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Lecture Comments (4)

3 answers

Last reply by: Professor Hovasapian
Sat Sep 14, 2013 2:08 AM

Post by Vinit Shanbhag on September 12, 2013

I was wondering how odd chain fatty acids are made, becoz you need a two carbon acetyl coa and a two carbon malonyl coa (after decarboxylation) as precursors.

Fatty Acid Catabolism II

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 Acid Catabolism 0:15
    • Fatty Acid Oxidation Takes Place in 3 Stages
  • β-Oxidation 2:05
    • β-Oxidation Overview
    • Reaction 1
    • Reaction 2
    • Reaction 3
    • Reaction 4
    • β-Oxidation Reactions Discussion
  • Notes On β-Oxidation 15:14
    • Double Bond After The First Reaction
    • Reaction 1 is Catalyzed by 3 Isozymes of Acyl-CoA Dehydrogenase
    • Reaction 2 & The Addition of H₂O
    • After Reaction 4
    • Production of ATP
  • β-Oxidation of Unsaturated Fatty Acid 21:25
    • β-Oxidation of Unsaturated Fatty Acid
  • β-Oxidation of Mono-Unsaturates 24:49
    • β-Oxidation of Mono-Unsaturates: Reaction 1
    • β-Oxidation of Mono-Unsaturates: Reaction 2
    • β-Oxidation of Mono-Unsaturates: Reaction 3
    • β-Oxidation of Mono-Unsaturates: Reaction 4
  • β-Oxidation of Polyunsaturates 32:29
    • β-Oxidation of Polyunsaturates: Part 1
    • β-Oxidation of Polyunsaturates: Part 2
    • β-Oxidation of Polyunsaturates: Part 3

Transcription: Fatty Acid Catabolism II

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

Today, we are going to continue our discussion of fatty acid oxidation, fatty acid catabolism, and we are going to actually discuss the oxidation, itself, something called beta-oxidation.0004

Let's jump right on in.0014

OK, fatty acid oxidation, as a whole, it takes place in 3 stages.0018

The first stage is the beta-oxidation.0043

Stage 2 is a citric acid cycle, so the acetyl-CoA that is formed in the beta-oxidation passes through the citric acid cycle just like the acetyl-CoA that was formed from the pyruvate from glycolysis and 3, the oxidative phosphorylation.0050

That is where all of those high-energy electrons from the FADH2 and the NADH are given over to the electron transport chain.0072

Oxygen is reduced to water, and ATP is produced- oxidative phosphorylation.0080

OK, now, we looked at no. 2 in the last unit; that is where we discussed the citric acid cycle.0087

Oxidative phosphorylation, we are going to talk about not the next unit but the unit after that.0094

The next unit, we are going to talk about the breakdown of amino acids, and then, after that, we will go ahead and take a look at the final phase, which all of these things funnel into- the oxidative phosphorylation.0099

Here, we are going to concentrate on beta-oxidation.0111

OK, now, beta-oxidation, this is going to be our primary concern here.0116

Beta oxidation is the successive removal of acetyl-CoA.0126

Well, it is the removal of acetyl groups to carbon groups as acetyl-S-CoA.0150

OK, now, it consists of 4 reactions repeated over and over again.0165

A free fatty acid, that is what we are doing; we have taken this fatty acid and used the carnitine shuttle to bring these fatty acids into the mitochondrial matrix, and at this point, a fatty acid is just some carboxylic acid end with this long chain carbon- 14, 18, 16, 20, 24, however long it is.0190

What we are going to be doing is we are going to be removing 2 carbons at a time as acetyl-CoA - 2, 2, 2, 2, 2 - until the last 2, and that is going to be another acetyl-CoA; and these acetyl-CoAs enter the citric acid cycle.0211

That is what is happening here; these 4 reactions that we are going to diagram in just a moment, they are the 4 reactions that actually split it up over and over and over again until you just run down the chain and you run out of carbons.0223

It consists of 4 reactions repeated over and over again until, well, until you run out of carbons- that is it.0237

