In this video today, we're going to be talking about the structure and function of paroxysms.

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All right, cool.

Paroxysms.

Really cool organelles.

So they're kind of a spherical membrane, so they have a membrane that encloses their actual contents inside of them.

And they have four particular functions, this is what I want you to remember.

So they're hollow, spherical, very interesting organelles that, again, play a role in four particular functions.

One is fatty acid oxidation, second one, hydrogen peroxide metabolism, third one, ethanol metabolism, and the fourth one is biosynthetic function of particular lipids.

All right, first one, fatty acid oxidation.

All we do with fatty acids, I don't want to get too crazy here because we'll cover this more in biochemistry, but fatty acids can actually naturally be metabolized by a very cool organelle that we've already discussed called the mitochondria.

So when we talked about the mitochondria, we said one of the things that occurs is something called beta oxidation, and then the mitochondria.

All it means is we take this fatty acid into the mitochondria, and it goes through this process of oxidation, hydration, and again, more oxidation, and then what's something called thylation, and you make something called acetyl-CoA.

And then what happens with the acetyl-CoA is generally in the mitochondria, it'll go through the electron, it'll actually go through the Krebs cycle, generate NADHs, FADH2s, and then from there, you can make something like energy, well, particularly FADH2s, NADHs, they can utilize in the electron transport chain to make ATP.

This is beta oxidation that occurs here.

So when we take this fatty acid and we make acetyl-CoA, this is called beta oxidation.

Now, the same thing can happen in peroxisomes, but in peroxisomes, these are called very long-chain fatty acids.

And then over here, we have another one called branch-chain fatty acids.

These will actually get taken into peroxisomes.

And what happens is the very long-chain fatty acids, they'll go through the same kind of So you'll break them down into two carbon chains at a time.

And when that happens, again, this process here is called beta oxidation.

So they can occur in both the mitochondria and the peroxisomes.

The big thing is for peroxisomes, it occurs to very long-chain fatty acids.

And again, the basic concept is you do oxidation, hydration, oxidation, and something called phylation.

We'll talk about that a little bit more in biochemistry.

But the other thing is the branch-chain fatty acids.

So the branch-chain fatty acids, when they get brought into the actual peroxisome, they actually go and you cut those branches off.

So when you cut the branches off to turn them into a very long-chain fatty acid with no branches on them, this process is called alpha oxidation.

So there's two particular processes that are going to occur here in the actual peroxisomes.

One is beta oxidation of very long-chain fatty acids.

And the second one is alpha oxidation of branch-chain fatty acids into very long-chain fatty acids.

And what's the end goal here?

You cut these things off two pieces at a time, these very long chains.

You cut them into two carbon segments called acetyl-CoA.

And generally, you make something called acyl-CoA, which is just a long, again, carbon chain.

So if this was 16 carbons, it would be 14 carbons.

And these generally, they just go back up.

And they continue this vicious cycle until you've broken the entire fatty chain down.

This is important, particularly in which organelle?

In peroxisomes.

So one of the functions of peroxisomes is to break down very long-chain fatty acids into acyl-CoA, and then usually one of these molecules that's, again, just two carbons shorter of this very long-chain fatty acid.

And it gets recycled and goes back down.

Or you take branch-chain fatty acids and cut the branches off and make it into very long-chain fatty acids.

It'll just go down the cycle.

That's called alpha-oxidation.

Okay.

Beautiful.

The second function that I want you guys to understand here is hydrogen peroxide metabolism.

So this one's actually really interesting.

So in the same concept here, you take in these molecules here.

So we're going to call one of these, this is our branch-chain fatty acid.

This is the one.

And we said we also bring the other one in, which is the very long-chain fatty acids.

We said that generally, these will undergo a beta-oxidation process.

And what happens is you make something, you make two molecules, right?

One is you make acetyl-CoA, and the other one is you make acyl-CoA, and we said all that does is it just goes back and gets recycled, right?

This process here is called beta-oxidation.

The next one is we take the branch-chain fatty acids and we break them down into very long-chain fatty acids.

This is called alpha-oxidation.

We already talked about this.

This occurs in peroxisomes.

What's really interesting is that in order for us to be able to take these very long-chain fatty acids and to do this process here to make these two molecules, we actually have to use water during the hydration or hydrolysis step.

And what that does is that takes water and oxygen and uses it in this step to make something called hydrogen peroxide.

Hydrogen peroxide.

Hydrogen peroxide is actually a nasty free radical, so it has the ability to cause free radical molecules which can cause a lot of damage to proteins and DNA and membranes.

So we don't want this thing to form.

This is bad.

So how do we actually prevent this thing from continuing to form?

We got this cute little enzyme here.

You see this pink enzyme?

This pink enzyme is called a catalase.

This is called a catalase enzyme.

And what catalase does is it takes the hydrogen peroxide that was formed and just converts it right back into water and oxygen.

So we take the free radical, which is nasty, and turn it back into water and oxygen, which is actually okay.

And that makes you happy, right?

So that's the big things that I really want you to remember here for this particular molecule is the catalase.

The same thing.

You can actually take from, you know what's called your electron transport chain?

From your electron transport chain, when you take FADHs and NADHs, these will actually work on the electron transport chain and generate things like free radicals.

One of them is hydrogen peroxide.

And these hydrogen peroxide molecules can actually go here and get converted into water and oxygen as well.

So this is really important for preventing free radicals.

So again, one thing I want you to remember here is that hydrogen peroxide is what we refer to as a free radical, and it can cause a lot of damage.

