Biochemistry More On Oxidation-Reduction Reactions

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

Today, we are just going to talk a little bit more about oxidation-reduction reaction, so let's just jump right on in.0004

OK, let's go ahead and continue the last example from the previous lesson.0010

We found that the δG standard for that particular reaction was -23.7kJ.0016

Now, we had the acetaldehyde ethanol reaction, right?0032

Do not worry; we are actually going to write it down in just a minute here.0037

And these were for standard concentrations- 1M concentration, 25°C, things like that.0040

Now, what if the concentrations were not standard, which is often going to be the case?0050

In fact, it is always going to be the case.0057

OK, what if our NADH concentration equals 0.8M, our acetaldehyde concentration equals 0.6M, our NAD⁺ concentration - excuse me - equals 0.2M and our ethanol concentration equals 0.1M?0069

OK, what if this is the case; now, what would the δG be?0113

Now, what is the δG?0118

And notice, I did not put the standard symbol here because now, it is just the δG for the reaction under the particular conditions, in this case, only changes in concentration.0124

The temperature is still going to be the same, and I have not mention anything about the pH.0133

OK, well, δG is equal to -nF times the E of the reaction.0139

And again, notice, there is no standard symbol, so N is the number of electrons transferred in the reaction.0149

F is the Faraday constant, 96,485 Coulombs of charge per mole of electrons that are transferred; and E is the E of the reaction that we are going to calculate with our new equation, which is going to be E of a reaction is equal to E standard minus the RT / nF ln Q, where Q is the reaction quotient, the products over the reactants.0154

I just want to say one thing quickly about this particular equation, the Nernst equation.0188

Often times, because this R, the T and the F, because they are all constants in general or at least the R and the F, temperature might change.0191

You are going to see different numbers here in this expression.0200

A lot of times what equations do in either chemical texts or biochemical texts is they will go ahead and put some numbers here because what they will do is they will just go ahead and take R and divide by F and maybe T under standard conditions 298K.0204

They will go ahead and just multiply and divide these numbers, and just put them in there as some number.0219

I do not really care for that, and the reason is because the equation, this is how the equation came out.0224

I do not like changing plus signs; I do not like changing...there is an R.0231

There is a T; there is an F, and there is an N.0236

One of the things that you are going to notice or maybe if you have not noticed, this is what happens.0239

Anytime an equation is simplified or anytime an equation starts to look more simple and more elegant, that means something is hidden.0244

Here, there is nothing hidden; everything is exactly where it should be.0251

Minus signs are where they should be, and constants are where they should be.0254

I just wanted you to be aware that you might see slightly different version of this equation.0257

This is the base version; this is the one where you will always get the right answer.0261

OK, let's go ahead and write the equation that we were talking about.0266

We said that we had acetaldehyde + NADH + H⁺, and that was going to go to NAD⁺.0269

Well, actually, let me go ahead and write the substrate first.0285

It does not really matter, but let's just do it that way.0290

Ethanol plus the NAD⁺- there you go.0293

Acetaldehyde is being reduced to ethanol, and NADH is being oxidized to NAD⁺- there you go.0300

Let's go ahead and see what is happening; well, let's go ahead and put our numbers in.0309

Again, with this particular equation, here is what we have; let me rewrite it in terms of with Q, actually.0314

E = E standard - RT / nF x the ln of the concentration of ethanol times the concentration of NAD⁺ over the concentration of acetaldehyde - I will just write acetyl - over the concentration of NADH.0321

Now, notice, the hydrogen ion concentration, it is important; this is an aqueous species; and it should show up in the reaction quotient.0351

However, because of this, the pH7 has been accounted for in this number.0359

So, we do not have to include it in the reaction quotient; it just depends on which standard you are using.0367

For the biochemical standard, these are the numbers that we are using; the H is accounted for, so you do not have to put them in the reaction quotient.0375

