The Cell Membrane

Summary

This video explores the cell membrane, focusing on the fluid mosaic model, which describes its fluid nature and diverse components like phospholipids, proteins, glycoproteins, and cholesterol. It delves into the amphipathic nature of phospholipids, the roles of different proteins, and how substances like water, ions, and glucose move across the membrane, highlighting the importance of cholesterol in maintaining membrane fluidity.

Takeaways

• 🧬 The cell membrane is described by the fluid mosaic model, which highlights its fluid nature and the ability of its components to move freely.
• 🔬 The membrane is composed of various components including phospholipids, proteins, glycoproteins, glycolipids, and cholesterol, each playing a distinct role.
• 🔴 Phospholipids are the primary constituents of the cell membrane, featuring a polar head and nonpolar tails, making them amphipathic.
• 🌐 The dual polarity of phospholipids, with hydrophilic heads and hydrophobic tails, contributes to the formation of the phospholipid bilayer in the cell membrane.
• 🌐 Proteins in the cell membrane can be categorized as peripheral, integral, or transmembrane, each with different functions and interactions with the membrane.
• 🌐 Glycoproteins and glycolipids are involved in cell interactions and signaling, and play crucial roles in the immune system and cell recognition.
• 🌊 The cell membrane is semi-permeable, allowing certain molecules like small nonpolar molecules and water to pass through, but requiring transport proteins for ions and larger molecules.
• 🚰 Aquaporins are integral proteins that facilitate the efficient transport of water across the cell membrane, crucial for maintaining cellular hydration.
• 🔋 Cholesterol acts as a buffer in the cell membrane, maintaining its fluidity by preventing phospholipids from moving too far apart or too close together, thus aiding in homeostasis.
• 🔥 The fluidity of the cell membrane is influenced by temperature, with increased temperature leading to increased fluidity, and cholesterol playing a role in regulating this process.

Q & A

What is the fluid mosaic model and how does it describe the cell membrane?

The fluid mosaic model is a concept that describes the structure of the cell membrane. It suggests that the membrane is fluid, allowing phospholipids and proteins to move freely in any direction within the membrane. The term 'mosaic' refers to the variety of components that make up the membrane, including phospholipids, proteins, glycoproteins, glycolipids, and cholesterol.

What are the main components of the cell membrane?

The main components of the cell membrane include phospholipids, proteins, glycoproteins, glycolipids, and cholesterol. Phospholipids form the bilayer structure of the membrane, while proteins can be integral or peripheral, with some spanning the entire membrane (transmembrane proteins) and others embedded within or associated with the surface of the membrane.

What is the dual polarity nature of a phospholipid?

A phospholipid has a dual polarity nature, meaning it has both hydrophobic (water-fearing) and hydrophilic (water-loving) parts. The hydrophobic tails are composed of fatty acid chains, while the hydrophilic head contains a phosphate group. This amphipathic nature allows phospholipids to form the bilayer structure of the cell membrane, with the hydrophobic tails facing away from water and the hydrophilic heads facing towards water.

How do proteins function within the cell membrane?

Proteins in the cell membrane serve various functions. Some are integral proteins that are embedded within the membrane, while others are transmembrane proteins that span the entire membrane. They can act as channels for ions, carrier proteins that transport larger molecules like glucose, or as enzymes to speed up chemical reactions. Surface proteins can be involved in cell signaling and interactions.

What is the role of cholesterol in the cell membrane?

Cholesterol plays a crucial role in maintaining the fluidity of the cell membrane. It has both polar and nonpolar regions, with the polar region facing outward and the nonpolar region interacting with the hydrophobic tails of phospholipids. Cholesterol acts as a buffer, preventing the membrane from becoming too fluid or too rigid by spacing the phospholipids appropriately in response to temperature changes.

How does the cell membrane control the passage of substances?

The cell membrane is semi-permeable, allowing certain substances to pass through while blocking others. Small nonpolar molecules like oxygen and carbon dioxide can diffuse easily across the membrane. Water, being a small polar molecule, can also diffuse but at a slower rate due to its interaction with the nonpolar interior of the membrane. Ions and larger polar molecules require transport proteins, such as channel proteins and carrier proteins, to move across the membrane.

What are aquaporins and what is their function?

Aquaporins are special proteins that facilitate the transport of water molecules across the cell membrane. They increase the efficiency of water movement, allowing water to pass through the membrane more easily than it would by simple diffusion alone.

