ATP

• Adenosine triphosphate (ATP) is a nucleotide derivative formed from the nucleotide base adenine, a ribose sugar, and 3 phosphate groups. Energy is stored in high energy bonds between the phosphate groups.
• Hydrolysis of ATP: when energy is needed, ATP is broken down into adenosine diphosphate (ADP) and an inorganic phosphate (Pi). This is catalysed by the enzyme ATP hydrolase.
• ATP hydrolysis can be coupled to energy-requiring reactions within cells.
• The inorganic phosphate released can be used to phosphorylate other compounds, often making them more reactive. (Phosphorylation)
• Phosphorylation: a reaction in which a phosphate group is added to another compound.
• Condensation of ATP: ATP is resynthesised by the condensation of ADP and Pi. This is catalysed by the enzyme ATP synthase during photosynthesis or respiration.
• ATP as energy source

  • hydrolysis of ATP releases small amounts of energy: less energy is lost as heat so less danger of thermal death
  • phosphorylates other compounds, making them more reactive
  • releases energy instantaneously, so energy is readily available
  • can be rapidly re-synthesised
  • does not leave cells