OK, we end up with the following; we get E = 0.123 - 8.315 - excuse me - x 298.0382

There were 2 electrons transferred in this reaction, so that is 2 multiplied by 96,485, and then we get the natural logarithm of...and then we will just go ahead and put the concentrations that we had, these concentrations right here, the non-standard ones.0399

The ethanol is going to be 0.1, and then the NAD⁺ is going to be 0.2 divided by the acetaldehyde, which is 0.6, multiplied by the NADH, which is 0.8.0419

Now, the rest is just putting in into your calculator and getting some number.0436

What you end up with is the following: = 0.123 - (-0.0408).0440

You end up with the total of +0.1638.0453

That is the new potential for this particular reaction under these conditions.0462

Now, we can go ahead and calculate δG; δG is equal to, as we said, -nF and the E of the reaction, which we just calculated.0466

So, that equals -2 x 96,485 times what we just got, 0.1638, and when we do this calculation, we end up with -31,610J/mol or if you prefer kJ, -31.6kJ.0476

This is actually more exergonic under these particular conditions.0503

Earlier, we had -23kJ; here, we have -31kJ.0507

OK, now, I am going to go ahead and demonstrate an alternate procedure for doing this problem if you prefer dealing with the half reactions individually, rather than putting it together in a net reaction.0513

Let me just write that down; let me go ahead and change this.0529

I am going ot go ahead and do this one in blue; let me make sure I actually get blue.0532

There I go; there is an alternate procedure - it is actually the same procedure, you are just doing it in a different pathway - that uses the half reactions individually - some people prefer this, it does not really matter - instead of the balanced net reaction - OK - if for any reason, you just prefer the half reactions.0537

Again, it does not really matter; if for any reason you prefer to work with a half reaction, it is just more comfortable that way for personal reasons, this is the alternate procedure.0595

You are actually going to be doing the same thing; here are the 2 reactions.0604

We have the acetaldehyde plus the 2 hydrogen ions plus the two electrons going to ethanol, and the standard reduction potential for that was -0.197V.0608

And, of course, the other reaction we had to reverse, right?0626

And we write it as a reverse, so NADH goes to NAD⁺ + H⁺ + 2 electrons, and the potential for that - we flipped it - it is +0.320.0635

OK, now, we just deal with the individual reactions as written.0655

The E for the acetaldehyde, that is going to equal the E standard - RT / nF ln of Q.0661

The E standard is the -0.197 - 8.315 x the 298.0678

Again, there are 2 electrons transferred here, 2 electrons transferred in this reaction.0691

So, that is 2 x 96,485, and this times the logarithm of ethanol concentration over the acetaldehyde concentration.0698

And notice, we still do not include the H because that is accounted for in this, right here, the biochem standard.0707

So, it is going to ln of the ethanol, which was 0.1 over the acetaldehyde, ethanol over acetaldehyde, 0.6.0714

This is the ethanol, and this is the acetaldehyde; and when we run this calculation, we get -0.174.0725

This is our first one; now, we go ahead and do the same thing for the second reaction, as is.0734

This is going to be the E for the NADH.0743

Again, that is going to equal the same thing, so the E standard, the biochem standard for that is this.0749

We take the 0.320 - I will not put the positive sign there, it is clear that it is positive - minus, again, 8.315; we run through the same procedure, 298.0755

There are 2 electrons transferred in this reaction, so that is 2 x 96,485 - OK - times the ln.0770

This time, it is going to be the NAD⁺ concentration over the NADH concentration.0780

It is going to be 0.2 / 0.8.0785

You are just doing this in 2 steps instead of the 1 step, which is the combined reactions; so that is all you are doing here.0790

Previously, we have a net reaction; we have dealt with that one individually.0795

Here, we are going to deal with the individual half reactions and then put them together at the end; it does not really matter.0799

