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Lecture Comments (8)

1 answer

Last reply by: Professor Hovasapian
Sun Jul 3, 2016 7:56 PM

Post by Kaye Lim on June 16 at 12:22:15 AM

-After being introduced to the coupling between endogenic and exogenic rxn, I kind of look at a random rxn between 2 reactants forming 2 products and asking myself if the reaction that I see is also coupled rxn as well in which to make deltaG of the rxn itself as a whole is thermodynamically favorable. My questions are:

-Is all or the majority of rxns in which deltaG is negative (not only biological rxns)are coupled rxn?

-If so, do I analyze the structure of reactants and the products to know which species went from high Energy to a lower Energy and which did the opposite to figure out if the rxn belongs to the coupled rxn theme?

-Does High Energy molecule have higher Energy stored in its bonds compared to low Energy molecule?

1 answer

Last reply by: Professor Hovasapian
Sun Jul 3, 2016 7:49 PM

Post by Kaye Lim on June 15 at 10:58:44 AM

At 29:20, would you please explain again how Tautomerization drives the rxn forward?

So the major product form is the Keto form which drive the rxn into making more of the enol form which also ends up turning into the stable keto form?

-For high Energy molecules, what make them high in Energy if the Energy in the bond is not that high as you said? Also does high Energy molecules mean these molecules are unstable and more reactive?

1 answer

Last reply by: Professor Hovasapian
Fri Feb 20, 2015 10:05 PM

Post by bea v on February 18, 2015

Wow! The ATP explanation is excellent. Thank you.

1 answer

Last reply by: Professor Hovasapian
Sat Sep 20, 2014 7:57 PM

Post by shafaq ahmad on September 18, 2014

Hi,
Why ATP hydrolysis is exothermic but have high activation energy?

ATP & Other High-Energy Compounds

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
  • ATP & Other High-Energy Compounds 0:10
    • Endergonic Reaction Coupled With Exergonic Reaction
    • Major Theme In Metabolism
  • Why the ∆G°' for ATP Hydrolysis is Large & Negative 12:24
    • ∆G°' for ATP Hydrolysis
    • Reason 1: Electrostatic Repulsion
    • Reason 2: Pi & Resonance Forms
    • Reason 3: Concentrations of ADP & Pi
  • ATP & Other High-Energy Compounds Cont'd 18:48
    • More On ∆G°' & Hydrolysis
    • Other Compounds That Have Large Negative ∆G°' of Hydrolysis: Phosphoenol Pyruvate (PEP)
    • Enzyme Pyruvate Kinase
    • Another High Energy Molecule: 1,3 Biphosphoglycerate
    • Another High Energy Molecule: Phophocreatine

Transcription: ATP & Other High-Energy Compounds

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

Today, we are going to continue our discussion and talk about ATP and other high-energy compounds.0004

Let's just go ahead and jump right on in.0009

Now, we saw previously that an endergonic reaction can actually be coupled with an exergonic reaction to run the endergonic reaction under circumstances where it would not, otherwise, go.0013

Let's start with that; we saw that the endergonic reaction...let's call it no. 1.0027

Glucose + inorganic phosphate goes to glucose 6-phosphate + H2O.0042

So, the δG for this one was +13.8kJ/mol.0051

OK, we saw that it could be coupled to the exergonic reaction.0061

We will call it reaction no. 2, which is the hydrolysis of the adenosine triphosphate.0078

ATP + H2O goes to ADP + inorganic phosphate, and the δG for this particular reaction ended up being very, very large, negative, so -30.5kJ/mol.0085

OK, we saw that they could be coupled to accomplish the result of the endergonic reaction but via a different pathway.0103

We saw glucose + PI goes to G6P + H2O; and over here, we have the ATP.0136

We have the H2O, and then, of course, we have the ADP and the PI.0147

Similar species, they cancel, and what you get is a net reaction.0155

We have Glc + ATP going to G6P + ADP; and the δG for this, which is just the sum of the δGs of the previous reactions, we ended up with -16.7 - and sorry about that, did not give myself enough room - kJ/mol.0160