What is the difference between a glycoprotein and a glycolipid?

A glycoprotein is a molecule where a carbohydrate (sugar) chain is attached to a protein, often found on the surface of cellular membranes and plays a role in cell recognition and immune system functions. A glycolipid, on the other hand, has a carbohydrate attached to a phospholipid and is also involved in cell interactions and signaling.

How does the cell membrane maintain homeostasis through cholesterol?

The cell membrane maintains homeostasis through cholesterol by调节 the fluidity of the membrane. As temperature increases, cholesterol helps to decrease fluidity by preventing phospholipids from moving apart. Conversely, when the temperature decreases and the membrane becomes more rigid, cholesterol acts as a spacer to increase fluidity, thus maintaining the membrane's stability and function.

What is the function of the sodium-potassium pump mentioned in the script?

The sodium-potassium pump is an example of an ion channel protein that helps to maintain the electrochemical gradient across the cell membrane by actively transporting sodium ions out of the cell and potassium ions into the cell. This process is crucial for nerve signal transmission and muscle contraction, among other functions.

How does the presence of unsaturated phospholipids affect the fluidity of the cell membrane?

The presence of unsaturated phospholipids, which contain double bonds causing kinks in their fatty acid chains, increases the fluidity of the cell membrane. These kinks prevent the fatty acid chains from packing tightly together, allowing for greater movement and flexibility within the membrane.

Outlines

00:00

🧬 Introduction to the Cell Membrane

This paragraph introduces the cell membrane and its components. The fluid mosaic model is discussed, highlighting the fluid nature of the membrane, allowing phospholipids and proteins to move freely. The model also emphasizes the membrane's composition of phospholipids, proteins, glycoproteins, glycolipids, and cholesterol. Phospholipids, with their polar heads and nonpolar tails, are the primary focus, described as amphipathic molecules that form the bilayer of the cell membrane. The role of proteins, including globular and surface proteins, is also touched upon, with a distinction made between integral and transmembrane proteins.

05:01

🌐 Proteins and Their Functions in the Cell Membrane

This paragraph delves deeper into the types of proteins found in the cell membrane, such as surface proteins and integral proteins. Surface proteins can be anchored to the cytoskeleton, functioning as enzymes or playing a role in the immune system. Glycoproteins, which are proteins with attached sugar chains, are highlighted for their role in cell interactions and immune system recognition. Glycolipids, which have sugar units attached to phospholipids, are also mentioned in the context of cell signaling. The paragraph further discusses the semi-permeable nature of the cell membrane, allowing certain molecules to pass through while blocking others, and the role of aquaporins in water transport across the membrane.

10:02

🚰 Transport Mechanisms Across the Cell Membrane

This paragraph focuses on how substances move across the cell membrane. Small nonpolar molecules like oxygen and carbon dioxide can easily diffuse, while water, being a small polar molecule, can diffuse but at a slower rate due to its interaction with the nonpolar interior. Special proteins called aquaporins facilitate water transport. Ions and large polar molecules like glucose require transport proteins to cross the membrane. Channel proteins, such as ion channels, and carrier proteins are discussed, with the sodium-potassium pump given as an example of how ions are transported.

15:03

🌡️ Cholesterol's Role in Membrane Fluidity

This paragraph discusses the role of cholesterol in the cell membrane. Cholesterol has both polar and nonpolar regions, with the polar region facing outward and the nonpolar region facing inward. Cholesterol acts as a buffer, maintaining the membrane's fluidity. As temperature increases, the membrane becomes more fluid, and cholesterol helps prevent the phospholipids from moving too far apart. Conversely, when the temperature decreases, cholesterol acts as a spacer to prevent the membrane from becoming too rigid. This function of cholesterol is crucial for maintaining homeostasis in the cell.

20:04

🔍 Review and Practice Questions on Cell Membrane Components

This paragraph reviews the key components of the cell membrane and poses practice questions to reinforce understanding. It covers the amphipathic nature of phospholipids, their role as the major components of the cell membrane bilayer, and the false statement regarding their composition. The paragraph also addresses which particles cannot pass through the cell membrane without transport proteins, highlighting the need for channel proteins and carrier proteins for ions and large polar molecules like glucose. The distinction between surface proteins, globular proteins, transmembrane proteins, and integral proteins is clarified through additional questions.