That is all that is happening here; OK, let me see if I want to do this on...I do not want to start it on this page.0259

I actually want to do all of the 4 reactions on 1 page, so I am going to go ahead and go to the next page; and I think I am going to keep this in black.0269

These are going to be the 4 reactions of beta-oxidation.0276

I am just going to choose some random fatty acid.0280

It is going to be written as R, C.0284

I am not going to put the Hs actually.0290

Well, maybe I should.0294

I do not know; it is always a tough call.0299

That is OK, I will go ahead and leave the Hs off, R, C, C, C, C, so 1, 2, 3, 4, and we will go ahead and put...this is the S, and this is the CoA.0301

OK, this is our starting fatty acid.0317

It is now an acyl-CoA.0323

Notice, there are no unsaturated, so this particular is for an even number of carbons of fully-saturated fatty acids.0327

Let's see here; let's see what we can do.0340

Our first reaction is going to be the following; our first reaction is going to take us to...let me see.0342

We are going to have FAD to FADH2, and this is catalyzed by - I will do the enzyme in red - acyl-CoA dehydrogenase; and when we do that, what we end up with is the following molecule.0349

This is reaction 1; this is reaction 1, go back here.0380

What we are left with is R, C, C, and here - I actually will put the Hs in to show you that this is actually a trans double bond, not a cis double bond - C, O, S-CoA.0386

OK, this is called a trans-delta2-enoyl- CoA.0410

1, 2, that is what the delta2 means; it means the 2.0423

It means trans, the double bond is trans.0427

OK, this is down; this is up, not cis, and the delta2 means on the no. 2 carbon, carbonyl is the no. 1 carbon, enoyl-CoA.0431

The name does not really matter all that much; it is this, it is the structure that matters.0442

That is what we want you to concentrate on: understanding where the structures are, where the double bonds are, particularly with fatty acid catabolism because double bonds are going to be moving as you will see in just a minute.0446

OK, now, the next reaction: 1, 2, 3.0456

I hope I have enough room for this; well, you know what, if I do not, it is not a problem.0464

H2O comes in, and this one...well, let me go ahead and draw the molecule, itself.0470

We have R; we have C.0478

We have COH, H.0482

we have CH, and H, 1, 2, 3 here and S-CoA.0487

Let's make sure 1, 2, 3, 4, 1, 2, 3, 4 good, that is nice.0498

Alright, this is enoyl-CoA hydrotase.0506

OK, and I will be going over this in just a minute; I am just drawing them out right now.0518

Let's go ahead and go...let me see.0522

I think I will go down this way.0529

Well, let me see; actually, you know what, I think i am going to go down this way.0535

I will go down here; this one, NAD+, NADH + H+.0541

By the way, this is reaction 2; this is going to be reaction 3, and the molecule that we are going to form is going to be - no, let's go ahead and go back to black - R1, 2, 3, 4.0556

This is going to be S; this is going to be CoA, alpha-beta.0577

We are going to be...that is ketone there; that is exactly right.0581

OK, and the enzyme that catalyzes this is called...oh, boy, this is beta-hydroxy acyl-CoA dehydrogenase.0585

And, of course, the last reaction is going to be...go ahead and do it like that, and what we have coming in is CoA, SH.0610

This is going to be reaction no. 4; it is going to be catalyzed by acyl-CoA, acetyl transferase, otherwise known as thiolase, and the molecule that you are going to end up with or the 2 molecules you are going to end up with is R, C, C, double bond, S-CoA + the CH3, C, this S-CoA.0634

Here, you are going to have your acetyl-CoA, your first acetyl-CoA group that has been taken off, and here you have the remaining molecule.0683

Let's go ahead and take a look at what is going on here; these are the reactions of beta-oxidation.0694

We start off with this acyl-CoA fully saturated even number of carbons.0699

The first reaction is going to be the conversion of this thing into an alpha-beta unsaturated acyl-CoA.0705

