PhotosynthesisPhotosynthesis

Photosynthesis in NaturePhotosynthesis in Nature Capturing the Energy in Capturing the Energy in

LightLight Light-dependent ReactionsLight-dependent Reactions

The Calvin CycleThe Calvin Cycle Light-independent ReactionsLight-independent Reactions

PhotosynthesisPhotosynthesisin Naturein Nature

• Autotrophy & HeterotrophyAutotrophy & Heterotrophy

• Chloroplast Structure & FunctionChloroplast Structure & Function

• Leaf Structure & FunctionLeaf Structure & Function

Trophic ProcessesTrophic Processes

• AutotrophAutotroph autoauto = “self”; = “self”; trophostrophos = “feeding” = “feeding” produce organic molecules from produce organic molecules from

inorganic substrates obtained from inorganic substrates obtained from the environmentthe environment

Types:Types:chemoautotrophy chemoautotrophy (prokaryotic bacteria (prokaryotic bacteria

only)only)photoautotrophyphotoautotrophy

Trophic ProcessesTrophic Processes

• PhotoautotrophPhotoautotroph obtains inorganic molecules from obtains inorganic molecules from

environmentenvironment energy sourceenergy source – radiant energy of – radiant energy of

sunlight (sunlight (photosynthesisphotosynthesis)) examples:examples:

cyanobacteriacyanobacteria (prokaryotes) (prokaryotes)all algae & many other protistsall algae & many other protistsall plants (w/ exceptions)all plants (w/ exceptions)

ProkaryoticProkaryotic PhotoautotrophsPhotoautotrophs

OscillatoriaOscillatoria - filamentous - filamentous cyanobacterium (blue-green alga)cyanobacterium (blue-green alga)

EukaryoticEukaryoticProtistProtist Photoautotrophs Photoautotrophs

EuglenaEuglena – a unicellular mixotroph – a unicellular mixotroph

EukaryoticEukaryoticProtistProtist Photoautotrophs Photoautotrophs

LaminariaLaminaria – a multicellular – a multicellular algal kelpalgal kelp

EukaryoticEukaryoticPlantPlant PhotoautotrophsPhotoautotrophs

fernfern

mossmoss

flowering flowering seed plantseed plant

Trophic ProcessesTrophic Processes

• HeterotrophHeterotroph heterohetero = “other”; = “other”; trophostrophos = “feeding” = “feeding” obtain organic molecules from feeding obtain organic molecules from feeding

on other organisms or their productson other organisms or their products Types:Types:

Photoheterotrophs Photoheterotrophs (prokaryotic bacteria (prokaryotic bacteria only)only)

chemoheterotrophschemoheterotrophs

Trophic ProcessesTrophic Processes

• ChemoheterotrophChemoheterotroph obtains organic molecules by obtains organic molecules by

ingestion of or absorption from other ingestion of or absorption from other organismsorganisms

energy sourceenergy source – breakdown of – breakdown of organic molecules ingested or organic molecules ingested or absorbed from other organismsabsorbed from other organisms

examples:examples:most most bacteriabacteriamany many protistsprotistsall all fungifungiall all animalsanimals

ProkayoticProkayotic ChemoheterotrophsChemoheterotrophs

SalmonellaSalmonella – a parasitic – a parasitic enteric bacteriumenteric bacterium

Eukaryotic Eukaryotic ProtistProtist ChemoheterotrophsChemoheterotrophs

AmoebaAmoeba – a free-living, – a free-living, unicellular protistunicellular protist

ingestedingested ParameciaParamecia

Eukaryotic Eukaryotic FungalFungal ChemoheterotrophsChemoheterotrophs

MycenaMycena – a club fungus – a club fungus

Eukaryotic Eukaryotic AnimalAnimal ChemoheterotrophsChemoheterotrophs

Oh my!Oh my!

