Biochemistry Fatty Acids & Triacylglycerols

Hello and welcome back to Educator.com, and welcome back to Biochemistry.0000

Today, we are going to start our discussion of lipids, another major class of biological macromolecule.0004

Remember we have lipids; we have carbohydrates.0012

We have proteins, and we have nucleic acids- four major classes.0015

Today, we are going to start talking about lipids, and we are going to start our discussion with the simplest of them- fatty acids and the triacylglycerols.0019

Let’s go ahead and get started.0029

OK, lipids are a profoundly, profoundly diverse group of biological macromolecule.0033

Lipids are a profoundly diverse group of biological macromolecule.0047

Their common feature - but they do have one common feature - their common feature among all of these, they are not soluble in water.0072

They are not soluble in water; that is their common defining feature as far as lipid is concerned.0087

They are going to be soluble in organic solvents as far as working in the lab is concerned, or they are going to soluble in other fats.0100

They are not soluble in water.0110

OK, now, their biological functions are as diverse as their structures.0113

The particular function that we are going to talk about today, as far as fatty acids and triacylglycerols, is fuel storage.0139

That is one function that fats serve; it is a primary function that they serve, is the storage of, it is a reserve.0146

It is a fuel reserve- is what it is, lipids as fuel storage.0154

Remember when we are talking about carbohydrates, we said that glycogen was actually a form of fuel storage.0169

It is a short term form of fuel storage; fat, triacylglycerols, fatty acids, lipids- they are long term storage.0175

And, we have a bunch of fatty acid derivatives.0187

We are going to talk about fatty acids first, and then we are going to talk about its simplest derivative- the triacylglycerol.0192

OK, a fatty acid- very, very simple.0198

I do not know why they have all these different names for things that we already know.0202

A fatty acid is just a carboxylic acid; it is a carboxylic acid whose hydrocarbon portion or chain runs from 4 to about 36 carbons- that is it.0207

And, this actually includes, this number, this includes the carbonyl carbon.0247

This includes the COO carbon.0253

OK, let’s just do a quick example.0261

I will do this one in a line form because it is often best to represent these in line representations.0265

That is 2, boom, boom, boom, boom, boom, boom; we just have to keep track of how many we have.0271

So, 1, 2, 3, 4, 5, 6, 7, 8 so 1, 2, 3, 4, 5, 6, 7, 8- yes, that is correct.0277

I will put the final one there, something like that.0283

This is a C8 fatty acid; this is a C8 fatty acid- that is it.0287

It is just a carboxylic acid with a certain length of chain.0295

In this particular case 1, 2, 3, 4, 5, 6, 7, 8- that is it.0299

We can write it as...let me go to blue here.0307

We can write it as, oops, you know what, that is fine; I will just keep it as black.0312

CH₃, (CH₂)6 and then COOH- you will often see it like that.0317

CH₃- that is the last one; we have these CH₂ groups.0325

We have 6 of them, 1, 2, 3, 4, 5, 6; and then, of course, we have our carboxyl group- the COOH.0329

That is this thing right here, so you will often see them in a shorthand written like that.0337

This is n-Octanoic acid, right?0342

That is how we name the carboxylic acids: propanoic acid, butynoic acid, pentanoic acid.0350

We take the pentane, hexane, heptane, octane, and we just add oic acid- that is it; that is all it is.0356

It is a carboxylic acid with just a really long carbon chain, generally from 4 to 36- that is all, nice and simple.0363

OK, a couple of more definitions here, let’s go to blue.0371

Now, a saturated fatty acid, which you hear about all the time, fatty acid, and I am going to start writing FA for that.0379

The hydrocarbon chain, it is just a fatty acid where the hydrocarbon chain has no double bonds.0392

In other words, it is saturated with as many hydrogens as you can stick on to the carbons- that is it; that is all a saturated means.0404

You put on as many hydrogens as you can; the molecule that we just saw, it is fully saturated.0411

