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Lecture Comments (7)

2 answers

Last reply by: Professor Hovasapian
Thu Feb 27, 2014 7:14 PM

Post by Alan Delez on February 27, 2014

Hello Professor Hovasapian,

Just to clarify when you say higher in degree of unsaturation, you mean higher in number of double bonds? wouldnt that make it more soluble in water? Great lecture

Alan D.

1 answer

Last reply by: Professor Hovasapian
Tue Nov 5, 2013 2:15 PM

Post by Razia Chowdhry on November 5, 2013

I wanted to ask, is there a lipid that has an alkyne group in the fatty acid because  I know that you can have alkane or an alkene chain. So can you ever have an alkyne chain in a fatty acid of a lipid?

1 answer

Last reply by: Professor Hovasapian
Sun Apr 7, 2013 3:29 AM

Post by Don Claudio on April 6, 2013

fuel @ 48:08, regardless, great lecture.

Fatty Acids & Triacylglycerols

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Fatty Acids 0:32
    • Lipids Overview
    • Introduction to Fatty Acid
    • Saturated Fatty Acid
    • Unsaturated or Polyunsaturated Fatty Acid
    • Saturated Fatty Acid Example
    • Unsaturated Fatty Acid Example
    • Notation Example: Chain Length, Degree of Unsaturation, & Double Bonds Location of Fatty Acid
    • Example 1: Draw the Structure
    • Example 2: Give the Shorthand for cis,cis-5,8-Hexadecadienoic Acid
    • Example 3
    • Solubility of Fatty Acids
    • Melting Points of Fatty Acids
  • Triacylglycerols 34:13
    • Definition of Triacylglycerols
    • Structure of Triacylglycerols
    • Example: Triacylglycerols
    • Recall Ester Formation
    • The Body's Primary Fuel-Reserves
    • Two Primary Advantages to Storing Energy as Triacylglycerols Instead of Glycogen: Number 1
    • Two Primary Advantages to Storing Energy as Triacylglycerols Instead of Glycogen: Number 2

Transcription: Fatty Acids & Triacylglycerols

Hello and welcome back to, 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

This is the eicosenoic acid- that is it, nice, straightforward, 20 carbons, no double bonds, boom; you are done.0831

At one end is the carboxylate; the rest is just a bunch of carbons and hydrogens.0838

OK, how about another one; let’s do this one in red.0842

Let’s try 18:1 and delta-9.0846

This is called the delta notation or delta x notation, and here is what it means.0852

We know what these 2 numbers mean; this is an 18 carbon, so this is 18 carbons long- that much I know.0857

I know it has 1 double bond because of the 1, and the delta-9 tells me that it is on the no. 9.0867

It starts at the no. 9 carbon, so it is between 9 and the 10, starting with the no. 1 carbon being the carbonyl carbon- that is it.0877

The delta-9, the delta part, it means the double bond starts at the no. 9 carbon, starting your count from the carbonyl carbon.0884

There is another convention that starts from the other end, that starts from the end of the chain.0922

That is called the omega notation; omega carbon is your last carbon.0930

Let me talk about an omega-3 fatty acid; that means starting from the other end of the chain, if I count 3 carbons, that is where the double bond is.0934

We are using delta notation, delta; carbonyl carbon is the no. 1 carbon.0943

Count to no. 9, that is where the double bond starts, so 18:1 delta-9- that is all that means.0948

This happens to be the oleic acid.0954

Actually, I do not need to write that; I will just write it down here.0959

This is the oleic acid; the one, the structure for which we just drew in the previous page- 18 carbons long, 1 double bond.0962

The double bond is at the no. 9 location, counting from the carbonyl being no. 1- nice and simple, really, really nice.0970

OK, let’s do just a quick example here for more practice.0979

You want as much practice as possible, although this stuff, I think, is pretty straightforward.0985

Draw the structure, so in this case, they are going to ask you for a structure of 18:3 delta 9, 12, 15- 18 carbons long.0990

OK, now, I am going to go ahead and start with my carboxylic acid on the left, instead of on the right, because I just prefer to go from left to right.1007

