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Chapter 10

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  • Figure 10.3 Zooming in on the location of photosynthesis in a plant
  • Figure 10.4 Tracking atoms through photosynthesis
  • Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
  • Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
  • Figure 10.12 How a photosystem harvests light
  • Figure 10.13 How linear electron flow during the light reactions generates ATP and NADPH
  • Figure 10.14 A mechanical analogy for the light reactions
  • Figure 10.17 The light reactions and chemiosmosis: the organization of the thylakoid membrane
  • Figure 10.16 Comparison of chemiosmosis in mitochondria and chloroplasts
  • Figure 10.18 The Calvin cycle
  • Figure 10.21 A review of photosynthesis
  • Transcript

    • 1. CAC and oxidative phosphorylation practice quiz1. What are the net products of the CAC?2. How is pyruvate converted into Acetyl CoA?3. Where does the CAC take place?4. Explain how the free energy and electronegativity changes as electrons arepassed down the ETC.5. ____is the enzyme used to pump protons back into the mitochondria.6. _____ and _____are the two steps that make up oxidative phosphorylation.7. Which step of cellular respiration produces the most energy for the cell? Howmuch ATP is produced per one molecule of glucose?8. True of False: Pyruvate is used in fermentation and aerobic cellular respiration.9. What are the products of alcohol and lactic acid fermentation?
    • 2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPowerPoint®Lecture Presentations forBiologyEighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan SharpChapter 10Photosynthesis
    • 3. Chloroplasts: The Sites of Photosynthesis in Plants• Chloroplasts– Uses light energy to make sugar by coordinating light anddark reactions– chlorophyll: the green pigment within chloroplasts• Light energy absorbed by chlorophyll drives the synthesis oforganic molecules in the chloroplast• in the membranes of thylakoids– CO2 enters and O2 exits the leaf through microscopic porescalled stomata• A typical mesophyll cell has 30–40 chloroplasts
    • 4. Fig. 10-3Leaf cross sectionVeinMesophyllStomata CO2 O2Chloroplast Mesophyll cellOutermembraneIntermembranespace5 µmInnermembraneThylakoidspaceThylakoidGranumStroma1 µm
    • 5. Photosynthesis is a redox process• Photosynthesis can be summarized as the following equation:• The electron flow is the opposite of what occurs in cellularrespiration– Chloroplasts split H2O into hydrogen and oxygen– Electrons are transferred from water to CO2– CO2 is reduced to sugar molecules• Electrons increase in potential energy as they move fromwater to sugar (endergonic process)– Sunlight provides energy6 CO2 + 6 H2O + Light energy → C6H12O6 + 6 O2Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    • 6. Reactants:Fig. 10-46 CO2Products:12 H2O6 O26 H2OC6H12O6Photosynthesis: H2O is oxidized and CO2 is reduced
    • 7. The Two Stages of Photosynthesis: A Preview• Light Reactions– Solar energy converted to chemical energy– Occurs in the thylakoids of chloroplasts1. H2O is split providing a source of electrons and protons2. Electrons transferred from water to NADP+– NADP+is reduced to NADPH– Driven by the energy from light1. ATP generated from ADP (Driven by chemiosmosis)2. O2 is released as a byproduct
    • 8. The Two Stages of Photosynthesis: A Preview• The Calvin cycle– AKA the Dark Reactions because they don’t require directlight– Occurs in the stroma:1. Incorporation of CO2 into organic molecules (carbonfixation)2. Fixed carbon is reduced to carbohydrate by the addition ofelectrons– Uses ATP and NADPH from light reactions
    • 9. LightFig. 10-5-2H2OChloroplastLightReactionsNADP+PADPi+ATPNADPHO2Light reactions use solar energy to make ATP and NADPH for the Calvin Cycle
    • 10. LightFig. 10-5-4H2OChloroplastLightReactionsNADP+PADPi+ATPNADPHO2CalvinCycleCO2[CH2O](sugar)The Calvin Cycle incorporates CO2 into organicmolecules which are converted to sugar
    • 11. A Photosystem: A Reaction-Center ComplexAssociated with Light-Harvesting Complexes• Chlorophyll is key to photosythesis• Chlorophyll molecules are organized into photosystems– reaction-center complex• when excited by light, chlorophyll donates an electron to anelectron acceptor which passes it to an ETC– light-harvesting complexes• captures light energy and transfers it to reaction-center pigments• funnel the energy of photons to the reaction centerCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    • 12. Fig. 10-12THYLAKOID SPACE(INTERIOR OF THYLAKOID)STROMAe–PigmentmoleculesPhotonTransferof energySpecial pair ofchlorophyllmoleculesThylakoidmembranePhotosystemPrimaryelectronacceptorReaction-centercomplexLight-harvestingcomplexes1. Photon strikes apigment molecule ina light-harvestingcomplex2. Energy is passedfrom pigment topigment until itreaches the reaction-center complex3. Excited electron ispassed to theprimary electronacceptor (1ststep inthe light reaction)How a photosystem harvests light
    • 13. • Photosystems convert light energy to chemical energy whichwill be used to synthesize sugars• Association of chlorophyll a molecules with different proteinsin the thylakoid membrane account for differences in light-absorbing properties• Photosystem I (PS I)– Absorbs a wavelength of 700 nm– The reaction-center chlorophyll a of PS I is called P700• Photosystem II (PS II)– Absorbs a wavelength of 680 nm– The reaction-center chlorophyll a of PS II is called P680Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsTwo types of photosystems
