Energy Conversions

• Phosphorylation


  Makes molecules less stable
• Adenosine triphosphate (ATP)


  High energy molecule that functions as an immediate power source for cells
• One molecule of ATP contains three covalently bonded phosphate groups which store potential energy in their bonds
• Phosphorylation


  Makes molecules less stable and hence ATP is a readily reactive molecule that contains high energy bonds
• ATP hydrolysis


  1. ATP is hydrolysed (to form ADP + Pi)

  2. The energy stored in the terminal phosphate bond is released for use by the cell
• ATP


  • Functions as the energy currency of the cell by releasing energy when hydrolysed to ADP (powers cell metabolism)
  • May transfer the released phosphate group to other organic molecules, rendering them less stable and more reactive
• ATP synthesis


  1. ATP is synthesised from ADP using energy derived from solar energy (photosynthesis converts light energy into chemical energy that is stored as ATP)

  2. Oxidative processes (cell respiration breaks down organic molecules to release chemical energy that is stored as ATP)
• Cell respiration


  The controlled release of energy from organic compounds to produce ATP
• Anaerobic respiration


  • Involves the incomplete breakdown of organic molecules for a small yield of ATP (no oxygen required)
• Aerobic respiration


  • Involves the complete breakdown of organic molecules for a larger yield of ATP (oxygen is required)
• The breakdown of organic molecules occurs via a number of linked processes that involve a number of discrete steps</b>
• By staggering the breakdown, the energy requirements are reduced (activation energy can be divided across several steps)
• The released energy is not lost - it is transferred to activated carrier molecules via redox reactions (oxidation / reduction)
• Redox reactions


  Involve the reduction of one chemical species and the oxidation of another
• Redox reactions typically involve the transfer of


  • Electrons
  • Hydrogen
  • Oxygen
• Reduction


  The gain of electrons / hydrogen or the loss of oxygen
• Oxidation


  The loss of electrons / hydrogen or the gain of oxygen
• Redox reactions can be summarised using mnemonics like OIL RIG, LEO goes GER, and ELMO
• NAD+ and FAD


  Hydrogen carriers that transport electrons and hydrogen ions to the cristae of the mitochondria
• The cristae is the site of the electron transport chain, which uses the energy transferred by the carriers to synthesize ATP
• Aerobic respiration can generate ATP from hydrogen carriers, as it requires oxygen to function
• Aerobic respiration unlocks more of the energy stored in the organic molecules and produces more ATP