It does not matter; you can draw it vertically.1013

You can draw it sideways, diagonally, however you want, as long as everything is there, so totally personal choice.1016

We have 18 carbons long; we have 3 double bonds, and the double bonds take place at the 9 carbon, the 12 carbon, the 15 carbon, so between 9 and 10, 12 and 13 and 15 and 16.1024

Let’s go ahead and draw it out; I am going to draw out my carbonyl first.1036

I will go ahead and do this and that is 1, 2, 3, 4, 5, 6, 7, 8, 9.1042

So I like to...10, 11, 12, wait, 10, 10, 11, 12, 12 is up here.1053

OK, delta 9, 12, I have got another bond that is 12; this is 13, 14, 15, 15, 16, 17, 18- there we go.1067

I have 18 carbons; this is my no. 1 carbon.1083

This is my no. 18 carbon; I have 3 double bonds, 1, 2, 3, delta 9, 12, 15- there we go, nice and straight forward.1086

Now, let’s talk about some names- the systematic name.1098

This is cis, cis, and do not worry about the dashes and comas; put them wherever you want.1107

It does not really matter, 9, 12, 15-octadecatrienoic acid.1115

This actually should be one word; I just, I tend to separate them, but it is up to you- trienoic acid.1132

Again, I think it just depends on your teacher and how rigid they are about do they want it as one word, do they want it as 2 words; I separate them.1139

It is the information that is important not the aesthetics.1147

This is the systematic name, cis, cis, cis; I have actually specified the stereochemistry at each of the locations of the double bonds 9, 12, 15-octadecatrienoic acid.1151

So, it is a little redundant, trien; I have 3 alkenes.1162

I know that because I have 9, 12, 15 cis, cis, cis, so it is a bit redundant; but that is the systematic IUPAC procedure.1166

Common name, let’s see, common name, this one happens to be alpha-linolenic acid.1176

I will just write this down, so clearly the 18-3 delta 9, 12, 15 is the best representation- nice and quick.1192

It tells you everything that you need to know about it.1209

OK, now, let’s do another example; let’s go back to red.1212

We have example no. 2; this time we will give you a structure and ask for the short hand.1219

so give the short hand - in other words, give the delta notation - for cis, cis, cis.1228

No, I only have 2, 5, 8 - see again, commas, dashes, it is enough to make you crazy - hexadecadienoic acid.1244

OK, well, hexadeca, so deca is 10, undeca, dodeca, trideca, tetradeca, pentadeca, hexadeca.1266

This is 16; hexadeca means 16.1276

I have got...go to blue, let me get my blue here; there we go.1279

I have got 16 carbons; I have cis, cis, 5, 8, so I have 2 double bonds delta 5, 8- that is it.1288

I am done, nice and simple, just start counting and putting it together, no worries.1299

OK, a little bit more information here.1307

So, most naturally occurring - I hope I spelled that right - most naturally occurring unsaturated fatty acids have the cis configuration.1311

I will go ahead and put Z because those of you in organic chemistry, we have the ZE, the zusammen-entgegen notation also.1337

So cis is Z; a trans is E, so most of these fatty acids, the naturally occurring ones, they have the cis configuration.1346

Now, if the trans or E configuration shows up, which it does, occasionally, it shows up, well, the notation reflects that, then the symbol reflects that- that is it.1356

Instead of writing cis, we just write trans; or instead of writing Z, we just write E.1386

OK, example no. 3.1393

We have something like, I will do it this way; I will do the (9Z, 12E)-tetradecadienoic acid.1399

In this particular case, I decided to use the ZE, so 9Z, 12E.1418

This is going to be cis trans, probably be something like this, cis trans 9, 12; and then the rest is the same- tetradecadienoic acid.1424

You can write it as 9cis, 12trans.1441

Again, there is no hard and fast; I mean, there is a lot of information here, and these things get really, really long, so I would not lose any sleep about what it actually looks like, as long as the information is there.1448

Your teacher will tell you how they want it, and you give it to them the way that they want it.1459

If you are just learning this on your own, as long as long as you understand it and are able to communicate it, that is all that matters.1465