OK, what we have done is...this is a dehydrogenase.0718

We are pulling away some hydrogens; we are going to pull away some hydrogens, and we are going to create this trans double bond.0722

That is what is important; this is trans, not cis.0727

OK, we are actually creating a point of unsaturation.0730

This is alpha; this is beta, so this is an alpha-beta or 2,3 if you want to think about it.0735

This is the no. 1 carbon; this is the no. 2 carbon.0741

Let me go ahead and mark these; this is the no.1.0745

This is the no. 2; this is the no. 3.0748

We are creating a double bond between the 2,3 carbon, and this is catalyzed by acyl-CoA dehydrogenase; and FAD, it is a dehydrogenase.0750

It is an oxidation; FAD is converted to FADH2, so, one of those is produced.0759

Now, from here, we have this thing called a trans-delta2-enoyl-CoA, and again, the name is unimportant.0767

What matters is the molecular structure.0772

You have a carbonyl, and at the 2,3 position, at the alpha-beta position, you have a point of unsaturation.0776

The next reaction catalyzed by enoyl-CoA hydrotase actually adds water across the double bond.0782

What you are going to be doing is adding H, adding OH.0790

Now, what you have is an alpha-beta hydroxy; it is a beta-hydroxy acyl-CoA, right?0794

Here is the carbonyl, and this is the alpha; this is the beta-carbon.0800

You have a hydroxy group attached to that; OK, at this point, the enzyme beta-hydroxy acyl-CoA dehydrogenase, now it dehydrogenase, it oxidizes that.0804

So, it is going to take away this hydrogen and this hydrogen to create a beta-keto.0814

Now, again, NAD+ is the electron acceptor at this point.0820

It is the oxidizer; it is going to turn into NADH, so we are forming one of these in the third step, and notice, now, this alcohol is now a ketone.0827

Now, you have 2 carbonyls on here, and at this point, here is where we are going to break it up.0837

This acyl-CoA acetyltransferase, this thiolase enzyme, another CoA comes in, and what ends up happening is you break this bond, right here.0842

OK, when you break this bond, you are going to release this molecule as your acetyl-CoA, and now, your original molecule, this CoA, it is now, turned into another acyl-CoA; but now, it is 2 carbons shorter.0854

That is what you are doing; you are just 2 carbons, 2 carbons, 2 carbons.0871

These 4 reactions happen over and over and over again, so you go from 12, 10, 8, 6, 4, 2- you are done.0875

That is what is going on; these are the reactions that are important.0883

Unsaturated, you introduce a point of... I am sorry; saturated, you introduce a point of unsaturation, alpha-beta.0887

It is in the trans configuration; you go ahead and you hydrate that double bond.0895

You convert that hydroxy to a keto, and then, you split that bond, right there; and then, you create 2 molecules.0899

You release acetyl-CoA, that is what is happening.0906

OK, let's go ahead and say a couple of words about this.0910

Let's say...take some notes here.0916

Now, first note: the double bond.0922

After the first reaction, is trans.0935

OK, it is a trans.0940

Most natural unsaturates are cis.0945

Natural unsaturation points are cis.0952

OK, reaction no. 1 is catalyzed by 3 isozymes - and we know what isozymes are - of acyl-CoA dehydrogenase.0965

OK, the one that is used depends on the length of the carbon chain in the fatty acid.0995

The one used depends on the length of the carbon chain.1002

If we have 12-18 carbon, it is called VLCAD, very long-chain acyl dehydrogenase- that is it.1019

B: if we have 4-14 carbon, we call it MCAD - exactly what you think - medium-chain acyl dehydrogenase, and if we have let's say 4-8 carbons, well, SCAD.1039

And again, these names, they are not important.1061

All you need to know is that this actually happens; it is the 3 isozymes, short-chain acyl dehydrogenase.1064

Biochemistry is just overfull of abbreviations.1070

Be able to separate what is important, what is not; it is the chemistry that is important, not the nomenclature.1076

You can always look up the nomenclature; there are glossaries of these things available, so do not worry about it.1081

