Wavefunction had an interesting post about ATP and bond energies. http://wavefunction.fieldofscience.com/2010/09/does-bond-cleavage-require-or-release.html. Like most of his posts, it got me to thinking, particularly about a lot of the blarney written about ATP.
Have you ever set a sugar cube on fire using a match? It burns quite nicely. One mole of glucose (180 grams) produces 3,000 kiloJoules/mole when completely oxidized to carbon dioxide and water (this is why sugars are called carbohydrates). Aerobic metabolism of glucose produces 38 moles of ATP, which when hydrolyzed each produce 25 kiloJoules. 38 * 25 = 950 kiloJoules. Not very efficient. Each ATP is worth a rather piddling 25 kiloJoules. That’s exactly the point. If we burned sugar with maximum efficiency, we’d ignite. Getting 38 moles of ATP from a mole of glucose lets the body produce energy in various places on demand in bitesized pieces without burning up.
Even this is too much sometimes. Red blood cells, sitting in the richest oxygen environment of all (arterial blood) use ANAEROBIC metabolism, despite its inefficiency. Actaully they use anaerobic metabolism because of its inefficiency. Like a drunk in a bar, they’d be destroyed if they used all that’s in front of them.