We saw that we could do that, an endergonic reaction, so we achieved the same purpose.0183

Our purpose was to take glucose and to convert it to glucose 6-phosphate.0188

Well, that is the same thing here; we want that reaction to take place, but we just gave it a different pathway by coupling it with a reaction that has enough energy to give away, to actually turn an endergonic reaction into an exergonic reaction.0192

This is a very, very, very important theme, and this is exactly what adenosine triphosphate does.0206

Well, it is almost all of it it does; let's go ahead and take a look at this just a little bit more clearly.0215

I am going to go ahead and draw a structural representation of this.0221

Let's go ahead and do a glucose molecule here.0226

Let's see; well, you know what, let me give myself a little bit more room.0231

I will draw it down here.0238

OH, CH2, we have the OH; and let me go ahead and draw my phosphate over here.0242

O, P, double bond O, (O-)-, OH, and let me go ahead and fill in the rest of my glucose so that we do not forget.0252

The normal endergonic reaction wants to happen as that and that ultimately, but hydroxide is not a very good leaving group, so this reaction is not very likely.0263

By providing an alternate pathway for this thing to take place, here is what happens.0279

Let me redraw the glucose; we have this, this.0287

We have CH2; I will put a little line there.0295

And now, we have O, P, O, P, O, P, O; and we have the ribose, and I will just go ahead and put the adenine here.0299

That is that, double bond, double bond, double bond.0314

I know writing these things out can be a bit tedious, but that is life.0318

OK, let me finish this, or I should say that is biochem.0323

Alright, this, that way, this goes that way; this is a very likely reaction.0330

This is highly likely and highly thermodynamically favorable- that is it.0338

That is all that is going on here.0344

Neither reaction 1 nor reaction 2 takes place.0348

In other words, we talk about using the energy from the hydrolysis of ATP to run an endergonic reaction, but ATP is not actually being hydrolyzed.0352

In other words, water is not coming and splitting ATP releasing an inorganic phosphate; and then that inorganic phosphate is reacting with the glucose- that is not what is happening.0364

Those reactions, they are separate; but when we couple them together via a different pathway, the same result is achieved.0374

So, when we talk about driving a reaction via ATP hydrolysis, the hydrolysis is not actually taking place; and I think it is very, very unfortunate that biochemistry still uses that kind of language, but as long as you remember that it is just a terminology, it is not actually taking place, the reaction is going via a different mechanism- this is what is happening.0385

This is going to be direct phosphorylation of this glucose substrate via ATP.0406

There is no free phosphate floating around that is going to react with the glucose.0412

OK, now, this is a major theme - the major theme - in metabolism, which we are going to be getting into very, very soon, using the energy of incoming nutrient molecules - in other words, the food that we ingest, the carbohydrates, the proteins and the fats - using the energy of incoming nutrient molecules to create the ATP, which will then drive, otherwise, endergonic reactions in the creation of the molecules the body needs.0418

That is it; that is all that is happening with metabolism.0505

You take in food, carbohydrates, proteins, lipids.0510

the breakdown of those foods, the catabolism, takes the energy from those foods and uses that energy, and it stores it in adenosine triphosphate.0517

The body creates adenosine triphosphate molecules, and it sends those adenosine triphosphate molecules out.0527

And now, it can use that energy to drive these endergonic reactions, which are necessary to create order in the body.0534

It needs nucleic acids; it has to form proteins.0543

It has to form carbohydrate polymers; it has to pump solutes across membranes.0546

It has to do all sorts of things, so we could take the energy from the nutrient molecules, put it into ATP.0551

ATP goes and does what it does- the anabolic process.0558

you have the catabolic process - the breakdown - converge into ATP.0562

ATP starts the anabolic process, building the molecules that it needs.0566

Let's go ahead and actually draw this out.0571

OK, I think I can do it on this page right here; let me go ahead and draw one little arrow going down like this.0575