OK, now, what is interesting about this is all 3 are flavoproteins - remember, we talked about these - having FAD as a prosthetic group, and you notice the first reaction, it is FAD that is actually used as the oxidizer.1086

OK, now, in reaction no. 2, H2O adds across the alpha-beta double bond - I will write it this way, how is this - to form a beta-hydroxy acyl-CoA.1118

OK, now, after reaction no. 4, you are left with acetyl-CoA and a fatty acyl-CoA that is 2 carbons shorter.1165

That is the idea.1200

OK, now, FADH2 goes and gives us electrons to the electron transport chain.1205

FADH2 produces 1.5 ATP per 2 electrons.1217

Well, the NADH that is formed also gives its electrons to the electron transport chain.1223

It produces 2.5 ATP.1230

Per cycle, those 4 reactions of beta-oxidation 2.5, 1.5, 4 ATP molecules are produced.1234

For every acetyl-CoA that is cut off, 2 carbons, you are producing 4 ATP.1243

If you end up with an 8-carbon fatty acid - well, that consists of 2, 4, 6, 8 - you end up producing 16 ATP.1248

You can see why oxidizing fatty acids is very, very highly energetic.1256

It produces a hell of a lot of adenosine triphosphate, so 4 ATP per 4 reaction cycle.1265

Every time you go through the cycle of 4 reactions, you create 4 ATP from those high-energy that are donated to the electron transport chain.1275

OK, now, let's see; let's go back to black here.1285

These 4 reactions - let's see - are the basic 4 reactions for saturated fatty acids having an even number of carbons.1289

OK, now, many - I should say most - of the fatty acids in triacylglycerols - in TAGs - are unsaturated.1330

They have 1 or more double bonds.1348

OK, beta-oxidation of the unsaturated fatty acids, we have bonds of unsaturation are cis.1357

Points of unsaturation in the fatty acids that make up most of the triacylglycerols, they are naturally cis.1396

They do not come and transform, they come as points of unsaturation that are cis stereochemistry at the double bond, but the enzyme enoyl-CoA hydrotase requires the fatty acid to be trans.1405

That is what that first reaction does, is when it creates that double bond, that dehydrogenase, it creates a trans double bond, not a cis double bond.1438

The reaction no. 2 cannot take a naturally occurring unsaturated fatty acid, and just go ahead and use it because it does not accept cis double bonds.1450

It needs trans stereochemistry; we need an enzyme that actually makes some changes before beta-oxidation can continue, and that is what we are going to do.1459

Bonds of unsaturation are cis, but the enoyl-CoA hydrotase, which is reaction no. 2, requires the fatty acid to be trans.1468

OK, now, let's go ahead and run through this scheme for the beta-oxidation of monounsaturates.1478

We are going to do this separately; we are going to do 1 point of unsaturation and then, multiple points of unsaturation.1484

The first one we want to look at is the beta-oxidation of monounsaturates.1490

OK, let's go ahead and start with just some random example here, so I will go ahead and draw this out.1507

I have got C, C, C.1513

There is my point of unsaturation; that is C, C.1518

I have got another couple, and I have got another couple just to...OK, and I have S-CoA.1523

Again, let me just make sure that I have the right number of carbons here: 2, 2, 2, 2, 2.1530

I have got 2 here, 2 here, 2 here; everything looks good.1535

OK, the first thing we are going to do is we are going to, of course...well, let me just go ahead and draw this out first.1540

It is 1 cycle; that is 2 cycle.1548

I have got 2 acetyl-CoAs come out; 2 acetyl-CoA comes out from 2 cycles, and what I am left with is the following.1552

I am left with C, C, C, double bond C.1565

This is C, and I have got 1.1570

I have got 2; I have got this one right here, so what I am left with is the following: S-CoA.1574

OK, the first thing that happens here is...let me see.1584

This is our unsaturated acyl-CoA; here is our point of unsaturation.1590

Up to here, it is actually normal; the 2 cycles of normal beta-oxidation, 4 reactions then another 4 reactions, we end up doing this.1596

