that was water-hating, right?
Most plasma membranes also have special proteins
embedded in their phospholipid bilayer.
These special proteins help with the transport
of molecules across that membrane,
and they serve other special functions,
like giving the cell shape
as well as adhering to other cells
to create tissues.
Thanks for watching, and if you want
to learn more about this subject,
click on the link below.
All right, and while we're at it,
we're gonna watch one more quick video,
and I'll show you a master link here
because this is just about a three and a half minute lecture
of Carl Shuster, who I think
his video lectures are excellent.
Some of them are a little bit more detailed
than I test you on, but again,
I think a little bit more detail
sometimes actually explains things better,
so I like his videos so much that I put a link to them
on the personal settings of my Canvas page,
so rather than put links to all his individual videos
in each and every one of our units,
I just put a link on my personal settings,
but I highly recommend that you check them out,
and this is just a sample of one of them.
The only thing I don't like about his videos
is that the screencording system he used
is currently not iPhone-friendly,
so--because of the Flash player it uses,
so you currently cannot watch them on your iPhone
unless I'm recording it through my player,
and then you can see it,
but if you're using his links,
you need to use a computer,
and I would imagine his college
will probably try to change that if they can,
but it has to do with how they recorded it.
So, let's take a look at the proteins
and cholesterol inside the cell membrane.
There we go.
Another molecule we commonly see embedded
in the plasma membrane is cholesterol.
Cholesterol, you will recall, is a lipid molecule.
In fact, it's a steroid.
And it is therefore soluble in other lipids.
How I want to describe the role of cholesterol
to you is that of rebar.
Rebar are these metal poles
that we put inside of concrete
in order to help concrete stay together.
The concrete molecules don't stick to each other very well.
Well, they do, but they tend
to fall apart on the outside edges.
By putting a structure inside of the concrete,
this allows the concrete molecules
to stick to something inside,
therefore they tend to stay together better,
and this is the role of cholesterol.
It floats inside of this Jell-O-like matrix
and stabilizes the membrane by allowing
these neighboring molecules to stick to it.
Besides carbohydrate and lipid molecules,
we also see a lot of proteins
embedded inside the plasma membrane.
As a matter of fact, proteins make up
more than half of the membrane by weight,
and we can categorize them in two types.
Some of these proteins are what we call integral proteins.
In other words, they are inserted
or built in directly into the plasma membrane,
as you're seeing here.
You know what it means to be an integral part of a team,
it means you're a basic part of the team.
Some of these proteins face to the outside,
some of them are inserted deep inside the bilayer.
These integral proteins can act in several ways
in the cell's physiology.
Sometimes they are receptors
and they act to attach to other molecules.
Sometimes they're gonna be used as recognition markers
for the immune system.
Sometimes they can be anchors,
whether on the inside of the cell here,
anchoring the cellular skeleton,
or on the outside anchoring one cell to another.
They could also often act as carriers or channels.
We're gonna talk a lot about integral proteins
as the semester goes on.
Your author gives you a table
outlining some of these basic functions:
receptors and enzymes and channels
and identity marker proteins.
Here we're seeing an anchor for a neighboring cell.
These are called Cell Adhesion Molecules,
or CAMs, a molecule that anchors
to a molecule in the membrane of a neighboring cell.
Another classification of proteins are those
that are not embedded in the plasma membrane
but rather sit on the outside.
Many of these on the extracellular side
are enzymes.
Many on the intracellular side
are anchors for the cytoskeleton.
So, here you're seeing a peripheral protein
attaching to the cytoskeleton inside of the cell.
I'm gonna pause him right there
'cause I don't remember if he's gonna mention
this or not, but this is
a pretty cool diagram here on the bottom
with all these little tubes
like the Doozers build in Fraggle Rock
or like scaffolding.
Because I am just gonna guess
if you ever think about the inside of a cell,
with the organelles floating around,
if you ever give it that much thought,
I would imagine you might think
about these little organelles
just floating about in a sea,
but there are actually little tubes,
little tubes of scaffolding,
there are little filaments of protein
that help hold them in place,
and this is important to hold elements
close to each other because there's
incredibly complex cascade reactions
of chemicals going on,
and having things in the right place
and then having these filaments kind of guide the process
is very important if everything
is sort of very time-critical
in order to get these chemical reactions to occur,
you even need to have these things close together
so you can kind of position things.
And these little filament proteins,
they also connect to the cell membrane itself.
This occurs, of course, within the intracellular matrix.
However, these proteins can attach to fibers
in the extracellular matrix as well.
This helps to give the cell some shape
and to stabilize it in place.
Another function of the cytoskeleton
you're seeing here is that it does hold
the internal organelles in place.
They are not just floating around freely
inside the cytoplasm.
All right, so, he just said a lot of stuff
that proteins do in the cell.
Let's take a look at it a little, teeny bit slower.