25:05

🌡️ Factors Affecting Membrane Fluidity and Summary

This paragraph explores factors that affect the fluidity of the cell membrane, such as temperature and the composition of phospholipids. It explains that increasing temperature generally increases membrane fluidity, while cholesterol helps maintain a balance. The paragraph also discusses the impact of saturated versus unsaturated phospholipids on fluidity. Finally, it provides a series of matching problems to review concepts like semi-permeable membranes, aquaporins, the fluid mosaic model, ion channels, cholesterol, glycoproteins, glycolipids, integral proteins, transmembrane proteins, carrier proteins, and peripheral proteins.

Keywords

💡Fluid Mosaic Model

The Fluid Mosaic Model is a fundamental concept in cell biology that describes the structure of the cell membrane. According to this model, the membrane is fluid, allowing phospholipids and proteins to move freely within it. This fluidity is crucial for the dynamic nature of the cell membrane, facilitating processes like cell signaling and transport. In the video, this model is used to explain how the cell membrane is composed of various components that can move and interact, contributing to its functionality.

💡Phospholipids

Phospholipids are the primary building blocks of the cell membrane. They are amphipathic molecules, meaning they have both hydrophobic (water-repelling) and hydrophilic (water-attracting) regions. The hydrophobic tails of phospholipids face away from water, while the hydrophilic heads face towards water. This arrangement forms the phospholipid bilayer, which is the basic structure of the cell membrane. In the video, phospholipids are highlighted as the major components of the cell membrane, essential for its integrity and function.

💡Proteins

Proteins in the cell membrane serve various functions, including transport, signaling, and structural support. They can be categorized as integral proteins (embedded within the membrane), transmembrane proteins (spanning the entire membrane), and peripheral proteins (associated with the membrane surface). The video discusses how these proteins contribute to the membrane's functionality, with examples like aquaporins for water transport and ion channels for ion transport.

💡Glycoproteins

Glycoproteins are proteins that have carbohydrate chains attached to them. They are found on the surface of cellular membranes and play crucial roles in cell recognition, immune responses, and cell-to-cell interactions. In the video, glycoproteins are mentioned as molecules that help in self-recognition and interactions, illustrating their importance in biological processes.

💡Glycolipids

Glycolipids are lipids with carbohydrate chains attached to them. They are involved in cell signaling and tissue recognition, contributing to the cell's ability to communicate and interact with its environment. The video script mentions glycolipids as components that play a role in these processes, emphasizing their significance in cellular communication.

💡Cholesterol

Cholesterol is an important component of the cell membrane that helps regulate its fluidity. It has both polar and nonpolar regions, allowing it to interact with both the phospholipids and the aqueous environment. The video explains how cholesterol acts as a buffer, maintaining the membrane's fluidity by preventing phospholipids from moving too far apart or too close together, depending on the temperature.

💡Semi-permeable

The term 'semi-permeable' describes the selective permeability of the cell membrane. It allows certain molecules, like small nonpolar molecules and water, to pass through while blocking others, such as large polar molecules and ions. In the video, this property of the cell membrane is discussed in the context of how substances move in and out of cells, highlighting the role of transport proteins in facilitating this process.

💡Aquaporins

Aquaporins are integral proteins that facilitate the transport of water molecules across the cell membrane. They increase the efficiency of water movement, which is crucial for maintaining cellular hydration and participating in processes like osmosis. The video script mentions aquaporins as proteins that help water pass through the membrane, emphasizing their role in water transport.

💡Transmembrane Proteins

Transmembrane proteins are integral proteins that span the entire cell membrane. They have parts both inside and outside the cell, allowing them to function in transport and communication. The video explains that all transmembrane proteins are integral proteins, but not all integral proteins are transmembrane proteins, highlighting their structural and functional importance in the cell membrane.

💡Integral Proteins

Integral proteins are proteins that are embedded within the lipid bilayer of the cell membrane. They can be either transmembrane proteins, which span the entire membrane, or proteins that are partially embedded within the membrane. The video script discusses integral proteins in the context of their role in the membrane's structure and function, noting that they are an essential component of the cell membrane.

💡Carrier Proteins

Carrier proteins are transport proteins that facilitate the movement of large polar molecules, like glucose, across the cell membrane. They bind to the molecule and change conformation to transport it across the membrane. The video script mentions carrier proteins as a means by which glucose and other large molecules are transported, illustrating their importance in cellular nutrition and metabolism.