The first cycle goes ahead and releases that one, so those 2 carbons are gone as acetyl-CoA; and then, the second cycle takes these 2.1605

So, now, we have released 2 molecules of acetyl-CoA and 2 cycles of beta-oxidation.1614

What we are left with is the following; now, we have a double bond on this carbon here, right?1620

That is this carbon; we have this acyl-CoA.1625

OK, it is at this point that some things are going to be happening.1630

Now, let me go ahead and do this in...yes, that is fine; I will go ahead and do this in blue again.1635

Here, what we have is the following; I will go ahead and draw this, and the enzyme that catalyzes this, this new enzyme that needs to make a change is called delta(3)-delta(2)-enoyl-CoA isomerase.1643

Basically, all we are going to do is we are going to shift the double bond.1667

We are going to move the double bond from here, the 3,4 position, and we are going to change it to a 2,3 double bond.1671

OK, what happens here is the following.1679

What this reaction does is it changes the double bond from 3,4 double bond to 2,3 double bond.1685

This is a 3rd carbon, 4th carbon, 2nd carbon, 3rd carbon.1700

This is 1, 2, 3, 4; we are just going to move the double bond over.1704

This delta(3)-delta(2)-enoyl-CoA isomerase, this enzyme affects this change, and what we end up with is the following.1709

Let me go back to blue here.1718

Let me go to the next page; oops, I am here.1722

Let me go to the next page, and what I end up with is the following molecule.1727

C, C, C, now, that is a single bond; I am going to leave them where they are, C, C, O, S-CoA.1732

I left the structure alone; I have moved the double bond from here to here- there we go.1743

Now, from this point, beta-oxidation is normal.1750

I have the acetyl-CoA, and then, I have an alpha-beta unsaturation.1754

This is where we got to after reaction 1, so from this point - I will write it up here, no, that is fine, I will write down here, I should say normal beta-oxidation - normal beta-oxidation continues starting with reaction no. 2.1759

OK, alright, now, I am going to take this and bring it over here.1800

Let me go ahead and bring this down here.1807

I will go ahead and put...reaction no. 2 of the normal beta-oxidation does the following.1812

It actually converts it to this.1819

I have got C, C, C, C, C, C.1822

I have that, and I have the S-CoA - right - and I have got myself a hydroxy here now.1832

I have an H here now; I have got an H, and I have got an H, and then, reaction no. 3 carries me to the keto.1847

I have got C, C, C, C.1857

This is, now, keto; this is C, C, O, S-CoA, and then, of course, I have got reaction no. 4, which gives is going to break the bond right here.1860

I produce C, C, C, C.1876

I produce 1 acyl-CoA, and, of course, I have my resulting acetyl-CoA plus the C, C, S-CoA.1882

I will go ahead and do that; from here on in, it just goes on with normal beta-oxidation.1894

It breaks this up to release this acetyl-CoA, and then, of course, you are left with that acetyl-CoA.1900

That is all that is happening here; as far as if you have a fatty acid that has 1 point of unsaturation, it will run beta-oxidation up until a certain point, but then, what it will do, this isomerase, it will actually change the double bond from a 3,4 position to a 2,3 position, in other words, from a beta-gamma to an alpha-beta double bond.1906

That is all that is going to happen for 1 point of unsaturation.1930

OK, and again, 2 more cycles produces your acetyl-CoA.1935

Now, let's go ahead and take a look at the beta-oxidation of a polyunsaturate, something that has 2 or more points of unsaturation.1940

OK, beta-oxidation of polyunsaturates, and the particular example that I am going to use for my fatty acid, it is going to be just something that has 2 points of unsaturation.1949

Let's go ahead and draw the molecule and run through the reactions.1973

We have got - let me see - 1, 2; yes, that is fine.1979

OK, we have got C, C, C, C, double bond C, C, C, double bond C, another carbon, another carbon, another carbon, another carbon, another carbon, another carbon, and I think we will go ahead and stop there.1986

