What needs to happen to ATP in order to get ADP?
ATP becomes ADP as it loses one phosphate group when the molecule is used as energy.
ATP (adenosine triphosphate) is an energy storage molecule, used mainly for intracellular energy transfer and is comprised of an adenosine (adenine + ribose sugar molecule) molecule and three phosphate groups. It is synthesized within the mitochondria and usually, when a catabolic reaction occurs (e.g. aerobic respiration) it stores this energy to be "used for later" if you will.
When ATP is used for its energy, it loses one of its phosphate groups and becomes ADP (adenosine diphosphate). When this reaction occurs, energy is released. We can summarise this reaction through a simple word equation:
#"ADP" -> "ADP" + "P"(i) #