Hydrolysis

• ATP has three phosphate groups. It can react with a molecule of water to break up into a phosphate group and a molecule of adenosine diphosphate (ADP), which is more stable and therefore lower in energy. This is a kind of hydrolysis or "water-splitting" reaction, since a molecule of water is broken up in the process. The difference in energy between ATP and the products is releases can be harnessed by proteins in your cell to drive processes that would not take place without an input of energy.
  
  

P-Type ATPases

• P-type ATPases are a family of proteins that transport ions across membranes using the same basic mechanism. All of them take a phosphate group from ATP, changing the shape of the protein in a way that causes it to carry the ions across the membrane. Important examples include calcium pumps, which serve to keep calcium concentration low inside your cells, and Na+K+ ATPases, which transport sodium ions out of your cells and pump potassium ions in. This process is extremely important for maintaining the solute concentration inside your cells with respect to the surrounding fluid; it's also vital for neuron function. While you are resting, sodium-potassium pumps accounts for an amazing 25 percent of your total energy consumption.
  
  

Biosynthesis

• Your cells need to synthesize molecules like amino acids, proteins and nucleotides; these processes all require energy. To form fatty acids, for example, cells use ATP to drive the formation of a type of structure called a thiol ester. Amino acids are also "activated" using ATP before being coupled to a type of molecule called a tRNA, which later couples with a matching sequence in a messenger RNA transcript as part of protein synthesis.
  
  

Muscle Contraction

• Whenever you breathe, move, talk or walk, you're using your muscles. Even when you're sitting still, the muscle of your heart is working. Consequently, muscle contraction is a very important energy expenditure inside your body. When calcium is released from the sarcoplasmic reticulum inside a muscle fiber, it binds to a protein called troponin, altering the structure of another protein so binding sites on a protein called myosin become exposed. The myosin heads bind to so-called "thin filaments," altering its configuration so it can now bind ATP. The ATP loses a phosphate group to become ADP, releasing the energy needed for the myosin head to "walk" down the thin filament. Myosin filaments pull thin filaments like people yanking on a rope, hauling it so the muscle fiber begins to contract.