Again, we want to make sure that we are concentrating on what is important, not on incidentals.1471

OK, we can write this as 14; in terms of symbolism, we can write it as 14:2.1479

We can write is as cis trans, delta 9, 12; that is one way of doing it.1488

14 carbons, that is the tetradeca; 2 double bonds, that is the dien.1494

Cis trans, cis delta 9, 12, the 9 is cis; the 12 is trans.1499

You can write it as 14:2, ZE, delta 9, 12.1505

You can specify it a little bit differently, if you want.1512

You can actually go something like cis delta 9, trans delta 12.1518

If you want go ahead be a little redundant with the delta, that is fine- you can.1525

Again, these are incidentals, as long as the information is there.1528

OK, that pretty much takes care of representing it symbolically and what it is that these things are.1533

Fatty acid, it is just a long chain carboxylic acid- that is all.1540

Now, let’s go to red here.1545

No, let's write this down- the length of the hydrocarbon chain and its degree of unsaturation.1559

Saturation accounts for the properties and chemistry of these fatty acids and lipids, so how long it is, how many double bonds it has or does not have.1579

That is what is going to affect all of the physical properties and all of the ultimate chemistry.1620

OK, let’s see a little bit more.1622

Now, the longer the chain - which makes sense, so the longer the chain, the hydrocarbon chain, let’s specify this - so the longer the hydrocarbon chain and the higher the degree of saturation, the less soluble it is in water.1628

Longer chain hydrocarbons like a C24 is going to be less soluble in water than, let’s say, a C7.1670

A saturated C24 is going to be less soluble than an unsaturated C24- that is all that means.1677

Now, at physiological pH, at physio pH, 7-7.4, somewhere in that range, the carboxylic acid group, the COOH, is actually ionized, is actually COOO-.1687

So, it is deprotonated at physiological pH.1708

Therefore - little triangle of three dots means therefore - the shorter fatty acids do display some degree of solubility in water, some fair degree of solubility in water.1713

I mean, they are not going to be like sugars that just dissolve and dissolve and dissolve or almost infinitely soluble in water, but they do display some degree of solubility.1733

And again, because now at one end, you have this charged thing that can interact with water, with the hydrogen bonding, electrostatically, not just hydrogen bonding, some degree of solubility in water.1744

OK, again, let me just draw a quick structure so you might have something like that.1762

So, you have this end, and if this is not too long, you are going to actually see a fair amount of solubility- that is it.1773

OK, also, the longer the chain and the fewer the double bonds, the higher the melting point.1781

This has very, very, important, important application in all kinds of things in our modern world.1809

OK, let’s take a look at this one, and talk about why this is the case.1822

When you have a certain compound, the measure of a melting point that the compound is going to come together, it is going to interact with itself.1828

The molecules are going to interact with themselves.1834

So, the melting point is a measure of how much energy I need to put in to it, in order to turn the solid into a liquid, to separate them out- that is all that is.1838

Well, one that is fully saturated is going to look something like this.1847

Let’s just have this end, so we have one end, and, of course, we have this long straight chain, no double bonds.1853

Well, I am going to represent this this way; I am going to represent it as that and just a little tail like that.1861

OK, so this is the polar end, and this is the nonpolar chain.1867

Well, in the case of something that does have a double bond, so actually does have some degree of unsaturation, you are going to end up with something like this.1871

It is going to bend, so what you are going to end up with is something like that.1885

There is going to be a kink in it; and, of course, the greater the degree of unsaturation, the more double bonds, the more kinky it is going to be.1889

Well, when these things aggregate, which they tend to do, you end up with something like this.1895

In these saturated compounds, because there is no kink, you will end up with something...they interact very, very tightly.1907

The hydrocarbon portions, they basically just lay on top of each other, and there is a lot of Van der Waals interactions, so they are pretty tightly bound.1924

It takes a hell of a lot of energy to actually separate them out.1931

In the case of the unsaturated fatty acids, when they aggregate, again, they are bent now.1935

They cannot really lay on top of each other all that much.1944

They are not as tightly bound, so the interaction among the hydrocarbon chains is not as strong.1952