We have S-CoA; we have something like that, 2 points of unsaturation.2002

Let's see what happens here; 2 cycles - OK - releases 2 acetyl-CoAs.2008

We have 2 cycles of normal, right?2020

We break this bond here; we release that acetyl-CoA.2024

We break this bond here; we release those 2 carbons as acetyl-CoA, and what we are left with is the following.2028

We have got C, C, C, C, double bond C, down to number C, up there, up there, up there.2035

This is C; this is C.2046

Now, what we are left with is that.2049

OK, at this point, this enoyl isomerase does the same thing.2054

Notice, we have...this is the no. 1 carbon; this is the no. 2.2060

This is the 3, and this is the 4; what we are going to do is we are going to remove this double bond from the 3,4 position to the 2,3 position.2065

In this particular case, what we are going to have is the reaction that is catalyzed by the delta-3 to the delta(2)-enoyl-CoA isomerase just like the reaction that we just did.2071

We are just dealing essentially with 1 saturation point at a time.2092

We have come to this 1 saturation point; now, we are going to move it here, and continue on with beta-oxidation until we get to the other unsaturation point.2096

OK, this gives us the following.2105

I have got C, C, C, C, double bond C, C.2112

Now, I have a single bond here, and I have a double bond, which is trans- OK, very, very important.2119

That double bond that is formed that is alpha-beta, that is trans.2125

That is the whole idea; this goes there, and this is S-CoA.2131

OK, now, at this point, what happens is the following.2142

We have...well, OK, at this point the normal reaction no. 2, reaction no. 3 and reaction no. 4 of your normal beta-oxidation take place in order to remove this acetyl-CoA.2152

OK, let me go ahead and write reactions 2, 3 and 4 of normal beta-oxidation take place, and what you end up with is the following.2173

You end up with the following molecules: C, C, C, C, double bond C.2194

This goes there; this goes there.2201

That goes there, and now, what you have broken is this bond to release this S-acetyl-CoA; and what you are now left with is this molecule right here.2205

OK, now, from this point, here is what happens.2225

Reaction no. 1 from normal beta-oxidation: when you do reaction no. 1, you are going to introduce that reaction no. 1 actually introduces a trans double bond into a point of saturation.2232

We are going to put a double bond between the 2 and the 3 carbon.2244

What you end up with is the following molecule.2249

You end up with blue; oops, where is my...OK, there is my...I am left with C, C, C.2255

There is 1 of my double bonds; there is that one I have moved.2266

I have introduced a double bond here- S-CoA.2273

OK, now, at this point, notice what I have got.2281

I have 2 double bonds now; this is 1, 2, 3, 4, 5 carbon.2285

I have a double bond on the 2,3; I have a double bond on the 4,5.2293

The next enzyme, what it does is it is a reductase.2298

What it is going to do is the opposite of the dehydrogenase; it is going to add hydrogens.2302

It is going to reduce this molecule, but it is going to take these 2 double bonds; and it is going to switch it to a single bond between the 3 and the 4.2307

Let's see what happens; let's go ahead and do this.2316

OK, this time, NADPH + H+ goes to NADP, and this is called 2,4-dienoyl-CoA reductase.2323

OK, and what it is going to do - let me actually draw up the molecule first - it is going to be C, C, C, C, double bond.2350

No, we just said that it is going to actually change that double bond; that is going to be single.2365

That is going to be double; that is going to be single, and that is going to be single- S-CoA.2370

OK, here, a 2,3 double bond and the 4,5 double bond are replaced by a 3,4 double bond- OK, very, very important.2380

The 2,3, the 4,5, that is why they call it 2,4 dien; this is a 2,4 dien.2405

These 2 double bonds are taken away; it is reduced, and it is replaced by a double bond between the no.3 and the no.4 carbon.2411

