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Lecture Comments (11)

2 answers

Last reply by: Swati Sharma
Mon Apr 23, 2018 6:27 PM

Post by Swati Sharma on April 22 at 03:21:28 PM

Dear Dr Rafi,

In class I haven't understood these three questions and would be grateful if you could explain these to me

1) Determine what reactions must be reversible and irreversible?
2)What reactions can potentially be the rate determining steps?
3)What reaction is the rate determining step?, the most important regulation point of glycolysis?


1 answer

Last reply by: Professor Hovasapian
Thu Jan 7, 2016 10:36 PM

Post by Rawan Shoair on January 1, 2016

I really am very thankful that a Prof. like you exists Prof. Raffi.

0 answers

Post by Peidong, He on December 11, 2014

You are awesome.

2 answers

Last reply by: Megan Ward
Fri May 2, 2014 7:52 AM

Post by Megan Ward on April 30, 2014

Hi Professor Hovasapian,
In the overall equation for glycolysis it is written that glucose+ 2ADP goes to products. I thought that it was ATP that was invested, not ADP?

1 answer

Last reply by: Professor Hovasapian
Thu Nov 21, 2013 1:01 AM

Post by Angela DiFabio on November 20, 2013

Hi Professor Hovasapian,

I have a question in regards to the amount of ATP produced if the cycle were to start with Sucroce? My teacher asked us this question and I wasn't sure exactly how to answer it. I do know that sucrose can be broken down into glucose and fructose - so does this mean that you would start with 1 molecule of glucose (net 2 ATP) and start with fructose additionally (net 3 ATP) for a total of 5 ATP?

Overview of Glycolysis I

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
  • Overview of Glycolysis 0:48
    • Three Primary Paths For Glucose
    • Preparatory Phase of Glycolysis
    • Payoff Phase of Glycolysis
    • Glycolysis Reactions Diagram
    • Enzymes of Glycolysis
  • Glycolysis Reactions 16:02
    • Step 1
    • Step 2
    • Step 3
    • Step 4
    • Step 5
    • Step 6
    • Step 7
    • Step 8
    • Step 9
    • Step 10
  • Overview of Glycolysis Cont. 27:28
    • The Overall Reaction for Glycolysis
    • Recall The High-Energy Phosphorylated Compounds Discusses In The Bioenergetics Unit
    • What Happens To The Pyruvate That Is Formed?

Transcription: Overview of Glycolysis I

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

Today we are going to start off with something really, really exciting.0004

We have gone ahead and we are going to be starting a new unit; we are going to be starting glycolysis today, but more than that, we have actually done the first half of Biochemistry- the structure, the bioenergetics and things like that.0008

Now, we are going to start on the second half of biochemistry, which is metabolism; and this is really, really exciting.0019

This is the section that is actually going to be testing a lot of your memory.0028

There is going to be a lot of reactions going on; there is going to be lots of enzymes, lots of mechanisms, but all of it absolutely beautiful, I promise.0031

After all these years, I am still fascinated by how extraordinary this stuff is.0039

Anyway, we are going to get started with glycolysis, so let's jump right on in.0044

In this lesson, it is just going to be an overview; I am going to be talking about glycolysis globally, and then, in subsequent lessons, I am going to go through each individual step.0050

We are going to go through a detailed mechanism, structures- things like that.0059

OK, glucose is the primary sugar monomer that your body uses to create energy.0063

That is what is ultimately metabolized; that is what is broken down and run through the metabolic pathways, and all of the energy is extracted from that.0073

It is used to make the adenosine triphosphate; all of the carbons are oxidized to carbon dioxide.0084

And then, of course, it is oxidized to water, but it all begins with glucose.0091

Let's take a look at what glucose can do.0096

Glucose has 3 primary paths that it can follow.0101

When we say primary, most of it happens this way.0118

There are few other things that glucose can do, but most of glucose goes to these 3 things.0121