Because it is not as strong, it takes less energy to convert them from a solid to a liquid- that is all that means.1959

And it is strictly a structural feature simply because they are bent and they are kinky- that is what happens.1967

They are not going to interact as much as the hydrocarbon portions.1972

There is going to be less Van Der Waals interaction.1977

So, you do not need as much energy to break them apart and turn them into a liquid, so they can slide all over each other- that is all that is happening.1980

A little bit of information, in the C12 to C24 range, saturated fatty acids are solids at room temperature - just think of lard - whereas unsaturated fatty acids are liquid oils, olive oil - that is it.1990

On the C12 to C24 range, saturated, they tend to be solid room temperature, 25°C, somewhere around there; and the unsaturated fatty acids are going to be liquid oils.2042

OK. now, let’s talk about triacylglycerols.2054

Now, triacylglycerols- very, very, very important group.2061

These are the simplest of the lipids, which are constructed from the fatty acids.2071

In some sense, the fatty acids are sort of analogy; well, you know what, no, there is no analogy here, never mind.2099

Sorry, sorry I brought it up.2107

OK, a triacylglycerol, which is just ALA ,not going to keep writing that, so I am just going to write as TAG.2108

TAGs or esters are esters of glycerol, and glycerol is the molecule OH, OH, OH, H2, H; and I will put an H2.2116

Glycerol- it is a 3 carbon molecule; each of those carbons has a hydroxy attached to it, so basically, it is just a triple alcohol, glycerol.2142

A triacylglycerol are esters of these - I should just have done this on a one page; sorry about that - where fatty acids are attached, where the OHs were before; and I will draw it out in just a minute.2153

Do not worry.2181

In other words, let’s go ahead and draw out glycerol again.2186

We have C, C, C; this is OH.2194

This is OH; this is OH, and it is very, very important to remember that this is a schematic.2197

Carbon is a tetrahedral molecule, so you are looking at something in free space.2206

When we draw it like this, we are draw it for convenience, so that we can see what the connections are.2211

In space it looks totally different than how I am drawing it.2215

This is glycerol, just to have it on this page.2219

And now, a triacylglycerol, it is just where these hydroxys are replaced with some fatty acid.2223

Let's go ahead and draw this again; let me do this one in black, actually.2228

I have C, C and C; I have O.2234

I have COO, and some R1; R1 is some hydrocarbon portion.2241

I have O, and I have COO, and I have R2; that is another one, and I will go ahead and put this one here.2247

This is O, and CO, and R3; so this is triacylglycerol.2263

You have the glycerol molecule, the 3 carbons; and then, you have these fatty acids that are attached.2272

Now, the fatty acids can all be the same; they can all be different.2282

You are going to have 2 of 1 and 1 of the other; all kinds of combinations are possible.2286

Now, these are called the triacylglycerols, and it makes perfect sense- triacylglycerol.2293

OK, now, they are also called tryglycerides.2307

You will often hear them talked about that way- triglycerides or just fats.2321

That is it, general term of what we know of as fat.2327

Now, of course, you have heard of mono and diglyceride.2331

A monoglyceride is just glycerol where there is 1 fatty acid attached.2333

A diglyceride is glycerol with 2 fatty acids attached, and the alcohol is the third one; it is a hydroxy.2338

A triacylglycerol or a triglyceride, it just means all of the alcohols have been replaced by fatty acid residues- that is it.2346

OK, again, R1, R2 and R3 can be the same.2355

If they are the same, if R1 is the same as R2, is the same as R3, we just call it a simple triacylglycerol; and if not, then, we call it a mixed- nothing strange about that.2359

OK, now, let's go ahead and do an example of this.2387

However, before I do that, what is important to remember, here, this glycerol, this has the hydroxys attached.2393

When glycerol actually reacts with fatty acids, it is going to go through 3 reactions.2402

Each one of the alcohol groups is going to react with a fatty acid.2406

When it does so, this oxygen right here, these oxygens, they actually belong to the glycerol; and I will talk a little bit more about that in just a minute, but let’s just do a quick example.2411

