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Figure 52. The ATP-ADP Cycle
Source: https://cdn.thinglink.me/api/image/590898944758775809/1240/10/scaletowidth
COUPLED REACTIONS
The instability of ATP is the very feature that makes it an effecve energy
carrier, keeping it from being an energy storage molecule. Unless quickly used
to perform work, ATP spontaneously dissociates into ADP + Pi, and the free
energy released during this process is lost as heat. To harness the energy within
the bonds of ATP, cells use a strategy called energy coupling.
Several metabolic reacons require energy. Energy can be obtained
when a reacon that requires energy, such as building a protein takes place in
the vicinity of a reacon that gives up energy, such as ATP breakdown. A coupled
reacon brings them together in such a way that the energy-releasing or
exergonic reacon can power the energy-requiring or endergonic reacon.
Because almost all chemical reacons in cells require less energy than what ATP
breakdown produces, ATP is able to drive many cellular acvies, producing heat
as a by-product.
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