Let's go ahead and write glucose here.0129

We can take one path, and that is going to be the storage path.0133

No, that is fine; I will go ahead and...the body can take the glucose and create those polymers that we talked about when talked about carbohydrates, the starch and the glycogen.0138

It can use it for storage purposes; now, the other path that it can take is actually glycolysis, which we are going to talk about.0154

When it runs through glycolysis, the products are pyruvate + adenosine triphosphate.0165

OK, and the third path that it can take is something called the pentose phosphate pathway, and we are going to be discussing that after we discuss glycolysis.0174

And the final products of that particular pathway are the ribose 5-phosphate + NADH.0193

And you remember NADH is the reduced form of that particular coenzyme NAD+- oxidized form, reduced form.0209

OK, now, in glycolysis - glycolysis, if you like - a molecule of glucose is broken down into 2 molecules of pyruvate - and then absolutely, it is amazing, it still just amazes me, OK - in 10 enzyme catalyzed steps.0217

Of course, we know that every reaction in the body is catalyzed by an enzyme.0265

Now, glycolysis can be considered to have 2 phases.0280

Now, again, when we talk about these 2 phases, the preparatory phase, the payoff phase - or sometimes they call it the investment phase and the payoff phase - please understand that this is an artificial categorization based on how we want to look at things.0300

When things tend to get a little bit too complex, we like to break them down into smaller pieces.0314

Now, it is true; I mean, there is a preparatory phase and a payoff phase.0318

You will see what that means when we actually get into the details, but understand that you do not have to actually look at glycolysis that way if you do not want to.0322

This is just one, sort of, categorization of it.0328

I personally do not tend to look at it this way necessarily; I just look at it as 10 steps, 10 biochemical reactions, but I think it is great to, sort of, see it as preparatory or investment and then payoff.0333

Again, this is not set in stone; this is just a way of looking at something.0346

Do not feel like it is this, a glycolysis; there is this, and then there is that.0352

It is not; it is just our way of organizing the information.0357

OK, the first is called the preparatory phase or the investment phase.0360

OK, this is where glucose in 5 steps is converted to 2 molecules of glyceraldehyde 3-phosphate.0375

Now, the second phase is called the payoff phase, and this is where these 2 molecules, the glyceraldehyde 3-phosphate...I will just write it as 2 glyce 3P.0401

Again, in another 5 steps, you see the little bit of symmetry here that we have divided it into.0418

It is converted to 2 molecules of pyruvate- that is it, so preparatory phase, payoff phase.0426

A preparatory phase, investment phase, that is where ATP is used to actually invest a little bit more energy into the glucose molecule to actually prime it, to prepare it for the other reactions.0432

And the payoff phase comes because during that process, ATP is actually produced.0450

There is a net gain in adenosine triphosphate during glycolysis in addition to the pyruvate, so it is actually really, really great.0454

Now, let's go ahead and take a look at what is going on.0462

I am going to list the steps; I am going to list the actual enzymes that catalyze these steps.0469

And, of course, when we get into the details of the individual steps, we will talk a little bit more about the enzymatic activity.0472

OK, let's see what we have go here; this is your overview of glycolysis.0479

This is exactly what is happening; let me run through this really quickly.0484

You know what, let me go ahead and do it in blue just because I like blue.0489

We have glucose here; we start off with glucose, and some ATP is invested, and it converts it to glucose 6-phosphate.0497

The glucose 6-phosphate is then converted to fructose 6-phosphate.0507

Again, another ATP is used up; another ATP is invested in this to create fructose 1,6-biphosphate.0513

Now, this fructose 1,6-biphosphate is split in half; OK, we have 6, right?0521

Glucose is 6-carbon sugar, so it is split right down the middle- 3 carbons, 3 carbons.0526

And one of the things that it actually produces is directly glyceraldehyde 3-phosphate.0532

The other thing that it produces in this reaction is dihydroxyacetone phosphate; this is the DHAP.0538

Do not worry; we will be writing all of these things down.0546

And, of course, this is in your book; so I absolutely encourage you to look at the arrangement in your book.0549

