Plasma membrane / Cell Membrane (updated)

Summary

This educational video delves into the intricacies of the cell membrane, highlighting its crucial role in regulating the transport of substances into and out of cells. It explains the semi-permeable nature of the membrane, allowing small, uncharged molecules like CO2 and O2 to pass while restricting larger or charged ones. The video breaks down the phospholipid bilayer, emphasizing the hydrophilic heads and hydrophobic tails, and introduces cholesterol's role in maintaining membrane fluidity. It also touches on the fluid mosaic model, detailing components like proteins, carbohydrates for cell recognition, and the cytoskeleton's dual function in support and transport. The engaging presentation invites viewers to test their knowledge through a quiz and encourages discussion.

Takeaways

• 🔬 The cell membrane, also known as the plasma membrane, is the outer boundary of cells and controls the passage of materials into and out of the cell.
• 🧬 The cell membrane is primarily composed of a double layer of phospholipids, which form a bilayer structure.
• 🔍 Phospholipids have a polar, hydrophilic 'head' and two hydrophobic 'tails', which arrange themselves with the heads facing the aqueous environments and tails facing each other.
• 🚫 The plasma membrane is selectively permeable, allowing small, non-charged molecules like CO2 and O2 to pass through but not larger or charged molecules like glucose or ions.
• 🌡️ Cholesterol molecules embedded in the phospholipid bilayer help maintain the membrane's fluidity and prevent the phospholipids from separating too far apart.
• 🌐 The plasma membrane is often referred to as a 'fluid mosaic model' due to its composition of various components that are in constant motion.
• 📦 Protein channels within the membrane facilitate the transport of larger molecules or charged molecules, such as glucose, that cannot pass through the phospholipid bilayer.
• 🧵 Carbohydrates attached to proteins or lipids protrude from the cell surface and serve for cell recognition and identification, including determining blood types.
• 🏠 The cytoskeleton, composed of protein threads like microtubules and microfilaments, provides internal support to the cell and acts as a pathway for molecular transport.
• 🌡️ The fluidity of the plasma membrane can be influenced by temperature and other environmental factors, with cholesterol playing a role in maintaining its structure.

Q & A

What is the primary function of the cell membrane?

The primary function of the cell membrane is to control the passage of materials into and out of a cell.

What is the basic structure of the cell membrane?

The cell membrane is a double layer of phospholipids, known as a phospholipid bilayer.

Why is the cell membrane described as semi-permeable or selectively permeable?

The cell membrane is semi-permeable or selectively permeable because it allows only certain materials to pass through, typically small molecules that are non-charged.

What are the characteristics of molecules that can freely pass through the plasma membrane?

Molecules that can freely pass through the plasma membrane tend to be small and non-charged, such as carbon dioxide and oxygen.

What is a phospholipid and what are its main components?

A phospholipid is a molecule with a polar head and two non-polar tails. The head consists of a phosphate group and glycerol, while the tails are made of fatty acid chains.

Why are the heads of phospholipids hydrophilic?

The heads of phospholipids are hydrophilic because they contain a phosphate group and glycerol, which can form hydrogen bonds with water molecules.

How do the tails of phospholipids contribute to the structure of the cell membrane?

The tails of phospholipids are hydrophobic, which means they do not interact with water. This property causes them to orient themselves away from the watery environment, forming the interior of the cell membrane.

What role does cholesterol play in the cell membrane?

Cholesterol helps to prevent the phospholipids from separating too far from one another, thus maintaining the cell membrane's compactness and flexibility.

What is the significance of carbohydrates in the plasma membrane?

Carbohydrates in the plasma membrane are used for identification or recognition purposes, such as determining blood type and helping the immune system to distinguish between self and foreign cells.

How do protein channels in the cell membrane facilitate the transport of molecules?

Protein channels allow larger molecules or charged molecules, like glucose, to pass through the cell membrane when they cannot pass through the phospholipid bilayer.

What is the cytoskeleton and what is its role in the cell?

The cytoskeleton is a network of protein threads that provide internal support to the cell, similar to the framing of a house. It also serves as a pathway for molecules to transport and travel within the cell.

Why is the plasma membrane referred to as a fluid mosaic model?

The plasma membrane is referred to as a fluid mosaic model because it is composed of a variety of components that are in constant motion, giving it fluidity, while also being a mosaic due to the diverse elements it is made of.

