How does interconversion between ADP and ATP release energy for cellular respiration?

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CarlBane
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I have read in my text about the bond breaking and bond forming of ADP and Pi to form ATP. How does this release energy for the body to use in reaction? Isn't the endothermic and exothermic bond enthalpy change the same? I also read that upon hydrolysing ATP to ADP, ADP & Pi forms bonds with water to release energy which is fair enough. However, to form ATP again don't you have to overcome this bond between water and ADP/Pi again to form ATP. Doesn't this leave the cell with no overall net energy outcome to be used? or does the chemiosis cycle/ETC chain provide this energy by setting up an electrochemical gradient for H+ ions to move through ATPase in order to convert kinetic energy to chemical energy?

If any ideas please respond, I'm in deep thought.
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Mini101
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(Original post by CarlBane)
I have read in my text about the bond breaking and bond forming of ADP and Pi to form ATP. How does this release energy for the body to use in reaction? Isn't the endothermic and exothermic bond enthalpy change the same? I also read that upon hydrolysing ATP to ADP, ADP & Pi forms bonds with water to release energy which is fair enough. However, to form ATP again don't you have to overcome this bond between water and ADP/Pi again to form ATP. Doesn't this leave the cell with no overall net energy outcome to be used? or does the chemiosis cycle/ETC chain provide this energy by setting up an electrochemical gradient for H+ ions to move through ATPase in order to convert kinetic energy to chemical energy?

If any ideas please respond, I'm in deep thought.
First and foremost, ADP + Pi gives ATP and this is a reversible reaction. In general chemistry terms, for a bond to break, energy is required whereas when a bond forms, energy is released. In the reaction where ATP is converted to ADP and Pi, a bond is broken and this might suggest that you require energy, however, you need to consider the overall enthalpy change of the reaction and in that case the reaction actually, overall, causes energy to be released. Therefore, when ATP is broken down, a hydrolysis reaction takes place which means that water is an essential part of the reaction. this also means that in the reverse reaction, ie: ADP+Pi to ATP, water is given out during the reaction, hence being a condensation reaction.
When respiration takes place, (glycolysis and/or kreb's cycle) reduced NAD, reduced FAD form which get oxidised in the ETC and hence cause H+ ions to be pumped out, resulting in an electrochemical gradient. As the H+ ions move down the electrochemical gradient, through ATP synthase, the energy released is used to produce ATP from ADP and Pi and simultaneously, 2H+ ---> H2 + 1/2O2 ----> H2O (condensation reaction).
I don't know if any of this is helpful to you or not (I hope it is in some way), however I tried my best... if you still have any questions... just ask, I or someone else will try to answer them.
If I've made some mistake somewhere please let me know...
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