Then, of course, when you calculate this, you end up with 0.3378.0804

Now, what we do, now, we take the E of the acetaldehyde.0813

We add it to the E of the NADH.0821

We just add the 2 numbers, so you get -0.174 + 0.3378.0826

Is that the number I got?0836

Yes, that is equal to 0.1638, which is exactly the number we got with the previous version of this problem, so same as before.0838

And, of course, we put this value into the δG.0850

δG = -2 x 96,485 x 0.1638, and we get the same answer we did before, -31,610J/m.0855

And again, if you prefer kJ, that is -31.6- that is it.0872

This is an alternate procedure: balance the reaction, deal with it just with 1 equation, deal with the individual half reactions, and then add them, just straight out add them.0876

The numbers, the positive and negative will take care of themselves- your choice completely.0886

OK, let's see; OK, now that we have done a little bit with the oxidation-reduction, we have worked with the Nernst equation, let's actually take a look at the NAD⁺ and the NADH.0892

Let's actually see what these are, what these oxidizing and reducing agents are- what they look like.0906

Let me go ahead and go to red here.0912

Let's now, look at this NAD⁺, NADH pair.0916

This is the oxidized version, and this is the reduced version.0927

OK, now, this is - this pair, I should say - this is one of a handful of coenzymes that act as universal electron carriers in aqueous medium.0931

Basically, that is just a fancy way of saying that they are...you have a particular substrate that is either going to be oxidized or reduced- some molecule, acetaldehyde, ethanol, whatever.0971

In the case of acetaldehyde, it is going to be reduced; an enzyme is going to actually reduce that, the actual enzyme itself.0985

That enzyme is generally called a dehydrogenase.0993

And the coenzyme that actually is the thing that is going to reduce it is going to be this.0997

In this particular case, if it is doing the reducing, it is going to be the NADH.1006

It has electrons to give if it is reducing, or if it is going to be oxidizing a substrate, ripping electrons away from it, it is going to take those electrons.1010

And then the coenzyme might go someplace else, and the electrons it took from, let's say, ethanol, it is going to give them to somebody else- that is it.1020

It is an electron carrier; it is an intermediate.1031

The enzyme facilitates, actually, does the reaction; but it is the coenzyme that actually is carrying the electrons.1033

It is the bag that is carrying the electrons that it is going to give up to something else or take from one thing and give.1040

That is what we mean by universal electron carriers.1045

The enzymes might change, but this particular handful of coenzymes - and then we will mention a few more - these are the ones that are the universal electron carriers.1049

They are involved in all of the oxidation-reduction processes that take place in the body.1057

OK, this is one of a handful of coenzymes that act as universal electron carriers in aqueous medium.1063

OK, in other words - sorry if I am repeating myself here - they participate as intermediate electron carriers, holders, by acting - I get so excited, I start to actually affect my handwriting - as both oxidizing agent and reducing agent in many metabolic processes- that is it.1069

The enzymes might be different, but the coenzyme is really what does the...it is the work horse.1133

It is what is actually carrying the electrons and giving them- moving someplace else, giving them over, going someplace else, getting another set of electrons, going someplace else, giving those electrons away.1137

This NAD⁺, NADH ping-pongs back and forth between oxidized and reduced form.1146

OK, here are the others; we know NAD⁺ and NADH^- that is one of the pairs.1154

This is the oxidized form; this is the reduced form.1161

I will go ahead and do this in blue.1167

The others are, we have NADP and NADPH.1171

This one is always the weirdest for me because there is so many letters.1186

This is NADP⁺- that is the oxidized form.1189

This is the reduced form; it is just the same thing as this except it has a phosphate, and we will draw the structure in just a minute.1191

There is FMN, FMNH, that and FMNH₂.1200

I will explain this in just a minute; this thing, flavin mononucleotide, it is one of the coenzymes that is involved in oxidation-reduction processes.1212

And what is interesting about this one is it can actually gain or lose 1 electron or gain or lose 2 electrons.1221