Highlights

Introduction to the cell membrane and its components.

Explanation of the fluid mosaic model of the cell membrane.

Description of the fluid nature of the membrane allowing phospholipids and proteins to move freely.

Identification of membrane components including phospholipids, proteins, glycoproteins, glycolipids, and cholesterol.

Detailed structure of a phospholipid with a polar head and nonpolar tails.

The amphipathic nature of phospholipids and their role in forming the phospholipid bilayer.

Differentiation between globular and surface proteins and their locations on the cell membrane.

Explanation of integral and transmembrane proteins and their functions.

Role of surface proteins in cell signaling and their potential anchoring to the cytoskeleton.

Function of glycoproteins in the immune system and cell interactions.

The role of glycolipids in cell signaling and tissue recognition.

Semipermeability of the cell membrane and the diffusion of small nonpolar molecules like oxygen and carbon dioxide.

Importance of aquaporins in facilitating water diffusion across the cell membrane.

Necessity of transport proteins like ion channels for ions to pass through the membrane.

The role of carrier proteins in transporting large polar molecules like glucose across the membrane.

Cholesterol's function as a fluidity buffer in maintaining the cell membrane's fluidity.

Impact of temperature on membrane fluidity and cholesterol's role in temperature regulation.

Practice problems to reinforce understanding of cell membrane components and functions.

Summary of the key points covered in the video about the cell membrane.

