Next Assignment?In lab time Friday March 27 or in class starting March 27 or March 30?•GMO plants?• Herbicide resistance• Pathogen/herbivore resistance• Improving nutrition• Making vaccines, other useful biochems

•Plant/Algal biofuels?

PSI and PSII work together in the “Z-scheme” Light absorbed by PS II makes ATPLight absorbed by PS I makes reducing power

cyclic non-cyclicUltimate e- source None waterO2 released? No yesTerminal e- acceptor None NADP+Form in which energy is ATP ATP &temporarily captured NADPHPhotosystems required PSI PSI & PSII

Z-scheme energetics

PSII Photochemistry1) LHCII absorbs a photon2) energy is transferred to P680

PSII Photochemistry3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptor

PSII Photochemistry3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptorcharge separation traps the electron

PSII Photochemistry4) pheophytin reduces PQA (plastoquinone bound to D2)moves electron away fromP680+ & closer to stroma

PSII Photochemistry

5) PQA reduces PQB (forms PQB- )

PSII Photochemistry6) P680+ acquires another electron , and steps 1-4 are repeated

PSII Photochemistry7) PQA reduces PQB - -> forms PQB2-

PSII Photochemistry8) PQB2- acquires 2 H+ from stroma forms PQH2 (and adds to ∆pH)

PSII Photochemistry9) PQH2 diffuses within bilayer to cyt b6/f- is replaced within D1 by an oxidized PQ

Photolysis: Making Oxygen1) P680+ oxidizes tyrZ ( an amino acid of protein D1)

Photolysis: Making Oxygen2) tyrZ + oxidizes one of the Mn atoms in the OECMn cluster is an e- reservoir

Photolysis: Making Oxygen2) tyrZ + oxidizes one of the Mn atoms in the OECMn cluster is an e- reservoirOnce 4 Mn are oxidized replace e- by stealing them from 2 H2O

Shown experimentally that need 4 flashes/O2

Shown experimentally that need 4 flashes/O2Mn cluster cycles S0 -> S4

Reset to S0 by taking 4 e-

from 2 H2O

Electron transport from PSII to PSI1) PQH2 diffuses to cyt b6/f2) PQH2 reduces cyt b6 and Fe/S, releases H+ in lumen

since H+ came from stroma, transports 2 H+ across membrane (Q cycle)

Electron transport from PSII to PSI3) Fe/S reduces plastocyanin via cyt fcyt b6 reduces PQ to form PQ-

Electron transport from PSII to PSI4) repeat process, Fe/S reduces plastocyanin via cyt fcyt b6 reduces PQ- to form PQH2

Electron transport from PSII to PSI

4) PC (Cu+) diffuses to PSI,

where it reduces an oxidized P700

Electron transport from PSI to Ferredoxin1) LHCI absorbs a photon2) P700* reduces A03) e- transport to ferredoxin via A1 & 3 Fe/S proteins

Electron transport from Ferredoxin to NADP+2 Ferredoxin reduce NADP reductase

Electron transport from Ferredoxin to NADP+2 Ferredoxin reduceNADP reductaseNADP reductase reduces NADP+

Electron transport from Ferredoxin to NADP+2 Ferredoxin reduceNADP reductaseNADP reductase reduces NADP+this also contributes to ∆pH

Overall reaction for the Z-scheme

8 photons + 2 H2O

+ 10 H+stroma + 2 NADP+

= 12 H+lumen + 2 NADPH

+ O2

Chemiosmotic ATP synthesisPMF mainly due to ∆pHis used to make ATP

Chemiosmotic ATP synthesisPMF mainly due to ∆pHis used to make ATP-> very little membrane potential, due to transport of other ions

Chemiosmotic ATP synthesisPMF mainly due to ∆pHis used to make ATP-> very little membrane potential, due to transport of other ionsthylakoid lumen pH is < 5 cf stroma pH is 8

Chemiosmotic ATP synthesisPMF mainly due to ∆pHis used to make ATP-> very little membrane potential, due to transport of other ionsthylakoid lumen pH is < 5 cf stroma pH is 8pH is made by ETS, cyclic photophosphorylation,watersplitting & NADPH synth

Chemiosmotic ATP synthesisStructure of ATP synthaseCF1 head: exposed to stromaCF0 base: Integral membrane protein

a & b2 subunits form stator that immobilizes & F1 subunitsa is also an H+ channelc subunits rotate as H+

pass through & also rotatec, & form a rotor

Binding Change mechanism of ATP synthesisH+ translocation through ATP synthase alters affinity of active site for ATP

Binding Change mechanism of ATP synthesisH+ translocation through ATP synthase alters affinity of active site for ATP

ADP + Pi bind to subunitthen spontaneously form ATP

Binding Change mechanism of ATP synthesisH+ translocation through ATP synthase alters affinity of active site for ATP

ADP + Pi bind to subunitthen spontaneously form ATP

∆G for ADP + Pi = ATP is ~0role of H+ translocation is toforce enzyme to release ATP!

Binding Change mechanism of ATP synthesis1) H+ translocation alters affinity of active site for ATP2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi

due to interaction with the subunit

Binding Change mechanism of ATP synthesis1) H+ translocation alters affinity of active site for ATP2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi

3) ATP is synthesized by rotational catalysisg subunit rotates as H+ pass through Fo, forces each active site to sequentially adopt the 3 conformations

Evidence supporting chemiosmosis1) ionophores (uncouplers)2) can synthesize ATP if create ∆pH

a) Jagendorf expt: soak cp in pH 4 in dark, make ATP when transfer to pH 8