Question About Hydrolysis of ATP

[ojyarumaru]

When ATP is hydrolyzed to ADP + Pi, is this an endothermic/ exothermic reaction? Also, is it exergonic/ energonic? I saw a destroyer problem that stated that hydrolysis of ATP is exergonic. But breaking a bond requires energy, so would that mean ATP hydrolysis is endothermic AND exergonic??? Please help, thanks!

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[casper22]

Thats true...

 

[loveoforganic]

It requires energy to get over the Activation energy

 

[DoCt0rPeTe]

When ATP is hydrolyzed to ADP + Pi, is this an endothermic/ exothermic reaction? Also, is it exergonic/ energonic? I saw a destroyer problem that stated that hydrolysis of ATP is exergonic. But breaking a bond requires energy, so would that mean ATP hydrolysis is endothermic AND exergonic??? Please help, thanks!

Some terms you should know:
ExerGonic: - delta G
Exothermic: - delta H


This is a crucial concept to understand. ExerGonic means delta G is negative, hence the reaction is spontaneous. I agree in that you may have to add energy to break the bond, but the reaction is often catalzyed by a kinase enzyme.

Think of the equation for delta G.

Delta G= delta H -TdeltaS

deltaH is not the only factor in determining whether a rxn is endergonic or exergonic (+ or - delta G).
Take a look at the first step of Glycolysis. It's highly unfravorable (+deltaG endergonic etc) to go from a stable glucose, to glucose-6-phosphate, but the hydrolysis of ATP which is a negative delta G will drive the reaction, as the summation of both rxn's delta G's is negative (spontaneous).

Therefore, coupling a highly exergonic rxn with an endergonic one will drive the endergonic rxn to become spontaneous. This is how many of the rxns in the human body are driven.

 

[drgummybear]

^ great explanation dr. pete!!

anyway to more specifically answer the OP's question, I think the hydrolysis of ATP is exergonic and exothermic (not endothermic). it does require energy to break the bond, but the energy released from the formation of the much more stable ADP is what makes this reaction exothermic.

 

[ojyarumaru]

Thanks a lot everyone, makes more sense to me!

 

[chromosome21]

Use reaction coordinate diagram from chemistry kinetics to understand this better. You have to have enough energy to pass by Ea (activation energy). When you want to break bonds, you have to apply energy so that you can easily pass over Ea. Now, when the products are formed, energy will be released, and if the products are more stable than reactants, more energy will be released, which will make the overall reaction exothermic.

In short, to break ATP bonds, we'll apply energy so that ATP molecules can get over Ea. And Products (ADP + P) are more stable than reactants, thus more energy will be lost at the end when products are formed.

 

[chromosome21]

Use reaction coordinate diagram from chemistry kinetics to understand this better. You have to have enough energy to pass by Ea (activation energy). When you want to break bonds, you have to apply energy so that you can easily pass over Ea. Now, when the products are formed, energy will be released, and if the products are more stable than reactants, more energy will be released, which will make the overall reaction exothermic.

In short, to break ATP bonds, we'll apply energy so that ATP molecules can get over Ea. And Products (ADP + P) are more stable than reactants, thus more energy will be lost at the end when products are formed.

Look at the attachment. Y-axis is energy, x-axis is progress of reaction.

 

[ojyarumaru]

Ah, I didn't even think to think of it as a reaction coordinate curve. Thanks for the explanation!