And, I will say "carbs, fats, proteins"; and this is going to be catabolic.0584

Actually, you know what, I am not going to write that just yet.0599

OK, and our depleted products are going to be CO2; I am going to have H2O, NH3.0603

Then, let's go ahead and draw a little circle like this.0613

We have adenosine phosphate + inorganic phosphate, and we have adenosine triphosphate.0618

Now, let me go ahead and draw another arrow; this time, I will make it go up, ATP.0623

OK, now, we have amino acids.0632

We have the sugar monomers.0640

OK, we have our basic fatty acids, and we have nitrogenous bases; and we are going to form our proteins, our polysacchs.0650

We are going to form our lipids; we are going to form our nucleic acids.0673

And then, of course, there is transport; there is mechanical work, osmotic work- whatever it is that we need that energy for.0681

We take in our nutrients.0691

The catabolic pathways of the body break things down.0695

They spit out the energy depleted products.0700

The energy that they take from these carbs, fats and proteins, they use it to take adenosine diphosphate + inorganic phosphate to create ATP.0704

Now, ATP can be used to drive the anabolic pathways.0712

Anabolic means the creation, to actually make the proteins, the polysacchs, the lipids, the nucleic acids, that the body needs in addition to all of the other energy needs- that is it.0718

That is all that is going on; this is metabolism.0727

Catabolism, anabolism- together, they are your metabolism.0731

That is all that is happening, ATP, as the primary energy intermediary in this whole process- that is it.0735

OK, now let's take a look at why ATP serves the function that it serves.0745

Let's see; let’s see the why.0753

Let's see why the δG of ATP - or ATP hydrolysis, I should say - is large and negative.0762

Well, let's go ahead and draw this out.0785

Let's draw out the 0, P, 0, P, 0, P, not zero - O.0789

Sorry about that; I am thinking about mathematics here.0797

Ribose and we have adenosine.0803

It will take me just another second here to finish this molecule; OK, now, we have an H2O molecule.0808

The hydrolysis, when this takes place, we end up with H, O, P, O-, O- plus our ADP, which is O, P, O, P, O.0814

And we have ribose, and we have adenosine.0838

Sorry about all these; this is just the nature of biochemistry, with these big molecules.0844

OK, the hydrolysis of adenosine triphosphate releases an inorganic phosphate and it release ADP, so this is ATP.0848

Now, why is it that the δG for this reaction is really, really large and negative?0860

Well, here is why; the first reason is...I will do this in blue.0865

Take a look at all the negative charges here- negative, negative, negative, negative.0870

Negative charges or positive charges, all the charges, they do not like being close together; there is going to be repulsion.0875

So, if some process can come along and relieve some of that electrostatic repulsion, it is going to happen really, really easily.0881

In other words, this step of the water coming in and kicking this off, it can actually remove 2 negative charges and move them far away from the rest of the molecule.0888

That is a stabilizing force; because of that stabilizing force, it tends to push the energy down.0897

That is why you get that nice -δG.0903

One of the things that contributes to the negative, large δG is relief of the electrostatic repulsion among the negative charges.0906

OK, the second reason.0930

Well, you notice that one of the products that is formed is the inorganic phosphate.0934

The inorganic phosphate has several - it has 4, actually - resonance structures.0939

And anytime you can form a product that is resonance stabilized, that is going to pull the reaction forward.0951

It wants to be stabilized; it wants to be low energy.0960

The inorganic phosphate, one of the products of the hydrolysis, has several resonance forms; so, its formation is highly favored.0963

And the resonance forms, let me go ahead and draw them out just so you see them.0982

Let me go ahead and draw it out this way, so P, boom, boom, boom, boom.0987

I will go ahead and do that, O, P, O, O.0995

Let me go ahead and just put that one there; I will put the double bond there, so that.1002

Let's move the double bond around in a circle here so, O, P.1006

I should have made it a little smaller; that is OK.1012

It is not a problem, O, O, and this time I will put the double bond here.1013

We will put the negative charges here, and we have one more resonance contributor.1019

