Lecture6Photosynthesis（光合作用）ZhangMengjieSchoolofLifeScience&TechnologyEmail:Tel:生物化學(xué)教程p359-370生物化學(xué)下冊(cè)p197-p229IntroductionPhotophosphorylation（光合磷酸化）Carbondioxidefixation（CO2固定）photosynthesis(光合作用):TraditionallyequatedwithCO2fixation.太陽能------化學(xué)能energyfromlightisharvestedtoprovidecarbohydratesforenergyproduction無機(jī)物------有機(jī)物

carbonreentersthebiosphere(fromCO2)水----------氧氣

themajorsourceofoxygen.1.IntroductionThelightreactionsofphotosynthesis----directlydependentontheabsorptionoflighttheresultingphotochemistrytakeselectronsfromH2Oanddrivesthemthroughaseriesofmembrane-boundcarriers,producingNADPHandATP.Thecarbon-assimilationreactionsofphotosynthesisreduceCO2withelectronsfromNADPHandenergyfromATP.Thelight-dependentandlight-independentreactionsofphotosynthesis.Lightreactionsareassociatedwiththethylakoid（類囊體）membranes,andlight-independentreactionsareassociatedwiththestroma（基質(zhì)）.Start

pointphotosyntheticbacteria：purple-sulfurbacteria(紫色硫細(xì)菌)

green-sulfurbacteria(綠色硫細(xì)菌)

CO２+2H２S→(CH２O)+2S+H２O

光下同化CO２而沒有O２的釋放1931C.B.VanNiel：overallequationforphotosynthesis：CO２+2H２A→(CH２O)+2A+H２O光合作用，是指光養(yǎng)生物利用光能把CO２合成有機(jī)物的過程Threephases：1.光能的吸收、傳遞和轉(zhuǎn)換成電能---原初反應(yīng)2.電能轉(zhuǎn)變?yōu)榛钴S化學(xué)能---電子傳遞和光合磷酸化3.活躍的化學(xué)能轉(zhuǎn)變?yōu)榉€(wěn)定的化學(xué)能---碳同化重點(diǎn)initiatesanoxidation-reductionchainEukaryoticPhototrophsPossessTwoDistinctPhotosystems重點(diǎn)TheStuctureofPSⅡ放氧復(fù)合體脫鎂葉綠素Oxygen-evolvingcomplex（放氧復(fù)合體）WatersplittingcomplexTheStuctureofPSⅠ鐵氧化還原蛋白質(zhì)體藍(lán)素P700葉綠醌葉綠素ANADPH重點(diǎn)2.photophosphorylation(光合磷酸化)NoncyclicPhotophosphorylation(非環(huán)式光合磷酸化）重點(diǎn)CyclicPhotophosphorylation（環(huán)式光合磷酸化）Inhibitorsofelectrontransport：NH2OH(羥胺)：H2OPSⅡ的電子流DCMU：PSⅡ上的Q

PQ的電子傳遞KCN和Hg：抑制PC的氧化InhibitorofphotosynthesisChemicaluncouplers

DNP,CCCP(羰基氰-3-氯苯腙)、短桿菌肽D、尼日利亞菌素、NH＋４等inhibitorsofphotophosphorylation二環(huán)己基碳二亞胺(DCCD)、對(duì)氯汞基苯(PCMB)：CF1Oligomycin：bindCfoandinhibitphotophosphorylation

C3途徑(C3pathway)C4途徑(C4pathway)CAM(景天科酸代謝，Crassulaceanacidmetabolism)途徑3.CarbondioxidefixationAlsocalledcarbondioxideassimilation（CO2同化）3.1C3

pathwayRibulose-1,5-Bisphosphate（RuBP）IstheCO2AcceptorinCO2Fixation重點(diǎn)(1)carboxylationphase(羧化階段)Ribulose-1,5-BisphosphateCarboxylase/Oxygenase（Rubisco）重點(diǎn)3-P-甘油酸Ribulose-1,5-BisphosphateCarboxylase（8L+8Ssubunits）

重點(diǎn)(2)reductionphase(還原階段)PGA（3-磷酸甘油酸）GAP（甘油醛-3-磷酸）PGA+ATP+NADPH+H+→→GAP+ADP+NADP++Pi

PGA是一種有機(jī)酸，要達(dá)到糖的能級(jí)，必須使用同化力（ATP與NADPH）使PGA的-COOH轉(zhuǎn)變成GAP的-CHO重點(diǎn)PGA+ATP+NADPH+H+→GAP+ADP+NADP++Pi

