Shadowing Practice: Cell Biology | Cell Structure & Function - Learn English Speaking with Video

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Alright InjNerds, in this video today we are going to be talking about the structure and function of the cell.

Also, if you guys haven't already, go watch our video where we talk about how I study and prepare for videos.

Within that, I kind of gave you guys a sneak peek of how I pretty much went through, studied this topic, developed notes,

diagrams, and then drew it all out on the board.

Now we're going to go through it.

Before we get into this video though please continue to support us by hitting

that like button commenting down the comment section and please subscribe.

Alright Ninja Nerds let's get into it.

Alright Ninja Nerds

so we're gonna take a tour through the cell talking about what all the structures of the cell are

and then what they do.

So the first thing we got to talk about is the brain of the cell.

The pretty much the center of the cell where everything

that a cell is kind of really begins and all centers around and that is the nucleus.

This is the big mama the nucleus.

Now what we have to talk about with the nucleus is a couple different components of the nucleus.

What are the different components of the nucleus?

Well the first part of the nucleus is as you can see you see this kind of like blue membrane

it's double layered here so you have an outer layer

and then you have a inner layer on this side right so this is our inner layer layer.

These two components make up what's called the nuclear envelope.

So you have an outer layer and then you have an inner layer.

I know that sounds pretty obvious, but there's different functions for the outer and the inner layers.

So the outer layer, let's actually first say the nuclear envelope, you have two layers, the outer layer and the inner layer.

What is the purpose of these layers?

So the first thing that you need to remember is that the outer layer is where you have lots of ribosomes.

So ribosomes are actually going to be kind of found outside on that outer layer.

The reason why is in the actual nucleus, you take DNA and convert it into a structure called mRNA.

And mRNA has to move out via the nuclear pores and bind onto ribosomes on these outer membranes, which then get moved to the rough ER.

We'll talk about that a little bit later.

But that's the big thing I want you to remember about the outer membrane, The inner membrane has a very,

very important protein structure that binds to the DNA and histone proteins and controls a lot of cell division.

It's this green protein here.

That green protein that lines the inner membrane is called lamins.

And lamins are very, very important structures that control the structure of the nuclear envelope.

They're also important for cell division and interacting a lot with the chromatin.

There's actually a disorder.

Whenever there's a mutation in this lamins, it causes progerias.

So it's important that we kind of know these two components of the nuclear envelope.

The next thing is in the nuclear envelope, you see these red proteins that are dispersed throughout it?

Those red proteins that are dispersed throughout it, these are called nuclear pores.

So what are these called?

Nuclear pores.

And the whole purpose is it's honestly pretty straightforward, right?

If we want to move things in, ions or proteins or nucleotides or different things in and out of the nucleus,

that's the function of the nuclear pores.

And there is things, we'll talk about this a little bit later in a more specific video where we go more in detail on the nucleus,

but there's special types of transporters that are associated with those nuclear pores.

We'll talk about those in other videos.

But again, another important thing that's a part of the nuclear envelope, if you will, that actually kind of separates different portions where there's little pores,

is called these nuclear pores.

And again, the whole purpose of this is to allow for transport.

And what kind of transport?

Transport between the cytoplasm to the nucleus or nucleus to the cytoplasm.

That's all it is.

Pretty straightforward.

The next one is this red diced up structure here called the nucleolus.

The nucleolus is very, very important.

And the reason why is this is the site of a particular type of RNA synthesis.

You know there is a particular the type of rRNA, what we call rRNA.

So we're going to denote this as rRNA synthesis.

This occurs in what structure?

This occurs within the nucleolus.

Now, the reason why that's important is when you take rRNA, you synthesize it within the nucleolus, and you combine this with protein.

So then combine with other types of small proteins, guess what you make?

You make ribosomes.

So really what we can say is that the nucleolus, which is a component in the nucleus, is important for making ribosomes,

which is made up of rRNA and small proteins.

The last part of the nucleus is all of these blue structures.

You see all these blue structures that are kind of dispersed throughout, I kind of made circles around them.

This is called chromatin.

This is called chromatin and chromatin is very very important because this is what really makes up who we are as

Kind of humans and it's very important for us to know the different components of chromatin

So within the nucleus you have this structure called chromatin.

So what in the heck is chromatin? chromatin is made up of two primary things DNA and proteins,

but the main protein is is histone proteins.

Histones.

These two things make up our actual genetic material.

And this chromatin can actually come in two forms, two important forms.

One is called euchromatin.

And euchromatin is the loose chromatin, and it's the one that's going to be more for expression of the DNA to transcribe the DNA

and make different types of mRNA or undergo replication.

So euchromatin should be more in the center of the actual nucleus.

And the next one here is going to be hetero, the heterochromatin.

And the heterochromatin is going to be the tight chromatin.

This is going to be the chromatin that you're actually going to see closer towards the inner membrane of that nuclear envelope.

So we're understanding this, right?

So we know the different structures and the different components here of the nucleus.

The last thing that I want us to understand here is what in the heck does the nucleus do?

We're going to go into way more detail in this in future videos, but what you need to remember is that chromatin,

which is made up of DNA, we can take DNA and do a bunch of things with it.

What can we do with it?

We can take DNA and we can make more DNA.

What is this called?

DNA replication.

I can take DNA and make RNA, and that is called transcription.

And then also you need to know that there's different types of RNA.

What are the different types of RNA?

There is tRNA, there is mRNA, and rRNA.

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So it's important for us to understand this kind of things that are happening with inside the nucleus, which is what?

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You have DNA replication and transcription, and particularly making of RNA molecules and these are the RNA molecules.

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And again, we'll go over these in more detail in future videos.

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But this tells us what the function of the nucleus is and what the components of it are.

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Let's move on to the next organelles.

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Okay, so the next thing that you guys need to know here is this next filamentous membranous structure

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that is located within the cell.

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This beautiful organelle is called the rough endoplasmic reticulum.

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So, it's called the rough endoplasmic reticulum.

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We're going to put ER.

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So, the rough ER, that's commonly how we refer to it as, right?

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So the rough endoplasmic reticulum or the rough ER.

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Now the rough ER, if you notice, it's this filamentous kind of network here.

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But there's another structure here called the smooth endoplasmic reticulum.

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So you have the rough endoplasmic reticulum and then you have the smooth endoplasmic reticulum.