Different books have different illustrations, and they are really fantastic.0555

This dihydroxyacetone phosphate is actually converted really quickly into glyceraldehyde 3-phosphate.0560

We end up with these 2 molecules; one molecule of glucose produces the 2 molecules of the glyceraldehyde 3-phosphate.0567

OK, now, each one of those goes through the same reaction.0575

This and this right here, the 2 columns- they are the same.0579

Glyceraldehyde 3-phosphate, inorganic phosphate, NAD+, is invested, and you end up oxidizing this, right?0582

Because, when this is oxidized, this NAD+ gets reduced.0593

NADH is produced, and it turns it into 1,3-biphosphoglycerate.0597

Well, now, ADP is put in; and ATP is produced in the step of converting the 1,3-biphosphoglycerate to the 3-phosphoglycerate.0602

3-phosphoglycerate is changed into 2-phosphoglycerate.0612

2-phosphoglycerate is converted to phosphoenolpyruvate; and the phosphoenolpyruvate, again, the ADP is brought in to create another molecule of ATP, and our final product is pyruvate.0617

Let's take a look at what is going on here.0630

We have 1, 2, 3, 4; 4 molecules of ATP are produced, but 2 are invested in the preparatory phase, so there is a net gain of 2 ATP molecules.0634

That is actually pretty, pretty great; I mean, basically this glycolysis pathway decides to use some of the extra energy to go ahead and create a little ATP in the process of breaking down the sugar, which it has to do, anyway.0647

That is what is magnificent about this; it is going to use up as much of the excess free energy that it can to do something that it can.0659

Now, most of the ATP in the body is not produced by this process; it is produced by oxidative phosphorylation, which we will talk about later, but it is kind of great that we are able to produce a little bit of ATP just to keep things going.0667

OK, let's number the steps here.0677

Let me see; should I do it on this side or that side?0683

I am going to do it here; this is step no. 1.0687

This is step no. 2; this is step 3.0691

This is step 4, and this is step 5.0695

When this breaks up, this, it produces a molecule of this and this.0699

We actually consider...I do not know.0705

If you want, we can consider this step 4; this step 4, this is probably best to do it this way.0709

And then, let's consider this step 5, the conversion of the dihydroxyacetone phosphate to the glyceraldehyde 3-phosphate.0713

OK, now, we have the other 5; we have 6.0721

This is step 7, step 8, step 9, and the final step, the conversion of the phosphoenolpyruvate to pyruvate.0726

OK, now, I am going to go ahead and write down the names of the enzymes just for the sake of seeing them.0735

One of the things that you want to do is you just want to see these things over and over again, the, sort of, passive learning process.0742

However - again, back to the actual learning - to learn these things, you actually have to write them down physically.0748

There is a deep connection between the actual physical active writing and the extent to which it actually stays in the brain.0753

My guess is you will have to actually memorize not just the molecules, but you will have to memorize the enzymes that catalyze these reactions.0762

OK, I am going to write no. 1 over here; the enzyme that catalyzes step 1 is hexokinase.0775

OK, no. 2, step 2 is phosphohexose isomerase or isomerase.0784

Again, you can do it anyway you want; step 3, we have phosphofructokinase-1 or PPK-1.0799

OK, the fourth enzyme is aldolase, and enzyme no. 5 is triosephosphate isomerase.0826

OK, now, let's come over here; you know what, I probably should have done that in black, but that is OK.0846

OK, now, enzyme no. 6, for this step right here, it is going to be glyceraldehyde 3-phosphate dehydrogenase.0851

Step 7 is catalyzed by phosphoglycerate kinase or kinase- it is up to you.0869

This is going to be no. 8, phosphoglycerate mutase.0886

I love these names; they are fantastic.0894

It is just they are really fantastic, and then, we have enolase.0896

And then, we have the pyruvate kinase- there you go.0901

This is the general scheme; 2 molecules of ATP are invested.0911

4 molecules of ATP are produced; there is a net gain of 2 molecules of ATP.0918

2 molecules of NADH are produced with their high-energy electrons; they can go on and do other things, reduce other things or enter the electron chain.0925

