Engineering algae (or plants) to make H 2 Changing Cyanobacteria to make a 5 carbon alcohol Photosynthesis Converts light to chemical energy 6 CO H 2 O + light energy C 6 H 12 O O 2 Photosynthesis 2 sets of rxns in separate parts of chloroplast Photosynthesis 1) Light rxns use light to pump H + use pH to make ATP by chemiosmosis Photosynthesis 1) Light rxns use light to pump H + use pH to make ATP by chemiosmosis 2) Light-independent (dark) rxns use ATP & NADPH from light rxns to make organics Photosynthesis 1) Light rxns use light to pump H + use pH to make ATP by chemiosmosis 2) Light-independent (dark) rxns use ATP & NADPH from light rxns to make organics only link: each provides substrates needed by the other Light Rxns 3 stages 1) Catching a photon (primary photoevent) Light Rxns 3 stages 1) Catching a photon (primary photoevent) 2) ETS Light Rxns 3 stages 1) Catching a photon (primary photoevent) 2) ETS 3) ATP synthesis by chemiosmosis Catching photons photons: particles of energy that travel as waves Energy inversely proportional to wavelength ( ) visible light ranges from nm Catching photons Photons: particles of energy that travel as waves caught by pigments: molecules that absorb light Pigments Can only absorb certain photons Pigments Can only absorb certain photons Photon has exact energy to push an e- to an outer orbital Pigments Can only absorb certain photons Photon has exact energy to push an e- to an outer orbital from ground to excited state Pigments Photon has exact energy to push an e- to an outer orbital from ground to excited state each pigment has an absorption spectrum: it can absorb Pigments Chlorophyll a is most abundant pigment chlorophyll a looks green -> absorbs all but green Reflects green Accessory Pigments absorb which chlorophyll a misses chlorophyll b is an important accessory pigment Accessory Pigments absorb which chlorophyll a misses chlorophyll b is an important accessory pigment others include xanthophylls & carotenoids Accessory Pigments action spectrum shows use of accessory pigments used for photosynthesis Accessory Pigments action spectrum shows use of accessory pigments used for photosynthesis plants use entire visible spectrum absorbed by chlorophyll work best Light Reactions 1) Primary photoevent: pigment absorbs a photon Light Reactions 1) Primary photoevent: pigment absorbs a photon e - is excited -> moves to outer orbital Light Reactions 4 fates for excited e-: 1) returns to ground state emitting heat & longer light = fluorescence Light Reactions 4 fates for excited e - : 1) fluorescence 2) transfer to another molecule Light Reactions 4 fates for excited e - : 1) fluorescence 2) transfer to another molecule 3) Returns to ground state dumping energy as heat 4 fates for excited e - : 1) fluorescence 2) transfer to another molecule 3) Returns to ground state dumping energy as heat 4) energy is transferred by inductive resonance excited e - vibrates and induces adjacent e - to vibrate at same frequency 4 fates for excited e - : 4) energy is transferred by inductive resonance excited e - vibrates and induces adjacent e - to vibrate at same frequency Only energy is transferred 4 fates for excited e - : 4) energy is transferred by inductive resonance excited e - vibrates and induces adjacent e - to vibrate at same frequency Only energy is transferred e - returns to ground state Photosystems Pigments are bound to proteins arranged in thylakoids in photosystems arrays that channel energy absorbed by any pigment to rxn center chlorophylls Photosystems Pigments are bound to proteins arranged in thylakoids in photosystems arrays that channel energy absorbed by any pigment to rxn center chls Need 2500 chlorophyll to make 1 O 2 Photosystems Arrays that channel energy absorbed by any pigment to rxn center chls 2 photosystems : PSI & PSII PSI rxn center chl a dimer absorbs 700 nm = P700 Photosystems Arrays that channel energy absorbed by any pigment to rxn center chls 2 photosystems : PSI & PSII PSI rxn center chl a dimer absorbs 700 nm = P700 PSII rxn center chl a dimer absorbs 680 nm = P680 Photosystems Each may have associated LHC (light harvesting complex) (LHC can diffuse within membrane) PSI has LHCI: ~100 chl a, a few chl b & carotenoids Photosystems Each may have associated LHC (light harvesting complex) (LHC can diffuse within membrane) PSI has LHCI: ~100 chl a, a few chl b & carotenoids PSII has LHCII: ~250 chl a, many chl b & carotenoids Proteins of LHCI & LHCII also differ Photosystems PSI performs cyclic photophosphorylation Absorbs photon & transfers energy to P700 cyclic photophosphorylation Absorbs photon & transfers energy to P700 transfers excited e - from P700 to fd cyclic photophosphorylation Absorbs