ATP

• exergonic reactions require a small amount of activation energy in order to proceed. Energy to power such reactions (both exergonic & endergonic) comes from an energy-supplying molecule called adenosine triphosphate, or ATP.
• ATP is a 


  small, relatively simple molecule, but within some of its bonds, it contains the potential for a quick burst of energy that can be harnessed to perform cellular work. The cells' primary energy currency. ATP powers the majority of energy-requiring cellular reactions.
• ATP


  Adenosine bound to three phosphate groups
• Adenosine


  • Nitrogenous base adenine
  • Five-carbon sugar ribose
• Not all bonds within the ATP molecule exist in a particularly high-energy state
• Phosphoanhydride bonds


  High-energy bonds that link the phosphates
• The high-energy bonds are between the second and third (or beta and gamma) phosphate groups and between the first and second phosphate groups
• High-energy bonds


  When broken, release sufficient energy to power a variety of cellular reactions and processes
• Breaking the high-energy bonds


  Produces adenosine diphosphate (ADP) and one inorganic phosphate group (Pi)
• The products of the bond breaking (ADP and Pi) have considerably lower free energy than the reactants (ATP and a water molecule)
• ATP hydrolysis


  1. Uses a water molecule

  2. Is a hydrolysis reaction
• ATP to ADP hydrolysis is reversible. The reverse reaction regenerates ATP from ADP + Pi. ATP hydrolysis releases energy, ATP regeneration must require an input of free energy. ATP formation:

  ADP+Pi+free energy→ATP+H2O
• ∆G for the hydrolysis of one ATP mole into ADP and Pi is −7.3 kcal/mole (−30.5 kJ/mol). Since this calculation is true under standard conditions, one would expect a different value exists under cellular conditions. In fact, the ∆G for one ATP mole's hydrolysis in a living cell is almost double the value at standard conditions: –14 kcal/mol (−57 kJ/mol).
• ATP is a 


  highly unstable molecule. Unless quickly used to perform work, ATP spontaneously dissociates into ADP + Pi, and the free energy released during this process is lost as heat.
• Energy coupling


  Cells couple the ATP hydrolysis' exergonic reaction allowing them to proceed.
• Example of energy coupling 


  Transmembrane ion pump that is extremely important for cellular function. This sodium-potassium pump (Na+/K+ pump) drives sodium out of the cell and potassium into the cell. energy released from the ATP hydrolysis couples with the energy required to power the pump and transport Na+ and K+ ions. ATP performs cellular work using this basic form of energy coupling through phosphorylation.
• Cellular respiration


  1. Glucose molecule breaks down in glycolysis

  2. ATP phosphorylates glucose, creating high-energy but unstable intermediate

  3. Phosphorylated glucose converts to phosphorylated fructose

  4. Fructose is necessary intermediate for glycolysis to move forward
• ATP hydrolysis' exergonic reaction


  Couples with the endergonic reaction of converting glucose into a phosphorylated intermediate
• Energy released by breaking a phosphate bond within ATP was used for phosphorylating another molecule, creating an unstable intermediate and powering an important conformational change
• Conformational change


  Certain molecules must alter slightly in their conformation to become substrates for the next step in the reaction series