111生物化学理论课件&中科大13photosynthesis09.ppt

1、2022-4-242022-4-24Introduction 2. Photophosphorylation 3 . Carbon-assimilation - Assimination of CO2 C3 pathway Photorespiration C4 / CAM Pathways2022-4-241. Introduction1. Introduction2022-4-24Solar energy - ultimate source of all biological energy.2022-4-24Photosynthetic catastrophe-If photosynthe

2、sis were to cease, all higher forms of life would be extinct in about 25 years. 2022-4-24光合作用(photosynthesis):绿色植物绿色植物吸收光能，把二氧化碳和水合成有机物，同时释放氧气的过程。太阳能-可贮存的化学能energy from light is harvested to provide carbohydrates for energy production无机物-有机物 carbon reenters the biosphere (from CO2)水-氧气 the major sou

3、rce of oxygen.光合作用是生物界获得能量、食物能量、食物以及氧气氧气的根本途径， “地球上最重要的化学反应”2022-4-24细菌光合作用细菌光合作用 photosynthetic bacteria蓝细菌、紫细菌和绿细菌等 蓝细菌的光合过程与真核生物相似 紫色硫细菌(purple-sulfur bacteria) 绿色硫细菌(green-sulfur bacteria) CO+2HS(CHO)+2S+HO 光下同化CO而没有O的释放1931 C.B.Van Niel 光合作用的通式： CO+2HA(CHO)+2A+HO 光合作用，是指光养生物利用光能把光合作用，是指光养生物利用光能

4、把COCO合成有机物的过程合成有机物的过程2022-4-24光合作用三个阶段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2022-4-24The light reactions of photosynthesis generate energy rich NADPH and ATP at the expense of solar energy.2022-4-24Light reactions of photosynthesis-directly dependent on the absorption of l

5、ightthe resulting photochemistry takes electrons from H2O and drives them through a series of membrane-bound carriers, producing NADPH and ATP.Carbon-assimilation - reactions of photosynthesis reduce CO2 with electrons from NADPH and energy from ATP.2022-4-242008年年8月月22日，美国麻省理工学院化学家丹尼尔日，美国麻省理工学院化学家丹

6、尼尔诺切拉诺切拉（DanielNocera）和马修和马修卡纳安卡纳安 （MatthewKanan）在科在科学上撰文宣布，他们发明了一种制作简单、价格低廉的催化学上撰文宣布，他们发明了一种制作简单、价格低廉的催化剂，能将水分子分解为氢气和氧气。剂，能将水分子分解为氢气和氧气。模拟光合作用储存太阳能模拟光合作用储存太阳能2022-4-24The Chloroplast2022-4-242022-4-24chloroplast envelope:控制物质的进出，维持光合作用的微环境Stroma: 碳同化的场所Thylakoid:光反应的场所单层膜围起的扁平小囊，膜厚度57nm，囊腔(lumen)空间

7、为10nm左右基质类囊体(stroma thylakoid)/基质片层(stroma lamella)，伸展在基质中彼此不重叠基粒类囊体(grana thlylakoid)/基粒片层(grana lamella)2022-4-24Cyanobacteria.蓝藻蓝藻A colony of the photosynthetic filamentous cyanobacteria Anabaen 项圈藻. Ancestors of these bacteria are thought to have evolved into present-day chloroplasts.2022-4-24In

8、 Plants, there are two pathways:Noncyclic electron transfer, “Z scheme” : involves PSI & PSII. the pathway of electron transfer from H2O to NADP. Cyclic electron transfer: involves only PSI; electrons return via the cyclic pathway to PSI, instead of reducing NADP to NADPH.Electron transfer chains202

9、2-4-24质体蓝素铁氧还蛋白2022-4-24Oxygen-evolving complex 放氧复合体Water splitting complex2022-4-24Four Photons Are Required to Generate One Oxygen Molecule. When dark-adapted chloroplasts are exposed to a brief flash of light, one electron passes through photosystem II. Monitoring the O2 released after each flas

10、h reveals that four flashes are required to generate each O2 molecule. The peaks in O2 release occur after the 3rd, 7th, and 11th flashes because the dark-adapted chloroplasts start in the S1 state-that is, the one-electron reduced state.2022-4-24pH5pH82022-4-242. 2. 光合磷酸化光合磷酸化( (photophosphorylatio

