7 -

• System


  Our interest
• Surroundings


  The rest of the universe
• Gibbs free energy

  Tells us if a change to our system will happen spontaneously or not
• dG

  Change in free energy
• ΔH


  Change in enthalpy
• ΔS


  Change in entropy
• T


  Temperature in Kelvin
• Mass action ratio


  q = [C][D]/[A][B]
• Mass action ratio


  • F-1,6-bP ⇌ G3P + DHP
• ΔG⁰


  Standard Free Energy
• R


  Gas constant
• T


  Absolute temperature
• q


  Mass action ratio
• ΔG⁰ is the change in Free Energy when concentration of all reactants and products are 1M at 25°C, 1 atm.
• ΔG⁰' is the Standard Free Energy at pH 7 at 25°C and 1 atm
• ΔG depends on the nature of the reaction and the concentrations
• If ΔG = 0


  No free energy change takes place, the system is at equilibrium
• Rate up


  Rate down
• Number of cars in


  Number of cars out
• Rate of degradation


  Rate of formation of F-1,6-bP
• The equilibrium constant is related to the standard free energy in a logarithmic manner
• R=8.31x10^-3 kJ mol^-1 K^-1
• T=298 K
• Relationship between ΔG⁰' and Keq


  • ΔG⁰' = -5.7 kJ/mol, Keq = 10
  • ΔG⁰' = -11.5 kJ/mol, Keq = 100
  • ΔG⁰' = -17.3 kJ/mol, Keq = 1000
• Relatively small changes in ΔG⁰' can lead to big changes in Keq
• Conversion of dihydroxyacetone-phosphate to glyceraldehyde-3-phosphate


  [G3P]/[DHAP] = 0.0475 at equilibrium at 25°C
• In vivo [DHAP] = 2 x 10^-4 M and [G3P] = 3 x 10^-6 M
• ATP is the main energy carrier in the cell
• Pi


  Inorganic phosphate
• Adenylate Kinase interconverts ATP, ADP and AMP


  ATP + AMP ⇌ 2 ADP
• In the body more energy is released as the reaction is not at equilibrium
• A cheetah running 110 km/h uses 55g ATP/s
• A cheetah weighs 20-70 kg
• A 10 s sprint uses 0.55 kg ATP or 3% of body weight for a small cheetah
• Humans apparently need about 70 kg ATP/day
• Glucose + Pi ⇌ Glucose-6-phosphate + H2O


  ΔG⁰' = +14.0 kJ/mol, Keq = 3.5 x 10^-3
• ATP + H2O ⇌ ADP + Pi


  ΔG⁰' = -30.5 kJ/mol
• Glucose + ATP ⇌ Glucose-6-phosphate + ADP


  ΔG⁰' = -16.5 kJ/mol, Keq = 8.0 x 10^2
• Coupling to ATP shifts the equilibrium 5 orders of magnitude
• This only works because Pi is a shared intermediate