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The smooth endoplasmic reticulum and rough endoplasmic reticulum differ in what way?

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This is very simple.

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You see these little red dots that are located on the rough endoplasmic reticulum.

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It's called ribosomes.

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So within the rough ER, this contains ribosomes on that outer kind of membrane structure.

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On the smooth ER, there is no ribosomes.

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That's really it.

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There's nothing much more

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that you have to know about kind of the structure of the rough ER and the structure of the smooth ER.

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You know that it's an organelle and the big difference between these structure wise is rough ER is ribosomes, Smooth ER does not have ribosomes.

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So now the next thing has to come down to what are the differences in function?

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Because that's really where it kind of lays in, right?

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So the first thing we have to do is before we move into what it does,

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we have to kind of pick up a quick point here from the nucleus and move to the rough ER.

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So you know, we said within the nucleus, you have DNA.

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And from DNA, you can undergo transcription.

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What is that called? whenever you go from DNA to RNA.

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Whenever I go from DNA and I make a molecule called mRNA and that mRNA then binds with a ribosome.

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Here's our ribosome, a little like red dot there.

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That ribosome will then do what?

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It'll undergo the process of translation, taking the RNA and making proteins.

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Well what happens is that ribosome it's going to start synthesizing and making proteins from the mRNA.

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So now I'm going to have this protein that gets pushed in here from the ribosome.

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Now that's important because the rough ER is obviously going to be a site of protein synthesis then.

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That's one thing we can say.

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It could be a site of protein synthesis because that's where the ribosomes are kind of sitting on.

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So that's one function of the rough ER.

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So one function of the rough ER we can say is is it's a site of protein synthesis.

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Site of protein synthesis.

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And we're going to talk a little bit because there's different types of proteins that we make.

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Proteins that can be within the cytosol, proteins that can be within different organelles, proteins that we can secrete,

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proteins that we can put into the membrane.

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Generally, the proteins that the rough ER is making is going to be proteins that will become lysosomes.

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So proteins that will be incorporated into our lysosomes.

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proteins that will go and get incorporated into the different organelles, like the membranes of organelles or the cell membrane,

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or proteins that will be excreted.

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So that is really the big thing that I want you to remember about the rough ER.

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Side of protein synthesis, but particularly for these types of proteins.

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The next thing is what else does it do with the proteins?

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We know it synthesizes them, but you know what else?

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Proteins have to fold a particular way for it to be particularly functional.

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So it also helps with the folding process.

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So it plays around what's called protein folding.

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That's very important.

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So it plays around protein folding.

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And the next thing is not only does it help with folding the protein in a particular way,

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it also has little enzymes located kind of in this actual endoplasmic reticulum that can add on little residues,

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little sugar residues onto this protein, making it active.

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What is this called?

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It's called glycosylation.

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So it can perform what's called glycosylation.

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And there's a particular type, we'll go into this in more detail, but for the most part, it is called N -type glycosylation.

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And all that means is if I were to take a protein here, I took the mRNA, took it to the ribosome,

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ribosome bound to the rough ER.

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It made the protein, pushed the protein in the filamentous network of the rough ER.

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It started folding.

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And then once we have that protein here that's folded properly, I'm going to just add on a little sugar residue.

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So this is going to be a little sugar residue, and this is going to be my protein.

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And this is important because this is the way that we activate these proteins.

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So that is the function of the rough endoplasmic reticulum.

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Now, the next thing, one last thing for this is, remember, I told you that the site of protein synthesis is for these particular things.

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So in order for, after the rough ER has kind of gone through these process of synthesizing it, folding it, and then glycosylating it,

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it then has to package it.

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So then what happens is it'll package off.

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So what happens, let's say that here's the protein, the protein will actually bud into this little portion of the actual rough endoplasmic reticulum.

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And when it does that, that'll actually bud off.

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And then I have a vesicle.

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And within that vesicle is going to be my protein.

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What protein will it become?

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A lysosomal protein and membrane protein are excreted protein.

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But in order for that to happen, I have to move this towards the next organelle, which will be the Golgi apparatus.

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We'll get to that one in a second,

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but here's going to be that protein that was coming from the rough endoplasmic reticulum and moving towards the Golgi.

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So now we know all the functions of the rough ER.

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Now we got to go over the functions of the smooth ER.

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The smooth endoplasmic reticulum, this is a very interesting structure.

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So there's a lot of different types of enzymes located within this smooth endoplasmic reticulum,

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particularly enzymes that are associated with lipid synthesis.

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That's a big thing I want you to take away from this.

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So it's primarily associated with what?

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Lipid synthesis.

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There's going to be a bunch of different enzymes located within this organelle.

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And what kind of lipids are we synthesizing?

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Fatty acids.

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Fatty acids are a big one.

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Phospholipids are a big one.

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What else?

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You know there's another really important cholesterol molecule, well cholesterol, so I kind of gave it away.

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So cholesterol and cholesterol is important because this can become hormones, steroid hormones, testosterone, progesterone, estrogen, all that good stuff.

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So this is the big thing I want you to remember is this is the site of lipid synthesis.

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So we take precursor molecules that we get from the cell.

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Let's say here's a precursor molecule.

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That precursor molecule for the fatty acids, phospholipids, cholesterol, it'll get taken up into this smooth endoplasmic reticulum.

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The enzymes in it will start using these precursors to pop out little cholesterol or lipid molecules.

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So now from this, we're going to have the Smoothie Art take the precursor molecules, perform the lipid synthesis process with the enzymes,

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and then bud off a particular vesicle which is going to contain what?

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Fatty acids, phospholipids, and cholesterol.

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And then guess where we could send this?

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We could send it again to the Golgi or maybe even send it to the cell membrane.

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And then from the cell membrane, we may release out cholesterol.

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We may release out fatty acids.

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Pretty cool, right?

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There's another set of enzymes that are important here.

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The next set of enzymes is called CYP450.

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You're like, what the heck is that?

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CYP450 enzymes are very, very important for detoxification.

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So you know whenever your liver, your liver has a very high concentration of these enzymes.

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Because that's our detox center, right?

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So if you go to your liver, there is lots of this enzyme.

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And the reason why is any drugs, any toxins, any alcohol, you know,

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alcohol, ethanol, ETOH, any of these things have to go to the liver.

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And what your liver does is, is it undergoes a process called biotransformation or xenobiotic metabolism.

