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ph tosynthesis

PhotosynthesisPhotosynthesis

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FlagFlag

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Green Maple LeafGreen Maple Leaf

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Green shoresGreen shores

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Chlorenchyma cells

Stoma

Chloroplast

Site of Photosynthesis in PlantsSite of Photosynthesis in Plants

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PhotosynthesisPhotosynthesis

Light reactions (require light)– Photochemistry

Dark reactions (light not required)– Carbon fixation

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Overview of PhotosyntheisOverview of Photosyntheis

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Conjugated double bonds

ChlorophyllChlorophyll

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Light reactionLight reaction

chl = chlorophyllA = electron acceptor

chl chl* (excited form)

chl* + A chl+ + A-

Light

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Light harvesting in a photosystemLight harvesting in a photosystem

Primary electron acceptor

Photon

Light harvesting centre (antenna)

Reactioncentre

e-

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Light reactionsLight reactions

Electrons are ejected from chlorophyll in reaction center

Energy from excited electrons is used – to pump protons (H+) across a membrane – to reduce NADP+

Proton motor force (PMF) across membrane drives ATP synthesis

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Stroma

Lumenof thylakoid

Reaction center

e donor

e acceptor

When we turn on the lights...

Light ReactionsLight Reactions

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Stroma

Lumenof thylakoid

Reaction center

e donor

e- acceptor

+

e-

separationcharge

+++

PhotonsPhotons

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+++

Stromahigh pH

lumenlow pH

H+

H+

H+H

+ H+

H+

H+

Proton pumpADP ATP

PMF

ATP'aseATP'ase

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Two modes of photosyntheticelectron transportTwo modes of photosyntheticelectron transport

Cyclic (purple bacteria- old)

Non-cyclic (the more recent mode)

1 = reaction centre

2 = quinones (e- transport)

3 = proton pump (cytochromes)

4 = cytochrome

5 = ATP’ase or CF0 CF1 complex

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+++

Cytosol

Exterior

H+

H+H

+ H+H

+ H+

LightATP?

H+

1

2

3

4

5

Cyclic electron transport (in purple bacteria)Cyclic electron transport (in purple bacteria)

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Non-cyclic electron transportuses TWO photosystemsNon-cyclic electron transportuses TWO photosystems

The old one, PS I (p700nm) and

A more recent one, PS II (p680 nm)

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+++

H+

H+H

+

H+H

+ H+

LightATP?

H+PS II PS I

e

e

H2O 2H+1/2 O2

NADP+ + H+ + 2e- NADPH

1

2

3

4

5

1

Non Cyclic Electron TransportNon Cyclic Electron Transport

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Non-cyclic e- flowNon-cyclic e- flow

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Cyclic electron FlowCyclic electron Flow

cyclic e- flow

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Logistics of chemiosmosisLogistics of chemiosmosis(mito) (chloroplast)(mitochondrion)

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Thylakoid MembraneThylakoid Membrane

Thylakoid space

Stroma

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Calvin & colleagues Applied radioisotopically labelled carbon (14C) to algae (in light) Killed them Separated the labelled products by chromatography Determined the pathway of carbon in photosynthesis

Dark Reactions of Photosynthesis Dark Reactions of Photosynthesis

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Calvin CycleCalvin Cycle

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EfficientSaves water too!

C4 photosynthesisC4 photosynthesis

Uses compartmentation of leaf

Two C-fixation steps (one is temporary)

Shuttles CO2 to inner compartment

Fixes CO2 by conventional C3

photosynthesis

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2. Bundle sheath

1. Mesophyll

CO2

C3+CO2 C4

C4

CO2

C3

ATP ADP

(low conc.)

(high conc.)

C4 AnatomyC4 Anatomy

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C4 PathwayC4 Pathway

C4-photosynthesis

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C4 vs CAM PathwayC4 vs CAM PathwayC4 CAM

Separation in space Separation in time

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Outer membrane

Inner membraneInter-membrane space

1. Stroma

2. Thylakoid space3. Thylak. membrane

What happens at 1,2 & 3?

Question??Question??

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Photosynthesis: OverviewPhotosynthesis: Overview

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Like life, our atmosphere is

evolvingLike life, our atmosphere is

evolving

Atmosphere....the dynamic gaseous boundary layer between our planet and space

The Atmosphere was (and is being) created by photosynthesis... oxygen, ozone (derived from oxygen), CO2 fixation are all regulated by photosynthesis.

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The End