ATP Clarification

[andafoo]

Hey all,

Sorry if this topic has been discussed before, but I have a question about ATP and how exactly does it "store energy".

It all seemed very simple to me before studying...


ATP is a less stable molecule than ADP, so it would require energy to form ATP from ADP + Pi. That so far seems clear enough.

However, from EK's general chemistry study guide, they cite the following:

"Notice ... that energy is always required to break a bond ... (Energy from ATP is released when the new bonds of ADP and iP are formed, and not when the ATP bonds are broken.)"

Now, does anyone see a disconnect between what they are saying and the factoid that I mentioned prior? Is it just me?

If anyone can clear this up for me, I'd be real grateful!

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[RySerr21]

Hey all,

Sorry if this topic has been discussed before, but I have a question about ATP and how exactly does it "store energy".

It all seemed very simple to me before studying...


ATP is a less stable molecule than ADP, so it would require energy to form ATP from ADP + Pi. That so far seems clear enough.

However, from EK's general chemistry study guide, they cite the following:

"Notice ... that energy is always required to break a bond ... (Energy from ATP is released when the new bonds of ADP and iP are formed, and not when the ATP bonds are broken.)"

Now, does anyone see a disconnect between what they are saying and the factoid that I mentioned prior? Is it just me?

If anyone can clear this up for me, I'd be real grateful!

hmmmm. i've always been taught as you break a bond you are releasing energy (exoxthermic) and as you form bonds you are absorbing energy (endothermic). when you cleave the 3rd phosphate on ATP, you release a certain amount of energy.

 

[andafoo]

This one has me really

 

[andafoo]

hmmmm. i've always been taught as you break a bond you are releasing energy (exoxthermic) and as you form bonds you are absorbing energy (endothermic). when you cleave the 3rd phosphate on ATP, you release a certain amount of energy.

Well, lets take a moment to think about what you've been taught.

The way chemists look at molecular bonds is that molecules can reach a more stable state/lower energy by forming the bond.

A typical graph that you can see describing this is:

like such.

So it makes sense that when bonds are formed, the system as a whole is more stable. That means that energy will be released when a bond forms.

But in the case of ATP, I've also 'learned' that ATP releases energy when the bond is broken.

Can anyone give a good analysis!?!?

 

[RySerr21]

Well, lets take a moment to think about what you've been taught.

The way chemists look at molecular bonds is that molecules can reach a more stable state/lower energy by forming the bond.

A typical graph that you can see describing this is:

like such.

So it makes sense that when bonds are formed, the system as a whole is more stable. That means that energy will be released when a bond forms.

But in the case of ATP, I've also 'learned' that ATP releases energy when the bond is broken.

Can anyone give a good analysis!?!?

im confused. don't you release energy when you break the bond of a molecule? doesn't that answer why ATP releases energy when it is broken? this is why i dont like chemistry, haha. i just need to know that it happens.

 

[rocuronium]

We covered this in biochem, but that was a few years ago, so let's see what I can remember.

ATP is an unstable molecule, so when it undergoes hydrolysis, energy is released. The energy doesn't come from the phosphate bond itself, but from the greater stability of the ADP molecule in relation to ATP molecule.

The reason that there is bonding in molecules is because it takes less energy for atoms to be bound than to be separate. For that reason, if you want to break the bonds and separate the atoms, you need to ADD energy. I think that's what that EK quote was saying.

 

[Christo1]

Just think of it in terms of activation energy. Although you need to input energy to break the phosphate bonds, the amount of energy you get out of the reformation of ADP, a lower energy molecule, is huge, something like 7kcal p mol. This exothermic reaction is then coupled with unfavorable, endothermic reactions to drive the forward reaction. This is one way in which enzymes can work.

So anyway, just think of that input energy to break the phosphate bond as the energy required to overcome the activation energy to drive the reaction forward. Quit thinking so deeply about it!

 

[andafoo]

Just think of it in terms of activation energy. Although you need to input energy to break the phosphate bonds, the amount of energy you get out of the reformation of ADP, a lower energy molecule, is huge, something like 7kcal p mol. This exothermic reaction is then coupled with unfavorable, endothermic reactions to drive the forward reaction. This is one way in which enzymes can work.

So anyway, just think of that input energy to break the phosphate bond as the energy required to overcome the activation energy to drive the reaction forward. Quit thinking so deeply about it!

I really havn't heard anything pertaining to your explanation of activation energy vs. change in Gibbs Energy, but I have a few issues with it.

First of all, every reaction has an activation energy of some sort. But if you want to inspect a molecule like ATP and its role as an energy carrier or storage molecule, activation energy -> thus kinetics should have nothing to do with it.

What is important is the overall change in Gibbs energy of the molecule, or what is commonly labeled as deltaG.

So that still doesn't explain: "Energy from ATP is released when the new bonds of ADP and iP are formed, and not when the ATP bonds are broken"


It seems like EK's statement is contradictory to both what you just explained and what had previously known. I'm just concerned because EK is saying it so boldly and no one has really brought it up - not even in the EK forums. Something is up...