Plant LeafPlant LeafStructure & FunctionStructure & Function

• LeafLeaf plant organ specialized for photosynthesisplant organ specialized for photosynthesis

• Leaf tissuesLeaf tissues epidermisepidermis – contains stomata (sing., stoma) – contains stomata (sing., stoma)

to allow influx of COto allow influx of CO22

mesophyllmesophyll – contains photosynthetic cells – contains photosynthetic cells vascular tissuevascular tissue::

xylemxylem – carries H – carries H22O to leafO to leafphloemphloem – carries photosynthetic products away to – carries photosynthetic products away to

plant stems & rootsplant stems & roots

Plant LeafPlant LeafStructure & FunctionStructure & Function

Plant CellPlant CellStructure & FunctionStructure & Function

• PlastidsPlastids chloroplastschloroplasts

plant organelles specialized for photosynthesisplant organelles specialized for photosynthesiscontain chlorophyll a and accessory pigments in contain chlorophyll a and accessory pigments in

thylakoid membranethylakoid membrane amyloplasts – amyloplasts – store starchstore starch chromoplastschromoplasts – – store colorful pigments for store colorful pigments for

animal attraction to flowersanimal attraction to flowers

• Central vacuoleCentral vacuole bounded by tonoplastbounded by tonoplast stores Hstores H22O, waste products, nutrients, O, waste products, nutrients,

protective toxinsprotective toxins

Plant ChloroplastPlant ChloroplastStructure & FunctionStructure & Function

• outer membraneouter membrane• intermembrane spaceintermembrane space• inner membraneinner membrane• stromastroma

site of site of light-independentlight-independent reactions reactions

• thylakoid membranethylakoid membrane grana (sing., granum)grana (sing., granum) site of site of light-dependentlight-dependent reactions reactions

• thylakoid spacethylakoid space site of site of [H[H++] (] (light-dependent reactionslight-dependent reactions))

Chlorophyll moleculeChlorophyll molecule

Capturing Light Energy Capturing Light Energy Light-dependent ReactionsLight-dependent Reactions

• Energy for Life ProcessesEnergy for Life Processes

• Light Absorption in ChloroplastsLight Absorption in Chloroplasts

• Electron TransportElectron Transport

• ChemiosmosisChemiosmosis

Learning Learning ObjectivesObjectives

1.1. Describe the role of chlorophylls & Describe the role of chlorophylls & other pigments in photosynthesisother pigments in photosynthesis

2.2. Summarize the main events of Summarize the main events of electron transportelectron transport

3.3. Explain how the structure of the Explain how the structure of the chloroplast relates to its functionchloroplast relates to its function

Energy &Energy &Life ProcessesLife Processes

• PhotosynthesisPhotosynthesis The conversion of light energy into chemical The conversion of light energy into chemical

energy stored in organic compoundsenergy stored in organic compoundsglucose glucose starch starchamino acids amino acids proteins proteins

• Biochemical PathwaysBiochemical Pathways A series of linked chemical reactions A series of linked chemical reactions The products of one reaction are consumed The products of one reaction are consumed

by the following reactionby the following reaction

Autotrophs & HeterotrophsAutotrophs & Heterotrophs

AutotrophsAutotrophs

Autotrophs & Autotrophs & heterotrophsheterotrophs

PhotosynthesisPhotosynthesisOverviewOverview

Chemical Equation:Chemical Equation:

66CCOO2 2 ++ 6 6HH22OO ++ LightLight EnergyEnergy

CC66HH1212OO66 ++ 6 6OO22

Tracking Atoms Through Tracking Atoms Through PhotosynthesisPhotosynthesis

Chloroplast StructureChloroplast Structure

• Outer membraneOuter membrane• Intermembrane spaceIntermembrane space• Inner membraneInner membrane• StromaStroma• Thylakoid membraneThylakoid membrane

Arranged in stacks: Arranged in stacks: granagrana (sing., (sing., granum)granum)

