Are all biological catabolic reactions exergonic?

[mktsgm]

TL;DR Summary

Generally it is said that all biological catabolic reactions are exergonic. But in chemistry it is said that breaking of bonds are considered endergonic and bond-forming is exergoic. It looks contradictory. What is the missing link?

Generally it is said that all biological catabolic reactions are exergonic. Famous example is ATP hydrolysis is exergonic. That's why it is called energy currency. Similarly breaking of glucose molecule into pyruvate also releases energy to form ATP.

But in chemistry it is said that breaking of bonds is endergonic. Famous example is water. The splitting of water is said to be endergonic (non-spontaneous) reaction, and thus would require energy (chemical work to be done) in order to happen.

The understanding from chemistry and biology seem to be contradictory to each other.

What is it, I am missing here?

Thanks.

 

[pinball1970]

@jim mcnamara @BillTre and from a pure chemistry perspective @Borek

 

[Borek]

Breaking bonds in only part of the process - some steps can be endergonic, yet the process as a whole can be exergonic.

 

[pinball1970]

TL;DR Summary: Generally it is said that all biological catabolic reactions are exergonic. But in chemistry it is said that breaking of bonds are considered endergonic and bond-forming is exergoic. It looks contradictory. What is the missing link?

Generally it is said that all biological catabolic reactions are exergonic. Famous example is ATP hydrolysis is exergonic. That's why it is called energy currency. Similarly breaking of glucose molecule into pyruvate also releases energy to form ATP.

But in chemistry it is said that breaking of bonds is endergonic. Famous example is water. The splitting of water is said to be endergonic (non-spontaneous) reaction, and thus would require energy (chemical work to be done) in order to happen.

The understanding from chemistry and biology seem to be contradictory to each other.

What is it, I am missing here?

Thanks.

Does the response from Borek give you some guidance?

 

[mktsgm]

With due respects... no. What determines a process or part of process endergonic or exergonic? And how and why chemistry and biology differs. This is what I wanted to know.

Thanks.

 

[morrobay]

These diagrams illustrate what @Borek said: That is the total net effect , bond breaking/bond formation determines if reaction is endo or exothermic. And see the Krebs cycle regarding ATP. IE. The formation of ATP is endothermic. But ATP to ADP is an exothermic reaction because the products are in lower energy state.

 

[Borek]

What determines a process or part of process endergonic or exergonic?

Change in ΔG.

And how and why chemistry and biology differs.

They don't. Whole process consist of breaking bonds (endergonic) and creating new bonds (exergonic), and the total effect is sum of these. Basically you are asking "why the exergonic process that I artificially stopped after the first step is no longer exergonic". Biology and chemistry have nothing to do with that.

 

[mktsgm]

I was confused when I read wikipedia article on ATP Hydrolysis.

[CODE title="ATP Hydrolysis - Wikipedia" highlight="3"]ATP hydrolysis is the catabolic reaction process by which chemical energy that has been stored in the high-energy phosphoanhydride bonds in
adenosine triphosphate (ATP) is released after splitting these bonds,
for example in muscles, by producing work in the form of mechanical energy.
The product is adenosine diphosphate (ADP) and an inorganic phosphate (Pi).
ADP can be further hydrolyzed to give energy, adenosine monophosphate (AMP),
and another inorganic phosphate (Pi).[/CODE]

I now understand that we should look at both catabolic and anabolic reactions in unison and look for the sum energy, if it is endergonic and exergonic.

 

[morrobay]

Yes .Here is my reply to one of your previous threads.