Biology: ATP and Energy Transfer

ATP: Energy Currency of the Cell

• ATP (Adenosine Triphosphate) is the energy currency of the cell. It is used for cellular work such as chemical, transport, and mechanical work.
• ATP is composed of:
  • Adenosine
  • Ribose (a sugar)
  • Three phosphate groups
• The bonds between the phosphate groups contain lots of energy and can be broken by hydrolysis to release energy.
• When the terminal phosphate bond is broken, the energy is released, and ATP becomes ADP (Adenosine Diphosphate).
• The cell converts ADP to ATP by adding a phosphate group through phosphorylation.

Redox Reactions: Oxidation and Reduction

• Redox reactions involve the transfer of electrons between reactants.
• Oxidation is the loss of electrons from a substance.
• Reduction is the gain of electrons by a substance.
• Redox reactions release energy that is ultimately used to synthesize ATP.

Energy Coupling: The Power of ATP

• Energy coupling is the use of an exergonic process to drive an endergonic process.
• ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to another molecule.
• This phosphate transfer increases said molecule's energy level.
• Cells use energy coupling to perform various tasks, including:
  • Transport: ATP phosphorylates transport proteins, moving solutes across membranes.
  • Mechanical: ATP binds to motor proteins to fuel movement.
  • Chemical: ATP provides energy for chemical reactions to occur.

Overview of ATP Production

• Living organisms require energy from the environment.
• Energy flows into an ecosystem as sunlight and leaves as heat.
• Photosynthesis in chloroplasts generates organic molecules and oxygen.
• The organic molecules fuel cellular respiration, a process that occurs in mitochondria.
• Cellular respiration uses oxygen and organic molecules to produce ATP.
• ATP is used to power most cellular work.