ATP is so interesting that it could have a whole community dedicated to it!

During middle school and high school in biology classes ATP would be referred to as the "energy currency of the cell", but at that time the concept of 'energy' was still so abstract to me. And I think it was the same for my teachers too, because whenever I tried to ask them what it actually meant that ATP had 'energy' in it they were also unable to provide me a concrete response. Best case scenario they would explain that energy is the ability to do work, but I was never given a more specific molecular-level description of what it meant.

It wasn't until the second or third year of biochem in college that it finally clicked. And it is thanks to this kind of work, in which the precise mechanical details of how the hydrolysis of ATP or the phosphorylation of ADP is coupled to the structural dynamics of a protein. With this type of work I could finally follow the microscopic steps that are responsible for these "energy" conversions, and to finally associate each individual step to the "energy change" that can be calculated using electrodynamics and quantum theory. I would put an understanding of "how ATP is the energy currency of the cell" on the list of my favorite fundamental concepts.