The importance of ATP

• Basic facts about energy:

  • Energy cannot be created or destroyed
  • Chemical energy is contained within food substances
  • Energy may be converted from one form to another
  • Green plants can convert light energy into chemical energy
  • All living organisms can convert chemical energy to other energy forms
• Metabolism has two parts: catabolism and anabolism

  • Both types of metabolic process require energy
  • In every cell, hundreds or even thousands of different chemical reactions take place, all of which need energy
  • Adenosine triphosphate (ATP) acts as an energy carrier in all living cells and is used to provide the energy needed for nearly all chemical reactions
  • ATP is sometimes referred to as the 'universal energy currency’ in living organisms
• Energy is required to combine ADP and phosphate to form ATP, which is an endergonic reaction where energy is stored in the molecule

  • The bond between the phosphate groups is formed in a condensation reaction
  • Energy is released when ATP is broken down to ADP and phosphate, which is an exergonic reaction
  • ATP is broken by a hydrolysis reaction, linked to energy-requiring reactions like active transport, muscle contraction, and synthesis of organic chemicals
• ATP is produced in two sets of reactions:

  • Photosynthesis: Light energy is transduced to chemical energy in ATP
  • Respiration: Chemical energy from glucose is transduced to chemical energy in ATP
• In both respiration and photosynthesis:

  • ATP is produced by an enzyme called ATP synthetase or ATP synthase, located in the internal membranes of mitochondria and chloroplasts
  • ATP is broken down by an enzyme called ATPase, found wherever energy needs to be released in a cell
• Advantages of using ATP as an energy carrier:

  • Only one enzyme is needed to break down ATP and release energy
  • Only one enzyme is needed to combine ADP and Pi to store energy
  • A small amount of energy (30.5 kJ mol-1) is released when ATP is hydrolyzed, so less energy is wasted
  • Energy release is controlled – it is released where and when it is needed