It is going to be O, P, O, O, O over here; and we will do that, something like this.1024

And, of course, we have our H+.1033

These 4 resonance structures, really, really, really drive this reaction forward.1036

Inorganic phosphate wants to be formed, and it will take every opportunity that it can in the easiest possible way.1041

This contributes to the stability, to the -δG, of this reaction.1048

OK, our third thing.1053

Well, the concentrations of the adenosine diphosphate and inorganic phosphate in cells is far less than their equilibrium values.1056

In the actual cell, the concentration of the ADP and the PI, the products, is a lot less than the equilibrium values would be.1088

That is going to pull the reaction forward by Le Chatelier's principle and their equilibrium values.1099

Mass action favors the forward reaction; excuse me.1110

And, I do not need to write the reaction over again.1125

OK, now, let's see; let me go back to red here.1128

Now, even though the δG for this is -30.5, again, this does not mean that the hydrolysis reaction just happens.1135

In other words, the ATP + H2O goes to ADP + PI.1163

Yes, it has a really, really large - δG; but that does not mean the reaction just happens anytime that ATP is in the presence of water.1167

OK, remember, δG is a measure of the tendency of a reaction to happen, the degree to which it wants to happen, not the fact that it actually does happen.1176

Circumstances have to be right in order for it to happen.1186

ATP is actually kinetically stable.1190

Remember, we talked about kinetic stability?1198

It has a high activation energy, so just because thermodynamically it is favorable, kinetically it is stable.1200

A lot has to happen for this thing to actually take place.1205

It is kinetically stable and requires an enzyme for an appreciable rate of hydrolysis.1209

And let me go ahead and draw this out in terms of an energy diagram for you; so we have something like this.1233

Even though the δG is really, really negative...you know what, let me make a little bit more room here.1241

I do not want to write over the words; let's go ahead and do it like let's say that.1248

This is our energy; this is our reaction coordinate.1254

We have that; we have that.1257

OK, δG is negative, but look at our activation energy.1261

Our activation energy is very, very high for ATP; and this is going to be the ADP + PI + water.1265

The hydrolysis of ATP has a very high activation energy, which means that it is kinetically stable.1278

Now, of course, we want it to be kinetically stable; we do not just want anytime adenosine triphosphate happens to be in the vicinity of some water, that it is just going to split up.1283

We do not want it to do that; we want adenosine triphosphate to be available, so that it can actually couple with endergonic reactions.1292

If anytime it is in the vicinity of water, if it just hydrolyzes and releases that heat into the surroundings, well, that is not going to do anything.1301

The body, the cells- these things are isothermal systems, so the transfer of heat, yes it will produce heat, but heat cannot do any work in an isothermal system.1310

In other words, there is no temperature differential from inside the cell to outside the cell.1319

They are at the same temperature so heat cannot flow; the only time heat, itself, can do work is when heat flows.1324

But, I mean yes, it can get hot; but no work can actually be done.1331

We want the ATP to be available to couple with other reactions.1337

We do not want it to just hydrolyze, to produce ATP; that does not do anything for us.1342

It is thermodynamically favorable, and it uses that favorability when it couples with other reactions.1348

It is kinetically staple, so ATP in the cell stays ATP.1354

There is a whole bunch of water around as you know, but it does not hydrolyze; it requires an enzyme to hydrolyze.1358

Only if it needs to hydrolyze, then it will do so; this is profoundly important.1363

OK, let's see, a little bit more information.1370

The δG of ATP hydrolysis - as we keep reiterating - is -30.5kJ/mol.1376

Now, and again, this is based on the transformed biochemical standard - 1M concentration for aqueous species, 1atm for gaseous species and so on - but concentrations in cells are not standard.1386

The result is that actual δG values for ATP hydrolysis are from about -50 all that way to, maybe, -65kJ/mol.1418

Under standard conditions, -30.5kJ/mol, that is a lot; but under cellular conditions, it is actually better.1450