Transcripts

in this video we're going to talk about

the cell membrane and we're going to

identify the components that make up

that membrane

now the first thing we're going to do is

talk about something known as the fluid

mosaic model

so this model describes

the cell membrane

it tells us that the membrane is fluid

which means that

the phospholipids are free to move

in any direction in this membrane even

the proteins highlighted in purple

they're also fluid they can move about

in this membrane as well

the word mosaic tells us that this

picture

is composed of many different parts

the membrane is composed of

phospholipids

proteins glycoproteins glycolipids

cholesterol and things like that so

there's many different parts that make

up the cell membrane

but the first component we're going to

talk about

is the phospholipid in red

the membrane is mostly composed of

phospholipids

the phospholipid has a polar head

and two

nonpolar cells

so keep in mind the phospholipid is

composed of

a phosphate group

it has two fatty acid chains

and it also has a glycerol molecule

the two fatty acid cells are nonpolar

which means that they're hydrophobic

they don't like water

the polar head is hydrophilic it loves

water

water

exists in the extracellular fluid

outside of the cell

and it also is present in the

intracellular space that is inside of

the cell

so all of the phospholipids the polar

heads are faced toward water the

nonpolar tails are faced away from water

in the interior of the cell membrane

now here's a question for you

what word

describes

the dual polarity nature of a

phospholipid

we said that a phospholipid has a polar

hydrophilic head

and two

nonpolar hydrophilic tails

there's a word that describes a molecule

with hydrophobic and hydrophilic parts

what word is that

that word is amphipathic

phospholipids are amphipathic

because they're both hydrophobic and

hydrophilic

so they make up the phospholipid bilayer

of the cell membrane

so that's the first component of the

cell membrane that you need to be

familiar with

now the cell membrane is consists of

a lot of proteins

and there's different types of proteins

they're highlighted in purple

what do you call this protein right here

so if you see a circular protein it's

known as

a globular protein

and the fact that it's on the exterior

it's also called

a peripheral

protein

this protein here is known as a surface

protein because it's on the surface

of the phospholipid

bilayer

now

how would you distinguish these two

proteins

what would you say

by the way this is another peripheral

protein

but it's not a globular protein

now

how would you distinguish between an

integral protein and a trans membrane

protein

this protein here is known as

a trans membrane protein i'm just going

to put tmp for that since i'm running

out of space a transmembrane protein

spans

across

the membrane so as you can see part of

it is outside of the membrane and the

rest of it is inside of the membrane

this here is called

an integral protein

an integral protein is embedded within

the membrane

now a transmembrane protein is also an

integral protein

because

for them to

span the entire membrane they also have

to be within the membrane as well

so all transmembrane proteins are

integral proteins

but not all integral proteins are

transmembrane proteins

so as we said before this is both a

transmembrane protein and an integral

protein but this right here is an

integral protein and not a transmembrane

protein

now i had to clear away a few things

because

the page was getting crowded

now one thing i do want to mention is

you could also have a surface protein on

the inside of a cell

but it's on the surface of the membrane

and some of these surface proteins

they could be anchored

to the cytoskeleton network of the cell

through filaments

now some of the

surface proteins and also the perfume

proteins

they could function as enzymes

so they can speed up chemical reactions

within the cell as well

now

here's another question for you what's

the difference

between these two structures there

what are they called

so here we have a protein

attach to a sugar chain

those hexagonal shapes represents

the six carbon

glucose unit

so we have a carbohydrate attached to a

protein

so this is called a glycoprotein

many glycoproteins which are found on

the surface of cellular membranes

they play a role in the immune system

with antibodies they function as a self

recognition and

cell to cell interactions

now over here

notice that we have

a sugar unit attached to a phospholipid

so in this case this would be

a glycolipid

which also plays a role in cellular cell

interactions and cell signaling

now the next thing we're going to talk

about

is how things flow into and out of the

membrane

the cell membrane is semi-permeable

which means it allows certain things to

get in

while blocking other things or prevent

other things from entering the cell

now small nonpolar molecules can easily

diffuse into or out of the cell

so when you take a breath when you

breathe in you're breathing in o2

oxygen

flows into the cell because the cell

needs it and then when you exhale you

breathe out carbon dioxide so carbon

dioxide tends to flow out of the cell

so both of these molecules

are nonpolar small molecules they can

easily

pass in and out of the cellular membrane

now water

is a small polar molecule and it turns

out that water

can diffuse

through the membrane

but

it can't do it easily it's a very slow

process because water is polar

and it doesn't

mix well with the nonpolar interior

region however because the concentration

of water is so high inside and outside

of the cell some of it will force its

way through the cellular membrane

but now there are special proteins

that can easily

transport water

into and out of the cell

and these are called aquaporins

so this protein right here this integral

protein also serves as a protein that

transports stuff

a protein that transports water through

the membrane as you said before

aquaporins

water can flow into or out of

you know that protein

so if you drink a glass of water

water is going to flow into your cells

if it's a hot day and you're jogging and

you're sweating you're dehydrated

water's flowing out of your cells so

water can go in either direction

now what about other

particles let's say like an ion

potassium and sodium

can they flow into and out of the

cellular membrane

now ions

they can't flow

in and out of the cellular membrane

