[Jfalken]

Alright, can we please clear this up.
Biochem says that ATP has "two high energy bonds", see this link for clarification:
https://socratic.org/questions/how-many-high-energy-bonds-does-atp-contain

But what is a "high energy bond" and in organic chemistry, when we are very interested in the separate bonds, how many bonds can we really assume could be high energy bonds?
https://upload.wikimedia.org/wikipedia/commons/3/31/Adenosintriphosphat_protoniert.svg

I am determined that it would be more than two of these bonds, while my biochem friend says that there are only two.
Regardless if we look at the molecule as a separate unit outside of the body.

Any thoughts?

[rolnor]

Do you agree that ATP containes 2 phospoanhydride bonds?

[Babcock_Hall]

The standard definition of a high-energy bond in biochemistry is one for which ΔG°'_hydrolysis is -25 kJ/mole or more negative than that.  The term "high-energy bond" can mislead the unwary.  I wish that there were more focus on how ATP does its job.

[Jfalken]

The standard definition of a high-energy bond in biochemistry is one for which ΔG°'_hydrolysis is -25 kJ/mole or more negative than that.  The term "high-energy bond" can mislead the unwary.  I wish that there were more focus on how ATP does its job.

It is clearly a misnomer.

Do you agree that ATP containes 2 phospoanhydride bonds?

A covalent bond (singular) is defined as a sigma bond (meaning two electrons share the same orbital).
Could you differentiate between these two sigma bonds that you are referring to?
Circle them on the molecule.

[rolnor]

I am completely stupid, its more bonds as you say, its 4 I was confused by the picture in you simplified structure in your link.
This picture is better:
https://en.m.wikipedia.org/wiki/Adenosine_triphosphate

It could be the two bonds connecting the middle phosporatom but the two other are also high energy?

[Babcock_Hall]

As a general rule, definitions are not right or wrong; they are useful or useless.  Why do you say that "high-energy bond" is a misnomer?  What is your interpretation of ΔG°' values that are < -25 kJ/mole?  One idea to move forward would be for you to apply this definition to the link you provided.

[rolnor]

It must be the two connecting the middle phosporatom that are high energy by deffinition but the other two are also higher then a normal, non-anhydride phospate ester bond

[Jfalken]

As a general rule, definitions are not right or wrong; they are useful or useless.  Why do you say that "high-energy bond" is a misnomer?  What is your interpretation of ΔG°' values that are < -25 kJ/mole?  One idea to move forward would be for you to apply this definition to the link you provided.

I say that it is a misnomer because it is clearly not the bond itself that is high in energy.
Here, biochemists are talking about the ester functional group that consists of more than one bond.
Imagine the peptide bond or the glycosidic bond which is really more than one sigma bond.

Please elaborate the 25kJ/mole theory.

It must be the two connecting the middle phosporatom that are high energy by deffinition but the other two are also higher then a normal, non-anhydride phospate ester bond

Hence the misnomer of being a "high-energy bond"

[Babcock_Hall]

I would focus on the reaction (hydrolysis) not the bond.  Suppose we have a molecule A with a HEP bond and a molecule B with a low energy phosphate bond (ΔG°' > -25 kJ/mole).  What is true about the relative equilibrium constants for the two hydrolyses?

[rolnor]

But in the link they do state that it is high-energy bonds and that is the problem, is this correct? I agree that it is a bad way of describing the molecules properties.

[Babcock_Hall]

I would focus on the particular bond being hydrolyzed.  Ado is the abbreviation for adenosine.  All values are kJ/mole.  Consider the following reactions:

1. ATP + water  ADP + P_i  ΔG°' = -30.5
2. ADP + water AMP + P_i  ΔG°' = -32.8
3. AMP + water Ado + P_i  ΔG°' = -14.2

In reactions 1 and 2, a phosphoanhydride bond is being hydrolyzed.  In reaction 3 a phosphomonoester bond is being hydrolyzed.  By the definition I provided (Nelson and Cox, Principles of Biochemistry, 7th ed.) the first two bonds broken are high-energy, and the third is low-energy.

These concepts are helpful in qualitative predictions of the equilibrium constants of transphosphorylation reactions.  A decent example is the phosphorylation of ADP by phosphocreatine during intense muscular activity.

[rolnor]

I guess you have to look on the actual mechanism of the hydrolysis, wich bond is actually broken in each step? What is the leaving group?

[Babcock_Hall]

For reaction 1, the attack is at the γ-phosphorus, and ADP is the leaving group.  For reaction 2, the attack is at the β-phosphorus, and the leaving group is AMP.  For Reaction 3, the attack is at the α-phosphorus, and the leaving group is adenosine.

Things get a little bit more complicated with acetyl phosphate, another high-energy phosphate compound and one that is a mixed anhydride.  IIRC whether hydrolysis is at the P-O bond or the C-O bond depends upon pH.  I would have to double-check this, however.

[rolnor]

That seems to be a full analysis of the matter, thanks.

[Babcock_Hall]

In reading over this thread, I realized on additional complication.  ATP is often cleaved into AMP and pyrophosphate in various biosynthetic reactions.  This bond is also high energy.