Energy and Whatnot! So so frustrating!

[BoneMental]

I have yet to see this actually be an MCAT question, so I'm asking it here rather than in the MCAT Question Forum.

Rather, it's more of a science questions that stumps me to this day.

When energy is "released" (ie, by bonds forming) and provides energy for other reactions, what form is this energy in?

For example, ATP hydrolysis results in "energy" that can be used to "fuel" other processes. How so? Is it heat? Work? I always find this topic danced around even in upper level biology courses, and its very frustrating to me.

Can someone please explain this concept to me? I don't understand how released energy fuels other reactions--what form is the energy in?

AHHHHH! I really want to know!

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[SN2ed]

Thread moved. This type of thread belongs in the Study Q&A forum.

 

[masscrash]

I'm no expert. This is my best guess. I think that it would be either mechanical or heat. For something like ATP in a Adenyl Cyclase making cAMP I would guess mechanical. The tri phosphate is unfavorable configuration and if you were able to connect to the last two phosphates it would create a mechanical energy as they break apart; however, there are enzymes that are activated by heat. If physics has taught us anything it is that transferring energy is very inefficient. So even though it is using mechanical energy there is no doubt in my mind that a lot of it is lost to heat. So there you have it, my feeble attempt at an explanation.

 

[ridethecliche]

Reactions are coupled.

Remember, energy isn't static. It can be made to change form and do work.

When you break a Phosphate bond, you release energy. If you're not doing anything, it's wasted as heat. If you couple the rxn to something that needs energy to proceed, then you do work.

Conformational changes in an enzyme that are caused by binding/being phos/dephosphorylated is a form of 'work'.

That's how it helps me to conceptualize it.

I think you meant, by bonds breaking.

In glycolysis for instance, G-> G-6-P as the phosphate being attached makes it hard for the glucose to leave the cell. So it might not be energetically favorable, per-se, but without that step, you'd have stuff jumping out of the cytoplasm and out of the cell!

 

[BoneMental]

Reactions are coupled.

Remember, energy isn't static. It can be made to change form and do work.

When you break a Phosphate bond, you release energy. If you're not doing anything, it's wasted as heat. If you couple the rxn to something that needs energy to proceed, then you do work.

Conformational changes in an enzyme that are caused by binding/being phos/dephosphorylated is a form of 'work'.

That's how it helps me to conceptualize it.

I think you meant, by bonds breaking.

In glycolysis for instance, G-> G-6-P as the phosphate being attached makes it hard for the glucose to leave the cell. So it might not be energetically favorable, per-se, but without that step, you'd have stuff jumping out of the cytoplasm and out of the cell!

Breaking bonds never releases energy.

However, it does make sense that the free energy can be utilized in coupled reactions...

 

[ridethecliche]

Oops.

That's what I get for posting before AM coffee.

 

[masscrash]

Breaking bonds never releases energy.

Please explain....

 

[Rabolisk]

A bond occurs because there is an attraction between two molecules. The potential energy is minimized when a bond forms. Hence bond formation lowers the energy of the molecule (system) and it releases energy into the surroundings. Likewise, bond breaking increases the energies of the molecules (system) and it takes energy in from the surroundings. The idea that there is energy "stored" in a bond is a misnomer. It is analogous to saying that at sea level you have potential energy "stored" as a result of your orientation to the earth. You do, but it's of no use since you're not going to go farther into the earth.

 

[masscrash]

A bond occurs because there is an attraction between two molecules. The potential energy is minimized when a bond forms. Hence bond formation lowers the energy of the molecule (system) and it releases energy into the surroundings. Likewise, bond breaking increases the energies of the molecules (system) and it takes energy in from the surroundings. The idea that there is energy "stored" in a bond is a misnomer. It is analogous to saying that at sea level you have potential energy "stored" as a result of your orientation to the earth. You do, but it's of no use since you're not going to go farther into the earth.