Here you go; you have 1, 2, 3, 4, 5.2418

That is what happens there; OK, now, at this point, what you have is another application of the enzyme enoyl-CoA isomerase, and what happens here is that the 3,4 double bond is converted to a 2,3 double bond because again, we need that alpha-beta double bond in order to continue with the normal reactions of beta-oxidation.2424

That is all that is happening here; we are just moving double bonds around.2459

3,4 double bond is converted to a 2,3 double bond, and what you end up with is the following molecule.2463

You get C, C, C.2475

This is C; this is C.2480

Now, this is single; now, this is double, and this is C.2483

This is O, S-CoA.2488

Now, we have 1, 2, 3.2492

We have a 2,3 double bond that we need; this is the one that can now undergo the hydrotase reaction, which attaches an alcohol group, and then, that alcohol group becomes a ketone group, and then, we can cut off those 2 carbons.2497

This is no. 2 carbon or if you like, alpha-beta- an alpha-beta double bond.2511

OK, now, at this point, we can go ahead and run our reactions 2, 3 and 4.2521

Under normal conditions, we are going to release an acetyl-CoA, which is this one, a C, C.2531

We are going to break the double bond here.2541

We are going to release this acetyl-CoA, and then, of course, now, we just have a couple of more cycles.2544

At this point, what we are left with is 1, 2, 3, 4, 5, 6 carbons.2550

OK, at this point, what you are left with is 1, 2, 3, 4, 1, 2, 3, 4, 5.2555

I will put the 6th carbon up here because I need to write the S-CoA.2564

Now, it is normal beta-oxidation at this point- 3 cycles of that 4-reaction sequence.2570

This is cut off and released as acetyl-CoA; this is cut off and released as acetyl-CoA, and, of course, the last 2 are released as acetyl-CoA.2575

Again, it looks like there is a lot that is going on here but there is actually not.2585

You have 4 basic reactions of the beta-oxidation.2590

When you introduce a point of unsaturation, there is only that 1 extra enzyme so that isomerase that needs to change the double bond from the 3,4 position to the 2,3 position, and then, beta-oxidation can just continue as normal.2596

But when you have multiple points of unsaturation, you actually need to take care of that first part first.2612

It goes through normal beta-oxidation, and then, you just start moving double bonds around.2620

That is all that is going on here; you are just moving double bonds around in order to get to a point where you have some acyl-CoA that looks like this.2624

You have the acyl-CoA part here, but you want your double bond to be in the alpha-beta; and you want it to be a trans.2634

That is what you want; you want to get a 2,3 double bond.2643

All of these enzymes, they are all geared to do that, so that reaction 2, reaction 3, reaction 4 of the normal beta-oxidation can take place.2647

Go through this very, very carefully.2658

There are several diagrams of this in your book, I promise you; or if you want, you can pull them up on the web.2663

It is not a problem; some of them have a lot of information on there.2670

It is a little hard to read; some of them have very, very little information, but definitely spend time with those diagrams and spend time...pick a couple of fatty acids.2672

They do not have to be very, very long chain, but go through the process yourself physically drawing it out, drawing out each individual step; because again, the only way to really understand what is going on is not to do it passively but to do it actively.2682

Draw out the carbons; draw out the double bonds.2697

Write in the enzyme names; that is the only way that any of this is going to make sense, but make sure you are very, very careful and very detailed about what is going on because the double bonds are moving, and it is very, very subtle.2701

It is very easy to get lost in all of these carbons and oxygens, I mean, very, very easy to get lost, to miss a carbon.2712

By missing a carbon, all of sudden, you have gone from an even number of carbons to an odd number of carbons; it is very difficult to keep track of.2719

When doing this I would recommend not using line structures.2726

I, myself, to this day, I do not use line structures; I like to see every single carbon that I am working with.2731

So, by all means, until you get really, really, really used to this stuff, do not use line structures.2737

They look good, but it is the understanding that you want; we want you to be able to recreate this, to replicate this.2743

OK, thank you for joining us here at; we will see you next time for the final words and the continuation of fatty acid catabolism, bye-bye.2750