11、nphotophosphorylation) )机理机理. .光合磷酸化与电子传递的偶联关系光合磷酸化与电子传递的偶联关系 ATP/e 每对电子通过光合电子传递链而形成的ATP分子数P/O 光反应中每释放1个氧原子所能形成的ATP分子数比值越大，表示磷酸化与电子传递偶联越紧密2022-4-24 经非环式电子传递时分解2分子HO，放1 个O与传递2对电子，使类囊体膜腔内增加12个H(放氧复合体处放4个H+，Cytb/f间的电子传递时放4个H+，2NADPH2)Noncyclic photophosphorylationelectrons in chloroplasts are energized

12、 by light.2022-4-24Absorption of Eight Photons Yields One O2Two NADPHThree ATP Molecules2022-4-24英国的米切尔(Mitchell，1961)提出由磷脂和蛋白多肽构成的膜对离子和质子的透过具有选择具有氧化还原电位的电子传递体不匀称地嵌合在膜内膜上有偶联电子传递的质子转移系统膜上有转移质子的ATP酶光合电子传递链的电子传递会伴随膜内外两侧产生质子动力(proton motive force, pmf)，并由质子动力推动ATP的合成2.化学渗透学说化学渗透学说 chemiosmotic theory202

13、2-4-24（1）化学渗透学说的实验证据）化学渗透学说的实验证据A.A.光下类囊体吸收质子的实验光下类囊体吸收质子的实验对叶绿体悬浮液照光，用pH计可测到悬浮液的pH升高由于光合电子传递引起了悬浮液中质子向类囊体膜腔运输，使得膜内H+浓度高而膜外较低的缘故2022-4-24B. 酸酸-碱磷酸化实验碱磷酸化实验 贾格道夫等(1963)在暗中把叶绿体的类囊体放在p4的弱酸性溶液中平衡，让类囊体膜腔的下降至4加进pH8和含有ADP和Pi的缓冲溶液,瞬间的pH变化使得类囊体膜内外之间产生一个H+梯度H梯度能使ADP与Pi生成ATP，而这时并不照光，也没有电子传递这种驱动ATP合成的类囊体内外的pH差在

14、活体中正是由光合电子传递和H+转运所形成的2022-4-243.3.ATPATP合成的部位合成的部位ATPATP酶酶 CF1-CFo复合体 质子反向转移, 合成ATP 突出于膜表面的亲水性的“CF1” 埋置于膜中的疏水性的“CFo”2022-4-24CFo是质子的“通道”，供应质子给CF1去合成ATPCF1利用H越膜所释放的能量来合成ATP美国的鲍易尔（Boyer 1993）认为，是H浓度递度引起CF1上亚基的转动变构而催化ATP合成的。2022-4-24(1)1)电子传递抑制剂电子传递抑制剂 羟胺(NH2OH)切断水到PS的电子流DCMU抑制从PS上的Q到PQ的电子传递KCN和Hg等则抑制P

15、C的氧化一些除草剂如西玛津(simazine)、阿特拉津(atrazine)、除草定(bromacil)、异草定(isocil)等也是电子传递抑制剂，它们通过阻断电子传递抑制光合作用来杀死植物。4.光合磷酸化的抑制剂光合磷酸化的抑制剂2022-4-24(2)2)解偶联剂解偶联剂 DNP,CCCP(羰基氰-3-氯苯腙)、短杆菌肽D、尼日利亚菌素、NH等增加类囊体膜对质子的透性或增加偶联因子渗漏质子的能力，消除了跨膜的H+电化学势，而电子传递仍可进行，甚至速度更快(因为消除了内部高H浓度对电子传递的抑制)，但磷酸化作用不再进行。2022-4-24(3)(3)能量传递抑制剂能量传递抑制剂 寡霉素作用

16、于CFo抑制了ATP酶活性从而阻断光合磷酸化。 2022-4-242022-4-24植物利用光反应中形成的NADPH和ATP将CO2转化成稳定的碳水化合物的过程。 C3途径(C3 pathway) C4途径(C4 pathway) CAM (景天科酸代谢，Crassulacean acid metabolism)途径。3 .3 .碳同化碳同化 CO2 assimilation2022-4-2420世纪的50年代，Melvin Calvin 单细胞光合有机体小球藻(Chlorella)悬液持续的光照和CO2，使光合作用处于稳态。接着，短时间内加入放射性同位素标记的14CO2以标记循环的中间物。然

17、后，将细胞悬液迅速倾入煮沸的乙醇溶液中杀死细胞，致使酶失活。最后，使用双相纸电泳和放射自显影分离、分析循环中的中间物 2022-4-241946年，美国加州大学放射化学实验室的M.Calvin 和A.Benson2022-4-24Tracing the Fate of Carbon Dioxide. Radioactivity from 14CO2 is incorporated into 3-phosphoglycerate within 5 s in irradiated cultures of algae.After 60 s, the radioactivity appears in