So, the proteins that are inside the cell membrane
can basically be divided into two different kinds:
integral and peripheral,
and basically, that's just saying
which proteins go right inside,
and in many cases, all the way
through the membrane, and that would be integral,
they go inside the membrane
and oftentimes all the way through,
versus on the surface of the membrane
and like sticking out of the membrane,
and those are called peripheral,
like on the periphery or the outer edges.
So, these proteins,
whether they're going through the membrane
or on the outside of the membrane,
they make up about half of the plasma membrane,
and that is by mass, in other words, by weight,
make up about half the plasma membrane.
So, about--approximately, roughly half
is the phospholipid soap bubble,
and then about half of it-- by weight, anyway,
although these proteins are gonna be
a lot heavier than these phospholipids--
they're gonna make up about half of it.
So, let's take a look at some of the jobs
these proteins have.
They have a lot of big, important jobs.
A lot of the proteins that go through the cell membrane
are involved in transport.
So, a lot of times, they are channels or pores,
which are, if we go back to the analogy
of the log cabin with the windows
and the doors wide open,
they would be like windows or doors,
so they're basically pores to let bigger stuff through,
like bears, but, you know,
and some of the ways the body can determine
and the membranes can determine what gets through or not
are just how big those pores are,
and we're gonna look at other ways
they determine what goes through or not,
but it'd be like putting a--
well, this wouldn't work for bears,
but let's say you put a screen door
on your house door, and now you have
this nice, little, fine mesh.
That fine mesh is gonna keep most everything outside,
like the mosquitoes.
But let's say your dog accidentally scratches
a hole in your screen door,
and now you have a hole,
a bigger hole, in that screen door.
Well, now your mosquitoes and other stuff
can get in your screen door.
Well, so, somehow these protein channels work
are as simple as just what size hole
is in the screen mesh, but then of course,
as you can probably guess, there are other ways
you can determine what goes in and out,
'cause that really wouldn't be that selective
to just have different sized holes,
and if it was big enough, you know,
if the hole was big enough, stuff would get through.
You have to have other ways to choose
what gets through or not.
Now, some of you may know a thing or two
about chemistry and physiology already,
but whether you know something or not,
go ahead and think about this like a puzzle
you're trying to solve.
If you wanted to think in chemical terms
and keep some stuff out and let other stuff in,
what did we look at when we looked
at the chemistry of water that was one
of the main determinants of how stuff worked chemically?
A lot of stuff works chemically based on charges
and whether it has any charge at all
or whether it has a positive or negative charge.
So, a lot of times, these just can be like a voltage-gated
or ion-gated channels whether they're gonna let
positive or negative stuff through.
And this is totally like, you know, the game,
"Red rover, red rover,
let phosphates come over!"
Yeah, no, we didn't play that version as kids,
it was a little bit different.
Where was I?
Oh, yes. Channels, pores.
How else do integral proteins work?
They can also bind with substances,
so certain chemicals can connect to the proteins,
and we'll take a look at this in detail next lecture.
They can also be receptors
for different chemical messengers like hormones.
One thing to start really getting a good grasp on
in your mind and forming a mental picture
is that proteins are really, really gigantic molecules.
They have lots and lots--
they're like this big, giant string,
and with this big, giant string,
you're gonna have a lot of areas
that are all kinked up and twirled on each other
like a big ball of yarn that got all snarly,
your cats have been playing with it,
and it's all a big mess, you're never gonna separate it,
or sometimes they'll end up forming
like a little twister tornado
and you get all these crazy, three-dimensional shapes
when you're talking about proteins.
And the shapes, and where there's
little positives and negatives
and where they're looking for carbons,
that's gonna determine a lot of what interacts with them.
The proteins that are peripheral,
on the periphery, sticking on the outside,
they have some different jobs.
They can be the little filaments,
so the little--basically like squiggly lines
that can hold one cell onto another cell
or hold together different parts of a cell,
giving it some stability and some structure.
They can be enzymes, which is basically--
and enzymes are an important concept.
Enzymes are basically a chemical
that helps other chemical--
or catalyzes other chemical reactions to happen faster
usually without being changed in structure themselves.
So, I mean, we have, like, I mean, just...
way more chemical processes than anybody could count
or comprehend going on at any one time,
and a lot of these things need to happen really quickly,
like when you're sending a nerve signal
or firing a muscle, and so a lot of times,
you need to catalyze or speed up chemical reactions.
I think this last one is pretty cool.
Your cells are actually sugar-coated,
so you have sweet, little cells,
and what it actually is,
it's a combination, basically,
of a protein and a carbohydrate,
the glycocalyx,
is this little purple antenna
on the little pink mountains.
That is the glycogen or the glyco--the sugary part
is the little purple antenna sticking out,
and then it's stuck to a protein.