So this has the ability to damage proteins and cell membranes and DNA.

We do not want that, so that's what peroxisomes help to prevent.

Okay, so we got fatty acid oxidation, beta oxidation of very long chain, alpha oxidation of branched chains.

We got hydrogen peroxide metabolism via catalases and preventing free radical reactions.

What are the other two functions?

The other two functions, my friends, are actually pretty cool, and they kind of coordinate with something called the smooth ER, which you guys better remember.

So you guys remember the smooth endoplasmic reticulum?

We said that one of the functions is that they play a role within lipid synthesis, right?

They synthesize phospholipids, they synthesize steroids, particularly steroid hormones, right?

Well, they can actually derive from cholesterol.

So you can take cholesterol, you can make steroid hormones, sex hormones, bile salts, lipoproteins, all that stuff.

Peroxisomes actually have the ability to do that as well.

So one of the things I want you to remember is the smooth endoplasmic reticulum does help with making things like what?

It does synthesize things like phospholipids.

They do help to synthesize things like cholesterol, and they also do help to synthesize a lot of other different things like fatty acids, right?

But I think this is the big thing to take away is the cholesterol and the phospholipids.

And then from cholesterol, you can synthesize a bunch of different things, steroid hormones, bile salts, et cetera.

Well, in the same concept, peroxisomes actually have that ability to do that as well.

So here's a peroxisome, right?

From this peroxisome, what it can do is it can bring in again these molecules that we talked about, the very long chain fatty acids and the branch chain fatty acids.

What is this process called?

We're going to hit this so many times, you guys won't forget it.

This is called alpha oxidation, where we cut the branches off.

Then we do this and we break these down into something called acetyl-CoA.

And then you can actually recycle this molecule, this acetyl-CoA, or you can make this other molecule here called acyl-CoA.

And this can actually get recycled and continue to go down.

What's this process called going down?

This is called beta oxidation.

Now, one of the cool things is that from this acetyl-CoA, I can actually use this to synthesize a particular molecule.

I can take the acetyl-CoA and I can synthesize something called what?

I can actually synthesize, I can synthesize cholesterol.

And you know what I can do with that cholesterol?

I can make a couple of different molecules.

I can make bile salts or bile acids.

I can make steroid hormones, steroid hormones, just in the same way that the smooth endoplasmic reticulum takes and makes phospholipids.

It makes cholesterol.

From the cholesterol, you can make things like bile and steroid hormones, so same concept.

So we can take the cholesterol that you get from acetyl-CoA and make steroid hormones or make bile salts.

Isn't that pretty cool?

The other thing is I can take this acyl-CoA, which is basically just a fatty acid.

That's all it is.

It's really just a fatty acid.

It's just a shorter chain of it.

And what I can do is I can add on things like phosphates.

I can add on things like phosphates to it and then convert this into what's called a phospholipid.

And there's one specific phospholipid, because when we talk about paroxysomal disorders, for USMLE Step 1, for the pathology point, the one particular type of phospholipid is called plasmaligin.

You know what plasmaligin is actually used in?

It's used in making myelin.

So we can actually synthesize phospholipids.

We can synthesize cholesterol, which can be used to make bile salts and steroid hormones.

So do you see how with just this paroxysome, from the breakdown products of fatty acid oxidation, I can make phospholipids, I can make cholesterol, and then subsequently the actual formation of cholesterol, I can use it to make bile salts, steroid hormones.

And the other concept here is that not only is it involved in the phospholipids and cholesterol synthesis, it's also even been shown to be involved in the activation of bile salts.

So you can add that one in there as well, is that it may also be involved in the activation of bile salts.

So not just the synthesis of them, but also the activation of them.

In other words, your Smoothie R helps to be able to make bile acids.

Not only does your paroxysomes do that as well, but they may come in and the paroxysomes may have particular enzymes that will stimulate or activate those bile acids.

So that's the last thing.

So biosynthetic functions, my friend, what do I need you to remember?

They have functions similar to the Smoothie R.

They can help to synthesize phospholipids from the breakdown products of fatty acid oxidation, such as plasmaligin.

I really need you to remember that one.

It's used in making myelin, which is important for our CNS.

The next thing is it can also use the breakdown products of acetyl-CoA to make cholesterol, which can then be used to make steroid hormones or bile acids.

And the last thing is we can even activate bile acids that come from the Smoothie R.

That's what I want you to remember.

Okay.

The last and final function of the paroxysomes is ethanol metabolism.

You know, one of the interesting things here is that the Smoothie R is involved in ethanol metabolism, right?

We know that the cytochrome P450 system.

So you know that ethanol is metabolized by the cytochrome P450 system in the smooth endoplasmic reticulum.

We know that.

So if we take something like ethanol and it moves through the Smoothie R, the actual cytochrome P450 system can metabolize this alcohol and it can convert it into particular metabolites that we're not going to go into at this moment.

All right.

But in the same concept, the paroxysomes also have that ability.

So you can have alcohol get metabolized by multiple pathways.

It could be metabolized by the cytochrome P450 system and the Smoothie R, but guess what else?

You can have it be metabolized by this pathway as well.

So this is going to be another quick recap.

So branch chain fatty acids, they get metabolized into what?

Very long chain fatty acids.

These also get brought in.

And this is called alpha oxidation.

Very long chain fatty acids get broken down into what?

We said one of these things is called acetyl-CoA and the other one is called the acyl-CoA, which then goes back up here.

This process is called beta oxidation.

Now one of the big things here is that we have alpha oxidation, beta oxidation.

And what else did we say happens in this process?