18、many compounds, the intermediates within the Calvin cycle.2022-4-24巧妙的实验设计巧妙的实验设计电泳技术和同位素示踪技术电泳技术和同位素示踪技术卡尔文获得了1961年诺贝尔化学奖 2022-4-244.1 C4.1 C3 3途径途径2022-4-24(1)羧化阶段羧化阶段(carboxylation phase)2022-4-24Structure of ribulose 1,5-bisphosphatecarboxylase (Rubisco)eight large subunits (blue) eight small on

19、es (gray), Mr 550,000. Rubisco concentration : 250 mg/mL in the chloroplast stroma, Yellow-Amino acid residues of the active siteGreen-Mg2+ ion2022-4-24Central role of Mg2+ in the catalytic mechanism of rubiscoMg2+ is coordinated in a roughly octahedral complex with six oxygen atoms: one oxygen in t

20、he carbamate氨基甲酸盐on Lys201; two in the carboxyl羧基 groups of Glu204 and Asp203; two at C-2 and C-3 of the substrate, ribulose 1,5-bisphosphate; one in the other substrate, CO2.2022-4-241) Ribulose 1,5-bisphosphate forms an enediolate intermediate烯二醇中间物at the active site.2022-4-242 ）CO2, polarized by

21、the proximity of the Mg2+ ion, undergoes nucleophilic attack by the enediolate, producing a branched six-carbon sugar.2022-4-243 ）Hydroxylation at C-3 of this sugar2022-4-244 ）aldol醛醇 cleavage , forms one molecule of 3-phosphoglycerate, which leaves the enzyme active site.2022-4-245 ）The carbanion 负

22、碳离子of the remaining three-carbon fragment is protonated by the nearby side chain of Lys175, generating a second moleculeof 3-phosphoglycerate. 2022-4-24E EC ECM2022-4-242022-4-24Role of rubisco activase in the carbamoylation甲氨酰化甲氨酰化 of Lys201 of rubisco2022-4-24(2)(2)还原阶段还原阶段( (reduction phase)reduc

23、tion phase)利用同化力将3-磷酸甘油酸还原为甘油醛-3-磷酸的反应过程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的羧基转变成GAP的醛基当CO2被还原为GAP时，光合作用的贮能过程便基本完成 2022-4-24(3)(3)再生阶段再生阶段( (regeneration phase) regeneration phase) 指由甘油醛-3-磷酸重新形成核酮糖-1,-5-二磷酸的过程 5GAP+3ATP+2H2O3RuBP+3ADP+2Pi+3H+2022-4-24interco

24、nversions of triose phosphates and pentose phosphates.2022-4-24Pentose phosphate pathway: breaks down glucose into carbon dioxide to generate NADPHCalvin cycle: uses NADPH to reduce carbon dioxide to generate hexoses- reductive pentose phosphate pathwaymirror imageshave in common several enzymes and

25、 intermediates that attest to an evolutionary kinship. 2022-4-246CO21Glc12NADPH18ATPStoichiometry of CO2 assimilation in the Calvin cycleFor every three CO2 molecules fixed, one molecule of triose phosphate (glyceraldehyde 3-phosphate) is produced and nine ATP and six NADPH are consumed2022-4-242022

26、-4-24alternative fates of the fixed carbon of glyceraldehyde 3-phosphateThe most is recycled to ribulose 1,5-bisphosphate “extra” glyceraldehyde 3-phosphateBe used immediately as a source of energyBe converted to sucrose for transport Be stored in the chloroplast as starch2022-4-242022-4-24The Pitri

27、ose phosphate antiport system of the inner chloroplast membrane. 2022-4-24nPhotorespiration nC4 / CAM Pathways2022-4-24in plantsmitochondrial respiration, In the dark, the oxidation of substrates to CO2 and the conversion of O2 to H2O. like mitochondrial respiration, consumes O2 and produces CO2 lik

28、e photosynthesis, is driven by light. photorespiration2022-4-24PhotorespirationC2 cycle2022-4-24The reaction with O2 results in no fixation of carbon salvaging the carbons from 2-phosphoglycolateribulose 1,5-bisphosphate carboxylase/oxygenase2022-4-24The modern atmospherecontains about 20% O2 and on

29、ly 0.04% CO2,so an aqueous solution in equilibrium with air at roomtemperature contains about 250 M O2 and 11 M CO2concentrations.significant O2 “fixation”-rubisco is a significant waste of energyThe Km for CO2 is about 9 M, The Km for O2 is about 350 MRubisco2022-4-24Photorespiration Results from R