Let’s do C and C and C, and let’s go O, C, O.2434

Let’s go CH2.2448

I do not know, however many, and then, of course, CH3.2454

Let’s see, 16, I think this is going to be 14, 15, 16, so this is 12.2460

No, this is going to be 14, I think.2465

So, let’s go ahead and use palmitic acid, and for this one, let’s go ahead and do O.2470

We have CO, and then let’s do CH2.2476

Let’s have 7 of these; let’s have a CH, a double bond, a CH; and let’s have another 7 of these, and over here, let’s go ahead and do an O and a C, and let’s go ahead and do 10 methylene groups.2482

This is CH2; there is 10 of those, and we have a CH3.2502

Here, on this side, this particular fatty acid that is attached, this is going to be palmitic acid.2507

I will do this in a different color here, go ahead and go back to black.2515

This is palmitic acid that is attached to the no. 1.2520

This is a 16:0 fatty acid; this one happens to be oleic.2528

This is our 18:1 delta-9, and this is a 10, 13, 14, this is myristic.2534

This is myristic acid, and it is a 14:0 acid; and that is it.2544

If I wanted to name this, here is how I would name it.2556

This is no.1 carbon, 2 carbon, 3 carbon; I have to specify which fatty acid is attached to which carbon.2558

Just go ahead and number them, so this becomes 1. Palmitoyl - I drop the I-C and I add O-Y-L - 2. Oleoyl, 3. Myristoyl glycerol - that is it.2564

If you have to name it, it is probably not going to be too much of an issue, but that is it.2594

Just drop the I-C on the common name, and just go ahead and add O-Y-L to it, and there you go, so O-Y-L, O-Y-L. O-Y-L.2597

Now, let me go ahead and just go back here and, this is oxygen, that is right here, OK.2612

These oxygens, that oxygen, that oxygen, these Os, they come from glycerol.2628

OK, they do not come from the fatty acid; they come from glycerol.2632

And just as a quick recap, let us recall ester formation.2637

OK, I am going to go ahead and draw out my gly...I will do this one in black.2652

I have C, C, C; I have CHOH.2654

I have CH2OH, and I have CH2OH.2662

I am going to go ahead and draw a couple of the electrons on those just to know which one is attacking which, and let me go ahead and draw in my fatty acid.2668

I am going to do CH3, CH2.2675

Let’s just do 6 of them, and then let’s go COO; and then, O and then, let’s go PO32-- there.2680

So, basically what I have done is instead of O-, I just have a little bit of phosphate in the body.2695

This thing right here is going to act as a leaving group, so it needs to be activated first because I cannot just attack it.2702

The O is not going to go anywhere; I have to convert it into a good leaving group - which is what the body does - by reacting this thing with adenosine triphosphate, and then it puts the phosphate on here, so now, this is a really, really good leaving group.2708

Here is how it happens; this is a nucleophile.2722

This carbon is an electrophile; it kicks the electrons up.2726

Tetrahedral intermediate kicks the electrons back down.2730

This goes away, and then, of course, what you end up with, once you actually take away the H that is attached right there, you end up with the following.2734

You end up with...I am going to do it in a reverse way.2745

Actually you know what, no, I will go ahead and just keep it like this.2751

C, C, C, I have an O; let me go ahead and write the H.2755

This is OH; this is H2.2765

This is OH; this is H2.2769

And now, let me go to a different color.2773

O, I have C, O, and I have (CH2)6; and I have CH3- that is what is going on.2778

When this reacts with that, so you notice, this oxygen, this ester linkage is actually, it comes from the glycerol; it is not that oxygen.2780

This oxygen that is originally attached to the carbon, that goes away with the phosphate as part of the leaving group.2782

And, of course, now, these are free to react with other fatty acids to actually form our triacylglycerol, so just a quick recap on ester formation.2795

This oxygen, the ester linkage on the fatty acid, this thing right here, it comes from the glycerol.2805

OK, now, let’s see; let’s talk a little bit about storage.2813

Now, we said - we are almost done, no worries - we said the body stores fuel.2840

Actually, it stores glycogen as a fuel source, glycogen as a reserve fuel source, and it does.2857