Outlines

00:00

🔬 The Cell Membrane: Structure and Function

This paragraph introduces the cell membrane, also known as the plasma membrane, as the outer boundary of cells. It discusses the membrane's role in controlling the passage of materials into and out of the cell. The cell membrane is primarily composed of a double layer of phospholipids, which are depicted as having a polar head and two hydrophobic tails. The paragraph explains the semi-permeable nature of the membrane, allowing small, uncharged molecules like carbon dioxide and oxygen to pass through freely, while larger or charged molecules, such as glucose and ions, have difficulty. The orientation of phospholipids in the membrane is also discussed, with the hydrophilic heads facing the aqueous environment and the hydrophobic tails facing inward, away from water.

05:03

🌐 The Fluid Mosaic Model of the Plasma Membrane

This paragraph delves deeper into the components of the plasma membrane, often referred to as the fluid mosaic model. It describes how the phospholipids, with their hydrophilic heads and hydrophobic tails, orient themselves in response to the watery environment surrounding and within the cell. The paragraph also introduces cholesterol molecules, which play a crucial role in maintaining the membrane's compactness and flexibility. Carbohydrates, either attached to proteins or lipids, are highlighted for their role in cell recognition and identification, including determining blood types. The paragraph further discusses protein channels that allow larger or charged molecules, such as glucose, to enter the cell. Lastly, it mentions the cytoskeleton, composed of protein threads that provide internal support and serve as pathways for molecular transport within the cell.

10:03

📝 Quiz and Conclusion

The final paragraph of the script transitions into a practice quiz for viewers, presumably students, to test their understanding of the material covered. It invites them to pause the video and answer the questions on a separate sheet of paper, offering to check answers and engage in discussion. The paragraph concludes by expressing hope that the viewers enjoyed the video and thanks them for watching.

Keywords

💡Cell Membrane

The cell membrane, also known as the plasma membrane, is the outer boundary of cells that controls the passage of materials into and out of the cell. It plays a crucial role in maintaining the cell's internal environment and protecting it from external threats. In the video, the cell membrane is described as being selectively permeable, allowing only certain materials to pass through, which is essential for the cell's survival and function.

💡Phospholipids

Phospholipids are the fundamental building blocks of the cell membrane, forming a double layer known as the phospholipid bilayer. Each phospholipid molecule has a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails. This structure is crucial for the membrane's selective permeability, as the hydrophilic heads face the aqueous environments both inside and outside the cell, while the hydrophobic tails face each other, preventing most water-soluble substances from passing through easily.

💡Semi-permeable

The term 'semi-permeable' or 'selectively permeable' refers to the property of the cell membrane that allows it to selectively allow certain substances to pass through while blocking others. This is essential for the cell to control the movement of nutrients, waste products, and signaling molecules. The video explains that small, uncharged molecules like oxygen and carbon dioxide can pass freely, while larger or charged molecules, such as glucose or ions, cannot.

💡Cholesterol

Cholesterol is a molecule that is embedded within the phospholipid bilayer of the cell membrane. Although high cholesterol is often associated with health issues, in the context of the cell membrane, cholesterol is beneficial. It helps to maintain the fluidity of the membrane and prevents the phospholipids from separating too far from one another, thus contributing to the membrane's overall health and function.

💡Carbohydrates

Carbohydrates in the cell membrane are often attached to proteins or lipids and extend outward from the cell surface. They serve as identifiers or recognition markers, which are crucial for cell-cell communication and immune system function. The video mentions that our blood type is determined by the specific carbohydrates present on our cells, highlighting their role in cell recognition.

💡Protein Channels

Protein channels are integral membrane proteins that form pores or channels through which certain molecules, such as glucose, can pass. These channels are selective and facilitate the transport of specific substances that cannot pass through the phospholipid bilayer due to their size or charge. The video explains that glucose, which is essential for cellular energy production, enters the cell through these protein channels.

💡Cytoskeleton

The cytoskeleton is a network of protein filaments that provide structural support and help maintain the cell's shape. It is composed of microtubules, microfilaments, and intermediate filaments. In addition to providing internal support, the cytoskeleton also serves as a pathway for intracellular transport, allowing molecules to move within the cell, as mentioned in the video.

💡Fluid Mosaic Model

The fluid mosaic model is a concept that describes the structure of the cell membrane. It suggests that the membrane is not static but is composed of a variety of components, including phospholipids, proteins, and carbohydrates, that are in constant motion. This fluidity allows the membrane to be dynamic and adaptable to various cellular needs, as discussed in the video.

💡Hydrophilic

Hydrophilic, derived from 'hydro' meaning water and 'philic' meaning loving, refers to molecules that are attracted to water. In the context of the cell membrane, the hydrophilic heads of phospholipids face the aqueous environments, allowing them to interact with water molecules. This property is essential for the membrane's interaction with the cell's surroundings and its selective permeability.