We have our enzymes; OK, now, let's go ahead and take a look at the structures of these molecules.0938

They are not just names; it is really, really important to because you are going to have to know what the structures are.0945

OK, let's start off with our...let's see; what should we do?0950

OK, alright; let's go ahead and start off with our glucose molecule here.0965

Let me see; I guess I will do it this way.0972

Alright, let's use this particular form: OH, OH, OH.0976

And then, of course, we have CH2; I think I am going to do the...that is OK.0985

I will go ahead and do the OH on this side; it is not a problem.0991

OK, this is our glucose molecule.0994

Should I do that in blue?1001

Yes, that is fine; OK, that is step 1.1003

Step 1, we are going to actually phosphorylate that thing right there, from glucose to glucose 6-phosphate.1007

We are going to have this.1015

It is just structures; it just takes a little while to write these things.1022

Also, you should know that I often do not write my hydrogens on carbons- sometimes I do, sometimes I do not.1029

Again, if there is a carbon that you see only has 2 bonds, the other 2 bonds are occupied by hydrogen- that is all that means.1034

OK, I will just go ahead and put a P here for the phosphoryl group.1043

OK, P, it is not PO4, the phosphoryl group.1050

This P is equivalent to PO32-; it is this molecule right here or this group.1057

It is this group that is attached to the...there is another oxygen here, but that oxygen comes from the alcohol that was attached to the carbon.1066

So, the phosphoryl group is actually PO32-; OK, not PO4.1074

It is not phosphate; it is a phosphoryl group.1077

OK, now, let's see.1080

Step 2, glucose 6-phosphate; now, we want to do fructose 6-phosphate.1085

Step 2 is going to look like this, boom, boom, boom, boom, here.1092

We will go ahead and put this here, CH2OH.1099

We have an OH here; I think it is going to be OH on top, OH on the bottom.1103

And then, of course, we have this C.1109

And then, we have this O, and you know what, I am going to go ahead and actually do it to the right, CO, P; how is that?1113

Fructose 6-phosphate, OK, let's see; should I go down, or should I go up?1125

How about if I go that way?1133

I will go that way, so step 3.1136

We are going to now, phosphorylate that one too.1140

So, we are going to have fructose 1,6-biphosphate; that is that, that, that.1145

We are going to have CH2, O, P.1150

We have OH; we have OH.1157

We have OH; there is still 6 carbons here, 1, 2, 3, 4, 5 and 6- there you go.1160

There is the CH2; there is the O, and there is the P.1168

This is fructose 1 - I am sorry - 1,6-biphosphate.1171

OK, now, we are going to actually split this up, and let me go ahead and just really quickly change.1178

The break is going to come right here.1185

OK, you are going to have this 3-carbon fragment and this 3-carbon fragment; and do not worry.1189

We will go through this again, but I just wanted you to see where the break actually takes place.1195

OK, and it does not take place while it is in its ring form; it takes place when it is in its extended form, its linear form.1200

That is the way it is attached in the enzyme; let me go back to blue.1207

Alright, from here, we go ahead and we create these 2 molecules.1212

Well, let me do it this way; let me go C, C, C.1222

There is that; there is this, glyceraldehyde-3-phosphate.1228

Let me just go ahead and put the P over here.1234

OK, this is our glyceraldehyde-3-phosphate, and it also produces the hydroxyacetone.1237

Let's go C, C, C.1243

Let me write it this way: CH2OH.1249

And then, let me just do H2; and well, I guess it does not really matter where we put the Hs and where we put the Os.1255

Let me just go ahead and put it over here.1266

This is in red; this is the dihydroxyacetone phosphate.1270

I am going to write it out: dihydroxyacetone phosphate.1278

And this is our glyceradehyde-3-phosphate, right?1290

Here is the aldehyde functional group; here is the phosphate.1299

Now, this thing right here, the dihydroxyacetone phosphate, that is the one that ends up getting converted.1303

