Written by Prerak Juthani (PEACE Advisor)
a) Because the molecule is degraded into its constituent elements, and this process releases energy.
b) High energy phosphate bond is cleaved – which releases energy.
c) By releasing one phosphate group, you decrease the negative/negative interactions, which stabilizes the molecule and releases energy.
d) Because ATP is powerhouse of the cell.
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More specifically, the thing that one needs to remember is that breaking bonds TAKES energy and creating bones RELEASES energy. The common misconception is that the hydrolysis of ATP generates energy because it breaks a high energy phosphate bond. This is incorrect because BREAKING ANY bone REQUIRES energy, which is the main reason that B is incorrect.
So what is the true reason then? Well, scientifically, speaking, the main reason is that the bonds that are FORMED from the hydrolysis of ATP (which usually involves water coming in between the beta and gamma phosphates and binding to the gamma phosphate - catalyzing its release from the molecule) release more energy than is needed to BREAK the bonds in the first place. Thus, the overall enthalpy is negative (as is the delta G since entropy is also increasing).
HOWEVER, another way to think about the reason why the delta G is negative is to think about the reactants and the products. If the products are more stable than the reactants, then the delta G will be negative because the reaction will proceed spontaneously (since we all want things to be stable as possible). Thus, in this case, the hydrolysis of ATP is going to release energy because the product, which is ADP is more stable due to the lack of repulsive negative charges (ATP has three negatively charged oxygens right next to one another, whereas ADP only has two). Thus, the correct answer is C.