It has a 1-electron version that is reduced, and it has a 2-electron version- 1-hydrogen-1-electron version, 2-hydrogen-2electron version.1228

It is really quite extraordinary, and then, of course, there is another version of this called FAD.1236

And that is same thing FADH, single-electron-single-hydrogen; and we have FADH₂ - woo, all these letters - 2-electrons-2-hydrogens.1243

Now, let's go ahead and discuss these just a little bit before we draw the structures.1255

NAD and - I will do it - NADP, when we do not put the charge on there, or we do not put the plus sign, we just talk about them generally.1262

The NAD and the NADP coenzymes - they are coenzymes, they are not the enzymes, themselves, they are part of the enzyme, the enzyme needs them to do what the enzyme does - are loosely associated with their enzyme, whatever enzyme they happen to be working with; and are free to move from one enzyme to the next, which is exactly what they do.1275

Now, FMN and FAD are usually very tightly bound to their enzymes - not so free to move around - sometimes covalently bound to their enzymes.1323

These enzymes that use the FMN and FAD are called flavoproteins.1357

And we will be discussing this in greater depth later on when we actually start to get into metabolism.1373

OK, let's take a look at the structure and see what they look like.1379

I can actually go to the next page because I want to draw it a little bit bigger than usual.1387

You know what, I think I will do it in black; excuse me.1394

Let's go ahead and do the NAD⁺, NADH pair; and I will go ahead and just put NADP⁺ and NADPH.1399

OK, these are called nicotinamide adenine dinucleotide.1417

That is the NAD - nicotinamide adenine dinucleotide - that is it, or nicotinamide adenine dinucleotide phosphate.1437

I will go ahead and put the phosphate here; it is just one little extra phosphate group that is added to the end.1447

Let me see how I want to draw this; I think I am going to go ahead and draw the sugars first.1454

Well, I guess it does not really matter.1464

No, that is fine; I will go ahead and draw the pyridine ring first.1467

OK, N, N, N, let's go ahead and put an H there.1470

Let's go ahead and do this; we are going to have that, that, that, that, that.1476

I hope we have enough room here, OH, OH.1485

Let's go ahead and put the CH₂ here; let's go this way, and let's go down this way.1490

Let's go ahead and put that there, that there, another O, another P.1497

Let's see; let's go ahead and do this.1503

This is going to be O, and let's go ahead and go down to - OK - CH₂.1506

Let's go down, and let's go that way, that way, that way, that way, O.1516

Let's go here; we will go OH there.1525

We will go OH there.1527

Yes, this is going to be adenine nucleotide.1532

Let's go ahead and make sure we have our ring structure here, COO and NH₂.1538

Let me see if I have forgotten anything; let me go ahead and put a positive charge on the nitrogen here.1548

OK, I think I have got everything.1555

I hope that you will actually confirm the structure with me; anytime we tend to write these big molecules, there is always something we forget.1559

At least, there is something that I always forget...nicotinamide adenine dinucleotide.1564

Nicotinamide or nicotinamide - depending on how you want to pronounce it - adenine dinucleotide, that is what is going on here.1571

The nicotinamide adenine dinucleotide phosphate is right here.1579

This oxygen right here - I will go ahead and do this in red - it is basically just another phosphate group here.1584

It is nothing more than that; to get rid of this H, and just add a phosphate.1598

So, I just decided to put a dash line; that is the only difference between the 2 molecules.1603

OK, the chemistry - now, let me do this in blue - all of the chemistry of this molecule, the chemistry happens here.1608

It happens at that carbon atom; that is where all of the chemistry takes place.1624

That is where the H and the 2 electrons are added.1628

That is where the H is added and subtracted from; that is where the chemistry takes place.1635

Let's go ahead and concentrate just on this; I wanted you to see the structure of it.1639

Now, let's go ahead and concentrate on the chemistry; let me go to the next page, and I am going to draw it as this.1643

This little pyridine ring, H, and I will just go ahead and put an R like that.1651