To use your analogy, ADP is at sealevel. When ADP goes through the ATP synthase its configuration is unfavorable. It's like taking a bucket of sea water and carrying it up a mountain. If the potential energy was minimized in in the conversion of ADP to ATP then when it goes to do work it would take an input of energy to make ADP, which kind of defeats the purpose.

 

[ridethecliche]

Okay. Then why is the syntax 'high energy phosphate' bonds?

Isn't there a coupling between the breaking of the ATP->ADP rxn and an unfavorable reaction?

Then again, if it was favorable for ATP to break to ADP, we'd have very little ATP to begin with.

Ahh conundrum. I guess the common conventions in bio are silly. This is how we always talked about it in biochem, etc. High energy phosphate bonds, yada yada yada.

 

[Rabolisk]

It is favorable for ATP to be hydrolyzed into ADP and Pi. However, biochemical reactions in bodies are regulated extensively, via enzymes and whatnot.

High-energy bond is one of the most misleading terms used. It just means that the free energy of hydrolysis of the bond is large and negative.

 

[LaurenMCAT]

Breaking bonds never releases energy.

Actually - breaking the phosphate bonds in ATP releases quite a bit of energy because the adjacent phosphate groups are unstable in their configuration.

http://en.wikipedia.org/wiki/Adenosine_triphosphate

Typically, though, we assume that breaking bonds in most compounds requires energy.

(I do realize that this post may be redundant given the content of the posts above, but I wanted to provide a simpler, straightforward reaction for other readers.)

 

[Rabolisk]

Actually - breaking the phosphate bonds in ATP releases quite a bit of energy because the adjacent phosphate groups are unstable in their configuration.

http://en.wikipedia.org/wiki/Adenosine_triphosphate

Typically, though, we assume that breaking bonds in most compounds requires energy.

(I do realize that this post may be redundant given the content of the posts above, but I wanted to provide a simpler, straightforward reaction for other readers.)

No, it does not. A bond would never form if it required energy to form it (equivalently stated, if energy was released upon breaking it). A bond is a reduction in potential energy due to the attraction between molecules. Whether we are talking about strong bonds or weak bonds, this is always true. It's true that ATP is relatively unstable due to the close proximity of the negative charges, but the energy released is not from the breaking of the "high-energy" bond. The energy is released when bonds form during ATP hydrolysis.

 

[ridethecliche]

Yeah, having read more about this while studying today:

Breaking the bonds require energy, but the bonds made by ADP and the Pi latching onto something releases energy > that needed to break the bond for ATP.

 

[PiBond]

The decrease in Gibbs Free Energy (and thus the energy available to do work in the cell) is a result of an increase in stability of the products as a result of more resonance structures in the products of ATP hydrolysis and an overall increase in entropy of the system (we have 2 molecules instead of one; ATP --> ADP + Pi).

At least that's how I think of it.

 

[LaurenMCAT]

The energy is released when bonds form during ATP hydrolysis.

True - but for MCAT purposes, sometimes we "gloss over" the deeper science!

 

[Swagster]

Actually - breaking the phosphate bonds in ATP releases quite a bit of energy because the adjacent phosphate groups are unstable in their configuration.

NO!!! Never does breaking a bond release energy, otherwise the bond would never have formed. You have to look at the energy of a reaction. The overall energy for a reaction results from summing the energy of all the bonds formed in the products and subtracting the energy required to break the bonds in the reactants.

The hydrolysis of ATP, where a phoshpate O-P bond and an O-H bond of water are broken and a new, stronger O-P bond is formed along with a new O-H bond, is what releases energy. The phosphodiester bond of ATP is weak, so it doesn't take a good deal of energy to break, resulting in energy being released when stronger bonds are formed in the products during hydrolysis.

Sorry to be so adament, but this is not deeper science. This is basic general chemistry.

deltaH for a reaction = Energy of bonds broken - Energy of bonds formed.

 

[masscrash]

NO!!! Never does breaking a bond release energy, otherwise the bond would never have formed. You have to look at the energy of a reaction. The overall energy for a reaction results from summing the energy of all the bonds formed in the products and subtracting the energy required to break the bonds in the reactants.