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And it breaks down these substances.

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And it's because of these enzymes located within the smooth endoplasmic reticulum.

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So it undergoes what's called biotransformation.

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Ba -boom.

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That is important.

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The next thing here, and this is an interesting one.

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You know within our cells, we have glycogen, right?

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You know glycogen, it's basically a big polymer of glucose.

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And whenever our body needs energy, that glycogen can get broken down into glucose.

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But there's a particular step.

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Whenever you're breaking down glycogen into glucose, there's an intermediate between this called glucose 6 -phosphate.

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Well, in order for glucose 6 -phosphate to get converted into glucose, guess what it needs?

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There's a particular enzyme on the smooth endoplasmic reticulum.

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And that enzyme will need to take the glucose in.

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You have a little transporter that'll take the glucose 6 -phosphate in

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and then a particular enzyme that'll rip off that phosphate on the 6 -carbon of glucose and make, well, off glucose 6 -phosphate and make glucose.

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So the important thing to remember here is that this actual smooth endoplasmic reticulum is also important for glucose 6 -phosphate metabolism.

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So it's also important for glucose 6 -phosphate metabolism.

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Ba -boom!

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roasted.

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Last one.

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Last function.

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You know this is a smooth endoplasmic reticulum.

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It's in a lot of different organs, but you know organs that contain lots and lots and lots of calcium,

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like in our muscles, there's kind of an analogous structure there called the sarcoplasmic reticulum.

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These can store lots of calcium.

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And you know there's little pumps that are located on the smooth endoplasmic reticulum.

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And whenever we need calcium, whether it be for different types of transport processes or for muscle contraction, guess what?

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We can pump that calcium out into the cytosol and utilize it for all these different types of chemical processes.

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So what is the last function here for the smooth endoplasmic reticulum?

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It also stores calcium.

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Ba -boom!

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All right, we've covered the functions of the rough ER and the smooth ER.

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Let's now move on to the Golgi apparatus.

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All right, engineers, so what have we established up to this point?

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So we know that we've understood the function of the rough endoplasmic reticulum.

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We understand the function of the smooth endoplasmic reticulum.

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And again, to kind of go off of that, that smoothie R, again, what did we say?

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It could also make the different phospholipids and cholesterol and different types of fatty acids.

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And that also, from the smooth endoplasmic reticulum, can get sent to the Golgi.

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Now, the vesicles that are coming from these two areas, primarily the rough endoplasmic reticulum, we're going to focus on from this point.

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But again, realize that everything from the Smoothie R as well.

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Alright, so what is the name of this next organelle that we have to talk about?

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This is a very, very important structure called the Golgi apparatus, right?

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So we're going to call it the Golgi.

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Now, the Golgi apparatus is a very important kind of like packaging organelle, if you will.

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So it takes these vesicles coming from the Roughie R, from the Smoothie R.

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And when it takes it into the Golgi, there's an anatomical term here.

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On this side of the Golgi, where these vesicles from the Roughie R and Smoothie R are going to,

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this part of the Golgi here is called the cis Golgi.

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Okay, or they call it the cis face of the Golgi, but we're gonna call it cis Golgi.

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Then what happens is through these systematic steps, these proteins and different types of fatty molecules

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that get taken to the Golgi will go through the Golgi and as it goes through the Golgi it'll actually bud off.

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Alright, so then you're gonna bud off some type of molecule in the Golgi, whether that be a protein, whether that be lipids, cholesterol, whatever.

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It buds off and then leaves the Golgi.

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This side where the vesicles are coming out of the Golgi and going towards lysosomes or cell membranes or whatever, this is called the...

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trans -Golgi or the trans -face of the Golgi.

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So that's an important kind of anatomical term or structure component of the actual Golgi that you need to know.

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The next thing here is we have to kind of primarily focus on the function.

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So primary function is it's receiving vesicles containing proteins

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and different types of sugar molecules maybe attached to it as well as different lipids from the rough ER and smoothie R.

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That's the first function.

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So first function that you need to know here.

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So it's receiving vesicles from the rough ER and the smooth ER.

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That's the first thing we know.

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It's receiving the vesicles containing proteins or fatty molecules.

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Now let's focus on those proteins because that's where it's more important.

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The proteins that are getting taken into the Golgi, it might have to modify.

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We saw that it was folded and modified a little bit in the rough ER,

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but the Golgi might have to modify it even a little bit more.

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And how does it do that?

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So this modification step is very important, and it's again through a couple different reactions.

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Remember we have what's called glycosylation reactions that we talked about with the rough ER?

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The Golgi can do the same thing.

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It can do what's called a glycosylation.

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But this glycosylation reactions where it adds on sugar residues, there's two types.

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One is the N -type and one is O -type.

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What's really important to remember is that the Golgi is the only one that can do O -type glycosylations.

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In other words, I'm adding a sugar residue onto the oxygen component of a protein.

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That's all it really means.

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N -type, you're adding a sugar residue to the nitrogen component of the protein.

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Nothing special.

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The other really important step here is that it also has to phosphorylate specific types of proteins and that is very important.

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There's a disease called Icel disease and it's actually related to this phosphorylation reaction.

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So that's why we need to know it.

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So it modifies proteins in some lipid molecules through these glycosylation and phosphorylation reactions.

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The next thing is, is it packages these molecules, right?

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And then after it packages these molecules into their own little vesicles, remember how we said that these molecules will go through the Golgi,

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undergo these modifications, get stuck into like a little vesicle, butt off, and then pop off here.

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It's going to pop off, right?

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So now I got my vesicle containing my proteins and my lipids and all these things that have been modified even more.

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Now what happens is these molecules, we already talked about where they're going to go.

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They're going to go and become lysosomal proteins.

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They're going to go and become membrane proteins or they're going to go and be excreted out of the cell.

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That is the destination and the function of the Golgi apparatus.

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So now we understand that.

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Now that we've done that, we have to talk about another little structure here, which is our cell membrane.

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It's another component of the cell.

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All right.

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So the next really, really important component of the cell is the cell membrane.

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So what we're going to do is we're going to kind of zoom in on a different part here of the cell,

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right, which is our cell membrane.

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And there's different components of the cell membrane.

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So if you look here, you see like these little red dots with like little, you know, fingers hanging out.

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This is a part of what's called our phospholipid bilayer.