💡Hydrophobic

Hydrophobic, from 'hydro' meaning water and 'phobic' meaning fearing, describes molecules that repel water. The hydrophobic tails of phospholipids in the cell membrane are an example. These tails do not interact with water and instead face the interior of the membrane, contributing to the membrane's selective permeability by preventing the passage of most water-soluble substances.

Highlights

The cell membrane or plasma membrane controls the passage of materials into and out of a cell.

The cell membrane is a double layer of phospholipids.

Phospholipids have a polar head and two hydrophobic tails, orienting with heads facing water and tails facing inward.

The plasma membrane is semi-permeable, allowing small, non-charged molecules like CO2 and O2 to pass freely.

Large molecules or charged ions, such as glucose and sodium, have difficulty passing through the phospholipid bilayer.

Cholesterol molecules embedded in the phospholipid bilayer prevent the phospholipids from separating and maintain membrane flexibility.

Carbohydrates attached to proteins or lipids on the cell membrane are used for cell identification and recognition.

The plasma membrane is referred to as a fluid mosaic model due to its composition of various components that are in motion.

Protein channels in the membrane allow larger molecules or charged molecules, like glucose, to enter the cell.

The cytoskeleton provides internal support to the cell and serves as a pathway for molecular transport.

The fluidity of the plasma membrane can be affected by temperature and other environmental factors.

Cholesterol molecules help maintain the integrity of the cell membrane by holding phospholipids together.

The cell membrane's structure allows for selective permeability, crucial for cellular function.

The plasma membrane's components are not static, illustrating the fluid nature of the membrane.

The orientation of phospholipids with hydrophilic heads and hydrophobic tails is essential for membrane function.

The plasma membrane's fluid mosaic model is a key concept in understanding cell biology.

The video includes a practice quiz for viewers to test their understanding of the plasma membrane concepts.