30、ubiscos Oxygenase ActivityRubisco(ribulose1,5-bisphosphate carboxylase/oxygenase)2-phosphoglycolate, a metabolically useless productsalvaging the carbons from 2-phosphoglycolateconsumes significant amounts of cellular energy and releases some previously fixed CO2.2022-4-242022-4-242022-4-24Electron

31、Micrograph of a Peroxisome Nestled between Two Chloroplasts.2022-4-24Many plants, grow in the tropics (high light intensity & high temperatures)such as maize, sugarcane甘蔗, and sorghum 高粱a mechanism has evolved to circumvent the problem of wasteful photorespirationThe C4 plants characteristics:high p

32、hotosynthetic rateshigh growth rateslow photorespiration rateslow rates of water lossa specialized leaf structure: mesophyll and bundle-sheath cellsCarbon assimilation in C4 plants2022-4-24The C4 pathway, involvingmesophyll cells bundle-sheath cells2022-4-24C4单子叶植物（甘蔗）C3单子叶（一种草）mesophyll and bundle-

33、sheath cellsPlasmodesmata 胞间连丝胞间连丝connects the two cells2022-4-24Mesophyll cell：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：Rubisco等参与C3途径的酶、乙醇酸氧化酶以及脱羧酶。这两类细胞中进行不同的生化反应。C4 Plants, CO2 Fixation and Rubisco Activity Are Spatially Separated2022-4-24C4 Pathway. Carbon dioxide is concentrated in bundle-sheath cel

34、ls by the expenditure of ATP in mesophyll cells.2022-4-24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C植物多,故在光强及温度较低的情况下，其光合效率还低于C植物。 意义2022-4-24景天科酸代谢途径景天科酸代谢途径 CAM途径crassulacean acid metabolism,the plants are called CAM plants.景天科等植物：2022-4-24晚上晚上: 气孔开启，叶肉细胞的细胞质中由PEPC固定CO2，形成的苹果酸贮藏

35、于液泡，使液泡的pH降低；白天白天: 气孔关闭，苹果酸脱羧，释放的CO2由Rubisco羧化2022-4-24 2022-4-24 C4植物: 在同一时间(白天)和不同的空间(叶肉细胞和维管束鞘细胞)完成CO2固定(C4途径)和还原(C3途径)两个过程；CAM植物: 在不同时间(黑夜和白天)和同一空间(叶肉细胞)完成上述两个过程的。 2022-4-242022-4-24(a) Illuminated Chlorella were grown with unlabeled CO2, then the light was turned off and 14CO2 was added (vertic

36、al dashed line in the graph below). Under these conditions, X was the first compound to become labeled with 14C; Y was unlabeled.Problem:Calvin and his colleagues used the unicellular green alga Chlorella to study the carbon-assimilation reactions of photosynthesis. They incubated 14CO2 with illumin

37、ated suspensions of algae and followed the time course of appearance of 14C in two compounds, X and Y, under two sets of conditions.Suggest the identities of X and Y, based on your understanding of the Calvin cycle.2022-4-24(b) Illuminated Chlorella cells were grown with 14CO2. Illumination was cont

38、inued until all the 14CO2 had disappeared (vertical dashed line in the graph below). Under these conditions, X became labeled quickly but lost its radioactivity with time, whereas Y became more radioactive with time.2022-4-24用同位素示踪法研究光合作用，被试植物先在用同位素示踪法研究光合作用，被试植物先在1%1%COCO2 2中进行光合中进行光合作用，而后将作用，而后将CO

39、CO2 2浓度降到浓度降到0.003%0.003%。测得。测得1414C C标记的标记的3 3磷酸甘油酸磷酸甘油酸（PGAPGA）和核酮糖二磷酸（和核酮糖二磷酸（RuBPRuBP）含量的变化如图所示。从这项含量的变化如图所示。从这项研究中能引出什么结论？研究中能引出什么结论？2022-4-24Differences between C3 and C4 Plants The plant genus Atriplex includes some C3 and some C4 species. From the data in the plots below (species 1, black cu

40、rve; species 2, red curve), identify which is a C3 plant and which is a C4 plant. Justify your answer in molecular terms that account for the data in all three plots.2022-4-24Some questionsPhotosynthesis? photophosphorylation?Light reaction? Dark reaction （carbon-assimilation reaction) ? Whats the r

41、elationship between Light reaction and dark reaction ?C3 cycle and the whole C3 cycle pathway? And C4, CAM cycle?Rubisco? How does the Rubisco Activase regulate the activity of Rubisco, that is , regulate the rate of carbon-assimilation reaction?1. How do you understand the role of photorespiration ? 2022-4-24