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So when we talk about the cell membrane, there's a bunch of different structures that are involved within the cell membrane,

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and they obviously carry out a very important function.

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So what are the different components of the cell membrane?

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Now the first component here is these little red little thingies.

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What are these little red thingies?

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These are called, this is a part of your phospholipid bilayer.

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So you have two components of it.

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If we kind of zoom out on this little guy, you have these two components.

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This head component of this phospholipid bilayer is actually the phospholipid.

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And what you need to know about this is that this is polar.

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What does that mean?

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Polar means it's water soluble.

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So it's the hydrophilic portion and it can interact with water because it has lots of negative charges on it.

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The other component here is the little tail.

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This tail, these are fatty acids, and fatty acids are really saturated with hydrogen, and so because of that, they are very non -polar.

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Hydrophobic, don't like to interact with water because they have no real negative or slight changes in charge.

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That's the important thing here.

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So we have this on both sides.

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On the inner cell surface, you would have this phospholipid kind of portion pointing inwards.

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On the outer side, you would have it pointing outwards.

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And then you have the tails pointing in towards one another.

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The next thing here is you see this little green structure, which is kind of lodged between these phospholipid.

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This green structure here is called cholesterol.

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Now you're like, what the heck?

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Why is cholesterol coming?

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Oh, and they even add on here.

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Where could that cholesterol come from?

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The smoothie R.

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We packaged it, sent it to the Golgi and then incorporated into the membrane.

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We're putting things together in NGNerds, but the cholesterol is also incorporated in there.

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And the cholesterol is important because it controls like fluidity.

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Okay.

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So it controls fluidity.

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All right.

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So again, to recap this whole idea of cholesterol with fluidity, again, it's just important to remember that the amount of cholesterol,

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if you wanted to think about it like this, the amount of cholesterol in the cell membrane, the more of it you have,

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the less space there's going to be between the phospholipids.

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So there's less fluidity.

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So more cholesterol, less fluidity.

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And the less cholesterol you have here, the more space there's going to be between the phospholipids.

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And so there's going to be more fluidity.

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So less cholesterol, more fluidity.

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So that's an important concept with that.

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The next component of the cell membrane, so we have the cholesterol, we have the phospholipid bilayer, the next big component here is the proteins.

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So the next one that you're going to have here is these little proteins.

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And these proteins here, my pink marker here, these proteins, there's different types of proteins.

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There's what's called integral proteins and peripheral proteins.

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And what is really, really important for these proteins is that they have various different functions.

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They can act as transporters.

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They can act as little enzymes.

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They can act as linker proteins between other cells.

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So they have a lot of different components and a lot of different functions to them.

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But again, there is integral proteins and peripheral proteins.

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The big thing I want you to take away from this, the cell membrane, is that it basically acts as a barrier.

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I mean, I know that sounds super obvious, but it is a barrier.

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It's a selectively permeable barrier and only allows for particular types of diffusion that we'll get into later.

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But there is what's called simple diffusion, right?

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There's what's called facilitated diffusion.

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And then there's different types of what's called vesicular transport.

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And all of these types of processes are involving the cell membrane.

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So in other words, moving things from outside the cell to inside the cell,

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we have particular types of processes that we'll have to go into more detail about.

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But again, big thing I want you to take away from the cell membrane is these different components

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and how it acts as a barrier for particular types of transport processes.

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Alright, let's move on to the lysosomes.

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Alright, so the next structure here is going to be our lysosomes, our beautiful little lysosomes.

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Now these are very, very cool kind of organelles.

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Now what lysosomes are important is they're like these little spherical organelles

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and they contain very interesting little enzymes inside of them and these enzymes are called

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hydrolytic enzymes

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and really the simplest way of describing these hydrolytic enzymes is you have different types you have proteases

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which means that they break down proteins you have nucleases

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which means that they break down nucleic acids you have lipases which means they break down lipids and And you have glucosidases,

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which means they break down carbohydrates.

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So all of these hydrolytic enzymes are located within these little organelles.

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So why is that important?

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Any macromolecules that you bring into the cell, whether that be from a white blood cell undergoing what's called phagocytosis,

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whether that be you actually undergoing an endocytosis process from, it's called clathrin -coated mediated endocytosis.

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That whole process, when you're bringing something in, you're bringing in particle matter.

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And these lysosomes are responsible for using these enzymes to break down macromolecules,

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such as proteins, nucleic acids, lipids, and carbohydrates.

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That's all they do.

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So that's important thing to remember from these hydrolytic enzymes is they're going to be responsible for doing what?

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These all break down macromolecules.

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They break down macromolecules.

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Their respective macromolecules, as we already said.

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Okay, that's one thing that I really want you to remember.

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The second thing, you know, when organelles are getting worn down, maybe our mitochondria has just had a rough day.

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Maybe the cytoskeleton is starting to get all jacked up.

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Maybe our ribosomes have just, they've pooped out and they're done.

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When these organelles have reached the end of their kind of, let's say functional capacity, we don't want to keep them anymore.

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We want to recycle them.

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We want to out with the old and with the new.

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So what happens is these lysosomes, you'll actually take and package.

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Let's say that the ribosomes are done.

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They're tired.

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They're pooped out.

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I'm going to form a little vesicle around these ribosomes.

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And then what I'm going to do is I'm going to send it to the lysosome.

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And what did I say that the ribosomes are made up of?

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Proteins and RNA.

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So what do you think?

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Which enzymes are going to start breaking down this ribosome if you bring it to this lysosome, the proteases and the nucleases,

435

and it'll start breaking down that actual organelle.

436

What is that called?

437

autophagy.

438

So another important thing that you have to remember is that this is one thing, breaking down macromolecules.

439

The second thing is it undergoes autophagy of organelles.

440

Ba -boom.

441

Last thing.

442

Let's say that a cell has actually been severely damaged.

443

You've really damaged this cell.

444

The point of the cell is living and surviving anymore is that it's not going to happen.

445

You know what I'm going to do?

446

I'm going to just have these lysosomes bust open and I'm going to have all of these enzymes,

447

proteases, nucleases, lipase, glucosidases, guess what they're going to do?

448

They're going to break down all the macromolecule components of the cell.

449

What is that called?

450

That's called autolysis.

451

So that's the next thing to remember is autolysis of damaged cells.

452

Okay.

453

So cells that even if they are damaged and you wanted to repair them.

454

There's no point of even repairing them at that point.