We have this, and again, we have a positive charge here; that is what that positive on the NAD⁺ is referring to.1659

The molecule, itself, is not positively charged; it is actually negatively charged.1667

You saw the phosphates; that NAD⁺ that is specifying that the nitrogen is carrying a positive formal charge, it is in its oxidized state.1670

That is all that plus means; OK, it is not the charge on the molecule.1679

It is referring to this; OK, this is going to be the NAD⁺, and the reaction that takes place is, we have 2 electrons coming in.1683

We have 2 Hs coming in, and we end up with the following: N, N.1697

Let's go ahead and put the R here; we end up with something like this.1705

Oh, I always forget the amide; I do not know why I always do that.1716

It is the funniest thing; again, I guess when you are concentrating on the chemistry of the pyridine ring, you sort of forget about the other substituents that are on there.1721

It is not the end of the word, but not generally a good practice.1729

COO, NH₂, let's make it a little bit bigger.1733

We have 2 electrons coming in, and we have 2 H⁺s coming in; and what we end up with is the following.1739

N, this is nitrogen; this is the R, the rest of the molecule.1748

We have that; we have an H, and we have an H.1752

We have a COO, NH₂ + H⁺.1760

This is going to be the NADH.1768

OK, here is what happens; this thing, when it is in its oxidized form, it is going to take 2 electrons and 2 hydrogens from some substrate.1773

Well, the 2 electrons and 1 of the hydrogens attaches here as a hydride.1786

Now, notice, this pyridine ring, it is actually a flat molecule.1792

So, if I take this molecule and turn it around like that, it is going to be flat.1796

This is an aromatic ring; it is flat, and here is the hydrogen.1800

Well, this hydride that is being added - 2 electrons + 1 of these hydrogens, the other hydrogen is released into aqueous medium - this is a hydride, so it is this species that is actually added to this to become this.1805

It can add on this side, or it can add from that side.1823

Different enzymes will add to different sides; they call it the A-side, B-side edition.1828

Again, this is going to be very, very important when we talk about mechanism.1833

I mean, ultimately, it does not matter; but as long as you know that you are dealing with a flat molecule, you have this attack this way, or you have attack this way.1838

So, we talk about A-side, B-side- that is what we mean.1847

But again, because they are hydrogens, if for example, if this - let's go ahead and make this red, that might be a little bit better - let's say we are adding that - let me change this, let me make this 2 red hydrogens - we are actually adding this, so one of them is going to be released to medium.1850

That is an H⁺, and now, let's go ahead and say that this one, it added to the front phase, to the A-phase or might add to the back phase - that is the B-phase - that is what we mean.1874

OK, that is all that is going on here; what is being transferred is actually a hydride.1887

2 electrons, yes, it is the electrons that are being pulled away and one of the hydrogens.1892

OK, let's talk about...let me just mention again.1898

The plus sign is not the charge on the molecule.1906

The molecule, as we said, is actually negatively charged - this thing - but is there to indicate the oxidized form of the molecule with a formal positive charge on the nitrogen.1921

Notice what happened here, when we added the hydride, it is bringing 2 electrons with it.1961

It does not need to share; it is bringing the electrons with it.1969

When it comes in here, there is going to be some electron pushing- this, and then it goes that way.1972

This is going to hop onto there; OK, that is why you end up with this.1979

That is why now, they have a double bond here and a double bond here.1983

And notice, now, the nitrogen is no longer carrying that positive formal charge.1987

Now, it is just normal nitrogen.1991

I hope that makes sense; OK, let's see.1994

Let's go back to black here.1998

Again, it is the nicotinamide ring that gets oxidized or...you know what, I do not have to write that.2005

I will just describe that; so, it is this ring that gets oxidized and reduced by the addition of a hydride ion or by the loss of a hydride ion.2016

