大二上学期文件-生物化学biochemistry lecture6photosynthesis光合作用

Lecture6Photosynthesis（光合作用）ZhangMengjieSchoolofLifeScience&TechnologyEmail:Tel:生物化学教程p359-370生物化学下册p197-p229IntroductionPhotophosphorylation（光合磷酸化）Carbondioxidefixation（CO2固定）photosynthesis(光合作用):TraditionallyequatedwithCO2fixation.太阳能------化学能energyfromlightisharvestedtoprovidecarbohydratesforenergyproduction无机物------有机物

carbonreentersthebiosphere(fromCO2)水----------氧气

themajorsourceofoxygen.1.IntroductionThelightreactionsofphotosynthesis----directlydependentontheabsorptionoflighttheresultingphotochemistrytakeselectronsfromH2Oanddrivesthemthroughaseriesofmembrane-boundcarriers,producingNADPHandATP.Thecarbon-assimilationreactionsofphotosynthesisreduceCO2withelectronsfromNADPHandenergyfromATP.Thelight-dependentandlight-independentreactionsofphotosynthesis.Lightreactionsareassociatedwiththethylakoid（类囊体）membranes,andlight-independentreactionsareassociatedwiththestroma（基质）.Start

pointphotosyntheticbacteria：purple-sulfurbacteria(紫色硫细菌)

green-sulfurbacteria(绿色硫细菌)

CO２+2H２S→(CH２O)+2S+H２O

光下同化CO２而没有O２的释放1931C.B.VanNiel：overallequationforphotosynthesis：CO２+2H２A→(CH２O)+2A+H２O光合作用，是指光养生物利用光能把CO２合成有机物的过程Threephases：1.光能的吸收、传递和转换成电能---原初反应2.电能转变为活跃化学能---电子传递和光合磷酸化3.活跃的化学能转变为稳定的化学能---碳同化重点initiatesanoxidation-reductionchainEukaryoticPhototrophsPossessTwoDistinctPhotosystems重点TheStuctureofPSⅡ放氧复合体脱镁叶绿素Oxygen-evolvingcomplex（放氧复合体）WatersplittingcomplexTheStuctureofPSⅠ铁氧化还原蛋白质体蓝素P700叶绿醌叶绿素ANADPH重点2.photophosphorylation(光合磷酸化)NoncyclicPhotophosphorylation(非环式光合磷酸化）重点CyclicPhotophosphorylation（环式光合磷酸化）Inhibitorsofelectrontransport：NH2OH(羟胺)：H2OPSⅡ的电子流DCMU：PSⅡ上的Q

PQ的电子传递KCN和Hg：抑制PC的氧化InhibitorofphotosynthesisChemicaluncouplers

DNP,CCCP(羰基氰-3-氯苯腙)、短杆菌肽D、尼日利亚菌素、NH＋４等inhibitorsofphotophosphorylation二环己基碳二亚胺(DCCD)、对氯汞基苯(PCMB)：CF1Oligomycin：bindCfoandinhibitphotophosphorylation

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

pathwayRibulose-1,5-Bisphosphate（RuBP）IstheCO2AcceptorinCO2Fixation重点(1)carboxylationphase(羧化阶段)Ribulose-1,5-BisphosphateCarboxylase/Oxygenase（Rubisco）重点3-P-甘油酸Ribulose-1,5-BisphosphateCarboxylase（8L+8Ssubunits）

重点(2)reductionphase(还原阶段)PGA（3-磷酸甘油酸）GAP（甘油醛-3-磷酸）PGA+ATP+NADPH+H+→→GAP+ADP+NADP++Pi

PGA是一种有机酸，要达到糖的能级，必须使用同化力（ATP与NADPH）使PGA的-COOH转变成GAP的-CHO重点PGA+ATP+NADPH+H+→GAP+ADP+NADP++Pi

(3)regenerationphase(再生阶段)

GAP（甘油醛-3-磷酸）RuBP（核酮糖-1,-5-二磷酸）

重点5GAP+3ATP+2H2O→3RuBP+3ADP+2Pi+3H+

见下页PPT转酮酶（2C）转醛酶（3C）反应式：

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

moleculesfixed,onemoleculeoftriosephosphate(glyceraldehyde3-phosphate)isproducedand9ATPand6NADPHareconsumed.重点alternativefatesofthefixedcarbonofglyceraldehyde3-phosphate（3-P-甘油醛）Themostisrecycledtoribulose1,5-bisphosphate“extra”glyceraldehyde3-phosphateBeusedimmediatelyasasourceofenergyBeconvertedtosucrose（蔗糖）fortransportBestoredinthechloroplastasstarch重点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-乙醇酸途径过氧化物酶体乙醇酸乙醛酸甘氨酸光呼吸中的CO2释放羟丙酮酸重点manyplants,growinthetropics(andintemperate-zonecropplantsnativetothetropics),suchasmaize玉米,sugarcane甘蔗,andsorghum高粱amechanismhasevolvedtocircumventtheproblemofwastefulphotorespiration（光呼吸）.Carbonassimilation（碳同化）inC4plantsTheC4pathway,involvingmesophyllcells（叶肉细胞）bundle-sheathcells（维管束鞘细胞）predominatesinplantsoftropicalorigin.mesophyll

cell

（叶肉细胞）：PEPcarboxylase（磷酸烯醇式丙酮酸羧化酶，PEPC)以及与C4二羧酸生成有关的酶BSC（维管束鞘细胞）：Rubisco等参与C3途径的酶、乙醇酸氧化酶以及脱羧酶。C4Plants,CO2FixationandRubiscoActivityAreSpatiallySeparatedPEPcarboxylase（磷酸烯醇式丙酮酸羧化酶，PEPC)以及与C4二羧酸生成有关的酶Rubisco等参与C3途径的酶、乙醇酸氧化酶以及脱羧酶mesophyll

cell

（叶肉细胞）BSC（维管束鞘细胞）重点三种亚类型依赖NADP的苹果酸酶(NADPmalicenzyme)的苹果酸型(NADP-ME型)；依赖NAD的苹果酸酶(NADmalicenzyme)的苹果酸型(NAD-ME型)；具有PEP羧激酶(PEPcarboxykinase)的天冬氨酸型(PCK型)。

NADP-ME型NAD-ME型重点PEP羧激酶PCK型重点是植物光合碳同化对热带环境的一种适应方式

有“CO2泵”浓缩CO2的机制，具有较高的光合速率C4植物同化CO2消耗的能量比C３植物多,故在光强及温度较低的情况下，其光合效率还低于C３植物。

意义重点CAM（景天酸代谢途径）

crassulaceanacidmetabolism,theplantsarecalledCAMplants.晚上气孔开启，叶肉细胞的细胞质中由PEPC固定CO2