PHOTOSYNTHESISPHOTOSYNTHESISTHE LIGHT REACTIONTHE LIGHT REACTION

ATMOSPHERIC COATMOSPHERIC CO22 IS “FIXED” BY IS “FIXED” BY PLANTS AND CYANOBACTERIAPLANTS AND CYANOBACTERIA

A LIGHT-DRIVEN PROCESSA LIGHT-DRIVEN PROCESS THE CARBON BECOMES AVAILABLE AS CARBO-THE CARBON BECOMES AVAILABLE AS CARBO-

HYDRATE ( CHHYDRATE ( CH22O )O )

THE OVERALL REACTION IS:THE OVERALL REACTION IS:

COCO2 2 + H + H22O O (CH (CH22O) + OO) + O22

COCO22 IS REDUCED IS REDUCED

HH22O IS OXIDIZEDO IS OXIDIZED

THERE ARE TWO PHASES IN THERE ARE TWO PHASES IN PHOTOSYNTHESISPHOTOSYNTHESIS

THE “LIGHT REACTION”THE “LIGHT REACTION” HH22O IS SPLIT O IS SPLIT

2 H2 H22O O O O22 + 4 [H + 4 [H]] NADPH AND ATP ARE GENERATEDNADPH AND ATP ARE GENERATED

THE “DARK REACTION”THE “DARK REACTION” NADPH AND ATP FROM THE LIGHT REACTION DRIVES CHNADPH AND ATP FROM THE LIGHT REACTION DRIVES CH22O O

PRODUCTION FROM COPRODUCTION FROM CO22 AND [H AND [H] :] :

4 [H4 [H] + CO] + CO22 (CH (CH22O) + HO) + H22 OO

IT’S REALLY A LIGHT-INDEPENDENT REACTIONIT’S REALLY A LIGHT-INDEPENDENT REACTION YOU HAVE ALREADY STUDIED ITYOU HAVE ALREADY STUDIED IT

THE “CALVIN CYCLE”THE “CALVIN CYCLE”

IN-CLASS QUESTIONIN-CLASS QUESTION

HH221818O IS ADDED TO A SUSPENSION OF O IS ADDED TO A SUSPENSION OF

CHLOROPLASTS CAPABLE OF PHOTOSYNTHESIS. CHLOROPLASTS CAPABLE OF PHOTOSYNTHESIS. WHERE DOES THE LABEL APPEAR?WHERE DOES THE LABEL APPEAR?

PHOTOSYNTHESIS OCCURS IN PHOTOSYNTHESIS OCCURS IN CHLOROPLASTSCHLOROPLASTS

CHLOROPLASTS CONTAIN:CHLOROPLASTS CONTAIN: AN OUTER MEMBRANEAN OUTER MEMBRANE

HIGH PERMEABILITYHIGH PERMEABILITY AN INNER MEMBRANEAN INNER MEMBRANE

NEARLY IMPERMEABLENEARLY IMPERMEABLE THE STROMATHE STROMA

AQUEOUSAQUEOUS CONTAINS ENZYMES, DNA, RNA, RIBOSOMESCONTAINS ENZYMES, DNA, RNA, RIBOSOMES

THE “THYLAKOID”THE “THYLAKOID” A MEMBRANEOUS COMPARTMENTA MEMBRANEOUS COMPARTMENT

DERIVED FROM INVAGINATIONS OF INNER MEMBRANEDERIVED FROM INVAGINATIONS OF INNER MEMBRANE A SINGLE HIGHLY-FOLDED VESICLEA SINGLE HIGHLY-FOLDED VESICLE ““GRANA” : DISK-LIKE SACSGRANA” : DISK-LIKE SACS GRANA ARE CONNECTED BY “STROMAL LAMELLAE”GRANA ARE CONNECTED BY “STROMAL LAMELLAE”

CHLOROPLASTSCHLOROPLASTS

STRUCTURE IS VERY SIMILAR TO MITOCHONDRIASTRUCTURE IS VERY SIMILAR TO MITOCHONDRIA PROBABLY EVOLVED FROM A CYANOBACTERIUM PROBABLY EVOLVED FROM A CYANOBACTERIUM

INCORPORATED INTO A NON-PHOTOSYNTHETIC INCORPORATED INTO A NON-PHOTOSYNTHETIC EUKARYOTE (SYMBIOSIS)EUKARYOTE (SYMBIOSIS)

IN EUKARYOTES, THE LIGHT REACTION OCCURS IN IN EUKARYOTES, THE LIGHT REACTION OCCURS IN THYLAKOID MEMBRANETHYLAKOID MEMBRANE

IN PROKARYOTES, THE LIGHT REACTION OCCURS IN PROKARYOTES, THE LIGHT REACTION OCCURS IN:IN: INNER (PLASMA) MEMBRANEINNER (PLASMA) MEMBRANE IN “CHROMATOPHORES”IN “CHROMATOPHORES”

INVAGINATIONS OF INNER MEMBRANEINVAGINATIONS OF INNER MEMBRANE

IN EUKARYOTES, THE DARK REACTION OCCURS IN IN EUKARYOTES, THE DARK REACTION OCCURS IN THE STROMATHE STROMA

CHLOROPHYLL IS THE MAJOR CHLOROPHYLL IS THE MAJOR PHOTORECEPTOR IN PHOTOSYNTHESISPHOTORECEPTOR IN PHOTOSYNTHESIS

A CYCLIC TETRAPYRROLE, LIKE HEME, BUT:A CYCLIC TETRAPYRROLE, LIKE HEME, BUT: HAS A CENTRAL MgHAS A CENTRAL Mg2+2+ ION ION A CYCLOPENTANONE RING (RING V) IS FUSED TO A CYCLOPENTANONE RING (RING V) IS FUSED TO

PYRROLE RING IIIPYRROLE RING III PARTIAL REDUCTION OF RING IVPARTIAL REDUCTION OF RING IV

IN EUKARYOTES AND CYANOBACTERIAIN EUKARYOTES AND CYANOBACTERIA CHLOROPHYLL aCHLOROPHYLL a CHLOROPHYLL bCHLOROPHYLL b

OR IN RINGS II AND IVOR IN RINGS II AND IV IN PHOTOSYNTHETIC BACTERIAIN PHOTOSYNTHETIC BACTERIA

BACTERIOCHLOROPHYLL aBACTERIOCHLOROPHYLL a BACTERIOCHLOROPHYLL bBACTERIOCHLOROPHYLL b

MOLECULAR EVENTS DURING LIGHT MOLECULAR EVENTS DURING LIGHT ABSORPTIONABSORPTION

PHOTONS (LIGHT “PARTICLES”)PHOTONS (LIGHT “PARTICLES”) ENERGY = hENERGY = h

PHOTORECEPTORS PHOTORECEPTORS HIGHLY CONJUGATED MOLECULESHIGHLY CONJUGATED MOLECULES

STRONGLY ABSORB VISIBLE LIGHTSTRONGLY ABSORB VISIBLE LIGHT

ABSORPTION OF A PHOTON USUALLY PROMOTES ABSORPTION OF A PHOTON USUALLY PROMOTES A GROUND-STATE ELECTRON TO A MOLECULAR A GROUND-STATE ELECTRON TO A MOLECULAR ORBITAL OF HIGHER ENERGYORBITAL OF HIGHER ENERGY LAW OF CONSERVATION OF ENERGYLAW OF CONSERVATION OF ENERGY