In the other way around, right now, we these 2 electrons on nitrogen, right?2028

We have 3 bonds, so there is no formal charge on it.2033

Now, when it is time to give up, when it is time to reduce this substrate, to give up this hydride ion, these electrons, they go there.2036

They push this there, and the hydride goes away; it does what it does.2043

It attaches to the substrate, so that is all that is happening here.2048

OK, let's see; what do we need here?2054

You know what, I think I will actually write it down.2061

It is the nicotinamide or nicotinamide ring that gets reduced or oxidized.2068

The NAD⁺ accepts an H^-, which is 2 H atoms.2088

2H atoms have been taken; an H plus its electron have been taken from the substrate.2110

H⁺ goes to NAD⁺, so 2 hydrogen atoms have been taken away, but 1 hydrogen atom, 2 electrons, the other hydrogen atom is released to aqueous medium.2130

OK, that is what is happening here; it goes to NAD⁺.2146

OK, and H⁺ is released to the environment.2154

OK, as far as reduction is concerned, let's go ahead and write the reduction half reactions, just so we see.2169

We have NAD⁺ + 2H⁺ + electrons goes to NADH + H⁺, and of course, the NADP version.2180

We have NADP⁺ + 2H⁺ + 2 electrons goes to NADPH + H⁺- that is it.2196

Those are the actual half reactions.2208

Now, in general - let me go to blue here, OK - the ratio of NAD⁺ to NADH is high - in other words, there is more NAD⁺ that NADH in a given environment in the cell - favoring oxidation of the substrate molecule.2211

In other words, there is more of the oxidized form that wants to be reduced, so if it is going to be reduced to NADH, it is going to oxidize the substrate.2257

There is more of this that is there to take electrons from the substrate and become reduced, itself.2265

OK, in general, the ratio of NAD⁺ to NADH is high favoring oxidation of the substrate.2275

OK, in contrast, the ratio of NADPH, the reduced form of the NADP to NADP⁺, the oxidized form, is high.2283

In other words, the reduced form of the NADPH is high, which favors reduction of a substrate, favoring reduction of a given substrate of a particular molecule.2307

OK, this reflects their specialized roles.2329

So, if you are wondering, what is the difference between the NAD and the NADP, well, here is the difference.2340

NAD⁺ is generally involved in oxidations.2354

And again, we say generally involved in oxidation reactions, the catabolic processes, the processes that breakdown the molecules into smaller constituents.2359

NADPH is generally involved in reduction reactions, reduction processes, the anabolic processes, the processes that build up, that take the smaller constituent molecules and build the carbohydrates and proteins and nucleic acids that the body needs.2378

And again, with biochemistry, we speak generally; we never say it is like this, and it is never like anything else.2406

OK, let's continue our discussion here.2414

I think I am going to go back to black; I like black today.2421

I do not know why; OK, now there are hundreds of enzymes that employ NAD and NADP coenzymes - I do not need to write coenzymes, we know that they are coenzymes, OK - in redox processes.2425

Now, the general name for these enzymes is an oxidoreductase.2463

Exactly what it sounds like, it is involved in oxidation-reduction processes- both.2486

It is more commonly called dehydrogenase; that is how you will hear it- dehydrogenase.2494

Alcohol dehydrogenase, something else dehydrogenase- that is it, that is the more common name for it.2507

OK, they catalyze the following general reactions.2516

When you see a dehydrogenase, this is usually what is going to be going on.2532

The oxidation, there is going to be some substrate that has 2 hydrogens attached to it.2536

It is going to be involved with NAD⁺, and it is going to be turned into S + NADH + H⁺.2542

2 hydrogens are going to be pulled away; it is going to be dehydrogenated.2554

That is the idea; dehydrogenase is something that dehydrogenates.2558

It is also involved in reduction, so it does also hydrogenate; but we call them dehydrogenases.2564

So, S, some substrate, plus NADH goes to S, H₂ - oops, I forgot my...we are going to hydrogenate, we are going to need another H⁺ here - it is going to go to S, H₂ + NAD⁺.2569