455

It's time to just start all over.

456

These things will just bust open and release their enzymes and start breaking down the cell.

457

This is the functions of the lysosomes.

458

They're little angry little buggers, aren't they?

459

All right, next one.

460

Pretty cool ones.

461

These are actually kind of one of my favorite organelles, and these are called peroxisomes. So peroxisomes.

462

These are also spherical kind of like little organelles.

463

And they contain a lot of different enzymes, but by far one of the most interesting enzymes that they contain is there's two of them.

464

One is called catalase and the other one is called oxidase.

465

They have other enzymes, okay?

466

They have like other like metabolic enzymes.

467

We're going to title them as that because it can be kind of confusing if you get into more detail than that.

468

But these are the big enzymes.

469

So the first one I want you to remember is the catalases, oxidases, and then other metabolic enzymes.

470

Why am I kind of telling you all of these things?

471

Well, the catalase and the oxidase is important for free radicals.

472

You know, whenever a cell not normally obtains oxygen, that oxygen can get sometimes converted into what's called a superoxide anion.

473

Then that superoxide anion can get converted into hydrogen peroxide.

474

And then that hydrogen peroxide can get converted into what's called a hydroxyl radical.

475

These things right here, from here to here, all of these molecules are free radicals,

476

very dangerous little suckers, combined onto proteins and nucleic acids and cell membrane and just jack the cell up.

477

We don't want these things to accumulate.

478

The particular one that loves to accumulate, though, in these peroxisomes because of what's called fatty acid metabolism is hydrogen peroxide.

479

It really likes to accumulate in there.

480

So what happens is these peroxisomes have lots of this catalase enzyme.

481

And what they do is they take this hydrogen peroxide and use that catalase enzyme to convert this into water and oxygen,

482

which is not that dangerous, right?

483

That's what we want.

484

So that's one of the beautiful things.

485

Be thankful for these suckers, these little peroxisomes.

486

They're constantly breaking down this hydrogen peroxide, which is a potential free radical, and making water and oxygen.

487

That's one thing.

488

You know that's important for fatty acid metabolism?

489

So they contain little enzymes here, particularly catalase.

490

You know catalase not only is important for these free radicals, but it also can break down fatty acids, the first step in fatty acid metabolism.

491

So it plays a role in what's called fatty acid oxidation.

492

Without going into too much detail, there's actually two types, alpha and beta.

493

And really all this is, is there's different, what's called branch chain, alpha breaks down what's called branch chain fatty acids.

494

And then beta breaks down what's called very long chain fatty acids.

495

But either way, you're breaking down these fatty acids into what's called acetyl -CoA molecules.

496

Then not only can it break down fatty acids, but it can actually break down the fatty acids into acetyl -CoA.

497

And then we can use those acetyl -CoA molecules to make lipids.

498

So we can actually make lipids and cholesterol.

499

You know cholesterol is important because this is also important for making different types of hormones, steroid hormones and bile acids.

500

But this is the one I want to focus on for a second.

501

The lipid that it makes is very important within the white matter of the brain called plasmalogen.

502

and this plasmalogen is a very particular type of lipid that is important for the white matter.

503

So it's an important component of the myelin within the white matter.

504

So you can have an idea that if there's an issue with the peroxisomes and they can't actually synthesize plasmalogen, what happens to the white matter?

505

There may be a decrease in white matter production and that may lead to some injuries to the actual nervous system.

506

The last thing I want you to remember is that there's also a teensy bit of...

507

alcohol metabolism.

508

So it also can break down ethanol.

509

There's a tiny little enzyme, that catalase enzyme again, coming into play, not only with the fatty acids, but also with the ethanol metabolism.

510

It can also break down ethanol.

511

So these are some of the functions of the paroxysm, very, very important type of little organelle.

512

Now that we've covered that one, let's go into the mitochondria.

513

All right, Ninjas, so the next organelle that we're going to talk about here is are mitochondria.

514

Now the mitochondria is a very cool enzyme, I'm sorry, a very cool organelle,

515

and this thing is commonly just broken down into like the simplest way of explaining it.

516

Everybody always knows this.

517

It's the powerhouse of the cell.

518

It's the the site of ATP synthesis.

519

Yes, that is true, but we're going to explain about how it actually does the ATP synthesis.

520

But before we do that again, let's kind of highlight some of the components of this mitochondria.

521

If you look at the mitochondria of an outer membrane, so this is the outer membrane,

522

and it's important to remember that the outer membrane is a smooth membrane.

523

And also, it has a very high permeability.

524

There's a lot of transport proteins on the outer membrane.

525

If you look here, you have this little folded membrane here on the inside.

526

That is called the inner membrane.

527

And usually on most cells, we call this inner membrane, the folding, cristae.

528

We call it the cristae of the inner membrane.

529

Now, this inner membrane has less permeability.

530

It's less permeable to the transport of different types of molecules going in and out of it.

531

Okay?

532

So that's the basics.

533

Inside of the mitochondria, you have this structure in here called the mitochondrial matrix.

534

And this is where a lot of the metabolic reactions are occurring.

535

And it's also where the mitochondrial DNA is found.

536

All right?

537

So we have an idea of the structure of the mitochondria.

538

The next thing is the function.

539

So it's obviously the site of ATP synthesis.

540

But if we were to just take it just a little step further, when we make ATP, we make it in two primary ways.

541

One is called oxidative phosphorylation.

542

The other one is called substrate phosphorylation.

543

The mitochondria has little proteins on its inner membrane

544

that are very important and in a component of what's called the electron transport chain.

545

So ATP synthesis on the mitochondria,

546

in the mitochondria, occurs via the electron transport chain and this type of ATP synthesis is called oxidative phosphorylation.

547

Okay?

548

And that's carried out by this electron transport chain.

549

The other thing that's important with the mitochondria is that there's a lot of metabolic reactions that occur here.

550

A lot of metabolic reactions.

551

What are some of these metabolic reactions that occur within the mitochondria?

552

Well, some of them, as we know, the Krebs cycle.

553

That's an easy one, right?

554

So the Krebs cycle occurs here where you have a lot of different intermediates

555

that are involved whenever acetyl -CoA gets converted into the entire complete structure, right?

556

Where you have the acetyl -CoA and then the isocitrate, citrate, alpha -ketoglutarate, all that stuff there.

557

That's a part of this metabolic reaction.