EACH ELECTRONIC ENERGY LEVEL HASEACH ELECTRONIC ENERGY LEVEL HAS VIBRATIONAL AND ROTATIONAL SUB-STATESVIBRATIONAL AND ROTATIONAL SUB-STATES

POSSIBLE FATES OF EXCITED POSSIBLE FATES OF EXCITED ELECTRONELECTRON

INTERNAL CONVERSION (A FAST PROCESS)INTERNAL CONVERSION (A FAST PROCESS) ELECTRONIC ENERGY CONVERTED TO KINETIC (HEAT) ENERGYELECTRONIC ENERGY CONVERTED TO KINETIC (HEAT) ENERGY

SOMETIMES “RELAX” BACK TO GROUND STATESOMETIMES “RELAX” BACK TO GROUND STATE IN CHLOROPHYLL, RELAXATION TO IN CHLOROPHYLL, RELAXATION TO LOWESTLOWEST EXCITED STATE EXCITED STATE

FLUORESCENCEFLUORESCENCE (A SLOWER PROCESS)(A SLOWER PROCESS) A PHOTON IS EMITTED, WITH DECAY TO GROUND ELECTRONIC A PHOTON IS EMITTED, WITH DECAY TO GROUND ELECTRONIC

STATESTATE

EXCITON TRANSFER (“RESONANCE TRANSFER”)EXCITON TRANSFER (“RESONANCE TRANSFER”) EXCITATION ENERGY TRANSFERRED TO NEARBY UNEXCITED EXCITATION ENERGY TRANSFERRED TO NEARBY UNEXCITED

MOLECULES WITH SIMILAR ELECTRONIC PROPERTIESMOLECULES WITH SIMILAR ELECTRONIC PROPERTIES

PHOTO-OXIDATIONPHOTO-OXIDATION THE EXCITED MOLECULE TRANSFERS ITS ELECTRON TO AN THE EXCITED MOLECULE TRANSFERS ITS ELECTRON TO AN

ACCEPTOR MOLECULEACCEPTOR MOLECULE A REDOX PAIRA REDOX PAIR

EXCITON TRANSFER EXCITON TRANSFER

““COUPLING” OF MOLECULAR ORBITALS COUPLING” OF MOLECULAR ORBITALS ALLOWS FOR SERIAL TRANSFER OF EXCITATIONALLOWS FOR SERIAL TRANSFER OF EXCITATION OR COUPLED MOLECULES ACT AS A “SUPERMOLECULE”OR COUPLED MOLECULES ACT AS A “SUPERMOLECULE”

THIS KIND OF TRANSFER IS SEEN AS LIGHT THIS KIND OF TRANSFER IS SEEN AS LIGHT ENERGY IS “FUNNELED” TO “PHOTOSYNTHETIC ENERGY IS “FUNNELED” TO “PHOTOSYNTHETIC REACTION CENTERS”REACTION CENTERS”

PHOTO-OXIDATIONPHOTO-OXIDATION

THE EXCITED ELECTRON IS TRANSFERRED TO THE EXCITED ELECTRON IS TRANSFERRED TO THE “PHOTOSYNTHETIC REACTION CENTER”THE “PHOTOSYNTHETIC REACTION CENTER”

EXCITED CHLOROPHYLL IS THE DONOR IN EXCITED CHLOROPHYLL IS THE DONOR IN PHOTOSYNTHESISPHOTOSYNTHESIS

AFTER THE TRANSFER, CHLOROPHYLL IS AFTER THE TRANSFER, CHLOROPHYLL IS OXIDIZED TO A CATIONIC FREE RADICALOXIDIZED TO A CATIONIC FREE RADICAL

RETURNS TO ITS GROUND STATE BY OXIDIZING RETURNS TO ITS GROUND STATE BY OXIDIZING ANOTHER MOLECULEANOTHER MOLECULE

““ANTENNA” CHLOROPHYLLSANTENNA” CHLOROPHYLLS

THERE ARE ~ 300 CHLOROPHYLL MOLECULES THERE ARE ~ 300 CHLOROPHYLL MOLECULES PER REACTION CENTERPER REACTION CENTER

THE FUNCTION OF MOST CHLOROPHYLLS IS THE FUNCTION OF MOST CHLOROPHYLLS IS TOTO GATHER LIGHTGATHER LIGHT

ACT LIKE ANTENNASACT LIKE ANTENNAS ““LIGHT-HARVESTING COMPLEXES (LHCs)LIGHT-HARVESTING COMPLEXES (LHCs)

LIGHT ENERGY IS PASSED BY EXCITON LIGHT ENERGY IS PASSED BY EXCITON TRANSFER TO THE REACTION CENTERTRANSFER TO THE REACTION CENTER THESE HAVE SLIGHTLY LOWER EXCITATION ENERGIESTHESE HAVE SLIGHTLY LOWER EXCITATION ENERGIES >90% EFFICIENCY OF THE TRANSFER PROCESS!>90% EFFICIENCY OF THE TRANSFER PROCESS!

THE REACTION CENTER CHLOROPHYLLTHE REACTION CENTER CHLOROPHYLL

ITS LOWEST EXCITED STATE IS AT A ITS LOWEST EXCITED STATE IS AT A LOWER ENERGY LEVEL THAN EXCITED LOWER ENERGY LEVEL THAN EXCITED STATES OF ANTENNA CHLOROPHYLLSSTATES OF ANTENNA CHLOROPHYLLS THE EXCITATION IS “TRAPPED” THERETHE EXCITATION IS “TRAPPED” THERE

LIGHT-HARVESTING COMPLEXES: LIGHT-HARVESTING COMPLEXES: ACCESSORY PIGMENTSACCESSORY PIGMENTS

DIFFERENT PHOTOSYNTHETIC PIGMENTS DIFFERENT PHOTOSYNTHETIC PIGMENTS ABSORB LIGHT AT DIFFERENT FREQUENCIESABSORB LIGHT AT DIFFERENT FREQUENCIES ALLOWS LIGHT TO BE ABSORBED AT ALL FREQUENCIES ALLOWS LIGHT TO BE ABSORBED AT ALL FREQUENCIES