Thylakoid spaceThylakoid space

Chlorophyll Chlorophyll Molecule – in ThylakoidMolecule – in Thylakoid

• Chlorophyll aChlorophyll a primary photosynthetic pigment primary photosynthetic pigment

molecule – molecule – in thylakoidin thylakoid absorbs light energy: peak absorbs light energy: peak λλ

420 nm (420 nm (violetviolet))680 nm (680 nm (orangeorange--redred))

reflects reflects blue-greenblue-green

Accessory Accessory Pigments – in ThylakoidPigments – in Thylakoid

• Chlorophyll bChlorophyll b passes absorbed light energy to passes absorbed light energy to

chlorophyll achlorophyll a absorbs light energy: peak absorbs light energy: peak λλ

480 nm (480 nm (violetviolet--blueblue))650 nm (650 nm (orangeorange))

reflects reflects yellowyellow--greengreen

Accessory Accessory Pigments – in ThylakoidPigments – in Thylakoid

• CarotenoidsCarotenoids absorbed light energyabsorbed light energy

passed to chlorophyll apassed to chlorophyll aphotoprotectionphotoprotection – absorption & – absorption &

dissipation of harmful, excess light energydissipation of harmful, excess light energy

absorbs light energy: peak absorbs light energy: peak λλ 470 nm (470 nm (violetviolet--blueblue))650 nm (650 nm (orangeorange))

reflects reflects yellowyellow--orangeorange

Photoexcitation:Photoexcitation:Chlorophyll in ThylakoidChlorophyll in Thylakoid

Electromagnetic SpectrumElectromagnetic Spectrum

Absorption & Action Absorption & Action Spectra of ChlorophyllSpectra of Chlorophyll

Absorption spectrumAbsorption spectrum – – plots a plots a pigment’s light absorption against the pigment’s light absorption against the wavelength of light absorbedwavelength of light absorbed

Action spectrumAction spectrum – – plots the plots the wavelength of light absorbed by a wavelength of light absorbed by a pigment against a measure of pigment against a measure of photosynthetic rate (like COphotosynthetic rate (like CO22 consumption or Oconsumption or O22 release) release)

PhotosystemsPhotosystems

• light harvesting complexes of the light harvesting complexes of the thylakoidthylakoid membranemembrane

• StructureStructure antenna complexantenna complex::

clusters of 100s of clusters of 100s of chl achl a, , chl bchl b, & , & carotenoidcarotenoid molecules molecules

proteinsproteins

reaction centerreaction center::chl achl a near a protein near a protein primary electron primary electron

acceptoracceptor

PhotosystemsPhotosystems

• FunctionFunction antenna complexantenna complex::

captures photons from lightcaptures photons from lightenergy passed from pigment molecule energy passed from pigment molecule

to pigment molecule until it reaches a to pigment molecule until it reaches a reaction centerreaction center

reaction centerreaction center::chl achl a absorbs energy and boosts absorbs energy and boosts

electron to higher energy level where it electron to higher energy level where it is captured by the is captured by the primary electron primary electron acceptoracceptor

Pathways of Pathways of PhotosynthesisPhotosynthesis

• Equation for PhotosynthesisEquation for Photosynthesis• Light-dependent ReactionsLight-dependent Reactions

– Non-cyclic electron flowNon-cyclic electron flow– Cyclic electron flowCyclic electron flow

• Light-independent ReactionsLight-independent Reactions– Calvin cycle (CCalvin cycle (C33))

– CC44 processes processes

– CAM CAM (crassulacean acid metabolism)(crassulacean acid metabolism)

PhotosynthesisPhotosynthesisOverviewOverview

In thylakoid In thylakoid membrane & membrane & spacespace In stromaIn stroma

Noncyclic Noncyclic Electron FlowElectron Flow

Light-dependent Reaction: Light-dependent Reaction: RequirementsRequirements

• requires radiant requires radiant energyenergy from from sunlightsunlight

• Involves 2 photosystemsInvolves 2 photosystems photosystemphotosystem I I (P700)(P700) photosystem II photosystem II (P680)(P680)