558

The other one is you have heme synthesis.

559

So you're making the heme component of different types of pigment molecules

560

that are part of the electron transport chain as well as synthesis of heme for hemoglobin or myoglobin.

561

The other one is the urea cycle occurs here.

562

So the urea cycle is another big one where you're taking different types of molecules like ammonia and turning it into urea.

563

The other one is called gluconeogenesis,

564

where you're taking things like amino acids and glycerol and odd chain fatty acids and converting it into glucose, a new glucose molecule.

565

And the last thing that can occur here is what's called ketogenesis, where you're making ketone bodies from acetyl -CoA.

566

So these are some of the metabolic pathways that occur within the mitochondria.

567

One other thing to remember is I already told you about this, but in the mitochondria, it has its own little DNA.

568

So we'll put this up here.

569

This is called mitochondrial DNA.

570

And this actually comes from the mother.

571

Okay.

572

So this is actually going to be DNA that comes from the mother.

573

And this DNA can actually make tiny little proteins that can be involved in some of these metabolic reactions on its own.

574

All right.

575

So the next structure here is going to be our ribosomes.

576

This is the next organelle.

577

Now, ribosomes, we've already kind of alluded to these already, so we're going to have a pretty quick run through these.

578

But obviously, we know that these ribosomes, let's kind of talk a little bit about their structure.

579

There's two components of the ribosome.

580

So you have this large ribosomal subunit.

581

So this is the large subunit.

582

And usually they always like to say this in eukaryotic cells.

583

This is your 60s ribosome.

584

S means Svedberg unit.

585

But again, large subunit.

586

And then the other one is called your small ribosomal subunit.

587

And in the eukaryotic cells, this is a 40S, our 40 Svedberg unit of the ribosome.

588

Again, kind of a very non -essential thing to remember, but again, big thing to remember is that there's two units,

589

a small subunit and a large subunit.

590

The next thing that we have to remember, ribosomes are made up of what two things?

591

We already talked about this.

592

rRNA and proteins.

593

So that's the next thing.

594

The next thing is that ribosomes can be found in two places.

595

We already know one.

596

It could be found on the rough endoplasmic reticulum.

597

Whenever ribosomes are bound to the rough endoplasmic reticulum, we call these, I know it's super obvious,

598

but it's called membrane -bound ribosomes.

599

Okay, so membrane -bound ribosomes.

600

But if these are just kind of in the cytosol freely circulating, then they are called cytosolic ribosomes or free ribosomes.

601

The reason why we should understand the difference between these two is that if you guys remember,

602

the ribosomes that were on the actual rough endoplasmic reticulum, what happened?

603

What do ribosomes do?

604

I guess that's the big question to ask.

605

Let's actually write that down first.

606

What do ribosomes do?

607

They take mRNA and another structure called tRNA and make proteins.

608

So they're basically a site of protein synthesis, right?

609

And we also give this a particular name called translation.

610

So whenever you're taking things like mRNA and making proteins.

611

Well, what happens is if you have ribosomes that are bound to the rough ER, what are those proteins going to become?

612

Remember what we said?

613

Those will become proteins that'll be a part of lysosomes.

614

Those would be proteins that'll become a part of the membrane, like integral or peripheral proteins,

615

or they'll be proteins that we're going to excrete out of the cell.

616

Cytosolic ribosomes, those are just going to be making little enzymes

617

and different types of proteins inside the cell that will not leave the cell.

618

So that is important.

619

So these are going to be making cytosolic proteins.

620

And I know that sounds obviously kind of pretty straightforward, but again, it's something worth mentioning.

621

These are making cytosolic proteins like different types of enzymes

622

that are involved in a lot of your metabolic pathways that occur in the cytosol.

623

Okay?

624

So that's important.

625

So that gives us the importance of ribosomes, what their structure is, and what they do.

626

Now let's finish off with the cytoskeleton.

627

All right, engineer.

628

So now we got to talk about the cytoskeleton.

629

Now, obviously when we talk about the cytoskeleton, the cytoskeleton, we're only showing it in this kind of one point here.

630

But if you really were to show the way the cytoskeleton looks,

631

it would, it would make this board look disastrous because there would just be lines and fibers all over the entire cell.

632

And that's an important thing to remember

633

that even though we're showing this in kind of like a static zoomed in view of these cytoskeletal elements,

634

remember they are scattered all around the cell.

635

That's an important thing to remember.

636

Okay, when we talk about the cytoskeleton there are three different structures of the cytoskeleton.

637

The first one that I want us to talk about is called your micro filaments.

638

Your micro filaments.

639

And sometimes to be honest with you we just refer to this as actin.

640

Okay, and I know you guys have heard of actin.

641

If you guys have watched our videos before you've heard this term actin.

642

It's one of the proteins that are commonly used in muscle contraction, right?

643

So that's an important thing to remember.

644

But when you look at actin, there's these little monomers of actin and they all come together

645

and make this long polymer of actin and you get multiple strands of it.

646

Big thing I want you to remember with this actin structure.

647

First thing when we talk about function,

648

you know when you have a muscle cell there's another protein that actin binds with to cause contraction and relaxation.

649

What is that protein?

650

My So whenever you have actin and myosin, particularly in a contractile type of cell, what can this do?

651

This can lead to muscle contraction and relaxation.

652

So this is going to be a protein that can be involved in muscle contraction.

653

That is a very important thing to remember.

654

So one thing I want you to remember with the microfilaments or actin is that if it's associated with myosin, it can be involved in contraction.

655

The second thing, you know in a cell, if we were to have like a, for example, there's a process called cytokinesis.

656

kinesis.

657

When a cell is undergoing mitosis, if you imagine, let's say that here I had a cell that was going to become two cells.

658

So here we had one cell that's becoming two cells.

659

Right around this central portion here, you form this little constriction ring.

660

This little constriction ring around this point here.

661

These actin filaments form that constriction ring and eventually squeeze it to the point where guess what happens?

662

You butt off from one cell, two daughter cells.

663

So it's important for the cytokinesis part of mitosis.

664

So cytokinesis of mitosis.

665

So it forms like a little constriction ring around that, which helps to split the cells apart.

666

The other thing it's important for, you know white blood cells.

667

If you take a white blood cell,

668

let's imagine here, I have a white blood cell and I I want to move a white blood cell from the blood,

669

I mean, from the blood and have it leave and go out into the tissues.