There is no double bond; it is all carbon, carbon single bonds, and when the carbon is not bonded to another carbon, it is bonded to hydrogens- that is all.0417

So, an unsaturated is exactly what you think; unsaturated or polyunsaturated - you will often hear that polyunsaturated - it is a fatty acid with one or more double bonds along the chain.0427

You will often hear of a monounsaturated fatty acid; it has 1 double bond.0455

You will hear of a polyunsaturated fatty acid that has 2, 3, 4, 6, 9 double bonds, however many.0460

Let’s do a saturated example, which we actually just did, but what the heck; we will do it again.0467

We will have, let’s say CH₃; let’s have (CH₂)18, and let’s have COOH.0479

We have 1 carbon, 18 carbons and 1 more carbon, so this is n-Eicosanoic acid; Eicosa is Greek for 20.0487

Now, the n here, the n part, n-Eicosanoic acid, that just means there is no branching in the chain.0502

It is just straight chain, there is no strange branching going on.0512

So, n just means there is no branching in the chain- that is all.0516

And, what I mean by branching is, let’s say if you have something like this, let’s say you have this, branching would mean something like that.0527

There is no branching; it is just a straight chain of 20 carbons.0537

OK, now, let’s do an unsaturated example.0545

Let’s actually draw this one out, so let’s see how many carbons have I got 1, 2, 3, 4, 5, 6, 7, 8.0559

Let’s go 2, 3, 4, 5, 6, 7, 8, 2, 3, 4, 5, 6, 7, 8, and then I will go, how about going down like that, double bond; and then 1, boom, boom.0570

That is always interesting when you have to start counting these carbons 1, 2, 3, 4, 5, 6, 7, 8, 1, 2, 3, 4, 5, 6, 7 and 8, so we have this.0595

OK, let’s make sure we have got 1, 2, 3, 4, 5, 6, 7, 8.0609

This is our 8 carbon; this is our number 1.0614

This is 9; this is 10, 11, 12, 13, 14, 15, 16, 17, 18.0616

OK, we have 18 carbons on this one.0622

This happens to be cis-9-octadecenoic acid.0628

Cis tells me - this is 9 - tells me that at the 9 carbon starting with the no.1 carbon of the carbonyl, at the 9 carbon is where the double bond starts, so between 9 and 10; that is where the double bond is.0640

Cis tells me it is the cis configuration, not the trans configuration.0654

Octadec is 18; that means it has 18 carbons total.0659

Decenoic acid- that means there is an alkene which is this thing.0664

There you go; that is all.0670

This is the systematic name, the common name.0672

All of these have systematic names, and all of these have common names.0678

This is oleic acid.; it is one of the primary components of olive oil, the fatty acid in the triacylglycerol that actually makes up olive oil- oleic acid.0681

OK, and again, take notice of the E in there because it is not octadecenoic acid.0693

That would be just the saturated version, 18 carbons, decenoic acid.0700

That is actually telling me that I have an alkene in there.0706

It is a little redundant because you have this as 9, but now, there it is.0711

OK, now, there is a notation; there are several notations, actually, but there is a notation that we will be using.0715

There is a notation for fatty acids or FAs, which gives you all the information that you need about that fatty acid, which specifies chain length.0726

It specifies the degree of unsaturation - in other words, how many double bonds there are - the degree of unsaturation and the location of those double bonds, so pretty much everything we need.0748

I think it is best to just do some examples and it will make sense that way.0772

Let’s run some examples here, so if I write 20:0.0781

OK, this first number, that is the number of carbons.0787

That is the chain length; it is the chain length.0793

That is the number of carbons you have, so in this particular case, we have a 20 carbon.0802

This second number here, the one after the colon, that is the number of double bonds there are along that chain.0807

OK, the number of double bonds along the chain.0813

In this particular case, we have a 20 carbon, nothing in there.0826