-5 to -65- that is fantastic; it is such a huge amount of free energy that the body can use per mole of ATP to do what it needs to do.1457

Now, for our problems, of course, we are just going to be using standard values because again, it is a standard.1469

It is something that we can always count on; we are going to be using the -30.5, but know that in cellular conditions, it is actually better than that.1474

OK, now that we have talked about ATP, let me go ahead and switch to black here.1482

Now, let's take a look at some other compounds that have high -δGs of hydrolysis.1489

ATP is not the only one; ATP is the primary one.1498

It is the one that all of the metabolic processes use, but there are other phosphorylated compounds that also have high δGs of hydrolysis.1502

Let's take a look at some of those.1512

Let's now look at other compounds - this gives us a chance to take a look at some other molecules, take a look at some other themes, that is it, that is all that is going on here - that have large -δGs of hydrolysis.1516

OK, the first one we are going to look at is something called phosphoenolpyruvate.1549

I think I am going to do this on another page, though; I need a little bit more room than what is available here.1553

The first one is - let's do it in blue - phosphoenolpyruvate.1560

Now, you are going to see it as one word; I tend to not like writing long single words, so I just write it as two words.1576

I do not think it really matters all that much; if you have a teacher that is really specific about it, you can write it as a single word, but just know that you will see it both ways.1583

Phosphoenolpyruvate and it is abbreviated as PEP- very, very important molecule.1590

Here is what happens; let's see.1596

How should I draw this?1600

That is OK; I will go ahead and draw it like this.1602

A little bit of C, let's do this C; this is CH2.1606

Let's go O, P.1616

So, this is phosphoenolpyruvate; this is our PEP.1621

Now, it is going to undergo the following transformation, and we are talking about hydrolysis.1626

Water comes in, splits off this phosphate.1635

Water is in; inorganic phosphate is out, and what you are left with is the following molecule.1642

O-, I have got C; I have got a double bond.1649

I have got my C; I have got my CH2, and I have got my OH.1652

You know what, I am going to write these later in red.1660

Let me just draw out the structures here.1665

Now, this...OK, and what takes place here is tautomerization.1669

You remember from organic chemistry- tautomerization.1677

A double bond switches places when a hydrogen moves, so what you end up with is the following.1682

O-, C, double bond, C, this is going to be CH3; and this is going to be O.1687

Now, let me go to red; this is our phosphoenolpyruvate.1697

In the process of hyrdolyzing and breaking off this inorganic phosphate, what you end up creating is this pyruvate molecule; but this is the enol form- enol, meaning it is an alkene and an alcohol.1701

Well, what happens is something called tautomerization, so this molecule is actually more stable in the keto from.1717

Just think of it as this H basically moving over here and this double bond moving over here.1725

The mechanism will not concern us right now, but that is what happens.1730

You have this molecule, the keto form of the pyruvate; and tautomerization really, really stabilizes a molecule.1735

It really wants to be this, but the fact that it tautomerizes and becomes this more stable, drives the reaction forward.1746

And because it pulls the reaction forward, it has a very large -δG.1754

So, this is another force; tautomerization is another driving force for large -δG.1759

Keto form, enol form and this is the pyruvate.1765

OK, let me go ahead and write this out in shortened notation.1777

What we have is PEP 3- + H2O goes to pyruvate plus - it is going to be pyruvate minus actually - inorganic phosphate, which is 2-.1781

Let's make sure the charge is balanced; yes, yes, we do.1800

2-, minus, and this is 3-; I think I wrote 3 but it is not really very clear, so how is that?1803

Now, this has a huge, huge -δG.1808

It is -61.9kJ/mol.1814

That is fantastic; that is virtually twice the hydrolysis δG of adenosine triphosphate, which is big in and of itself.1820

This is a very, very high energy phosphorylated molecule.1827

OK, now, let's see.1832

OK, notice how large the δG is.1839

Notice how large it is, virtually twice that of ATP.1849

Now, notice something else; notice the inorganic phosphate as one of the products.1854