OF THE VISIBLE SPECTRUMOF THE VISIBLE SPECTRUM

LHCs CONTAINLHCs CONTAIN CHLOROPHYLLCHLOROPHYLL

EACH CHL. HAS A RED AND A BLUE ABSORPTION BANDEACH CHL. HAS A RED AND A BLUE ABSORPTION BAND

““ACCESSORY” PIGMENTS: “FILL IN” THE SPECTRUMACCESSORY” PIGMENTS: “FILL IN” THE SPECTRUM CAROTENOIDS (LIKE CAROTENOIDS (LIKE ββ-CAROTENE AND LYCOPENE)-CAROTENE AND LYCOPENE) FOUND IN ALL GREEN PLANTSFOUND IN ALL GREEN PLANTS IN MANY PHOTOSYNTHETIC BACTERIAIN MANY PHOTOSYNTHETIC BACTERIA

LHCs IN PURPLE PHOTOSYNTHETIC LHCs IN PURPLE PHOTOSYNTHETIC BACTERIABACTERIA

LH-2 FROM LH-2 FROM Rhodospirillium molischianumRhodospirillium molischianum TWO 8-FOLD SYMMETRIC CONCENTRIC TWO 8-FOLD SYMMETRIC CONCENTRIC

RINGSRINGS -SUBUNITS ON INNER RING-SUBUNITS ON INNER RING -SUBUNITS ON OUTER RING-SUBUNITS ON OUTER RING

32 PIGMENT MOLECULES BETWEEN THE 32 PIGMENT MOLECULES BETWEEN THE RINGSRINGS 24 OF THESE ARE 24 OF THESE ARE

BACTERIOCHLOROPHYLL aBACTERIOCHLOROPHYLL a 8 ARE LYCOPENE MOLECULES8 ARE LYCOPENE MOLECULES

LH2 FROM Rs. acidophhilus

LHC-LHC-IIII

MOST ABUNDANT MEMBRANE PROTEIN IN MOST ABUNDANT MEMBRANE PROTEIN IN CHLOROPLASTS OF GREEN PLANTSCHLOROPLASTS OF GREEN PLANTS

A TRANSMEMBRANE PROTEINA TRANSMEMBRANE PROTEIN BINDSBINDS

~ 7 CHLOROPHYLL a MOLECULES~ 7 CHLOROPHYLL a MOLECULES ~ 5 CHLOROPHYLL b MOLECULES~ 5 CHLOROPHYLL b MOLECULES TWO CAROTENOIDSTWO CAROTENOIDS

COMPRISES ABOUT 50% OF ALL CHLOROPHYLL IN COMPRISES ABOUT 50% OF ALL CHLOROPHYLL IN BIOSPHEREBIOSPHERE

ONE-CENTERONE-CENTER ELECTRON ELECTRON TRANSPORT IN PHOTOSYNTHETIC TRANSPORT IN PHOTOSYNTHETIC BACTERIABACTERIA

LOOK AT THE REACTION CENTER OF PURPLE LOOK AT THE REACTION CENTER OF PURPLE PHOTOSYNTHETIC BACTERIA (PbRC)PHOTOSYNTHETIC BACTERIA (PbRC)

CONTAINS 3 HYDROPHOBIC SUBUNITSCONTAINS 3 HYDROPHOBIC SUBUNITS H,L,MH,L,M INCLUDES 11 TRANSMEMBRANE HELICESINCLUDES 11 TRANSMEMBRANE HELICES

THESE BIND THE FOLLOWING PROSTHETIC GPS:THESE BIND THE FOLLOWING PROSTHETIC GPS: 4 MOLECULES OF BACTERIOCHLOROPHYLL4 MOLECULES OF BACTERIOCHLOROPHYLL 2 MOLECULES OF BACTERIOPHEOPHYTIN2 MOLECULES OF BACTERIOPHEOPHYTIN

ALSO BINDALSO BIND Fe(II) IONFe(II) ION 2 MOLECULES OF UBIQUINONE2 MOLECULES OF UBIQUINONE

OR ONE UBIQUINONE AND ONE MENAQUINONEOR ONE UBIQUINONE AND ONE MENAQUINONE

O

O

O

O

CH3

R

H3CO

H3CO

OH

OH

OH

OH

CH3

R

H3CO

H3CO

CH3

QUINONE HYDROQUINONE

COENZYME Q REDUCED COENZYME Q

(UBIQUINONE)

QUINONES CAN SERVE AS BIOLOGICAL REDOX REAGENTS

"R" IS: -(-CH2-CH=C-CH2-)10-H

|

IN-CLASS EXERCISEIN-CLASS EXERCISE

EXPLORE THE STRUCTURE OF THE EXPLORE THE STRUCTURE OF THE PHOTOSYNTHETIC REACTION CENTER FROM PHOTOSYNTHETIC REACTION CENTER FROM Rb.Rb.

sphaeroidessphaeroides

LOCATE ALL STRUCTURES DESCRIBED ON LOCATE ALL STRUCTURES DESCRIBED ON THE PREVIOUS SLIDETHE PREVIOUS SLIDE

..

ACCESS THIS MOLECULE FROM THE WEB SITEACCESS THIS MOLECULE FROM THE WEB SITE

PDBid 2RCRPDBid 2RCR

GEOMETRY OF THE PROSTHETIC GEOMETRY OF THE PROSTHETIC GROUPS IN PbRC OF GROUPS IN PbRC OF RHODOPSEUDOMONAS VIRIDISRHODOPSEUDOMONAS VIRIDIS

ALMOST PERFECT TWO-FOLD SYMMETRYALMOST PERFECT TWO-FOLD SYMMETRY A “SPECIAL PAIR” OF BACTERIOCHLOROPHYLL MOLECULESA “SPECIAL PAIR” OF BACTERIOCHLOROPHYLL MOLECULES

CAN BE Bchl a : MAXIMUM ABSORBPTION AT 870 nm (P870)CAN BE Bchl a : MAXIMUM ABSORBPTION AT 870 nm (P870) OR Bchl b : MAX. ABS. AT 960 nm (P960)OR Bchl b : MAX. ABS. AT 960 nm (P960)

EACH MOLECULE OF SPECIAL PAIR CONTACTS, IN TURN:EACH MOLECULE OF SPECIAL PAIR CONTACTS, IN TURN: AN ACCESSORY Bchl b MOLECULEAN ACCESSORY Bchl b MOLECULE A BPheo b MOLECULEA BPheo b MOLECULE

THE MENAQUINONE MOLECULE IS NEAR THE L-SUBUNIT’S THE MENAQUINONE MOLECULE IS NEAR THE L-SUBUNIT’S BPheo bBPheo b

THE UBIQUINONE ASSOCIATES WITH THE M-SUBUNIT OF THE UBIQUINONE ASSOCIATES WITH THE M-SUBUNIT OF BPheo bBPheo b

THERE IS AN Fe (II) BETWEEN THE UBI- AND MENAQUINONETHERE IS AN Fe (II) BETWEEN THE UBI- AND MENAQUINONE

IN-CLASS QUESTIONIN-CLASS QUESTION

PURPLE PHOTOSYNTHETIC BACTERIA HAVE PURPLE PHOTOSYNTHETIC BACTERIA HAVE DIFFERENT PIGMENTS THAN HIGHER PLANTS. DIFFERENT PIGMENTS THAN HIGHER PLANTS. WHY IS THIS AN ADVANTAGE FOR THESE WHY IS THIS AN ADVANTAGE FOR THESE BACTERIA?BACTERIA?

