Biochemistry 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