malikhind

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Hi,

I'm very curious as to what determines how much energy is in a given bond, specifically, why is the P-O bond in metabolic energy sources (ATP, GTP, etc...) so good compared to other molecules? I probably don't need to know this but I would really love to understand this and cannot find any good online resources that answer this question.

Thank you.
 

NextStepTutor_2

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Hi malikhind,

When considering the energy released by breaking a bond, it is best to consider the energy difference between the starting product (e.g. ATP) and the end product (e.g. ADP + Pi). [Remember that more stable species have lower energy.] Reasons why removing a phosphate from ATP is so favorable include:

1 - The products (ADP + Pi) have less electrostatic repulsion between positively charged phosphates and between negatively charged oxygen atoms.
2 - Resonance stabilization of the products is greater than that of the reactants.
3 - There is greater solvation of ADP and Pi than there is of ATP.
4 - The entropy (disorder) of two molecules - ADP + Pi - is greater than one molecule of ATP.

I hope this helps!

Alicia
 

orgoman22

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Hi,

I'm very curious as to what determines how much energy is in a given bond, specifically, why is the P-O bond in metabolic energy sources (ATP, GTP, etc...) so good compared to other molecules? I probably don't need to know this but I would really love to understand this and cannot find any good online resources that answer this question.

Thank you.
You have asked an interesting question. Many times a molecule is reactive for reasons such as instability. However, another reason looms. Perhaps a molecule can attain greater stability if it decomposed, or rearranged or even reacted with other functionalities. In the case of ATP, we have two main reasons for its high reactivity. One is that by reacting we remove some of the repulsion forces between the O atoms in the molecule. Another is that the Phosphate group that leaves attains resonance stabilization. Many molecules other than ATP are high energy and very reactive. A molecule called octanitrocubane is highly reactive. The reason is very different. If a GAS can be released from a molecule, this is another HUGE DRIVING FORCE!!! Your question is also explained with nice resonance drawings in my Bio notes.

Hope this helps.

Dr. Romano
 
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