THE TRANSPORT OF ELECTRONS IN THE TRANSPORT OF ELECTRONS IN PHOTOSYNTHETIC BACTERIAPHOTOSYNTHETIC BACTERIA

THE FOLLOWING EVENTS OCCUR IN THE L- THE FOLLOWING EVENTS OCCUR IN THE L- SUBUNIT AFTER THE ABSORPTION THE FIRST SUBUNIT AFTER THE ABSORPTION THE FIRST PHOTON BY THE SPECIAL PAIRPHOTON BY THE SPECIAL PAIR AN EXCITED ELECTRON IS DELOCALIZED OVER THE AN EXCITED ELECTRON IS DELOCALIZED OVER THE

SPECIAL PAIR: P960 SPECIAL PAIR: P960 P960* P960* P960* TRANSFERS ELECTRON TO BPheo b P960* TRANSFERS ELECTRON TO BPheo b

NOW WE HAVE P960NOW WE HAVE P960++ BPheo b BPheo b--

THE ACCESSORY BChl b IS PART OF PATHWAY FOR THE ACCESSORY BChl b IS PART OF PATHWAY FOR ELECTRON FLOW; IT IS NOT REDUCEDELECTRON FLOW; IT IS NOT REDUCED

ELECTRON MIGRATES TO QELECTRON MIGRATES TO QAA

IS NOW REDUCED TO QIS NOW REDUCED TO QAA--

NOTE: THIS IS THE NOTE: THIS IS THE SEMIQUINONE SEMIQUINONE FORM OF QFORM OF QAA

QQAA-- TRANSFERS ITS ELECTRON TRANSFERS ITS ELECTRON

TO QTO QBB

THE Fe(II) ATOM DOES IS NOT DIRECTLY THE Fe(II) ATOM DOES IS NOT DIRECTLY INVOLVED DURING THE TRANSFERINVOLVED DURING THE TRANSFER

QQAA NEVER BECOMES FULLY REDUCED NEVER BECOMES FULLY REDUCED

A SECOND PHOTON EVENT REDUCES QA SECOND PHOTON EVENT REDUCES QAA AGAIN AGAIN SAME EVENTS AS FOR THE FIRST EVENTSAME EVENTS AS FOR THE FIRST EVENT REDUCED QREDUCED QAA PASSES THE SECOND ELECTRON TO Q PASSES THE SECOND ELECTRON TO QBB

--

FULLY REDUCED QFULLY REDUCED QBB IS AN IS AN ANIONIC QUINOL ( QANIONIC QUINOL ( QBB

2-2- ) )

QQBB2- 2- TAKES UP TWO H TAKES UP TWO H++ FROM THE CYTOPLASM FROM THE CYTOPLASM

THE TWO ELECTRONS THAT HAVE BEEN TAKEN THE TWO ELECTRONS THAT HAVE BEEN TAKEN UP BY UP BY QQBBHH22 ARE RETURNED TO THE OXIDIZED ARE RETURNED TO THE OXIDIZED SPECIAL PAIRSPECIAL PAIR THE REDOX CARRIERS CAN INCLUDETHE REDOX CARRIERS CAN INCLUDE

A POOL OF MEMBRANE-BOUND UBIQUINONESA POOL OF MEMBRANE-BOUND UBIQUINONES CYTOCHROME bcCYTOCHROME bc11 COMPLEX COMPLEX CYTOCHROME cCYTOCHROME c22

AN “ELECTRON TRANSPORT CHAIN”AN “ELECTRON TRANSPORT CHAIN” OCCURS WITHIN BACTERIAL PLASMA MEMBRANEOCCURS WITHIN BACTERIAL PLASMA MEMBRANE

WHEN QHWHEN QH22 TRANSFERS ELECTRONS TO CYT bc TRANSFERS ELECTRONS TO CYT bc11, , THE PROTONS ARE TRANSLOCATED ACROSS THE THE PROTONS ARE TRANSLOCATED ACROSS THE PLASMA MEMBRANEPLASMA MEMBRANE

ELECTRON TRANSFER FROM QHELECTRON TRANSFER FROM QH22 TO TO CYT cCYT c22 OCCURS VIA A TWO-STAGE OCCURS VIA A TWO-STAGE “Q-CYCLE”“Q-CYCLE”

QHQH2 2 IS A TWO-ELECTRON CARRIERIS A TWO-ELECTRON CARRIER

CYT cCYT c22 IS A ONE-ELECTRON CARRIER IS A ONE-ELECTRON CARRIER

FOR EVERY 2 ELECTRONS TRANSFERRED FROM FOR EVERY 2 ELECTRONS TRANSFERRED FROM QHQH2 2 TO CYT cTO CYT c22 , 4 H , 4 H++ ENTER THE PERIPLASMIC ENTER THE PERIPLASMIC

SPACESPACE A TRANSMEMBRANE PROTON GRADIENTA TRANSMEMBRANE PROTON GRADIENT DISSIPATION OF THE GRADIENT DRIVES ATP DISSIPATION OF THE GRADIENT DRIVES ATP

PRODUCTIONPRODUCTION ““PHOTOPHOSPHORYLATION”PHOTOPHOSPHORYLATION”

ELECTRON TRANSPORT IN PURPLE ELECTRON TRANSPORT IN PURPLE PHOTOSYNTHETIC BACTERIA IS A PHOTOSYNTHETIC BACTERIA IS A CYCLIC PROCESSCYCLIC PROCESS

THERE IS THERE IS NONO NET OXIDATION-REDUCTION NET OXIDATION-REDUCTION

OVERALL PROCESS IS IRREVERSIBLEOVERALL PROCESS IS IRREVERSIBLE

ELECTRONS ARE TRANSFERRED TO PROGRESSIVELY ELECTRONS ARE TRANSFERRED TO PROGRESSIVELY LOWER ENERGY STATESLOWER ENERGY STATES

STANDARD REDUCTION POTENTIALS ARE PROGRESSIVELY STANDARD REDUCTION POTENTIALS ARE PROGRESSIVELY MORE POSITIVEMORE POSITIVE

IN-CLASS QUESTIONIN-CLASS QUESTION

THE STANDARD REDUCTION POTENTIAL FOR THE THE STANDARD REDUCTION POTENTIAL FOR THE OXIDATION OF WATER IS 0.815 V.OXIDATION OF WATER IS 0.815 V.