without the help of a transport protein

so they can't just pass through the

membrane

their charges are significantly greater

than water water is neutral but it has

partial charges which makes it polar

ions have a complete full positive or

negative charge

so they just can't flow through the

membrane

without the help of a transport protein

so the protein that they need is called

a channel protein specifically it's

known as ion channels

so the ion channels will help sodium and

potassium to flow either into or out of

the cell

one example is the sodium potassium pump

which i'm not going to go

into detail into this video

so

integral proteins they could serve as

channel proteins they could serve as

carrier proteins

and things like that

now this right here is an example of a

carrier protein

let's say if you have a big molecule

like glucose

the carrier protein can

take in glucose

and then this part can close

this part

will open

and then glucose will travel through

glucose is a big polar molecule it can't

simply diffuse

through the membrane so it needs the

help of a carrier protein to get it

across the membrane

so just to review

small molecules like oxygen carbon

dioxide water they can diffuse

through the membrane for what it's a

little bit difficult

big molecules like glucose

big polar molecules

they can't diffuse through the cell and

ions like sodium potassium they can't

diffuse across the membrane without the

help of a protein

now there's one more thing that we need

to talk about

regarding the cell membrane another

important component and that is

cholesterol

which is right here

now cholesterol has

a polar region and a nonpolar region

the circle in blue is the hydroxyl group

of the cholesterol molecule

and the hydroxyl group is polar because

of hydrogen bonding

it's very attracted to water

and so it's going to be

facing

outside of the cellular membrane

now the four fuse rings of cholesterol

and that's the nonpolar region the

hydrophobic region

and so that's going to be pointing

towards the interior

of the membrane

now the function of cholesterol in the

membrane is very important cholesterol

acts as a buffer

it maintains

the fluidity of the membrane

here's a question for you

if you increase the temperature

what happens to the membrane

will it become more fluid or less fluid

will the phospholipids

will they move apart from each other

or

will they move closer to each other

now let's think of water

at room temperature water is fluid

if you decrease the temperature let's

say if you put it in a freezer it's

going to turn to ice it's not going to

be fluid anymore so whenever you

increase the temperature

you increase the fluidity of a material

now

as you increase the temperature of the

cellular membrane

the phospholipids will move apart from

each other and so they will become more

fluid

cholesterol

it functions to maintain a fluid

so it's going to try to

decrease the fluidity

and so what it does is

it kind of prevents the phospholipids

from moving apart from each other so

that the cell membrane just doesn't

dissolve

now if we decrease the temperature

the fluidity of the membrane will

decrease it will become more rigid

cholesterol

will act to prevent that it's going to

try to increase the fluidity so it acts

as a spacer

so these phospholipids when the

temperature goes down they want to get

closer and so what happens is

cholesterol prevents them from getting

too close

so whenever the fluidity goes up

cholesterol tries to bring it down when

the fluidity goes down cholesterol tries

to bring it up so it maintains the

fluidity

of the cell

so it's another example of homeostasis

or equilibrium

so that's the function of cholesterol

in the cell membrane

now let's work on some practice problems

just to review some of the things that

we covered early in this video

number one

which of the following statements is not

true

concerning phospholipids

would you say a

phospholipids are amphipathic

b

phospholipids contain a hydrophilic head

c

the tails of a phospholipid point toward

the interior of the cellular membrane

d phospholipids are the major components

of the cell membrane bilayer or e

phospholipids contain a phosphate group

three fatty acetals and the glycerol

molecule

so which of these statements is not true

or which one is false

so let's go through each one

this is a true statement

phospholipids are

amphipathic

they contain a hydrophilic polar head

and the tails

are hydrophobic

so answer choice a is the true statement

b

phospholipids contain a hydrophilic head

that is also true as you can see that

here

and for c

the tails of a phospholipid point toward

the interior of the cellular membrane

that is also true

the membrane looks like this

and as you can see the tails are

definitely in the interior of the

membrane

now for antichoice d

phospholipids are the major components

of the cell membrane bilayer that is

definitely a true statement

the only thing that's false is e

phospholipids do contain a phosphate

group

and they contain a glycerol molecule

but they don't have three fatty acid

cells

they only have two

and so that's why e is not true

number two

which of the following particles cannot

pass through the cell membrane without

the assistance of a transport protein

so we're going to circle each one

because there can be multiple answers

so let's say

this is

the cell membrane

can water pass through the cell membrane

what would you say

now it's not that easy but because

there's a lot of water inside and

outside the cell the human body is

mostly composed of water

it can

fit through it it's very small

so water can pass through the cell

membrane

so this is not what we're looking for

now what about the potassium ion can

that pass do it

ions

are not able

to go through the membrane

they can't get to this hydrophobic

region

so

b is one of the answers that we're

looking for

nonpolar molecules like o2

this can easily diffuse in the cell

membrane

and carbon dioxide which is another

nonpolar molecule that can that can

easily diffuse out of the membrane

out of the cell into the extracellular

fluid

so we can eliminate anti-choice c and d

now glucose

glucose can't diffuse

through the membrane without the

assistance of a transport protein

so glucose it needs a carrier protein to

get through the membrane

so e would also be an answer so it's

both b and e

ions and big polar molecules like

glucose

and they need a transport protein to

pass through the membrane

number three

