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Message: <blockquote data-quote="NextStepTutor_1" data-source="post: 19893297" data-attributes="member: 611996">Hi [USER=891933]@ScrubswithnoSleeves[/USER] -Yes, there are a few reasons why the bonds in ATP are relatively high-energy/unstable. A major one is that the triphosphate unit of ATP carries four negative charges at physiological pH that are in close proximity to each other. The repulsion among these charges can be minimized by hydrolysis. Also, the free phosphate group (Pi, sometimes referred to as orthophosphate) has resonance stabilization, which improves the energetic favorability of ADP + Pi compared to ATP. Additionally, ADP and Pi are more stabilized by hydration than is ATP, because additional negatively charged groups are made available to interact with and bind water following hydrolysis. Finally, ATP hydrolysis is entropically favorable.In terms of how to square this fact with the general principle that bond formation is exergonic and bond breakage is endergonic, a key insight is that this principle is used to compare bonded to non-bonded atoms, not to compare various bonds. Basically, the idea is that bond formation in general is exergonic, but not all bonds are equally exergonic (or equally energetically favorable). Physical elevation might be a good analogy. All mountains are "up" from the reference point of someone at sea level, but some mountains are more "up" than others. Therefore, going from a 10,000-foot mountain to a 5,000-foot mountain is going "down", even if both of those mountains are "up" from the point of view of sea level. In this analogy, "up" or "down" from sea level is like "endergonic"/"exergonic" in the context of bond formation—that's a baseline comparison with the corresponding unbonded atoms. ADP + Pi is like the 10,000-foot mountain, while ATP is like the 5,000-foot mountain.Hope this helps clarify the issue <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite191" alt=":)" title="Smile    :)" loading="lazy" data-shortname=":)" />!</blockquote>

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