OK, this is step 3; this is step 4, and we said step 5, and it gets converted to this right here.1309

Let me rewrite that again; we have C, C, C.1316

We have the aldehyde group; we have the hydroxy group, and we have the phosphate group, and that is fine.1321

I will go ahead and put those like that.1330

The hydroxyacetone phosphate is converted to another molecule of glyceraldehyde-3-phosphate.1334

This is glyceraldehyde-3-phosphate, here and here.1340

Step 4, when it breaks it up, it produces 1 molecule of the glyceraldehyde-3-phosphate directly.1348

The other one is converted into another molecule of glyceraldehyde-3-phosphate.1355

This is the preparatory phase, and these are the structures of the particular molecules.1360

OK, now, let's take a look at the rest of the structures.1364

Let me go to another page here; let me go back to blue.1370

We have glyceraldehyde-3-phosphate, C, C, C.1375

And again, you want to just keep drawing these things out over and over again.1382

Just look at your book and draw it; look at your book and draw it- that is all you have got to do.1386

It is just a process of getting used to; I know there is a lot of molecules to draw in biochemistry.1388

There is a lot of molecules to remember in biochemistry; some of them will only be passive recognition.1393

Some of them, you will have to be able to reproduce, but believe me, we all understand.1398

We have all been through it; we know how painful it can be.1402

OK, now, we have the O and the P; that is the glyceraldehyde-3-phosphate.1407

I will just write glyceraldehyde-3-phosphate over here.1415

Step 6 is going to convert it to 1,3-biphosphoglycerate.1420

We have C, C, C; and then we have O and a P.1425

Let me put a circle around the phosphate; we have our hydroxy group, and we have this over here, which stays, so 1,3-biphosphoglycerate.1431

Notice, this H was taken out; it was replaced by an O and a P.1440

OK, this is 1,3-biphosphoglycerate.1445

It is no longer glyceraldehyde; it is glycerate.1455

This is the carboxyl group; OK, step 7.1460

Now, this 1,3-biphosphoglycerate is going to be turned into 3-phosphoglycerate.1465

We are basically going to be getting rid of this phosphoryl group.1470

This is going to be C, C, C; and then we have this carboxy over here.1474

We have the OH over there, and we have our O and our P.1480

This is 3-phosphoglycerate, and I am hoping that you are going to confirm these structures.1484

Because again, as I am doing this, we all make mistakes.1491

I make a ton of them, so please confirm my structures; I might be missing a hydroxy.1497

I might be missing an oxygen; I might have an extra hydroxy- that happens.1501

OK, and then step 8, we want to change this into 2-phosphoglycerate; so we basically want to switch the P and the OH.1512

We will just write C, C, C.1522

I need a little bit more room here; no, that is OK.1529

OK, C, C, C, and then, we have this.1535

And then, of course, we have 2-phosphoglycerate; now, the phosphate group is there.1541

And now, the OH group is here, and I will go ahead and put that there.1545

This is going to be 2-phosphoglycerate.1552

OK, let's go ahead and do step 9; we are going to actually end up going to the next page.1562

Let's go ahead and we are going to be converting this to phosphoenolpyruvate.1568

We have got our 3 carbons still, C, C, C; but we have this beautiful double bond.1574

We have this, and we have O; and we have P.1584

Now, we have just the H2 there; this is the PEP.1589

This is the PEP, which is phosphoenolpyruvate.1595

And again, I do not know; I like separating my words.1603

Sometimes, they write them as 1; sometimes, they write them as 2.1606

It just depends how much of a strict what your teacher is.1608

That is the phosphoenolpyruvate, and, of course, our final conversion in glycolysis.1612

We are going to convert this phosphoenolpyruvate to pyruvate, which is C, C, C.1617

We have that, and we have this; and we have that.1625

This is our pyruvate.1631

There you go; those are the structures of the molecules involved in glycolysis, from 1 molecule of glucose going to 2 molecules of pyruvate.1638