You should start to think about the coupling of reactions.1865

If something is a product, you should think to yourself "well, wait a minute, do I have a reaction where this particular product happens to be a reactant, and if so, can I actually couple those reactions to run a particular reaction?".1870

Well, let's see.1882

The question is: Is it possible to use all this energy - this is a lot of energy, we do not want to waste it - to somehow make adenosine triphosphate?1886

Because the hydrolysis δG of ATP is -30.5, but the hydrolysis δG of the phosphoenolpyruvate is -62, so it has more energy.1906

It can actually drive the reverse reaction of ATP hydrolysis.1920

It can take adenosine diphosphate, combine it with the inorganic phosphate and actually create ATP instead of using it up; that is extraordinary.1924

We want to see if the following i possible; is it possible to use all this energy to somehow make ATP?1933

Can we do this; can we couple this reaction: ADP + PI goes to ATP + H2O?1940

Now, notice, I have reversed the reaction, so the δG for this is going to be a +30.5kJ/mol.1951

And can I combine it with the hydrolysis of the phosphoenolpyruvate, which goes to...I will just write Pyr + inorganic phosphate.1960

Well, let's see; we have that and that cancel.1972

We have H2O, and H2O cancel.1974

So, theoretically, we can take phosphoenolpyruvate, combine it with ATP - I am sorry, ADP, adenosine diphosphate - and it will transfer its phosphoryl group to the adenosine diphosphate to form adenosine triphosphate + pyruvate.1977

And, well, the answer to this question is yes; you can actually do this, and the δG for this is going to end up being -31.4kJ/mol.2000

Now, the enzyme that accomplishes this - I should not say "accomplishes this" - that facilitates this is pyruvate kinase - and do not worry, we will be talking about that later on when we talk about glycolysis, so we will definitely be revisiting this reaction - and this happens to be the final step of glycolysis.2016

This happens to be the final step of glycolysis - woo, all these long words - and here is the best part.2051

This reaction is a testament.2067

These are the kinds of things that completely, completely amaze me to this day.2073

I think that it is fantastic that the body has come up with these amazing things to save energy to be efficient- absolutely extraordinary.2078

This happens to be the final step of glycolysis and is a testament to the body's efficiency in taking this opportunity to remake ATP that was used up earlier in the glycolytic pathway and not just waste all this free energy.2088

It is fantastic; this reaction is going to end up taking place.2158

It might as well couple it with something, and in the process, let's go ahead and actually form some ATP that we ended up using up earlier in the process- recycling.2162

This is absolutely fantastic; this is really, really beautiful.2173

OK, let's talk about another molecule here; this time, let's just write another high-energy molecule.2177

Now, when we say high-energy molecule, we are not talking about the energy in the bonds.2190

The energy in the bonds, themselves, is actually not that high; when we talk about high-energy, we are talking about the amount of free energy.2195

We are talking about the δG, that it has this much free energy to give up.2205

That is what we mean when we say high-energy molecule.2209

OK, this time we are going to do 1,3-biphosphoglycerate.2214

OK, again, the hydrolysis of 1,3-biphosphoglycerate, this is another phosphorylated compound, that when I hydrolyze it, it has a large -δG.2228

Let's go ahead and draw this out.2239

We have C, C, and C.2243

Let's see; we have O.2249

We have P; this is there.2252

This is there; this is there.2253

Let's go ahead and put the Hs here, CH2, CH2.2256

We have O, P here, O-, O-.2260

OK, this is the no. 1 carbon; this is the no. 2 carbon.2265

This is the no. 3 carbon, so we have 1,3-biphosphoglycerate; so there are 2 phosphoryl groups on here.2271

Now, the reaction of this one, what happens here is H2O comes in as the other reactant.2276

And, of course, it spits out one of the PIs, and what you end up with is the following: C, C, C.2286

Let's put H2 here, H2 here; this is going to be O-.2296

This is going to be O, and this is P; I have switched the double bond here.2302

Here, I put it on the right; here, it does not really matter.2307

Again, resonance forms there, so it is not a big deal; this is the 1,3-biphosphoglycerate.2312