which of the following proteins span

across the entire cell membrane

is it a surface proteins

b

the globular proteins c

transmembrane proteins

d

integral proteins or e carrier proteins

what would you say

so let's say this is the cell membrane

so this would be a surface protein

this would be a globular protein

and it's also a peripheral protein

because it sticks out of

the membrane but doesn't pass through it

this would be

an integral protein

and this would be

a transmembrane protein

the best answer

is the transmembrane protein

this it spans across the entire cell

membrane

the integral protein

it's simply embedded within the cell

membrane

now keep in mind all transmembrane

proteins are integral proteins but not

all integral proteins are transmembrane

proteins

and carrier proteins as we mentioned in

the video they simply

carry stuff across the cell membrane

so this is really not the best

description of a transmembrane protein

they could be transplanting proteins

they could be integral proteins but

this answer is the best answer

number four

which of the following molecules act as

a fluidity buffer in the cellular

membrane

is it cholesterol aquaporins ion

channels glycoproteins or glycolipids

it's not going to be aquaporins keep in

mind these are proteins

that can carry water across the membrane

it's not going to be ion channels ion

channels are protein channels that carry

ions like potassium and sodium

across the cell membrane

and it's not going to be glycoproteins

so these

exist on the surface of the cell and

it's not going to be glycolipids

the answer is cholesterol

so keep in mind as the temperature goes

up

the fluidity of the membrane goes up the

phospholipids move apart

but cholesterol

kind of anchors the phospholipids

together so prevents them from moving

apart thus maintaining the fluidity

so whenever the temperature goes up

cholesterol tries to decrease the

fluidity of the membrane

under colder conditions

the membrane becomes more rigid

cholesterol acts as a spacer increasing

the fluidity of the membrane

so cholesterol maintains the fluidity of

the membrane

now here's another question for you

number five

which of the following can increase the

fluidity of the cellular membrane

so number one we've already covered this

we know that increasing

the temperature

will increase the fluidity of the

membrane so number one is a true

statement

what about number two increasing the

number of saturated phospholipids

will that increase or decrease

the fluidity of the cellular membrane

well let's talk about saturated fatty

acids

a saturated fatty acid if you recall

has no double bonds

and these

tend to be solid at room temperature

now an unsaturated fatty acid

they do carry double bonds and this

creates a kink in the structure

so these type of fatty acids tend to be

liquid

or oils at room temperature

so you need to understand that saturated

fatty acids

and saturated phospholipids

they tend to be

more rigid

whereas the unsaturated phospholipids

will have more fluidity

they're going to be more liquid

so the correct answer

will be

increasing the number of unsaturated

phosph excuse me increase the number of

unsaturated phospholipids that's going

to increase the fluidity if you increase

the number of saturated phospholipids

that will decrease the fluidity

so number two is false

the answer is going to be one and three

which is ants choice b

so this will be an example of a

saturated

phospholipid because

both of the fatty acids

they're straight

this is an example of an unsaturated

phospholipid

as you can see one of the fatty acid

chains has a kink in the structure which

means it has a double bond

so if you have more of these

phospholipids

the membrane is going to be more fluid

phospholipids of this nature

will create a membrane that's more rigid

and less fluid

now let's work on some matching problems

feel free to pause the video

and

work out these questions

for the sake of a review

so let's go ahead and begin number one

so this allows some molecules to pass

through while preventing others from

doing so

so which word best describes that

sentence

so the answer for this

would be a semi-permeable

membrane it allows certain molecules to

pass through the membrane while

preventing others from doing so

number two

so which word goes with this sentence

it allows water to pass through the

membrane efficiently

so this would be

an aquaporin

number three

this explains how phospholipids and

proteins

are free to move in the cell membrane

so this is going to be

the fluid mosaic model

so

we're going to put letter i for number

three number four

this allows particles like potassium and

sodium ions to pass through the membrane

so this is going to be

ion channels

so let's put g for number four

number five

this maintains the fluidity of the cell

membrane

so this is going to be cholesterol

so let's put b for five number six

and this molecule plays

this should be plays a role

in cell communication and

self-recognition in the immune system

what molecule is that

this is going to be the glycoproteins

so that's a d

number seven

an amphipathic molecule that makes up

the cell membrane bilayer

which one is that

so the answer is going to be l

phospholipids are amphipathic

they contain hydrophobic and hydrophilic

parts to themselves and they make up

the phospholipid bilayer of the cell

membrane

number eight

so this plays a role in cell signaling i

said that wrong cell signaling and

tissue recognition

so this is going to be the glycolipids

and number nine

this macromolecule is completely

embedded within the lipid layer i mean

the lipid bilayer

my words is just not coming out right

today

so this is going to be uh the integral

proteins

they're completely integrated

in the lipid bilayer

number 10

this molecule completely spans through

the membrane

so this is going to be the transmembrane

protein

so that's c

number 11

this component transports

molecules across

the membrane

so that's going to be the carrier

protein that's h

and 12 this molecule lies on the

exterior of the cell membrane

which is f

the peripheral proteins

surface proteins also lie on the

exterior of the cell membrane

but the peripheral proteins

part of it is

inside the membrane and part of it is

outside of the membrane but it doesn't

span completely through the membrane

so that's basically it for this video

that's an introduction into the cell

membrane thanks again for watching and

if you like it

don't forget to subscribe to this

channel