4 - Chemiosmosis

• Why is it relevant to study ATP synthesis?

  ATP is the currency for energy exchange in all living systems, and it plays a central role in energy metabolism
• How much energy does the release of inorganic phosphate from ATP release?

  -30 kJmol
• Where does this energy come from?

  The high energy phospho-anhydride bond
• What components are necessary for chemiosmosis?

  - Membrane impermeable to H+

  - Electron transport chain to pump H+ against a concentration gradient
• What can the electrochemical gradient be used for?

  - Synthesis of ATP via ATP synthase

  - Transport of a molecule against its concentration gradient via Antiporters and Symporters

  - Rotation of bacterial flagella
• What can ion electrochemical gradients be defined as?

  Quantifiable stores of potential energy
• How can the chemical work to move a solute across a membrane be calculated?

  DeltaUS = RTln(Si/So)
• Describe this equation


  Chemical potential gradient = gas constant X temperature X log of solute inside over solute outside
• What is the gas constant?

  8.314 J K-1 mol-1
• How can we calculate the electrical work done when moving ions across a membrane?

  ZxFxdeltaE
• Describe this equation


  Charge of ion x faraday constant x membrane voltage difference or chemical gradient relative to outside
• What is the faraday constant?

  96500 J V-1 mol -1
• Therefore how do we calculate the electrochemical potential?

  Chemical potential gradient + electrical potential gradient in J mol-1
• What does chemiosmosis describe?

  The coupling of electrochemical potential energy stored across membranes with cellular work
• How can we experimentally demonstrate the energy in chemiosmotic coupling of the proton circuit at ATP synthesis?

  Use an uncoupled such as DNP to make leaky membranes, ATP synthesis is inhibited so energy is released as heat that can be measured
• What is the electron transport chain?

  A series of membrane proteins which can be oxidised and reduced
• What is the redox potential?

  The more negative the value, the lower affinity the reduced form has for electrons, so it will donate them
• What happens to the redox potential as you move down the electron transport chain?

  It becomes more positive
• What is a common protein for H+ translocation?

  Ubiquinone, which is reduced by 2 electrons to ubiquinol. When it is oxidised, it can release the protons on the other side of membrane
• What do electron transport chains end in?

  The terminal electron acceptor
• What is a complex?


  Groups of redox couples
• What aspects of ATP synthesis are evolutionarily conserved?

  1) proton pumps to establish H+ electrochemical gradient

  2) Pumps and electron transport chains

  3) H+ pumped from negative side to positive side

  4) Membranes impermeable to H+

  5) H+ translocation via ATP synthesise, so electrochemical energy is stored in phosphoanhydride bond
• Describe the structure of mitochondria

  - Outer membrane permeable to solutes, impermeable inner membrane

  - Surface area of inner membrane enhanced via Cristian

  - Matrix is approx -200 mV and is more negative
• How much ATP do we turnover in a day?

  65kg day-1