• requires requires HH22OO from environment as from environment as source of Hsource of H++ & e & e--

• utilizes utilizes electron transport chains electron transport chains ((ETCsETCs))

Light-dependent Reaction Light-dependent Reaction StepsSteps

(1)(1) Photoexcitation stepPhotoexcitation step: light energy forces a : light energy forces a pair of epair of e-- to enter a higher energy level in to enter a higher energy level in two chlorophyll molecules of two chlorophyll molecules of photosystem photosystem IIII

(2)(2) Electron capture stepElectron capture step: excited e: excited e-- leave leave chlorophylls & are captured by a chlorophylls & are captured by a primary primary ee-- acceptor acceptor

Light-dependent Reaction Light-dependent Reaction StepsSteps

(3) (3) Pq-Pc ETC stepPq-Pc ETC step: photoexcited e: photoexcited e-- pass from pass from primary e- acceptor to photosystem I via primary e- acceptor to photosystem I via ““Pq-PcPq-Pc” ” ETCETC; e; e-- lose energy which is used lose energy which is used to pump protons (Hto pump protons (H++) into thylakoid ) into thylakoid space; space; NoteNote - photosystem I has - photosystem I has previously lost and epreviously lost and e-- by photoexcitation by photoexcitation

(4) (4) Photoexcitation stepPhotoexcitation step: light energy forces a : light energy forces a pair of epair of e-- to enter a higher energy level in to enter a higher energy level in two chlorophyll molecules of two chlorophyll molecules of photosystem photosystem II; e; e-- move to another move to another primary eprimary e-- acceptor acceptor

Light-dependent Reaction Light-dependent Reaction StepsSteps

(5)(5) NADPH formation stepNADPH formation step: : primary electron primary electron acceptoracceptor of photosystem I passes of photosystem I passes photoexcited ephotoexcited e-- to “ to “FdFd” ” ETCETC; e; e-- pass down pass down ETC to enzyme; eETC to enzyme; e-- from chain & H from chain & H++ are are attached to attached to NADPNADP++ to produce to produce NADPHNADPH. . NoteNote: NADPH will be used in the light-: NADPH will be used in the light-independent reactions of photosynthesisindependent reactions of photosynthesis

Light-dependent Reaction Light-dependent Reaction StepsSteps

(6)(6) Restoration of photosystem II eRestoration of photosystem II e--: 2 : 2 HH22O O are split by a are split by a water-splitting enzyme water-splitting enzyme to to produce: produce:

2H2H22O O 4H 4H++ + 4e + 4e-- + O + O22

ChemiosmosisChemiosmosis

Mechanical AnalogyMechanical Analogyfor Light Reactionsfor Light Reactions

Light-dependent Reaction: Light-dependent Reaction: ProductsProducts

• produces produces OO22 as as byproductbyproduct

• produces produces energyenergy from e from e-- moving moving downdown ETCs ETCs used to used to pump Hpump H++ across a membrane across a membrane creates a creates a proton motive forceproton motive force

• produces produces ATPATP from flow of Hfrom flow of H++ through through ATP synthaseATP synthase

• produces produces NADPH NADPH as final electron acceptoras final electron acceptor

Organization of the Organization of the Thylakoid MembraneThylakoid Membrane

The “Light” Reactions

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Light-dependent ReactionsLight-dependent ReactionsThe Calvin CycleThe Calvin Cycle

• Carbon Fixation by the Calvin Carbon Fixation by the Calvin CycleCycle

• Alternative PathwaysAlternative Pathways

• Rate of PhotosynthesisRate of Photosynthesis

LearningLearningObjectivesObjectives

1.1. Summarize the main events of the Summarize the main events of the Calvin cycleCalvin cycle

2.2. Describe what happens to the Describe what happens to the compounds made in the Calvin cyclecompounds made in the Calvin cycle