So, it's like a sugar on top of a protein,
but these are those little markers or those little flags,
little identity markers of your body
identifying its own cells,
which are a very important part of the immune system.
All right, so, that's the basic structure
of a cell membrane.
Let's see.
I got to get out of drawing mode here,
excuse me, we can't move on.
We're stuck till I get out of the drawing mode.
There we go, okay.
So, now that you know more
about how a plasma membrane is formed,
the phospholipid, bubble-like part
making up about 50 percent of it by weight,
and then proteins and cholesterol
forming the little lily pads and filaments, channels,
now that you know more about the cell membrane,
if you think back to some of our questions about bubbles
and how we could take something like a soap bubble
but give it more defined structure and shape
to have the shapes of our over 200 different kinds of cells,
and then how could we actually get substances
to travel through a cell membrane?
So, let's take a little look at a little science experiment.
And then, after we take a look at the bubble experiment,
just what's next, the next slideshow,
we're gonna look at how substances
actually cross over the membrane,
but let's take a quick look at a little lab.
This--she's mostly using a bubble...
soap mix with some glycerin, by the way.
Or you can say like, "Here you go.
Find three ways to get that pencil through."
Way number one:
take the plastic tubing,
submerge it in bubble solution,
so that when we pull our contraption up here,
we can actually put this through
and the pencil slides on through...
All right, and so, in that little part
of the experiment, what is the little tube--
in the cell membrane, what acts like the little tube,
and why did she have to put the soap solution on it
before she put it in there?
...without breaking the membrane,
so the membrane's still intact.
That's the first way of getting the pencil through
without breaking your membrane.
All right, second way: using the string.
The easy way is just to kind of like,
place the string right on the top
so that as you pull this up,
now you see the string is embedded in there,
you can actually poke the middle out of the string,
so you see that we have this hole here
where the pencil can pass on through.
And again, think about in cell membranes
what is acting like the string embedded in there.
What's the material made out of,
and what's the name of it?
You get the idea.
And the cool thing about showing this
or having the students do this is you can show
that, you know, even though you now have this hole,
this opening in your cell membrane
that allows you to pull things through,
you can take your paper clip,
you can actually pull that string out,
and you see that the membrane closes right behind it,
kind of demonstrating endo- and exocytosis of the...
So that she mentioned endo- and exocytosis,
which we're gonna get to next time,
but it also demonstrates how
when the membrane itself is disturbed
that with a fluid mosaic model,
the little phospholipids are self-orienting,
and they will go back into position
and they will re-seal themselves when torn.
...cell membrane.
All right, and lastly,
and the most fun for the students,
actually take the pencil,
you just submerge it in bubble solution,
and we find out that anything
that is made of the same properties
will actually pass through the membrane there.
And think about why is that.
Why if you coated the material in the same material,
why could it pass through,
and in the body, how would cell membranes
be structured for that to work
and for substances to cross through?
And when you're thinking about that,
think about the hydrophilic and hydrophobic
and positive--and charged sides and non-charged sides,
and, you know, lipids and all that.
It's usually at this point when they figure this out
that kids get the crazy, zany idea
that, "You know what?
If I can get the pencil to do that,
I bet I can get my hand to do it,"
and the answer is yeah, they totally can.
So, you can actually take your entire hand
and start placing it through
and pull it back without popping the membrane.
I've had kids actually get their whole arms through.
It's a complete mess, but the great thing is
is that it's soap, which means
that after the lab, your kids have completely
washed all your tables, which is great.
Things that are made of the same material such as the lipid
will actually pass through the cell membrane
without any need of a protein channel,
or endo- or exocytosis, such as with using the string.
So, like I said, this is a great way
to help kids understand the properties
of the cell membrane, it's a fun lab for them,
they really, really enjoy it and they really have a good--
All right, cool, thank you for your time,
and I hope you spend some time thinking
about how the cell membrane is structured,
the phospholipid part, the protein part,
the cholesterol part, and start to think
about how we're gonna get substances across
and why that is so important,
and then start thinking about the other functions
of the cell membrane, too, because as we study
each system in the body, you're gonna see
that the cell membrane is critical
for functions throughout the entire body.
So, sometimes these basic concepts at first--
anatomy and physiology kind of builds in layers,
and when you first look at a concept,
it may not quite make sense,
but these are kind of the important,
critical building blocks, the foundation,
that you kind of have to spend time
grappling with them with your mind,
and until you're on a walk
and random things like trees
start to remind you of anatomy and physiology,
you're not thinking about it enough.
So, just start to think about it
as you're going about your day,
and there's so many things when you're making your dinner
or making a cup of coffee.
I mean, there's chemistry, there's biochemistry,
there's anatomy and physiology in action.
You can start to think about how all these systems
in the body actually work.
And then, anatomy and physiology comes alive
and it's completely amazing.
Thank you for your time.