That is all that is taking place here; it is just a transfer of electrons, the transfer of a hydrogen molecule, but one of those hydrogens goes off into medium.2590

It is actually a transfer of a hydride particle, an H with 2 electrons carrying a negative charge- that is what is going on.2604

OK, here are some examples; it is always good to see examples.2612

Well, we have got 3, C, C.2620

This is H; this is H.2626

This is OH; this is ethanol + NAD⁺.2629

We are going to oxidize the ethanol; we are going to turn it into acetaldehyde.2635

I will leave the oxygen there, and I will do that, +NADH + H⁺.2644

What we have done is, we have pulled off that hydrogen; we have pulled off that hydrogen.2654

One of these hydrogens ends up going away into aqueous medium; the other hydrogen is attached to the NAD.2659

Now, the electrons that held one of these together, well, this one, are now, it is a double bond here.2665

It has lost 2 hydrogens; it has lost 2 hydrogen atoms across the bond, across this bond- the C, this H and this H.2672

Notice, it is not this H and this H; it is this H and this H- dehydrogenation.2682

OK, that is an oxidation example; we will write it in word form as ethanol + NAD⁺ goes to acetaldehyde + NADH + H⁺.2689

Now, let's go ahead and do a reduced version, a reduced example.2712

Let me go back to red; let's take pyruvate to lactate.2717

OK, we have 1, 2, 3.2723

Do we have enough...yes, OK.2728

Let's see; let's go 1, 2, 3.2733

I will write is as...yes, that is fine; I will go ahead and do it this way.2738

That is that; that is that, and we have got CH₃.2742

Let's go ahead and add NADH; let's go ahead and convert this to C, C, CH₃, COO^-.2747

I will go ahead and add my H over here, my O over here and my H over here.2761

That is going to turn into...this is actually a + H⁺.2768

We are in reduction, so this is going to give us NAD⁺, pyruvate to L-lactate.2771

We have added this hydrogen and this hydrogen across the double bond.2785

It is there and there; we have hydrogenated it.2791

That is what we are doing; we have turned this double bond into 2 single bonds- that is all that is happening here.2794

OK, and OK, well, good.2802

Now, let's go back, and now, let's talk about the flavin nucleotides.2808

Let me see; OK.2820

So, we have talked about the nicotinamide adenine dinucleotides, now, we will talk about the flavin nucleotides.2825

FMN and FAD are coenzymes, as we said, used by flavoproteins in redox reactions- that is it.2832

It is the thing that is happening that is most important, not the species that is actually doing it; it is still just an oxidation-reduction.2858

It is still just something that carries electrons- that is all it is.2863

OK, now, what is interesting about FMN and FAD, they are much more versatile than the NAD and the NADP because they can actually transfer 1 electron or 2 electrons; and they can actually do it by different mechanisms.2867

The same mechanism does not necessarily have to apply; for the NAD and the NADP, it is one mechanism.2884

FAD can transfer 1 or 2 electrons in the form of hydrogen atoms, in the form of actual hydrogen atoms.2894

OK, the equations would be FMN goes to FMNH that goes to FMNH₂.2912

These are the symbolic representations, and we have FAD; and in a perfectly analogous fashion, we have FADH with a little of that because that actually does form a stable radical, FADH₂.2928

OK, now, let's go ahead and draw the structures.2947

Let's see if I can do this on one page; hopefully, I can.2951

Let me draw the general...you know, I do not know if I should...that is fine; I will go ahead and do it that way.2959

This is a triple ring system, and it has a nitrogen here.2977

It has a nitrogen there; it has a nitrogen there.2983

It has a nitrogen there; we have a carbonyl here.2986

We have a carbonyl there.2992

You know what, I am going to draw...well, I do not know.2996

I mean, you have the picture in your book, so if my picture is not exactly beautiful, then I hope you understand.2998