Transcripts

okay so in this video we're going to

discuss the cell membrane or the plasma

membrane the outer boundary of our cells

so let's get

started so you've probably heard that

the cell membrane or the plasma membrane

the job is to control the passage of

materials into and out of a cell and

that's kind of that's what we're going

to be discussing today what is

controlled and also what is the cell

membrane itself made

from well its most basic the cell

membrane is a double layer of what are

called phospholipids so here we have a

zoomed in a zoomed in image of a

phospholipid and we're going to dissect

this and and analyze a phospholipid in

more detail but notice how there's are

two rows of phospholipids it almost

looks like one is standing right side up

and almost looks like one is standing

upside down well we'll explain why that

is in a little

bit so an important feature of the

plasma membr is that it is

semi-permeable or selectively permeable

and this means that only some materials

may pass through the plasma membrane not

everything notice how the black circles

are freely able to pass but the larger

orange hexagons are not so molecules

that are easily able to pass tend to be

small molecules and they tend not to

have a charge to them carbon dioxide and

oxygen are two great examples of this

molecules that are unable to pass or

have difficulty passing tend to be large

molecules or molecules that have a

charge or ions ions are atoms that have

a charge you know glucose is a large

molecule unable to pass freely through

the plasma membrane sodium and chlorine

are ions atoms with a with a charge to

them and because of their charge they're

not able to freely pass through the

phospholipid

bilayer well I actually want to look

into a phospholipid in more detail so

here's our phospholipid from earlier

notice how it has a lump of atoms at the

top a cluster of atoms you know we call

this the head and then dangling down

there appear to be two chains of of

atoms and these are the

Tails now when we look at the head of a

phospholipid it's actually uh chemically

it's polar and I want you to know that

it's made from two parts there's the

phosphate group and notice how there's

phosphorus at the bottom of of that of

that structural diagram there and then

the second part of the Polar head is the

glycerol part and there's the glycerol

part now if you recall polar molecules

are molecules where an area is slightly

positive and another area is slightly

negative well it turns out by the

nitrogen turns out this is where the the

phosphate group tends to have a positive

charge to it and down by the oxygens

tend to have a negative charge so this

is the reason why the head is

polar and as a result the head is said

to be hydrophilic now when we break

apart the word into prefix and suffix

you know Hydro implies water and philic

means loving so the head is water loving

it will seek out water uh and that's

going to be important once we get into

the the cell membrane and all the other

parts in a moment

and then there are the tails that we

said earlier so the Tails tend to be two

chains of fatty acids that have attached

to the blue glycerol and notice how one

of the fatty acids has a kink in it well

that's because it's a unsaturated fatty

acid and the one that's perfectly

straight is a saturated fatty

acid and so the the two tails there are

what are called hydrophobic they don't

have a charge Hydro still implies water

phobic implies that it's fearing now it

doesn't actually fear and run away from

water it's just not attracted to water

so when we look at uh phospholipids in

the cell membrane in a few moments

you're going to see how the hydrophilic

head and the hydrophobic Tails Orient

themselves you know for Simplicity

you're often going to see phospholipids

just drawn as a circle with two lines

dangling down and from from now on for

the rest of this video this is how I'm

going to illustrate a phospholipid as

well

so when we look at the arrangement we

mentioned earlier that the cell membrane

is a phospholipid bilayer there are two

layers of phospholipids that make up our

cell membrane and the heads the polar

heads tend to be on the outside and the

non-polar Tails tend to be sandwiched on

the inside well why is this this is

because cells are surrounded by water on

both sides outside the cell the cells

are in a watery solution inside the cell

cell contains cytoplasm which is mostly

made from water so you know water is

polar and the heads of the phospholipids

are polar so they're attracted to one

another that's why the the phospholipids

Orient themselves with the heads facing

the watery environment and so we have

the hydrophilic heads on the outside and

the hydrophobic tails on the inside

because of their attraction to water

so now I'd like to discuss all the

components of the plasma membrane not

just the phospholipid bilayer the plasma

membrane is also referred is often

referred to as a fluid mosaic model now

when I hear the word Mosaic I tend to

think of artwork you know various

artworks are called mosaics because

they're made from a a wide variety of

elements you know here we have two

pieces of art made from tiles different

size color shapes and they've been

arranged to make these two beautiful

pieces of Art and so the plasma membrane

is very much a mosaic because it's made

from a wide variety of of components and

it's also called a fluid model and I'll

explain why that is in a little bit

later first of all let's start looking

at the components the phospholipids we

already mentioned with their hydrophilic

heads and their hydrophobic Tails will

tend to allow small nonpolar or

non-charged molecules to pass carbon

dioxide oxygen are two gases that can

freely pass through the phospholipid

bilayer we also see these yellow

geometric shaped structures embedded

within the Tails of the phospholipids

these are colesterol molecules now when

we hear cholesterol we tend to think of

you know someone with too high of

cholesterol and some negative health

effects but cholesterol plays a very

important role it helps to prevent the

phospholipids from separating too far

from one another therefore it keeps the

cell membrane Compact and um and bound

together and thus giving the cell

membrane its flexibility so cholesterol

plays a really important role in the

overall health and function of the

plasma

membrane in the green chain of circles

these are carbohydrates now sometimes

these carbohydrates are attached to

proteins and sometimes they're attached

to lipids but these carbohydrates are

sticking out of the cell and they are

used for identification or recognition

purposes this is one way our immune

system knows to Target foreign cells but

to ignore cells that belong to us and

for instance our blood type is

determined by the carbohydrates that are

on our

cells another part I want to mention is

this blue channel in the middle the

protein Channel now like the implies

it's made from protein and it allows

certain objects to pass objects that

can't just pass through the phospholipid

bilayer Like Oxygen and like carbon

dioxide but larger molecules or even

molecules that have a charge to them

glucose is a great example glucose is

unable to pass through the phospholipid

bilayer but cells need glucose so

glucose is actually taken in through

these protein channels to the interior

of the

cell another part I want to mention is

the cytoskeleton notice how there are

these threads that crisscross and zigzag

on the inside of the cell well these are

the protein threads that make up the

cytoskeleton now there's different kinds

of protein threads there are the

microtubules and the microfilaments and

the intermediate

filaments and the this the proteins of

the cytoskeleton help to give internal

support you know the analogy is is like

it's like the framing on a house they

help to support the house uh so it

doesn't topple

over but they also play another role the

cytoskeleton is also a pathway for

molecules to transport and travel along

here we see some molecules trans being

transported uh throughout the cell and

even uh some of the molecules uh being

exiting and uh and exiting from the cell

but you can see they are traveling along

the protein threads of the

cytoskeleton so this is the reason why

again the plasma membrane is called the

fluid mosaic model well Mosaic because

it's made from a variety of Parts but

fluid because those parts can drift

around and are in motion the parts are

not static the phospholipids are able to

drift left and right the carbohydrates

the proteins the cholesterol molecules

and so the fluidity can be affected by

temperature and other Environmental

factors but holding a lot of the

phospholipids together again are those

cholesterol molecules that are embedded

within the Tails of the

phospholipids so there you have it

there's our um our practice quiz here if

you're in my biology class you know

pause the video try to answer these

questions on a separate sheet of paper

and I'd love to check your answers

before school or after school one day

I'd also like to hear your comments in

the box below so I hope you enjoyed

thanks for

watching for