Bond Energy vs. ATP Hydrolysis

[MDJerome]

This concept is confusing me. Could someone clarify please?

If energy must be ADDED to break bonds and energy is RELEASED when bonds are formed, then why does breaking a bond from ATP release heat/energy?

Thanks in advance guys! I appreciate any input!

---

Members don't see this ad.

 

[sizillyd]

It's because the energy you gain is greater than the energy you put in.

So it's an OVERALL release of energy. Hope this helps.

 

[Hemichordate]

Also, can bond energy only be positive, or can it be negative as well?

 

[MDJerome]

It's because the energy you gain is greater than the energy you put in.

So it's an OVERALL release of energy. Hope this helps.

That's weird. I guess the reason it's confusing me is because it contradicts the general rule of Bond Energies:

- Energy must be put in to break a bond
- Energy is released when a more stable bond is formed

Hmmm. ATP is a more high energy bond and releases energy upon hydrolysis forming a more stable form (ADP). Is this right?

Disregard this - trying to help myself understand the concept:
ADP + Pi -> ATP (BE = Very High, Unstable) formed by ETC via ATPase using H+ concentration (reaction coupling w/ favorable reaction)
ATP -> ADP (BE = Low, Stable) + Pi

Enthalpy of Reaction: Bond Energy of Reactants broken - Bond Energy of Products formed
so, for ATP -> ADP + Pi

delta H = (total BE reactants) - (total BE products)
delta H = (High Bond Energy of ATP) - (Low Bond Energy of Products ADP + Pi).

So I guess the takeaway idea is that anything more stable being formed releases energy. In this case, ADP is a more stable than ATP.

 

[Rabolisk]

You guys are right that the overall reaction is exergonic because the resultant molecules are more stable. Bond energies are only positive, and energy must be put in to break all bonds. Bonds are also formed in hydrolysis of ATP, namely the OH bonds. This makes the overall reaction favorable.

 

[MDJerome]

You guys are right that the overall reaction is exergonic because the resultant molecules are more stable. Bond energies are only positive, and energy must be put in to break all bonds. Bonds are also formed in hydrolysis of ATP, namely the OH bonds. This makes the overall reaction favorable.

Awesome. Thanks guys for clarifying. I get it now.

 

[Charles_Carmichael]

Technically, the statement that ATP hydrolysis drives ATP-dependent reactions is wrong, at least for most reactions. Generally, either a phosphoryl or pyrophosphoryl group is transferred to the substrate or enzyme and raises its free energy. In a subsequent step, the transferred phosphoryl/pyrophosphoryl group is displaced, generating a product with lower free energy. Thus, the free energy released from ATP doesn't really come from breaking a bond. It comes from the products having lower free energy than the reactants.

Hope this helps.