OO22 + 4 e + 4 e-- + 4 H + 4 H++ 2 H 2 H22OO

CAN THIS VALUE BE OBTAINED FROM PURPLE CAN THIS VALUE BE OBTAINED FROM PURPLE PHOTOSYNTHETIC BACTERIAL PHOTOSYNTHESIS?PHOTOSYNTHETIC BACTERIAL PHOTOSYNTHESIS?

(ASSUME THAT THE SPECIAL PAIR CONSISTS OF BChl a)(ASSUME THAT THE SPECIAL PAIR CONSISTS OF BChl a)ANOTHER WAY OF ASKING THE SAME QUESTION: CAN P870ANOTHER WAY OF ASKING THE SAME QUESTION: CAN P870++ OXIDIZE OXIDIZE

WATER? (EXPLAIN YOUR ANSWER.)WATER? (EXPLAIN YOUR ANSWER.)

WHERE DO THE REDUCING WHERE DO THE REDUCING EQUIVALENTS COME FROM?EQUIVALENTS COME FROM?

IN PLANTS AND CYANOBACTERIAIN PLANTS AND CYANOBACTERIA FROM OXIDATION OF HFROM OXIDATION OF H22OO

NET RXN’ OF PHOTOSYNTHESIS: NET RXN’ OF PHOTOSYNTHESIS: COCO22 + 2 H + 2 H22O O (CH (CH22O) + HO) + H22O + OO + O22

IN PURPLE PHOTOSYNTHETIC BACT.IN PURPLE PHOTOSYNTHETIC BACT. FROM OXIDATION OFFROM OXIDATION OF

HH22SS SS SS22OO33

2-2-

HH22

ETHANOLETHANOL NET REACTION: CONET REACTION: CO22 + 2 H + 2 H22A A (CH (CH22O) + HO) + H22O + 2 AO + 2 A

IN-CLASS PROBLEMIN-CLASS PROBLEM

SOME PHOTOSYNTHETIC BACTERIA USE SOME PHOTOSYNTHETIC BACTERIA USE HH22S AS A HYDROGEN DONOR AND S AS A HYDROGEN DONOR AND

PRODUCE ELEMENTAL SULFUR, WHILE PRODUCE ELEMENTAL SULFUR, WHILE OTHERS USE ETHANOL AND PRODUCE OTHERS USE ETHANOL AND PRODUCE ACETALDEHYDE.ACETALDEHYDE. WRITE THE NET REACTIONS FOR PHOTO-WRITE THE NET REACTIONS FOR PHOTO-

SYNTHESIS CORRESPONDING TO THESE SYNTHESIS CORRESPONDING TO THESE BACTERIABACTERIA

WHY IS NO OXYGEN PRODUCED?WHY IS NO OXYGEN PRODUCED?

WHAT HAPPENED WHEN AVAILABLE WHAT HAPPENED WHEN AVAILABLE REDUCTIVE RESOURCES WERE REDUCTIVE RESOURCES WERE EXHAUSTED?EXHAUSTED?

A PHOTOSYNTHETIC SYSTEM EVOLVED A PHOTOSYNTHETIC SYSTEM EVOLVED THAT HAD ENOUGH EMF TO ABSTRACT THAT HAD ENOUGH EMF TO ABSTRACT ELECTRONS FROM WATERELECTRONS FROM WATER

OO22 BUILT UP AS A “TOXIC WASTE BUILT UP AS A “TOXIC WASTE

PRODUCT”PRODUCT” PHOTOSYNTH. BACTERIA ARE PHOTOSYNTH. BACTERIA ARE

ANAEROBES, SO THEY NOW INHABIT ANAEROBES, SO THEY NOW INHABIT NARROW ECOLOGICAL NICHESNARROW ECOLOGICAL NICHES

PHOTOSYNTHESIS IN PLANTS AND PHOTOSYNTHESIS IN PLANTS AND CYANOBACTERIA IS CYANOBACTERIA IS NON-CYCLICNON-CYCLIC

A MULTI-STEP PROCESSA MULTI-STEP PROCESS TWO PHOTOSYNTHETIC REACTION CENTERSTWO PHOTOSYNTHETIC REACTION CENTERS

PSII AND PSIPSII AND PSI

EACH CENTER IS INDEPENDENTLY ACTIVATED BY LIGHTEACH CENTER IS INDEPENDENTLY ACTIVATED BY LIGHT ELECTRONS FLOW FROM PSII ELECTRONS FLOW FROM PSII PSI PSI PSII OXIDIZES HPSII OXIDIZES H22OO

PSI REDUCES NADPPSI REDUCES NADP++

HH22O OXIDATION IS COUPLED TO NADPO OXIDATION IS COUPLED TO NADP++ REDUCTION REDUCTION

ELECTRON TRANSFER OCCURS ELECTRON TRANSFER OCCURS BETWEEN MEMBRANE-BOUND BETWEEN MEMBRANE-BOUND PARTICLESPARTICLES

PSIIPSII CYTOCHROME bCYTOCHROME b66f COMPLEXf COMPLEX PSIPSI

MOBILE ELECTRON CARRIERS SHUTTLE THE MOBILE ELECTRON CARRIERS SHUTTLE THE ELECTRONS BETWEEN THESE COMPLEXESELECTRONS BETWEEN THESE COMPLEXES PLASTOQUINONE (Q) LINKS PSII TO CYTOCHROME bPLASTOQUINONE (Q) LINKS PSII TO CYTOCHROME b66f f

COMPLEX COMPLEX Q IS REDUCED TO QHQ IS REDUCED TO QH22 BY PSII BY PSII THEN QHTHEN QH22 REDUCES CYTOCHROME b REDUCES CYTOCHROME b66f COMPLEXf COMPLEX

PLASTOCYANIN (PC) LINKS CYTOCHROME bPLASTOCYANIN (PC) LINKS CYTOCHROME b66f TO PSIf TO PSI

THE ELECTRONS ULTIMATELY THE ELECTRONS ULTIMATELY REDUCE NADPREDUCE NADP++

THE ENZYME IS FERREDOXIN-NADPTHE ENZYME IS FERREDOXIN-NADP++ REDUCTASE REDUCTASE (FNR)(FNR)

DURING THE ENTIRE FOUR-ELECTRON PROCESSDURING THE ENTIRE FOUR-ELECTRON PROCESS WATER IS OXIDIZEDWATER IS OXIDIZED THE ELECTRONS PASS THROUGH A Q-CYCLETHE ELECTRONS PASS THROUGH A Q-CYCLE A TRANSMEMBRANE PROTON GRADIENT IS GENERATEDA TRANSMEMBRANE PROTON GRADIENT IS GENERATED

