Why phosphate bond is necessary to provide energy in the form of ATP ? Why not other bonds? and Bonded Warehouse 2005 2006

Why phosphate bond is necessary to provide energy in the form of ATP ? Why not other bonds?

Why only phosphate bond is there in the cell to provide energy ? Why not the other bonds ? why espp. phosphate bond in PO4 in ATP provides energy ? There are so many elements and ions in our cells then why only phosphate is selected for to provide energy ? Why not others ? Why not HYDROGEN bonds ?


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Answer by Steph
Ah, that requires an explanation of cellular energetics.

You see, what makes a molecule energetic is the change in hydrolysis for hydrolysis of that molecule. What does that mean? It means that the released molecules are more "free". The triphosphate bond in ATP has several factors to destabilize it, for example:
-Electrostatic repulsion between the negative charges
-Inhibition of rotation of the phosphodiesterbond in comparison to a free O- ion
-Inhibition of resonance - While negative charges and double bonds can alternate in ATP, they can do so so much more in a free anorganic phosphate. Anorganic phosphate(PO4) has one double bond, but this double bond is shared between all oxygen atoms. This increases entropy and adds for more flexibility and mobility, so is energetically beneficient to achieve.

So, what this means is that it's more profitable for ATP to not be ATP but to be ADP and free anorganic phosphate, or even better, AMP and two free anorganic phosphates. This will raise the question, "why doesn't ATP just dissolve?" which is answered by the activation energy of the hydrolysis reaction. To hydrolyze ATP, you need a certain energetic input to bring it to the "transition state". This might seem uncomfortable, requiring the input of energy before being able to release it, but this allows for regulated usage of ATP.

Other bonds simply do not have the same kind of change in energy. There are, however, more energetic bonds than the phosphodiester bonds in ATP - However, ADP can accept energetic groups from those molecules and pass them off to other, lower energetic molecules(Like glucose, to begin glycolysis). ATP is an intermediary on the energetic scale, meaning that it can give and accept energetic bonds.

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