The hydrolysis of ATP, where a phoshpate O-P bond and an O-H bond of water are broken and a new, stronger O-P bond is formed along with a new O-H bond, is what releases energy. The phosphodiester bond of ATP is weak, so it doesn't take a good deal of energy to break, resulting in energy being released when stronger bonds are formed in the products during hydrolysis.

Sorry to be so adament, but this is not deeper science. This is basic general chemistry.

deltaH for a reaction = Energy of bonds broken - Energy of bonds formed.

Ok I can agree with you. Now back to the OP's question. How does the "formation of ADP" power cellular processes.

 

[jissho]

Okay. Then why is the syntax 'high energy phosphate' bonds?

Isn't there a coupling between the breaking of the ATP->ADP rxn and an unfavorable reaction?

Then again, if it was favorable for ATP to break to ADP, we'd have very little ATP to begin with.

Ahh conundrum. I guess the common conventions in bio are silly. This is how we always talked about it in biochem, etc. High energy phosphate bonds, yada yada yada.

ATP + H20 -> ADP + Pi is favorable
However the activation energy is high and the spontaneous reaction occurs slowly. Enzymes that hydrolyze ATP decrease activation energy for this reaction and speed up the process considerably.

 

[BerkReviewTeach]

ATP + H20 -> ADP + Pi is favorable
However the activation energy is high and the spontaneous reaction occurs slowly. Enzymes that hydrolyze ATP decrease activation energy for this reaction and speed up the process considerably.

Good point about spontaneity versus rection rate. Hard to get a spontaneous reaction to go if the activation energy is too high.

 

[movax]

True - but for MCAT purposes, sometimes we "gloss over" the deeper science!

"Deeper science" aaaaaaaaagh, echoing Swagster here. Breaking bonds never release energy directly!

Nature prefers a low energy state. When you form a solution for instance, the most exothermic will form the strongest intermolecular bonds (with the lowest vapor pressure); energy leaves that system as copious amounts of heat, resulting in very stable (and strong!) intermolecular bonds. This energy release upon bond formation.

That's inorganic chem though, like previous posters have said, biochemistry operates based on coupling reactions; if it didn't we wouldn't be around to suffer through the MCAT

Perhaps it's because of my engineering background, but a perfect understanding of basic concepts leads to rapid mastery of advanced concepts and no need to memorize (because you can just derive based on your background knowledge).

 

[Swagster]

"Deeper science" aaaaaaaaagh, echoing Swagster here. Breaking bonds never release energy directly!

I hope I didn't come across as harsh, as that was not my intention. It's definitely not "deeper science" and is an easy concept from general chemistry. She just crossed it up an should have corrected her error rather than try to brush it off as a hard concept. When your title says you're an elite instructor, people are bound to take your answers seriously, so they need to be correct.

 

[Charles_Carmichael]

Generally, the term ATP "hydrolysis" isn't entirely accurate when you're talking about how a reaction is driven. Sometimes it's true that ATP/GTP hydrolysis itself can drive a reaction, but I don't believe that's the case for most reactions. What really happens is that a phosphate group is first transferred from ATP to the substrate (it becomes covalently attached to the substrate) or enzyme. This raises the free-energy of that molecule. In the next step, the phosphate group that was transferred is displaced. So, the energy from ATP doesn't really come from its hydrolysis; the energy comes from the products of this reaction having a lower free-energy content compared to what you started out with. Others in this thread have mentioned that breaking of bonds requires input of energy and they're right; ATP is not an exception to this rule.

Just plain hydrolysis of ATP doesn't really do anything except generate heat.

At least, that's how I remember it from biochem 2 years ago. I remember being pretty shocked that "ATP hydrolysis" driving a reaction isn't really true.