 

[chemnerd31]

It is 100% correct to say that it requires energy to break a bond. No matter what the bond is it will require energy to break it. The key is how much energy will it take to break the bond. For the third phosphate on ATP it does not require much energy at all to break the bond and form Pi and ADP. The new bonds formed when the something is phosphorolated are much stronger and more stable than the ones in ATP and therefore the net result is a release of energy. So it energy is stored in ATP because the bond is so weak.

The key thing it remember is it requires energy to break bonds and you get energy when you form bonds.

 

[G1SG2]

However, from EK's general chemistry study guide, they cite the following:

"Notice ... that energy is always required to break a bond ... (Energy from ATP is released when the new bonds of ADP and iP are formed, and not when the ATP bonds are broken.)"

Now, does anyone see a disconnect between what they are saying and the factoid that I mentioned prior? Is it just me?

I think what they're saying is that, energy is required to break the bonds of ATP, but when the bonds of ADP and iP are formed in the transition state, it releases energy that exceeds the amount of energy needed to break the bonds of ATP. In this sense, breaking bonds of ATP releases energy, but not directly as bond breaking always requires energy.

 

[andafoo]

I think what they're saying is that, energy is required to break the bonds of ATP, but when the bonds of ADP and iP are formed in the transition state, it releases energy that exceeds the amount of energy needed to break the bonds of ATP. In this sense, breaking bonds of ATP releases energy, but not directly as bond breaking always requires energy.

Right-O.

Glad you all could clarify! It'd clear to me now

Thanks

 

[unsung]

Hey all,

Sorry if this topic has been discussed before, but I have a question about ATP and how exactly does it "store energy".

It all seemed very simple to me before studying...


ATP is a less stable molecule than ADP, so it would require energy to form ATP from ADP + Pi. That so far seems clear enough.

However, from EK's general chemistry study guide, they cite the following:

"Notice ... that energy is always required to break a bond ... (Energy from ATP is released when the new bonds of ADP and iP are formed, and not when the ATP bonds are broken.)"

Now, does anyone see a disconnect between what they are saying and the factoid that I mentioned prior? Is it just me?

If anyone can clear this up for me, I'd be real grateful!

What you're describing is the difference between kinetics & thermodynamics. It takes energy to go from a reactant to the transition state (higher energy), before it goes back down to a lower energy product. So, just because it takes energy to reach that transition state, does not mean the product is higher energy than the reactant (although it can be, in an endothermic reaction). The eventual product is lower in energy than the original reactant, making it thermodynamically favored.

 

[werd]

What you're describing is the difference between kinetics & thermodynamics. It takes energy to go from a reactant to the transition state (higher energy), before it goes back down to a lower energy product. So, just because it takes energy to reach that transition state, does not mean the product is higher energy than the reactant (although it can be, in an endothermic reaction). The eventual product is lower in energy than the original reactant, making it thermodynamically favored.

as discussed above, the EK book is saying that breaking the ATP bond in isolation is thermodynamically unfavorable, but the reaction is made favorable by the co-incident formation of a P to O bond as hydrolysis occurs.

i don't think this is a kinetics vs. a thermodynamics thing, but rather multiple thermodynamic processes which occur at the same time and we have to sum in order to describe the reaction. "transition state" usually refers to a situation with bonds half formed and/or half broken. transition states can not be isolated. "intermediate" refers to a stable intermediary compound that occurs during a reaction. it's not that the ATP bond breaks and then the other P-O bond forms... they are happening at once and the "transition state" is likely a situation where the new bond is half formed and the ATP bond is half broken. keep in mind that reactions do not need to proceed with just one thing happening at a time (if our reaction were sequential, the "bonds broken/new bond not yet formed" entity would be called a "high energy intermediate" but this isn't how hydrolysis rxns move forward).

 

[Alvarez13]

Check this out: http://www.blobs.org/science/article.php?article=30

Yep. It takes energy to break a bond. The reason ATP gives off energy (exothermic) is because the NET energy is negative. Look at the overall reaction. It requires a bunch of energy to break all the bonds. However, the amount given off from the formation of bonds is even greater...so the systems gives off a net 30.5 kJ or whatever. Pretty cool how that works.

 

[andafoo]

Check this out: http://www.blobs.org/science/article.php?article=30

Yep. It takes energy to break a bond. The reason ATP gives off energy (exothermic) is because the NET energy is negative. Look at the overall reaction. It requires a bunch of energy to break all the bonds. However, the amount given off from the formation of bonds is even greater...so the systems gives off a net 30.5 kJ or whatever. Pretty cool how that works.

That's a killer page there. Explains the question perfectly. Thank everyone.

 

[engineeredout]

When trying to keep in mind if breaking bonds releases or requires energy, you have to keep in mind that if breaking bonds released energy, then bonds would be breaking all over the place and everything we know would spontaneously be falling apart right now.

That is a kickass site though.