(3)regenerationphase(再生階段)

GAP（甘油醛-3-磷酸）RuBP（核酮糖-1,-5-二磷酸）

重點(diǎn)5GAP+3ATP+2H2O→3RuBP+3ADP+2Pi+3H+

見下頁P(yáng)PT轉(zhuǎn)酮酶（2C）轉(zhuǎn)醛酶（3C）反應(yīng)式：

5GAP+3ATP+2H2O→3RuBP+3ADP+2Pi+3H+5GAP+3ATP+2H2O→3RuBP+3ADP+2Pi+3H+6CO21Glc12NADPH18ATPStoichiometryofCO2assimilationintheCalvincycle.ForeverythreeCO2

moleculesfixed,onemoleculeoftriosephosphate(glyceraldehyde3-phosphate)isproducedand9ATPand6NADPHareconsumed.重點(diǎn)alternativefatesofthefixedcarbonofglyceraldehyde3-phosphate（3-P-甘油醛）Themostisrecycledtoribulose1,5-bisphosphate“extra”glyceraldehyde3-phosphateBeusedimmediatelyasasourceofenergyBeconvertedtosucrose（蔗糖）fortransportBestoredinthechloroplastasstarch重點(diǎn)mitochondrialrespiration,Inthedark,theoxidationofsubstratestoCO2andtheconversionofO2toH2O.photorespiration,inplants,likemitochondrialrespiration,consumesO2andproducesCO2,likephotosynthesis,isdrivenbylight.PhotorespirationandtheC4andCAMPathwaysThereactionwithO2resultsinnofixationofcarbonsalvagingthecarbonsfrom2-phosphoglycolate（2-磷酸乙醇酸）ribulose1,5-bisphosphatecarboxylase/oxygenase磷酸乙醇酸磷酸乙醇酸乙醇酸甘油酸Theoxygenasereationofrubisco-乙醇酸途徑過氧化物酶體乙醇酸乙醛酸甘氨酸光呼吸中的CO2釋放羥丙酮酸重點(diǎn)manyplants,growinthetropics(andintemperate-zonecropplantsnativetothetropics),suchasmaize玉米,sugarcane甘蔗,andsorghum高粱amechanismhasevolvedtocircumventtheproblemofwastefulphotorespiration（光呼吸）.Carbonassimilation（碳同化）inC4plantsTheC4pathway,involvingmesophyllcells（葉肉細(xì)胞）bundle-sheathcells（維管束鞘細(xì)胞）predominatesinplantsoftropicalorigin.mesophyll

cell

（葉肉細(xì)胞）：PEPcarboxylase（磷酸烯醇式丙酮酸羧化酶，PEPC)以及與C4二羧酸生成有關(guān)的酶BSC（維管束鞘細(xì)胞）：Rubisco等參與C3途徑的酶、乙醇酸氧化酶以及脫羧酶。C4Plants,CO2FixationandRubiscoActivityAreSpatiallySeparatedPEPcarboxylase（磷酸烯醇式丙酮酸羧化酶，PEPC)以及與C4二羧酸生成有關(guān)的酶Rubisco等參與C3途徑的酶、乙醇酸氧化酶以及脫羧酶mesophyll

cell

（葉肉細(xì)胞）BSC（維管束鞘細(xì)胞）重點(diǎn)三種亞類型依賴NADP的蘋果酸酶(NADPmalicenzyme)的蘋果酸型(NADP-ME型)；依賴NAD的蘋果酸酶(NADmalicenzyme)的蘋果酸型(NAD-ME型)；具有PEP羧激酶(PEPcarboxykinase)的天冬氨酸型(PCK型)。

NADP-ME型NAD-ME型重點(diǎn)PEP羧激酶PCK型重點(diǎn)是植物光合碳同化對(duì)熱帶環(huán)境的一種適應(yīng)方式

有“CO2泵”濃縮CO2的機(jī)制，具有較高的光合速率C4植物同化CO2消耗的能量比C３植物多,故在光強(qiáng)及溫度較低的情況下，其光合效率還低于C３植物。

意義重點(diǎn)CAM（景天酸代謝途徑）

crassulaceanacidmetabolism,theplantsarecalledCAMplants.晚上氣孔開啟，葉肉細(xì)胞的細(xì)胞質(zhì)中由PEPC固定CO2