THE pH IS LOWER IN THE THYLAKOID LUMENTHE pH IS LOWER IN THE THYLAKOID LUMEN

THE FREE ENERGY OF THIS GRADIENT DRIVES ATP THE FREE ENERGY OF THIS GRADIENT DRIVES ATP SYNTHESISSYNTHESIS

THE “Z-SCHEME”THE “Z-SCHEME”

A ZIG-ZAG DIAGRAM REPRESENTING A ZIG-ZAG DIAGRAM REPRESENTING PROSTHETIC GROUPS INVOLVED IN PROSTHETIC GROUPS INVOLVED IN PHOTOSYNTHESISPHOTOSYNTHESIS

TWO LOCI REPRESENT PSII AND PSITWO LOCI REPRESENT PSII AND PSI

ELECTRONS FLOW FROM ELECTRONS FLOW FROM LOW TO HIGHLOW TO HIGH REDUCTION POTENTIALSREDUCTION POTENTIALS

PSIIPSII

CRYSTALLIZES AS A SYMMETRIC DIMERCRYSTALLIZES AS A SYMMETRIC DIMER EACH PROTOMER WITH PSEUDO TWO-FOLD EACH PROTOMER WITH PSEUDO TWO-FOLD

SYMMETRYSYMMETRY REACTION CENTER COFACTORS ORGANIZED REACTION CENTER COFACTORS ORGANIZED

SIMILARLY TO PbRCSIMILARLY TO PbRC Chl a INSTEAD OF BChl bChl a INSTEAD OF BChl b Pheo a INSTEAD OF BPheo bPheo a INSTEAD OF BPheo b PLASTOQUINONE INSTEAD OF MENAQUINONEPLASTOQUINONE INSTEAD OF MENAQUINONE

P680 : TWO Chl a RINGS SIMILAR TO “SPECIAL P680 : TWO Chl a RINGS SIMILAR TO “SPECIAL PAIR”PAIR”

PHOTOSYSTEM II (PDB 1s5I ) : “MOLECULE OF THE MONTH” NOVEMBER 2004

PSII (1s5I): TOP VIEW, SHOWING PIGMENT MOLECULES

CENTRAL CHLOROPHYLLOF REACTION CENTER

LIGHT HARVESTING PROTEIN

LIGHT HARVESTING PROTEIN

REACTION CENTER

EVENTS AT PSIIEVENTS AT PSII

FIRST PHOTON EVENT FIRST PHOTON EVENT EJECTED ELECTRON EJECTED ELECTRON

TRANSFERRED THRU ACCESSORY Chl a TO TRANSFERRED THRU ACCESSORY Chl a TO

Pheo a, AND THEN TO QPheo a, AND THEN TO QA

QQA IS THE BOUND PLASTOQUINONE

THEN THE ELECTRON IS TRANSFERRED TO QB

A SECOND PHOTON EVENT OCCURSA SECOND PHOTON EVENT OCCURS

THE SECOND ELECTRON IS TRANSFERRED TO QTHE SECOND ELECTRON IS TRANSFERRED TO QB B

QQB (WITH 2 ELECTRONS) TAKES UP 2 PROTONS AT STROMAL SURFACE

QBH2 (PLASTOQUINOL) EXCHANGES WITH MEMBRANE-BOUND POOL OF PLASTOQUINONE MOLECULES

DCMU INHIBITS PHOTOSYNTHESIS IT COMPETES WITH PLASTOQUINONE MOLECULES FOR IT COMPETES WITH PLASTOQUINONE MOLECULES FOR

THE QTHE QB-BINDING SITE ON PSII

THE OXYGEN EVOLVING CENTER THE OXYGEN EVOLVING CENTER (OEC) (OEC)

A “WATER-SPLITTING” ENZYMEA “WATER-SPLITTING” ENZYME MUST UNDERGO 4 LIGHT-DEPENDENT MUST UNDERGO 4 LIGHT-DEPENDENT

REACTIONS BEFORE RELEASING OREACTIONS BEFORE RELEASING O22

4 PROTONS ARE RELEASED TO INNER THYLAKOID SPACE IN A STEPWISE MANNER

REACTION DRIVEN BY EXCITATION OF PSII RC

A Mn4CaO4 COMPLEX

THE OXYGEN EVOLVING CENTER

THE TYROSINE RADICAL BRIDGES THE WATER MOLECULE AND THE CHLOROPHYLL MOLECULE

MECHANISM OF OECMECHANISM OF OEC

NOT CLEARNOT CLEAR OEC PROGRESSES THROUGH 5 STATESOEC PROGRESSES THROUGH 5 STATES Mn CHANGES ITS OXIDATION STATE AS THE OEC Mn CHANGES ITS OXIDATION STATE AS THE OEC

CYCLES THROUGH ITS STATESCYCLES THROUGH ITS STATES PROTONS, ELECTRONS ABSTRACTED AS Mn PROTONS, ELECTRONS ABSTRACTED AS Mn

CYCLES THROUGH II,III,IV, AND V STATESCYCLES THROUGH II,III,IV, AND V STATES EACH ELECTRON IS INDIVIDUALLY EACH ELECTRON IS INDIVIDUALLY

TRANSFERRED TO P680TRANSFERRED TO P680++

TyrO , A TRANSIENT RADICAL, RELAYS THE e-

WHERE ELSE HAVE YOU SEEN THE TYROSYL RADICAL?WHERE ELSE HAVE YOU SEEN THE TYROSYL RADICAL?

PSII OECPSII OEC

RECENT REFERENCES:RECENT REFERENCES:J. Ch. Ed. Vol. 82 (5) May 2005, pages 791 – 794J. Ch. Ed. Vol. 82 (5) May 2005, pages 791 – 794

Although this article describes experiments regarding this Although this article describes experiments regarding this bioinorganic molecule, there is a good diagram of the bioinorganic molecule, there is a good diagram of the proposed catalytic mechanism on page 792 for “complex 1”, a proposed catalytic mechanism on page 792 for “complex 1”, a synthesized molecule which is a functional model of the Mnsynthesized molecule which is a functional model of the Mn44

cluster.cluster.