That is true; we did not lie to you.2867

The reserve fuel source, OK, reserve fuel source, forgetting how to spell today, I do not know what is going on.2874

Fuel, is it F-E-U or F-U?2884

It is F-E-U, yes.2886

OK, now, the body’s primary fuel reserve is not glycogen.2887

Fuel reserve, reserves, are stored as triacylglycerols in fat cells.2902

Fat cells are called adipocytes or adipocytes.2919

Again, it just depends on where you want to put your stress; it does not really matter.2923

Yes, it is true that the body does store glycogen as a fuel reserve, but that will last maybe a day, if you are lucky.2928

Probably not even that, maybe just 5 or 6 hours.2935

The body’s primary fuel reserves, the one that goes to when you really are not ingesting any food, it is fat.2938

Fat is how it actually stores most of its fuel reserves; That is triacylglycerols.2947

So, glycogen is just if you need something quickly, but if you need something over an extended period of time, it is going to go to the fat stores.2953

OK, now, let’s see, 2.2962

I will go ahead and do this in red.2968

There are 2 primary advantages, so you are probably thinking to yourself "Wait a minute, why not just store it as glycogen, why does it have to store anything that is fat at all?".2974

There are 2 primary advantages to storing energy as triacylglycerols instead of glycogen.2985

Now, the first one, since I have another page?3005

Yes, I do.3014

Now, since the hydrocarbon portion of fatty acids on the triacylglycerols - wow, we have got a whole bunch of acronyms here - so since the hydrocarbons of the fatty acids on the triacylglycerols are more reduced than sugars - and more reduced means they have more hydrogens on them, more oxidized means they have more oxygen attached to them - sugars, they have a whole bunch of hydroxys attached to every single carbon.3015

Those carbons are reasonably oxidized, not fully oxidized yet; they are reasonably oxidized.3053

The fatty acids, they have no oxygens attached to them at all; they are all hydrogens, so they are completely reduced.3060

There is more energy available- that is the whole point.3065

Since the hydrocarbon portions of the fatty acids on the triacylglycerols are more reduced than the sugars, oxidation of fatty acids releases about 2 times the energy of sugar oxidation, so that is one reason.3068

If I store my energy as glycogen, there is a certain amount of energy that I am going to get out of it.3101

If I store the same amount of fat, I end up getting twice as much energy, gram per gram - that is the reason why, one of the reasons why.3105

OK, the second reason, and this is an interesting one.3114

Now, triacylglycerols are completely nonpolar; they are completely hydrophobic.3120

The fatty acids, we said, have a little bit of a polar end; but that is tied up now, in an ester linkage in a triacylglycerol, so it is all hydrocarbon all over the place.3129

There is nothing, there is no polar part for it to actually interact with water at all, so triacylglycerols are hydrophobic.3138

They do not want to be anywhere near water.3150

They do not bind water unlike carbohydrates, which have a bunch of highly polar molecules, bunch of hydrogen bonding going on.3158

Each sugar molecule is just surrounded with water, unlike carbohydrates.3173

They do not have the extra weight of the water attached that comes with hydration, the extra water weight associated with stored glycogen, which runs at about a 2:1 ratio, 2:1 grams of water to grams of carbohydrate.3187

So, when the body stores glycogen, because glycogen is a carbohydrate, there is a whole bunch of water that is associated with that carbohydrate.3236

It is heavily hydrated; it is very, very, very hydrophilic.3243

There is a whole bunch of water attached to it.3247

For every gram of carbohydrate that is stored as glycogen, there is about 2g of water attached to that.3250

So, you can imagine, if you, let’s say, have a kilogram of glycogen that you are storing, that is going to be 2kg of extra water weight that you are carrying because triacylglycerols are nonpolar.3256

They do not associate with water.3270

So storing, you can store a whole bunch of fat and not have to store all of the water that comes with it simply because it is hydrophobic, and that is it - 2 major advantages for using triacylglycerols and fats as long term fuel storage, that is it.3272

Thank you for joining us here at

We will see you next time for a further discussion of lipids, bye-bye.3291