photon & transfers energy to P700 transfers excited e - from P700 to fd fd returns e - to P700 via PQ, cyt b 6 /f & PC cyclic photophosphorylation Absorbs photon & transfers energy to P700 transfers excited e - from P700 to fd fd returns e - to P700 via PQ, cyt b 6 /f & PC Cyt b 6 /f pumps H + Cyclic Photophosphorylation Transfers excited e - from P700 to fd Fd returns e - to P700 via cyt b 6 -f & PC Cyt b 6 -f pumps H + Use PMF to make ATP Cyclic photophosphorylation first step is from P700 to A 0 (another chlorophyll a) charge separation prevents e - from returning to ground state = true photoreaction Cyclic photophosphorylation first step is from P700 to A 0 (another chlorophyll a) next transfer e - to A 1 (a phylloquinone) next = 3 Fe/S proteins Cyclic photophosphorylation first step is from P700 to A 0 (another chlorophyll a) next transfer e - to A 1 (a phylloquinone) next = 3 Fe/S proteins finally ferredoxin Cyclic photophosphorylation 1)Ferredoxin = branchpoint: in cyclic PS FD reduces PQ Cyclic photophosphorylation 1)Ferredoxin reduces PQ 2)PQH 2 diffuses to cyt b 6 /f 2) PQH2 reduces cyt b 6 and Fe/S, releases H + in lumen since H + came from stroma, transports 2 H + across membrane (Q cycle) Cyclic photophosphorylation 3) Fe/S reduces plastocyanin via cyt f cyt b 6 reduces PQ to form PQ - Cyclic photophosphorylation 4) repeat process, Fe/S reduces plastocyanin via cyt f cyt b 6 reduces PQ - to form PQH2 Cyclic photophosphorylation 4) repeat process, Fe/S reduces plastocyanin via cyt f cyt b 6 reduces PQ - to form PQH2 Pump 4H+ from stroma to lumen at each cycle (per net PQH2) Cyclic photophosphorylation 5) PC (Cu + ) diffuses to PSI, where it reduces an oxidized P700 Cyclic photophosphorylation energetics: light adds its energy to e - -> excited state Eo' P700 = V Eo' P700 * = -1.3 V Cyclic photophosphorylation energetics: light adds its energy to e - -> excited state Eo' P700 = V Eo' P700 * = -1.3 V Eo' fd = V Cyclic photophosphorylation energetics: light adds its energy to e - -> excited state Eo' P700 = V Eo' P700 * = -1.3 V Eo' fd = V Eo' cyt b 6 /f = +0.3V Cyclic photophosphorylation energetics: light adds its energy to e - -> excited state Eo' P700 = V Eo' P700 * = -1.3 V Eo' fd = V Eo' cyt b 6 /f = +0.3V Eo' PC = +0.36V Cyclic photophosphorylation energetics: light adds its energy to e - -> excited state Eo' P700 = V Eo' P700 * = -1.3 V Eo' fd = V Eo' cyt b 6 /f = +0.3V Eo' PC = +0.36V e - left in excited state returns in ground state Cyclic photophosphorylation e - left in excited state returns in ground state Energy pumped H + Cyclic photophosphorylation Limitations Only makes ATP Cyclic photophosphorylation Limitations Only makes ATP Does not supply electrons for biosynthesis = no reducing power Photosystems PSI performs cyclic photophosphorylation Makes ATP but not NADPH: exact mech for PQ reduction unclear, but PQ pumps H+ Photosystem II Evolved to provide reducing power -> added to PSI Photosystem II Evolved to provide reducing power Added to PSI rxn center absorbs 680 nm (cf 700 nm) Photosystem II rxn center absorbs 680 nm (cf 700 nm) can oxidize H 2 O redox potential of P680 + is V (cf V for H 2 O) Photosystem II rxn center absorbs 680 nm (cf 700 nm) can oxidize H 2 O redox potential of P680 + is V (cf V for H 2 O) Use e - from H 2 O to reduce NADP+ (the e - carrier used for catabolic reactions) Photosystem II rxn center absorbs 680 nm (cf 700 nm) can oxidize H 2 O redox potential of P680 + is V (cf V for H 2 O) Use e - from H 2 O to reduce NADP+ (the e - carrier used for catabolic reactions) use NADPH c.f. NADH to prevent cross- contaminating catabolic & anabolic pathways PSI and PSII work together in the Z-scheme - a.k.a. non-cyclic photophosphorylation General idea: redox potential from H 2 O to NADP + is so great that must boost energy of H 2 O e - in 2 steps PSI and PSII work together in the Z-scheme General idea: redox potential from H 2 O to NADP + is so great that must boost energy of H 2 O e - in 2 steps each step uses a photon PSI and PSII work together in the Z-scheme General idea: redox potential from H 2 O to NADP + is so great that must boost energy of H 2 O e - in 2 steps each step uses a photon 2 steps = 2 photosystems PSI and PSII work together in the Z-scheme 1) PSI reduces NADP + PSI and PSII work together in the Z-scheme 1) PSI reduces NADP + e - are replaced by PSII PSI and PSII work together in the Z-scheme 2) PSII gives excited e - to ETS ending at PSI PSI and PSII work together in the Z-scheme 2) PSII gives excited e - to ETS ending at PSI Each e - drives cyt b 6 /f PSI and PSII work together in the Z-scheme 2) PSII gives excited e - to ETS ending at PSI Each e - drives cyt b 6 /f Use PMF to make ATP