A fully manipulable Chime version of the four-manganese center A fully manipulable Chime version of the four-manganese center in PSII is available at the following web site:in PSII is available at the following web site:

http://www.jce.divched.org/JCEWWW/Features/MonthlyMolecules/http://www.jce.divched.org/JCEWWW/Features/MonthlyMolecules/2005/May/2005/May/

Journal of Chemical Education : Vol 82(5) May 2005 Pages 791-794

ELECTRONS ARE TRANSFERRED ELECTRONS ARE TRANSFERRED THROUGH Cyt bTHROUGH Cyt b66f COMPLEX

VIA A Q POOL (PLASTOQUINONE)VIA A Q POOL (PLASTOQUINONE) ELECTRON FLOW OCCURS THROUGH A “Q-ELECTRON FLOW OCCURS THROUGH A “Q-

CYCLE”CYCLE” FOR EACH eFOR EACH e-- TRANSPORTED, 2 PROTONS ARE

TRANSPORTED ACROSS THYLAKOID MEMBRANE 8 H8 H++ ARE TRANSPORTED (THERE ARE 4 e- FROM THE

TWO WATER MOLECULES THAT ARE SPLIT

THIS ELECTRON TRANSPORT IS RESPONSIBLE THIS ELECTRON TRANSPORT IS RESPONSIBLE FOR GENERATING MOST OF THE ELECTROCHEM-FOR GENERATING MOST OF THE ELECTROCHEM-ICAL PROTON GRADIENTICAL PROTON GRADIENT

PLASTOCYANIN : A “BLUE PLASTOCYANIN : A “BLUE COPPER” PROTEINCOPPER” PROTEIN

MEDIATES ELECTRON TRANSFER BETWEEN CYT f MEDIATES ELECTRON TRANSFER BETWEEN CYT f AND PSIAND PSI CYT f IS THE TERMINAL ELECTRON CARRIER OF THE CYT f IS THE TERMINAL ELECTRON CARRIER OF THE

CYT bCYT b66f COMPLEXf COMPLEX

ON THE THYLAKOID LUMENAL SURFACEON THE THYLAKOID LUMENAL SURFACE

ITS REDOX CENTER CONTAINS COPPERITS REDOX CENTER CONTAINS COPPER CYCLES BETWEEN Cu(I) AND Cu(II) OXIDATION STATESCYCLES BETWEEN Cu(I) AND Cu(II) OXIDATION STATES

IN-CLASS CHIME EXERCISEIN-CLASS CHIME EXERCISE

LOOK AT PDBid 1PLCLOOK AT PDBid 1PLC

FIND:FIND:THE “THE “ββ-SANDWICH”-SANDWICH”IDENTIFY THE COPPER IONIDENTIFY THE COPPER IONFIND THE 4 LIGANDS THAT TETRAHEDRALLY COORDINATE THE Cu FIND THE 4 LIGANDS THAT TETRAHEDRALLY COORDINATE THE Cu IONION

LOCATE THE 6 ASP AND GLU RESIDUES THAT FORM A (-) CHARGED LOCATE THE 6 ASP AND GLU RESIDUES THAT FORM A (-) CHARGED PATCH ON THE SURFACEPATCH ON THE SURFACE

CYT f HAS A LYS 187 SIDECHAIN THAT IS ONE OF 5 (+) CHARGED CYT f HAS A LYS 187 SIDECHAIN THAT IS ONE OF 5 (+) CHARGED RESIDUES ON ITS SURFACE. IT CAN BE CROSS- LINKED RESIDUES ON ITS SURFACE. IT CAN BE CROSS- LINKED (EXPERIMENTALLY) TO ASP 44 ON PC, WHICH IS ONE OF THE ASPs IN (EXPERIMENTALLY) TO ASP 44 ON PC, WHICH IS ONE OF THE ASPs IN THE (-) CHARGED PATCHTHE (-) CHARGED PATCH

SUGGEST AN INTERMOLECULAR MECHANISM BY WHICH CYT SUGGEST AN INTERMOLECULAR MECHANISM BY WHICH CYT f AND PC ASSOCIATEf AND PC ASSOCIATE

““TUNING” THE REDOX TUNING” THE REDOX POTENTIALPOTENTIAL

PROTEINS CAN CHANGE THE STANDARD PROTEINS CAN CHANGE THE STANDARD REDUCTION POTENTIALS OF THEIR REDOX REDUCTION POTENTIALS OF THEIR REDOX CENTERS THROUGH A STRAIN MECHANISMCENTERS THROUGH A STRAIN MECHANISM

FOR EXAMPLE:FOR EXAMPLE: EEO’O’ FOR THE NORMAL Cu(II)/Cu(I) HALF-REACTION IS FOR THE NORMAL Cu(II)/Cu(I) HALF-REACTION IS

0.158 VOLTS0.158 VOLTS EEO’O’ FOR THE SAME HALF-REACTION IN PC IS 0.370 V FOR THE SAME HALF-REACTION IN PC IS 0.370 V

LIGAND GEOMETRY OF 4-LIGAND GEOMETRY OF 4-COORDINATED COPPER ATOMS COORDINATED COPPER ATOMS

USUALLY SQUARE PLANAR FOR Cu(II)USUALLY SQUARE PLANAR FOR Cu(II) USUALLY TETRAHEDRAL FOR Cu(I)USUALLY TETRAHEDRAL FOR Cu(I)

IN PC, THE Cu ATOM HAS A DISTORTED IN PC, THE Cu ATOM HAS A DISTORTED TETRAHEDRAL GEOMETRYTETRAHEDRAL GEOMETRY CYSCYS METMET TWO HIS RESIDUESTWO HIS RESIDUES

THE PROTEIN IMPOSES THE TETRAHEDRAL THE PROTEIN IMPOSES THE TETRAHEDRAL GEOMETRY ON THE Cu(II) GEOMETRY ON THE Cu(II) STRAIN STRAIN LOOKS MORE LIKE THE Cu(I) GEOMETRYLOOKS MORE LIKE THE Cu(I) GEOMETRY

ELECTRON TRANSFER IS ELECTRON TRANSFER IS FACILITATED BY THE STRAINFACILITATED BY THE STRAIN

THE THE EEOO IS GREATER FOR THE ELECTRON IS GREATER FOR THE ELECTRON TRANSFER EVENT IN PLASTOCYANINTRANSFER EVENT IN PLASTOCYANIN

SINCE SINCE GGOO = -nF = -nF EEOO , THE REACTION IS MORE , THE REACTION IS MORE SPONTANEOUS UNDER STANDARD CONDITIONSSPONTANEOUS UNDER STANDARD CONDITIONS

PSIPSI

IN CYANOBACTERIA, THESE ARE TRIMERSIN CYANOBACTERIA, THESE ARE TRIMERS EACH PROTOMER HASEACH PROTOMER HAS

31 TRANSMEMBRANE HELICES ANCHOR EACH MONOMER31 TRANSMEMBRANE HELICES ANCHOR EACH MONOMER 96 CHLOROPHYLL MOLECULES96 CHLOROPHYLL MOLECULES 22 CAROTENOIDS22 CAROTENOIDS

CHLOROPHYLLS AND CAROTENOIDS OPERATE AS A LIGHT-CHLOROPHYLLS AND CAROTENOIDS OPERATE AS A LIGHT-HARVESTING COMPLEXHARVESTING COMPLEX