670

Well, here's a vessel.

671

And you know the vessel is lined with what's called endothelial cells, right?

672

Well, what happens is that this actual white blood cell wants to be able to squeeze through those actual capillaries.

673

What is that called?

674

Diapodesis.

675

In order for it to do that, it needs to be able to change the shape of the cell.

676

What do we say cytoskeletal elements do?

677

They help to control cell shape, structure, all that good stuff.

678

So what happens is the actins polymerize in such a way

679

that it allows for this cell to kind of create a particular shape.

680

So all the actin molecules will come at this point

681

and create like this little shape where the white blood cell can squeeze out of the cell.

682

So what is that called?

683

Diapedesis.

684

Diapedesis of white blood cells.

685

And let's take this one more step.

686

Let's see you have a white blood cell, okay?

687

And here's a little pathogen out here.

688

Here's a little pathogen.

689

And I wanted to take this pathogen in.

690

In order for me to do that, I need to create these little things called pseudopods.

691

And what happens is, I create these little arms or little extensions that come out here to surround that pathogen.

692

The actin molecules need to come in

693

and help to create these little arms that'll basically wrap around the pathogen and bring it in.

694

What is that called?

695

Phagocytosis.

696

So it's also involved in phagocytosis of white blood cells.

697

Babushka, we did it.

698

All right, next one.

699

The next one is the intermediate filaments.

700

The intermediate filaments.

701

The intermediate filaments are a very interesting type of structure.

702

And one of the things that we need to know about the intermediate filaments is that they're primarily very tough, high tensile, not very much movement.

703

They don't have a lot of give to them.

704

So why that is important is let's say that we take here a cell.

705

Here is another cell.

706

Okay, we have two cells.

707

And then you know around the cell, there's a lot of protein network out here.

708

What is this called?

709

All this protein network that sits outside of the cell.

710

This is called your extracellular matrix.

711

It's made up of collagen and elastin and a bunch of different types of proteins.

712

We know that, right?

713

What happens is we take this protein here, let's actually draw it in another color here.

714

Let's use this blue here.

715

This protein here, let's say here we have one end of it.

716

It can connect to, from the cell, it can connect the cell to the extracellular matrix.

717

That's one thing it can do.

718

So it can help to hold the cell and anchor it to the extracellular matrix.

719

The other thing here is maybe I have another protein here, another protein here, and these cells.

720

These can connect cell to cell.

721

So they help to anchor and hold the cells to each other.

722

And then let's add another thing in here.

723

You know, these little organelles, remember I told you that if you imagine the cytoskeleton, they're all over this cell.

724

Imagine here, I draw an organelle, a mitochondria, or, you know, the nucleus, whatever.

725

Here's our nucleus, right?

726

These cytoskeletal elements are also going to be bound to these organelles.

727

So it helps to anchor

728

Anchor the actual cell to the extracellular matrix, anchor cell to cell, and anchor the organelles inside of the cell

729

so they're not just kind of like freaking floating around everywhere.

730

Right?

731

So that is the function of the intermediate filaments.

732

So three functions is an anchor, if you will, and it anchors what things?

733

One is cell to cell.

734

Two is cell to the extracellular matrix.

735

And three is cell to different organelles.

736

Ba -boom.

737

We done did it.

738

Okay.

739

So the last component here, the last part, is this microtubules.

740

These are very, very cool cytoskeletal elements.

741

Okay.

742

And what I really want you to remember about microtubules.

743

Okay is they're made up of two different types of protein units.

744

So I drew these in different colors.

745

A pink protein, maybe that represents what's called alpha tubulin.

746

Pretty straightforward, right?

747

And then with my blue marker here, another little dot here is called beta tubulin.

748

These things come together and form these little filaments.

749

And then like 13 filaments come together and eventually form this entire microtubular structure.

750

Why this is important is very, very interesting.

751

So microtubules, one of the really big function here is that it provides what's called intracellular transport.

752

Okay.

753

Now, it seems odd, but on these microtubules, you have these little proteins.

754

Imagine here you have like a little protein here.

755

Okay.

756

these proteins there's two different types of them there's what's called dynein

757

and another one which is called kinesin and these are called motor proteins

758

and what these motor proteins can do is they can bind on to organelles

759

they can bind on to different vesicles which maybe have proteins

760

or lipids or things that you're moving towards the cell membrane

761

or bringing in to the cell these are transporting them throughout the cell to different places that they need to go to.

762

That is very important.

763

So again, it's acting as the railway, right?

764

Or the railroad system by which you're transporting different substances by having to use these motor proteins.

765

Big thing to take away from this, there's no free lunch on this.

766

This requires ATP to drive this process.

767

This is an ATP dependent process for this intracellular motor protein transport.

768

The second thing that's important for is cell division.

769

You know, whenever a cell is going through the mitosis phase, there is this phase where you have the chromosomes like this, right?

770

And they're all lined up.

771

Okay. And metaphase.

772

Well, at that point here, the centromere, there's little proteins on the side called the kinetochore.

773

What happens is these microtubules, they click in to that kinetochore.

774

And what happens is as they start to break down, they depolymerize, it separates these chromosomes into the two separate sister chromatids.

775

So again, big thing, microtubules connect to the kinetochore where the centromere is, the center part of the chromosome, and separate them into sister chromatids.

776

So that's the other important thing is cell division, particularly separating separates the chromatids.

777

Okay, the third thing here is it is important for cellular extensions, cell extensions.

778

And what I mean by these extensions is there's two big structures that you form the base of these structures.

779

And you form what's called the cilia, which is a very important structure structure and you form what's called flagella.

780

These are structures that again, you have motor proteins like dynes and things like that that are incorporated into this, these cellular extensions.

781

But what happens is these cilia and flagella, they create a beating like motion or twisting like motion.

782

And what that helps for is that if you have these motor proteins, which are constantly utilizing ATP to beat and create this movement here,

783

cilia is good in our respiratory tract because it helps to clear out mucus.

784

It's also in the fallopian tubes.

785

You know when you have to move the oocyte or the ovum in this case, if it's fertilized, you have to move it towards the uterus.

786

We need those things and microtubules make up the base of that cilia.

787

Flagella, in order for the sperm to be able to move towards the oocyte or the, in this case, the secondary oocyte,

788

it needs to have that type of motion.