 

[SmurfinUSA]

can't you have a bond release gibbs free energy if the reaction is entropically favored even if the reaction is enthalpically disfavored? dG= dH -TdS

more entropy ie 1 molecule to 2 creates positive dS..

or is entropy not as significant as enthalpy? (where a high dH would not be too much lower due to positive entropy)

 

[Rabolisk]

Generally, the term ATP "hydrolysis" isn't entirely accurate when you're talking about how a reaction is driven. Sometimes it's true that ATP/GTP hydrolysis itself can drive a reaction, but I don't believe that's the case for most reactions. What really happens is that a phosphate group is first transferred from ATP to the substrate (it becomes covalently attached to the substrate) or enzyme. This raises the free-energy of that molecule. In the next step, the phosphate group that was transferred is displaced. So, the energy from ATP doesn't really come from its hydrolysis; the energy comes from the products of this reaction having a lower free-energy content compared to what you started out with. Others in this thread have mentioned that breaking of bonds requires input of energy and they're right; ATP is not an exception to this rule.

Just plain hydrolysis of ATP doesn't really do anything except generate heat.

At least, that's how I remember it from biochem 2 years ago. I remember being pretty shocked that "ATP hydrolysis" driving a reaction isn't really true.

I wouldn't say it's inaccurate to say that ATP hydrolysis drives many reactions in biochemistry. I also think it's ok to say that energy from ATP comes from ATP hydrolysis. It's certainly true that ATP hydrolysis alone would just generate heat, and that reactions are coupled through phosphoryl transfer reactions between ATP, enzymes, subtrates, and even coenzymes at times. The best way I would describe it is that the free energy of ATP hydrolysis is conserved through these group transfer reactions. It's sort of like saying that ATP has a high-energy bond; it can be misleading for many students, but nevertheless is a perfectly correct statement. What is wrong, as has already been drilled multiple times in this topic, is the idea that breaking bonds alone releases energy.

On a deeeeeeper level, if you think about it, the point of ATP is indeed to conserve free energy rather than letting it just dissipate through heat. ATP is like the dollar; in and of itself, it has no value. Money matters because of its purchasing power and its wide applicability, not because of the papers themselves, and you're paid money for work as a means of conserving your purchasing power. In the same sense, ATP is generated in catabolic pathways (e.g. cellular respiration) so as to conserve the energy released by the pathway. Without ATP, there would be no way to couple the energy released from the oxidation of glucose and other nutrients to energy-consuming processes (i.e. everything else your body does). It would be like if you worked, but you weren't paid in dollars, so you couldn't use what you gained from working anywhere else... I think that rant became a bit more convoluted than I initially wanted, but nevertheless, enjoy.

 

[SmurfinUSA]

I wouldn't say it's inaccurate to say that ATP hydrolysis drives many reactions in biochemistry. I also think it's ok to say that energy from ATP comes from ATP hydrolysis. It's certainly true that ATP hydrolysis alone would just generate heat, and that reactions are coupled through phosphoryl transfer reactions between ATP, enzymes, subtrates, and even coenzymes at times. The best way I would describe it is that the free energy of ATP hydrolysis is conserved through these group transfer reactions. It's sort of like saying that ATP has a high-energy bond; it can be misleading for many students, but nevertheless is a perfectly correct statement. What is wrong, as has already been drilled multiple times in this topic, is the idea that breaking bonds alone releases energy.

On a deeeeeeper level, if you think about it, the point of ATP is indeed to conserve free energy rather than letting it just dissipate through heat. ATP is like the dollar; in and of itself, it has no value. Money matters because of its purchasing power and its wide applicability, not because of the papers themselves, and you're paid money for work as a means of conserving your purchasing power. In the same sense, ATP is generated in catabolic pathways (e.g. cellular respiration) so as to conserve the energy released by the pathway. Without ATP, there would be no way to couple the energy released from the oxidation of glucose and other nutrients to energy-consuming processes (i.e. everything else your body does). It would be like if you worked, but you weren't paid in dollars, so you couldn't use what you gained from working anywhere else... I think that rant became a bit more convoluted than I initially wanted, but nevertheless, enjoy.