Bioenergetics Flashcards
How O2 changed the planet:
- Redox buffers filled (releasing O2 into air)
- Respiration evolved to O2 (more efficient)
- Metal ion availability (solubility linked to redox)
- O2->O3 (shields UV)
- Many species died (O2 is toxic)
O2 Thermodynamics and Kinetics
Thermodynamically - unstable (2e- reduction favorable)
Kinetically - stable (spin-state change required)
H2O/O2 EM7
820mV
NADH/NAD+ EM7
-320mV
Nernst equation
E = E˚ - (RT/nF)ln(red/ox) E = E˚ - 59log(red/ox)
∆G to ∆E conversion
∆G = -nF∆E = n-96.5∆E 100meV = -9.6kJ/mol
Energy to pump proton and ATP synthesis
1 proton = 200meV = -19.2kJ/mol
1 ATP = 50kJ/mol
therefore: 2.5 protons = 48kJ/mol = 1 ATP
Redox Potentials in Photosynthesis
680nm = 1.82eV
PD1/PD1+ = 1.25V Ph/Ph- = -500mV Qa/Qa- = -150mV Tyr-/Tyr = 1.2V Qb/Qb- = -20mV Qb-/QbH2 = -20mV
Energy transfer in photosynthesis
Of 1.82eV from red photon:
- 600mV lost stabilising charge separation
- 150-200meV used to produce free QH2 and other steps in charge accumulation (S0-S1)
a. for every e- transferred, 1H+ is taken from stroma and released to lumen (chemical protons), the energy stored is ~200mV - Energy needed to do water oxidation and quinone reduction is ~820meV (ΔE = -819meV at functional conditions)
- Energy used = 600+200+820 = 1.62eV
a. Remainder: driving force available for water oxidation by the oxidised S4 state and O2 release (~200meV)
Overall reaction in PSII
2H2O + 2PQ -> 2PQH2 + O2
Overall reaction in Cytochrome C Oxidase
4Cytc (Fe2+) + O2 + 4H+ 4Cytc (Fe3+) + 2H2O
Enzyme name for PSII
Water/Plastoquinone photo-oxidoreductase
Enzyme name for Cytc Oxidase
Ferrocytochrome c/oxygen oxidoreductase
1 Cytochrome oxidation (EH)
300mV
1 Oxygen reduction (EH)
800mV