789

And again, microtubules make up the base of the flagella and utilize these dynein proteins to create that whipping motion.

790

So now we have an idea of what these microtubules do.

791

All right, Ninja Nerds.

792

So in this video, we covered the structure and function of the cell.

793

It was a long one, but I hope it made sense.

794

And I truly hope that you guys enjoyed it.

795

I hope you guys learned a lot.

796

If you guys followed through this entire process of how I study, prepare, draw, and then go through the lecture,

797

I hope that you guys were able to come up with a similar process and I hope it helped.

798

All right, Ninja Nerds, as always, we thank you, love you, and until next time.

799

Thank you.

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Vocabulary and speaking notes for this lesson

This speaking lesson is built on the video “Cell Biology”. The speaker keeps coming back to these words: protein, cell, type, structure, membrane. This video has 799 sentences and 9181 words to shadow. The speech runs for 55:08. The speaker talks at a natural 167 words per minute, close to everyday conversation. Only 80% of the words are among the 3,000 most common in English, so the vocabulary is demanding.

Key vocabulary in this video

15 words from the video worth learning, with pronunciation and meaning:

Word	Pronunciation	Meaning
membrane noun	/ˈmɛm.bɹeɪn/	A mechanical, thin, flat flexible part that can deform or vibrate when excited by an external force.
enzyme noun	/ˈɛn.zaɪm/	A biomolecule that catalyses a biological chemical reaction: either a globular protein with this function or an RNA molecule with this function.
component noun	/kəmˈpoʊ.nənt/	A smaller, self-contained part of a larger entity. Often refers to a manufactured object that is part of a larger device.
molecule noun	/ˈmɑ.lɪ.kjul/	The smallest particle of a specific element or compound that retains the chemical properties of that element or compound; two or more atoms held together by…
acid noun	/ˈæsɪd/	A sour substance.
cholesterol noun	/kəˈlɛstəɹɒl/	A sterol lipid synthesized by the liver and transported in the bloodstream to the membranes of all animal cells; it plays a central role in many biochemical…
nucleus noun	/ˈnuː.kli.əs/	The core, central part of something, around which other elements are assembled.
smooth adjective	/smuːð/	Having a texture that lacks friction. Not rough.
synthesis noun	/ˈsɪnθəsɪs/	The formation of something complex or coherent by combining simpler things.
glucose noun	/ˈɡluː.kəʊz/	A simple monosaccharide (sugar) with a molecular formula of C₆H₁₂O₆; a principle source of energy for cellular metabolism.
layer noun	/ˈleɪ̯ɚ/	A single thickness of some material covering a surface.
bind verb	/ˈbaɪ̯nd/	To tie; to confine by any ligature.
occur verb	/əˈkɜː/	To happen or take place.
fold verb	/ˈfəʊld/	To bend (any thin material, such as paper) over so that it comes in contact with itself.
undergo verb	/ˌʌndɚˈɡoʊ/	To experience; to pass through a phase.

Phrasal verbs you will hear

Word	Pronunciation	Meaning
break down verb		To stop functioning.
go through verb		To travel from one end of something to the other.
make up verb	/ˌmeɪk ˈʌp/	To constitute, to compose.
take away from verb		To subtract a quality from; make something seem not so good or interesting.
come together verb	/ˈkʌm tʊˈɡɛðɚ/	To assemble; to congregate; to combine.
carry out verb	/ˈkæ.ɹi aʊt/	To hold while moving it out.
go over verb		To look at carefully; to scrutinize; to analyze.
play around verb		To behave in a silly, childish, or irresponsible way.

Sentences worth repeating

Short, complete lines from the video that you can reuse in everyday conversation:

What can we do with it?
You're like, what the heck is that?
You know what I'm going to do?
You know that's important for fatty acid metabolism?
What do we say cytoskeletal elements do?

Grammar in this video

The structures the speaker uses most, with the exact words from the video:

Structure	In the video
Present perfect have/has + past participle — a past action that still matters now	we've covered · have we established · we've understood
Passive voice be + past participle — the focus is on what happens, not who does it	is called · are dispersed · are associated
Relative clauses who / which + clause — extra information about a person or thing	nucleolus, which is · nucleus, which is · organelle, which will

Pronunciation to watch

The speaker uses 108 contractions and reduced forms, such as we're, they're, you're. Say them the short way, as you hear them.

The “th” sounds: smooth /smuːð/, synthesis /ˈsɪnθəsɪs/, pathway /ˈpæθˌweɪ/, smoothie /ˈsmuːði/, pathogen /ˈpæθəd͡ʒn̩/
The “sh” and “zh” sounds: extension /ɪkˈstɛnʃən/, translation /tɹænzˈleɪʃən/, transcription /tɹænˈskɹɪpʃən/, relaxation /rᵻˌlækˈseɪ.ʃən/, glycosylation /ˌɡlaɪ.koʊ.səˈleɪ.ʃən/
Long words — get the stress right: cholesterol /kəˈlɛstəɹɒl/, metabolic /mɛtəˈbɒlɪk/, metabolism /məˈtæb.əˌlɪz.əm/, intermediate /ɪn.tə(ɹ)ˈmi.di.ət/, incorporate /ɪŋˈkɔɹ.pɚ.eɪt/

How to practise with this video

Listen to the whole video once without speaking and note the words you do not know.
Start at 0.75× speed, shadow it sentence by sentence, then go back to normal speed once it feels easy.
Record yourself and compare with the original, paying attention to words like membrane, enzyme, component.

What is the Shadowing Technique?

Shadowing is a science-backed language learning technique originally developed for professional interpreter training and popularized by polyglot Dr. Alexander Arguelles. The method is simple but powerful: you listen to native English audio and immediately repeat it out loud — like a shadow following the speaker with just a 1–2 second delay. Unlike passive listening or grammar drills, shadowing forces your brain and mouth muscles to simultaneously process and reproduce real speech patterns. Research shows it significantly improves pronunciation accuracy, intonation, rhythm, connected speech, listening comprehension, and speaking fluency — making it one of the most effective methods for IELTS Speaking preparation and real-world English communication.

Shadowing technique: read the full step-by-step guide →

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Vocabulary and speaking notes for this lesson

Key vocabulary in this video

Phrasal verbs you will hear

Sentences worth repeating

Grammar in this video

Pronunciation to watch

How to practise with this video

What is the Shadowing Technique?