    • 14. Electron Flow• Light drives the synthesis of ATP and NADPH by energizingthe two photosystems within chloroplasts• Two possible routes for electron flow: cyclic and linear• Linear electron flow– Occurs during the light reactions and involves both photosystems– Produces ATP, NADPH and O2 using light energy– Net electron flow is from water to NADPH• Cyclic electron flow– Occurs during the light reactions but only involves PS I– Produces ATP but not NADPH or O2Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    • 15. Fig. 10-13-5PigmentmoleculesLightP680e–Primaryacceptor21e–e–2 H+O2+3H2O1/24PqPcCytochromecomplexElectron transport chain5ATPPhotosystem I(PS I)LightPrimaryacceptore–P7006FdElectrontransportchainNADP+reductaseNADP++ H+NADPH87e–e–6Photosystem II(PS II)Linear electron flow during the light reactionsgenerates ATP and NADPH
    • 16. 1. A photon hits a pigment and its energy is passed among pigment molecules untilit excites P6802. An excited electron from P680 is transferred to the PEA (P680  P680+)3. H2O  2 electrons + 2 Hydrogen ions + 1 oxygen atom– electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680– O2 is released as a by-product of this reaction1. Electron travels from PEA of PS II  PS I via an ETC2. Exergonic fall of electrons provides energy for synthesis of ATP (chemiosmosis)3. In PS I (like PS II), transferred light energy excites P700, which loses an electronto an electron acceptor (P700  P700+)– Electrons are transferred from PS II to P700+ via the ETC (P700+  P700)1. Electrons are passed from PEA of PSI to a second ETC (doesn’t produce ATP)2. NADP+ is reduced to NADPH by the transfer of two electrons (NADP+ reductase)– The electrons of NADPH are available the Calvin cycleCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsLinear electron flow
    • 17. MillmakesATPe–NADPHPhotone–e–e–e–e–PhotonATPPhotosystem II Photosystem Ie–A mechanical analogy for the light reactions•Photon exciteselectron•Electron goesdown ETC•Photon exciteselectron•NADP+ reducedto NADPD
    • 18. Fig. 10-17LightADP+iH+ATPPATPsynthaseToCalvinCycleSTROMA(low H+concentration)ThylakoidmembraneTHYLAKOID SPACE(high H+concentration)STROMA(low H+concentration)Photosystem II Photosystem I4 H+4 H+LightNADP+reductaseNADP++ H+NADPH+2 H+H2OO2e–e–1/2123The light reactions and chemiosmosis:The organization of the thylakoid membrane
    • 19. A Comparison of Chemiosmosis in Chloroplastsand Mitochondria• BOTH generate ATP by chemiosmosis, but use differentsources of energy• Mitochondria (during cellular respiration)– transfer chemical energy (electrons) from food to ATP– protons are pumped to the intermembrane space and drive ATPsynthesis as they diffuse back into the mitochondrial matrix• Chloroplasts (during photosynthesis)– transform light energy into the chemical energy of ATP– Transfer chemical energy from water to NADPH– protons are pumped into the thylakoid space and drive ATP synthesisas they diffuse back into the stromaCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    • 20. Fig. 10-16KeyMitochondrion ChloroplastCHLOROPLASTSTRUCTUREMITOCHONDRIONSTRUCTUREIntermembranespaceInnermembraneElectrontransportchainH+ DiffusionMatrixHigher [H+]Lower [H+]StromaATPsynthaseADP + P iH+ATPThylakoidspaceThylakoidmembrane
    • 21. The Calvin cycle uses ATP and NADPH to convertCO2 to sugar• regenerates its starting material after molecules enter and leave the cycle• builds sugar from smaller molecules by using ATP and the reducing powerof electrons carried by NADPH• Carbon enters the cycle as CO2 and leaves as a sugar namedglyceraldehyde-3-phospate (G3P)– For net synthesis of 1 G3P, the cycle consumes 9 ATP and 6 NADPH• The Calvin cycle has three phases:– Carbon fixation (catalyzed by rubisco)– Reduction– Regeneration of the CO2 acceptor (RuBP)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    • 22. 1. CO2 is reduced2. 6 ATP  6 ADP3. 6 NADPH  6 NADP+4. 3-phosphoglycerate isreduced to G3P5. G3P used to createglucose or othersugars6. RuBP is regeneratedfrom G3P7. 3 ATP  3 ADP
    • 23. Alternative mechanisms of carbon fixation haveevolved in hot, arid climates• Photorespiration caused by dehydration– plants close stomata which conserves H2O but also limits photosynthesis– reduces access to CO2 and causes O2 to build up– consumes O2 and organic fuel and releases CO2 without producing ATP orsugar• C4 plants– Calvin cycle is preceded by reactions that incorporate CO2 into a four-carboncompound instead of a three-carbon compound (C3 plants)– Organic acids release CO2 to the Calvin cycle• CAM plants– Stomata close during the day and are open during the night– CO2 is released from organic acids and used in the Calvin cycle (at night)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    • 24. The Importance of Photosynthesis: A Review• The energy entering chloroplasts as sunlight gets stored aschemical energy in organic compounds• Sugar made in the chloroplasts supplies chemical energyand carbon skeletons to synthesize the organic moleculesof cells• Plants store excess sugar as starch in structures such asroots, tubers, seeds, and fruits• In addition to food production, photosynthesis produces theO2 in our atmosphereCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    • 25. Fig. 10-21LightReactions:Photosystem IIETCPhotosystem IETCCO2NADP+ADPPi+RuBP 3-PhosphoglycerateCalvinCycleG3PATPNADPHStarch(storage)SugarChloroplastLightH2OO2Light reactions:•Thylakoid membranes•Convert light energy to ATP and NADPH that canbe used by the Calvin Cycle•Split water and release O2 into atmosphereCalvin Cycle:•Stroma•Use ATP and NADPH to convert CO2 to G3P•Return ADP, P and NADP+ to the light reactions