OK, now, let's go ahead and talk about a little bit about the energetics.1648

Let me go back to black here; the overall reaction for glycolysis, when we take everything into account, everything that is happening, is as follows.1654

We have 1 molecule of glucose, 2 molecules of NAD+, 2 molecules of ADP plus 2 inorganic phosphates, produces 2 pyruvate plus 2 NADH plus 2 H+s plus 2 ATP plus 2 H2O.1671

That is the overall reaction; 1 glucose, 2 NAD+s, 2 ADPs, 2 PIs.1722

These are the molecules; these are the actual reactants, creates 2 pyruvates, 2 NADHs, 2 hydrogen ions, 2 molecules of ATP, and 2 molecules of water.1728

Now, we can resolve this, in other words, we can break it up into.1739

What this resolves into is the following; actually, let me go to the next page here.1743

OK, this resolves into the following.1750

We have 1 equation, which is actually the glucose plus the NA - oops, I have 2 of these - plus 2 of the NAD+, producing 2 pyruvate plus 2 NADH, plus 2H+1759

That is one of the reactions; now, the ΔG for this reaction is -146kJ/mol of glucose.1785

That is huge; it is a highly exergonic process.1796

Now, let's go ahead and take a look at this second part, the other part of this, the ADP.1800

2 ADP plus 2 PI goes to 2 ATP, the formation of adenosine triphosphate plus 2 H2O, in other words, the reverse of the hydrolysis of ATP.1807

We knew that the ATP hydrolysis is actually an exergonic process, but in this case, we are running it backwards.1821

We are taking ADP, and we are forming ATP; we are reversing hydrolysis.1826

We are doing a condensation here, and this one is going to be endergonic.1831

The ΔG for this, ΔG2 equals the +30.5 because we have reversed the reaction times 2 because now, it is 2 moles.1837

Oops, this is ADP.1849

I love it when you get all crazy into this, and all of a sudden, you are leaving letters off, which is very characteristic of me.1853

We have a +60 - I cannot even add - 61kJ.1860

So, this is an endergonic process, but notice, there is more than enough energy to account for this.1871

I mean, there is plenty of energy left; we can use part of this 146 to actually make the ATP in our process, and we still have more than enough free energy to carry this process forward.1876

ΔG, the net reaction is equal to the sum of the ΔGs: ΔG1 plus our ΔG2, which is equal to -146 plus our 61.1887

We have -85kJ/mol of glucose.1905

In glycolysis, even though some energy is invested into glucose by the 2 molecules of ATP, glucose by 2 ATPs, 4 ATPs are created by this coupling process, by coupling the highly exergonic glycolysis reactions to the endergonic ATP synthesis, to the endergonic ATP formation.1915

Now, recall back when we did bioenergetics.1992

OK, recall the high-energy phosphorylated compounds that we talked about in addition to ATP, high-energy phosphorylated compounds we discussed in the bioenergetics unit.2001

In addition to ATP, we talked about something; we talked about phosphoenolpyruvate.2040

We said that the free energy of hydrolysis of phosphoenolpyruvate - remember this equation, PEP + H2O, which goes to pyruvate + inorganic phosphate - the ΔG of this reaction was -61.9kJ/mol.2045

That is huge; that is a lot more than what is needed for ATP synthesis.2069

I mean, we know that ATP hydrolysis has -30.5kJ, so, its synthesis is +30.5kJ.2079

Well, we can couple that endergonic to a highly exergonic process, and this happens to be one of the reactions of glycolysis to actually create ATP in the process, rather than just wasting it.2089

We also had another one; we had the 1,3-biphosphoglycerate.2100

1,3- I will just write it as biphosphoglycerate.2106

That one also had a high negative free energy of hydrolysis, so 3-phosphoglycerate + inorganic phosphate.2112

This ΔG was -49.3; it is still very, very high.2124

This is kJ, not J; and notice, phosphoenolpyruvate and 1,3-biphosphoglycerate are intermediates in the glycolysis pathway.2130