And here, we have the 3-phosphoglycerate.2319

Let's write the reaction; this is going to be 1,3-BPG, 4- + H2O, the actual equation.2330

We have 3-phosphoglycerate plus a PI, which is 2-.2340

This is actually 3- - 1, 2, 3, 1, 2, 3, 4, yes, everything is good - plus an H+.2346

What actually happens here is you form the 3-phospohglyceric acid.2352

The protonation, there is an H right here, but then it deprotonates; so it becomes a 3-phosphoglycerate.2357

All the charges balance here and the δG for this particular reaction, again, very, very huge- -49.3kJ/mol.2362

OK, and let's go ahead and close off our discussion with just one more high-energy molecule.2373

This is going to be phosphocreatine.2383

You know what, I think I am going to do this one in blue just for a change of pace.2391

OK, we have phosphocreatine, and let's see.2396

How shall we draw this one?2404

Yes, that is fine; we can draw it from here.2407

OK, this is P; and let's go ahead and do that.2410

Let's go ahead and put those on there; let's go ahead and put the NH.2415

And then we have the C, and then we have another N; and we have a CH3.2420

Let's do CH2 and CO...you know what, I think I am just going to write this as COO-.2430

That is the carboxyl group there, then, of course, we have the nitrogen here with a positive charge.2437

So, this is phosphocreatine, and it is going to undergo...you know what, I should probably have made that smaller, but that is OK.2444

Let's go ahead and do that; here we go.2453

Again, water comes in; we are talking about hydrolysis.2458

The inorganic phosphate leaves the reaction, and what you end up with is the following: H2N.2460

This is C, NH2; we have another N.2468

We have CH2; we have COO-, and we have another CH3.2475

OK, this is phosphocreatine; let me do this in red.2481

This is phosphocreatine, and this right here is creatine.2487

I will write it on top because I am actually going to write some resonance structures here.2493

It might be nice if I actually wrote the words; how is that?2498

You get so into it; OK, that is creatine.2503

Let me go back to blue; let me put my positive charge here.2506

So, you notice you have a nitrogen that is protonated; there is 4 bonds on it, so it is carrying a formal charge of that.2509

Well, notice you have a carbon; you have a nitrogen here.2514

You have a nitrogen here, and you have a nitrogen here.2518

Basically, what can happen is this thing has resonance structures; this double bond can actually move around because of that resonance stabilization that is provided by creatine.2521

The phosphocreatine is a highly thermal dynamically favorable reaction, that it wants to give up that phosphoryl.2531

It wants to give up this phosphoryl group; it wants to transfer it to someplace else in order to form creatine, which has this resonance stabilization, which really, really drops the energy very low to give us a very large δG negative.2540

Let me go ahead and draw the resonance structures in here.2557

Let's go ahead and put the double bond on this side.2562

H2N, we will go ahead and put that there, C, NH2, N, CH2, COO-; and we have CH3.2566

So, we will put the positive charge on that one, and then we have one more resonance structure; and it is going to be right there.2577

Let's go H2N, single bond carbon; let's go NH2, right there.2586

Let's go double bond on the N there; we have our CH3 group.2593

We have our CH2, and we have our COO-.2599

These 3 resonance structures, the positive charge is shared among the 3 nitrogens- high degree of stability.2604

Anytime you have resonance structures in a product, it is going to be a very stable molecule.2611

That stability is what pulls the reaction forward and drops the energy content of the product that gives you the high -δG.2617

Let's see here; for creatine, we have a resonance stabilization.2628

It just means the 3 nitrogen share the positive charge.2644

And notice, in this particular case, the P, the phosphoryl group is attached to a nitrogen not an oxygen.2655

So, it can do that; that is not a problem.2660

And so, this is the bond that we are breaking between the nitrogen and the phosphorus.2663

OK, thank you for joining us here at Educator.com2668

We will see you next time, bye-bye.2671