3.3. Distinguish btw/ CDistinguish btw/ C33, C, C44, & CAM plants, & CAM plants

4.4. Explain how environmental factors Explain how environmental factors influence photosynthesisinfluence photosynthesis

Light-independent Reaction:Light-independent Reaction:

The Calvin CycleThe Calvin Cycle

Light-independent Light-independent Reaction: RequirementsReaction: Requirements

• requires 6 requires 6 COCO22 from environment from environment as as CC source source

• requires 6 requires 6 NADPHNADPH noncyclic enoncyclic e-- flow of light-dep. Rx flow of light-dep. Rx

• requires 9 requires 9 ATP ATP 6 from 6 from noncyclic photophosphorylationnoncyclic photophosphorylation 3 from 3 from cyclic photophosphorylationcyclic photophosphorylation

• requires 3 requires 3 RuBPRuBP molecules molecules

Calvin CycleCalvin CycleReactionsReactions

• Carbon fixationCarbon fixation incorporation of incorporation of COCO22 into into RuBPRuBP – –

ribulose biphosphateribulose biphosphate enzyme that fixes (attaches) COenzyme that fixes (attaches) CO22 to to

RuBP: RuBP: rubisco rubisco – – RuBP carboxylaseRuBP carboxylasemost abundant protein on earthmost abundant protein on earth

• Cycles Cycles 2 times2 times using using 3 CO3 CO22 @ time @ time

to make to make CC66HH1212OO66

Light-independent Light-independent Reaction: ProductsReaction: Products

• produces a sugar produces a sugar G3PG3P (glyceraldehyde-3-phosphate)(glyceraldehyde-3-phosphate)

2 G3Ps 2 G3Ps combinecombine CC66HH1212OO66

• regenerates 6 regenerates 6 NADPNADP++

• regenerates 9 regenerates 9 ADP ADP + 9+ 9 P Pii

• regeneratesregenerates 33 RuBP RuBP

Light-independent Light-independent Reaction StepsReaction Steps

(1)(1) Phase 1Phase 1: : Carbon fixationCarbon fixation3 CO3 CO22 ++ 3 RuBP 3 RuBP ––rubiscorubisco 3 unstable 3 unstable intermediate intermediate 6 3-phosphoglycerate 6 3-phosphoglycerate

(2)(2) Phase 2Phase 2: : ReductionReduction 6 3-phosphoglycerate 6 3-phosphoglycerate ++ 6 ATP 6 ATP 6 1,3-biphosphoglycerate 6 1,3-biphosphoglycerate ++ 6 ADP 6 ADP

6 1,3-biphosphoglycerate 6 1,3-biphosphoglycerate ++ 6 NADPH 6 NADPH 6 G3P 6 G3P ++ 6 NADP 6 NADP++ ++ 6 6

PPii

Light-independent Light-independent Reaction: Fate of G3PReaction: Fate of G3P

NoteNote: :

(a)(a) one of the 6 G3P shunts off to be one of the 6 G3P shunts off to be used by plant in biosynthesis of glucose, used by plant in biosynthesis of glucose, a.a., F.A., or other organic compoundsa.a., F.A., or other organic compounds

(b)(b) the other 5 G3Ps will be used to the other 5 G3Ps will be used to regenerate RuBPregenerate RuBP

Light-independent Light-independent Reaction StepsReaction Steps

(3) (3) Phase 3Phase 3: : Regeneration of RuBPRegeneration of RuBP

complex set of reactionscomplex set of reactions

rearrange the 3-C skeletons of 5 G3Ps (15 rearrange the 3-C skeletons of 5 G3Ps (15 C total) C total) 3 RuBP (@ w/ 5-C skeleton = 15 C 3 RuBP (@ w/ 5-C skeleton = 15 C total)total)

3 ATP 3 ATP ––interact in Rxinteract in Rx 3 ADP 3 ADP ++ 3 P 3 Pii

The Calvin Cycle

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Review of PhotosynthesisReview of Photosynthesis