So, we can use these reactions to actually make ATP.2140

These are 2 intermediates in the glycolytic pathway and have more than enough free energy to couple with ATP formation in the...2148

These are 2 intermediates in the glycolytic pathway and have more than enough free energy to couple with ATP formation in the process of glucose breakdown.2197

That is amazing; it is just truly amazing.2213

I love it; this is great.2219

I mean, the glucose has to be broken down, anyway; and this is just a highly exergonic process, especially with these two - the phosphoenolpyruvate and the 1,3biphosphoglycerate - that it is going to take that excess free energy and not just waste it.2221

It is going to use it to actually get back some of the ATP that it invested - in fact, create to, it used to - but it created for.2233

So, you actually have a net gain of adenosine triphosphate.2240

This is fantastic, using that excess energy that is going to be just wasted, anyway, use it to do something productive- absolutely fantastic.2244

OK, now, let's finish off this overview by discussing some of the fates of pyruvate.2253

What happens to the pyruvate that is formed in glycolysis; well, let's see.2257

No, let's go red; what the heck.2265

Actually, you know what, I think I am going to go blue.2272

The question is: what happens to the pyruvate that is formed?2280

Well, here is what happens; let's go ahead and write glucose, glucose, glycolysis.2297

We ended up forming 2 molecules of pyruvate.2306

Here is some of the things that happens.2313

OK, under aerobic conditions, in other words, when there is plenty of oxygen to go around, it is converted to 2 molecules of acetyl-CoA, which enters the citric acid cycle, which goes on to produce ultimately 3 electron transport chain, oxidate the phosphorylation, CO2, H2O and ATP.2317

This is the standard; this is what we are going to be running through.2343

It enters the citric acid cycle, and it goes through the oxidative phosphorylation cycle.2351

I will just go ahead and put electron transport chain.2360

You know what, no, I will just put oxidative phosphorylation, the end products being the CO2 plus the H2O- there you go.2365

That is under aerobic conditions, OK, pyruvate.2384

Under anaerobic conditions - in other words, no oxygen, not enough oxygen - it ends up producing the pyruvate.2390

It is converted to 2 molecules of lactate.2401

This is what you feel when your muscles start getting sore from overexertion.2406

The muscles are not getting enough oxygen to burn properly, to burn aerobically; so they have to turn to another process.2412

The by-product of that process is lactate, lactic acid.2421

That is what you feel when your muscles start to feel that sore, really painful feeling.2425

The pyruvate actually, it is fermentation.2434

The other fate is fermentation in heavily worked muscle.2441

OK, now, in general, I should say, fermentation is the general term for the breakdown or catabolism - I will write it over here, how is that - of organic molecules, nutrients, under low oxygen or no oxygen conditions.2453

It is a general term; when there is very little or no oxygen at all, the particular pathway, it is fermentation.2511

That is what is happening; it is fermenting.2519

And what you have in the third fate of pyruvate also under anaerobic or hypoxic - low oxygen as opposed to no oxygen - it will actually turn into ethanol.2523

This is how we get our drinking alcohol.2544

Ethanol + CO2- there you go.2548

Those are the fates of the pyruvate; the pyruvate will either go on to enter the citric acid cycle and go all the way in before they oxidized.2553

That is under aerobic conditions; under anaerobic conditions, it will produce lactate.2563

Under anaerobic and/or hypoxic conditions, under certain circumstances, it will end up forming ethanol and CO2.2568

That was our nice, broad overview of glycolysis.2579

In the next lesson and subsequent lessons, we are actually going to start looking at each individual step.2583

We are going to look at mechanisms, so we definitely, definitely want to make sure we understand glycolysis very, very well.2588

It is the model pathway for all the other metabolic pathways.2594

It is the one pathway that we elucidated first; it is the one that we understand the best.2598

Understanding what goes on here will pay multiple dividends in all of your future studies.2604

Take care; we will see you next time, bye-bye.2610