EACH MONOMER HAS AN ACTIVE CENTEREACH MONOMER HAS AN ACTIVE CENTER ONE OR TWO CHLOROPHYLL MOLECULES (P700)ONE OR TWO CHLOROPHYLL MOLECULES (P700)

P700 IS EXCITED BY PHOTONS FUNNELED THROUGH P700 IS EXCITED BY PHOTONS FUNNELED THROUGH ANTENNAE PIGMENTSANTENNAE PIGMENTS EXCITON TRANSFEREXCITON TRANSFER

PSIPSI

P700 IS PHOTO-EXCITED TO P700P700 IS PHOTO-EXCITED TO P700**

P700P700** PASSES ITS EXCITED ELECTRON ON THROUGH A PASSES ITS EXCITED ELECTRON ON THROUGH A CHAIN OF ELECTRON CARRIERSCHAIN OF ELECTRON CARRIERS EACH ONE AT A LOWER REDUCTION POTENTIALEACH ONE AT A LOWER REDUCTION POTENTIAL

THE CARRIERS INCLUDETHE CARRIERS INCLUDE Chl aChl a PHYLLOQUINONEPHYLLOQUINONE THREE [4Fe-4S] CLUSTERSTHREE [4Fe-4S] CLUSTERS

OXIDIZED P700 (P700OXIDIZED P700 (P700++) IS A WEAK OXIDANT) IS A WEAK OXIDANT EEO’O’ IS ABOUT 0.4 V IS ABOUT 0.4 V

THE PROSTHETIC GROUPS HAVE AN APPROXIMATE 2-FOLD THE PROSTHETIC GROUPS HAVE AN APPROXIMATE 2-FOLD SYMMETRYSYMMETRY

PHOTOSYSTEM I ( ) : MOLECULE OF THE MONTH

AN IRON-SULFUR CLUSTER

PHYLLOQUINONE

CHLOROPHYLL

CHLOROPHYLL

PS I AS VIEWED FROM THE TOP

ANTENNA CHLOROPHYLLS AND CAROTENOIDS

PHOTOSYNTHETIC REACTION CENTER

PDB 1jbo : PHOTOSYSTEM I COFACTORS

A SPECIAL PAIR CHLOROPHYLL

THERE ARE 2 POSSIBLE PATHWAYSTHERE ARE 2 POSSIBLE PATHWAYSFOR ELECTRON FLOW IN PSI FOR ELECTRON FLOW IN PSI

NON-CYCLICNON-CYCLIC

CYCLICCYCLIC

THE NON-CYCLIC PATHWAYTHE NON-CYCLIC PATHWAY

THE NON-CYCLIC PATHWAYTHE NON-CYCLIC PATHWAY MOST ELECTRONS FOLLOW THIS PATHWAYMOST ELECTRONS FOLLOW THIS PATHWAY PASSED ON TO A SOLUBLE FERREDOXINPASSED ON TO A SOLUBLE FERREDOXIN

LOCATED IN THE STROMALOCATED IN THE STROMA CONTAINS A [2Fe-2S] CLUSTERCONTAINS A [2Fe-2S] CLUSTER

TWO REDUCED Fd MOLECULES EACH SEND AN ELECTRON TWO REDUCED Fd MOLECULES EACH SEND AN ELECTRON ON TO THE ENZYME “FERREDOXIN-NADPON TO THE ENZYME “FERREDOXIN-NADP++ REDUCTASE (FNR) REDUCTASE (FNR)

CONTAINS FADCONTAINS FAD

FAD IS REDUCED TO FADHFAD IS REDUCED TO FADH22

FADHFADH22 REDUCES 2 NADP REDUCES 2 NADP++ MOLECULES MOLECULES

NADPH IS THE FINAL PRODUCT OF CHLOROPLAST LIGHT-NADPH IS THE FINAL PRODUCT OF CHLOROPLAST LIGHT-REACTIONREACTION

OVERALL RESULT OF NON-CYCLIC OVERALL RESULT OF NON-CYCLIC PATHWAYPATHWAY

4 ELECTRONS ARE TRANSFERRED FROM 2 4 ELECTRONS ARE TRANSFERRED FROM 2 WATER MOLECULES TO 2 NADPWATER MOLECULES TO 2 NADP+ + s TO PRODUCE 2 s TO PRODUCE 2 NADPH MOLECULESNADPH MOLECULES

A TRANSMEMBRANE HA TRANSMEMBRANE H++ GRADIENT IS GRADIENT IS ESTABLISHEDESTABLISHED 12 H12 H++ TRANSLOCATED INTO THYLAKOID LUMEN TRANSLOCATED INTO THYLAKOID LUMEN CAN DRIVE SYNTHESIS OF ~ 3 ATP MOLECULESCAN DRIVE SYNTHESIS OF ~ 3 ATP MOLECULES

NOTE: 2 HNOTE: 2 H++ ARE RELEASED INTO LUMEN FOR ARE RELEASED INTO LUMEN FOR EACH HEACH H22O SPLIT. 4 HO SPLIT. 4 H++ ARE USED UP IN STROMA ARE USED UP IN STROMA WHEN 4 eWHEN 4 e-- REDUCE 2 NADP REDUCE 2 NADP++

1 O1 O22 MOLECULE IS FORMED MOLECULE IS FORMED A TOTAL OF 8 PHOTONS ARE ABSORBEDA TOTAL OF 8 PHOTONS ARE ABSORBED

THE CYCLIC PATHWAYTHE CYCLIC PATHWAY

THE RETURN OF SOME ELECTRONS TO THE THE RETURN OF SOME ELECTRONS TO THE POOL OF PLASTOQUINONES (Q-POOL)POOL OF PLASTOQUINONES (Q-POOL)

OCCURS THROUGH CYT bOCCURS THROUGH CYT b66

PROTONS ARE TRANSLOCATED ACROSS THE PROTONS ARE TRANSLOCATED ACROSS THE THYLAKOID DURING THIS PROCESSTHYLAKOID DURING THIS PROCESS

BECAUSE IT’S A CYCLIC PROCESS:BECAUSE IT’S A CYCLIC PROCESS: INDEPENDENT OF PSIIINDEPENDENT OF PSII NO ONO O22 EVOLVED EVOLVED

PROBABLE REASON FOR A CYCLIC PROBABLE REASON FOR A CYCLIC ALTERNATIVEALTERNATIVE

INCREASES LEVEL OF ATP RELATIVE TO THAT OF INCREASES LEVEL OF ATP RELATIVE TO THAT OF NADPHNADPH

CELL PRODUCTION OF EACH OF THESE CELL PRODUCTION OF EACH OF THESE ACCORDING TO ITS NEEDSACCORDING TO ITS NEEDS

THE REGULATORY MECHANISM IS NOT YET THE REGULATORY MECHANISM IS NOT YET KNOWNKNOWN