Let me just start again; let me go this way.3005

OK, I am going to go ahead and leave that; and I will just put the Ns right on top.3012

Probably not the most clear thing to do, but I hope you will understand.3018

N, N, carbonyl, carbonyl, we have CH₃.3024

We have CH₃; we have that, and we have this, and we have this, and let me see.3033

Are we missing anything?3044

We have an H attached there; I think that pretty much covers it.3046

Yes, now, we have CH₂; we have COH.3053

We have COH; we have COH, and there are Hs over here.3060

We have CH₂; we have O.3066

We have P; we have O^-.3070

We have O, and I will draw a little dash here; and I will go ahead and draw this one.3073

O, there is another P; I will go ahead and do this O, this O^-.3083

This is going to be CH₂, and that is going to be attached to our sugar, O like that, OH, OH.3090

And, of course, we have our adenine.3105

OK, this part up to - actually, let me go ahead and put the Hs in here, I do not want to forget those - the dash line, where this bond is just this free O, is carrying a negative charge, this is the FMN- flavin mononucleotide.3109

This whole thing that includes this extra phosphate and this sugar, this is the flavin adenine dinucleotide- that is it.3134

It is this molecule attached to one sugar and a phosphate, flavin mononucleotide, and if it has this second sugar and phosphate, then it is flavin adenine dinucleotide.3146

OK, the chemistry takes place up here, and in fact, the chemistry takes place right along here.3157

This is what is going to be important; here is what is going to happen.3169

I am going to do it this way; I am going to do arrow there, an arrow there.3172

When it takes 1 hydrogen ion and 1 electron, here is what this becomes.3178

I am going to redraw this ring structure, but I am just going to put R for that.3186

It is going to be...OK.3190

And we are going to end up with the H.3200

There is an N; there is an N.3205

There is an N; there is an N.3208

This is going to be O^-; that is still going to be a carbonyl.3211

We are going to have that move there; we are going to have this move there.3215

That is going to push that one over to here, push that over there.3220

OK, and we are going to put a little dot there.3226

OK, this H and this electron, in other words, this hydrogen atom, adds this way, right to this.3230

This double bond moves over here, pushes these electrons up to oxygen.3238

Here we have R, and sorry, there is CH₃, and CH₃.3243

Is there anything else that I have forgotten?3247

Oh, I always forget my H there; OK, that is the first addition of 1 electron or from this case, the loss of 1 electron- reduction, oxidation.3249

No, no, no, let's go ahead and add another electron and a hydrogen ion, in other words, another hydrogen atom; and you end up with this structure.3262

There is an N; there is an N.3289

There is an N; there is an N.3291

We go back to our carbonyl; we go back to our carbonyl.3294

Now, we have this H; the other H actually ends up attaching right there.3298

Now, what we have is this and this and this is the R-group, and this is the H.3303

The first hydrogen attaches right there, and notice, we put a little dot there because this is actually a stable free radical.3312

The other H adds to this one right here.3322

So, we end up with an H there and an H there, and, of course, there is some electron pushing.3328

When the H adds right here, these electrons go here; these electrons pop back up, and everything is fine.3333

Everything is nice and stable now; there is a redistribution of electrons.3339

We will get to mechanism a little bit later on, but I just wanted you to see what was happening.3343

Here is where the chemistry takes place; 1 H is attached there, so this is a fully reduced FMN to FMNH₂.3347

This is the semi-reduced- that is it, that is all that is going on here.3359

We have the NAD; we have the NADP.3366

We have the FMN, and we have the FAD.3369

These are coenzymes that are involved in the oxidation-reduction processes in the metabolic processes.3372

They are the universal electron carriers; they are the work horses.3379

They are part of enzymes that facilitate these things, that make these things happen; but they are the ones that are actually being oxidized and reduced.3384

OK, thank you for joining us here at Educator.com and Biochemistry.3390

We will see you next time, bye-bye.3393