Inner membrane Chloroplast Outer membrane€¦ · ADP + NADP+ NADP NADPH ADP + P i ATP Calvin Cycle Photon Photon H O 2e– 2e– 2e– Fd PC PQ 1. Photosystem II absorbs photons,

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Vascular bundle Stoma

Cuticle Epidermis Mesophyll

Chloroplast Inner membrane Outer membrane

Cell wall

1.58 µm

Vacuole

Courtesy Dr. Kenneth Miller, Brown University

1


O2

Stroma

Photosystem

Thylakoid

NADP+

ADP + Pi

CO2

Sunlight

Photosystem

Light-Dependent Reactions

Calvin Cycle

Organic molecules

O2

ATP NADPH

H2O

2


400 nm

Visible light

430 nm 500 nm 560 nm 600 nm 650 nm 740 nm

1 nm 0.001 nm 10 nm 1000 nm Increasing wavelength

Increasing energy

0.01 cm 1 cm 1 m

Radio waves Infrared X-rays Gamma rays

100 m

UV light

3


Wavelength (nm) 400 450 500 550 600 650 700

Lig

ht

Ab

sorb

tio

n

low

high carotenoids chlorophyll a chlorophyll b

4


H2C CH

CH2CH3

H

H H

C O CH CCH3

CHCH3 CH2 CH2 CH2 CHCH3 CH2 CH2 CH2 CHCH3 CH3

O CO2CH3

O

N N

N N Mg

H

H Chlorophyll a: = CH3 Chlorophyll b: = CHO

R R

R

H Porphyrin head

H3C

H3C CH3

CH2 CH2

CH2

CH2 CH2 CH2

Hydrocarbon tail

5


Oak leaf in summer

Oak leaf in autumn

© Eric Soder 6


e– Photon

Photosystem

Thylakoid membrane

Chlorophyll molecule

Electron acceptor

Reaction center chlorophyll

Thylakoid membrane

Electron donor e–

7


Light

e–

– + – +

Excited chlorophyll molecule

Electron donor

Electron acceptor

Chlorophyll reduced

Chlorophyll oxidized

Donor oxidized

Acceptor reduced

e– e– e–

e– e–

e–

e–

8


En

erg

y o

f el

ectr

on

s

e–

Photon

Excited reaction center

Excited reaction center

Plastoquinone

Plastocyanin

Ferredoxin

Photosystem II

Photosystem I

Photon

b6-f complex

2. The electrons pass through the b6-f complex, which uses the energy released to pump protons across the thylakoid membrane. The proton gradient is used to produce ATP by chemiosmosis.

3. A pair of chlorophylls in the reaction center absorb two photons. This

excites two electrons that are passed to NADP+, reducing it to NADPH. Electron transport from photosystem II replaces these electrons.

H2O

H+ PC

Fd

2H+ + 1/2O2

NADP+ + H+ NADPH

2

2

2

2

2

1. A pair of chlorophylls in the reaction center absorb two photons of light. This excites two electrons that are transferred to plastoquinone (PQ). Loss of electrons from the reaction center produces an oxidation potential capable of oxidizing water.

Reaction center

Proton gradient formed for ATP synthesis

Reaction center

NADP reductase

e–

e–

e–

e–

PQ

9


Photosystem II Photosystem I b6-f complex

Stroma

Plastoquinone Proton gradient Plastocyanin Ferredoxin

H+

H+ H+

H+

NADPH ATP

ADP + NADP+

NADPH NADP ATP ADP + Pi

Calvin Cycle

Photon Photon

H2O 2e–

2e–

2e– Fd

PC PQ

1. Photosystem II absorbs photons, exciting electrons that are passed to plastoquinone (PQ). Electrons lost from photosystem II are replaced by the oxidation of water, producing O2

2. The b6-f complex receives electrons from PQ and passes them to plastocyanin (PC). This provides energy for the b6-f complex to pump protons into the thylakoid.

3. Photosystem I absorbs photons, exciting electrons that are passed through a carrier to reduce NADP+ to NADPH. These electrons are replaced by electron transport from photosystem II.

4. ATP synthase uses the proton gradient to synthesize ATP from ADP and Pi

enzyme acts as a channel for protons to diffuse back into the stroma using this energy to drive the synthesis of ATP.

NADP reductase

ATP synthase

1/2O2 2H+

Water-splitting enzyme

Thylakoid space

Antenna complex Thylakoid

membrane


H+

H+

2e–

10


4 Pi 12 NADP+

12

12 ADP

NADPH NADP+

A T P ADP + Pi

Glucose and other sugars


Calvin Cycle

6 molecules of 12 molecules of

12 molecules of 1,3-bisphosphoglycerate (3C)

12 molecules of Glyceraldehyde 3-phosphate (3C) (G3P)

10 molecules of

Glyceraldehyde 3-phosphate (3C) (G3P)

Stroma of chloroplast 6 molecules of

Carbon dioxide (CO2)

12 NADPH

12 ATP

6 ADP

6 ATP

Rubisco

Calvin Cycle

Pi

Ribulose 1,5-bisphosphate (5C) (RuBP) 3-phosphoglycerate (3C) (PGA)

Glyceraldehyde 3-phosphate (3C)

2 molecules of

11


O2

Heat

ATP NADPH NADH

ATP

Sunlight

Pyruvate

CO2

Glucose

ADP + Pi NAD+ NADPi

H2O Photo- system

II

Photo- system

I

Electron Transport

System ADP + Pi

ADP + Pi

ATP

ATP

Calvin Cycle

Krebs Cycle

12

13


Heat

Stomata

O2 O2

CO2 CO2

Under hot, arid conditions, leaves lose water by evaporation through openings in the leaves called stomata.

The stomata close to conserve water but as a result, O2 builds up inside the leaves, and CO2

cannot enter the leaves.

Leaf epidermis

H2O H2O

14


CO2

RuBP

3PG (C3)

a. C4 pathway

Bundle-sheath cell Mesophyll cell

Stoma Vein

G3P

b. C4 pathway Stoma Vein

Mesophyll cell

G3

CO2

CO2

C4

Bundle- sheath cell

Mesophyll cell

Bundle- sheath cell

Calvin Cycle

Mesophyll cell

Calvin Cycle

a: © John Shaw/Photo Researchers, Inc. b: © Joseph Nettis/National Audubon Society Collection/Photo Researchers, Inc.

15


Oxaloacetate

Pyruvate Malate

Glucose

Malate Pyruvate

+ Pi

Mesophyll cell

Phosphoenolpyruvate (PEP)

Bundle-sheath cell

Calvin Cycle

AMP + PPi

ATP

CO2

CO2

16


night

day

CO2

CO2

C4

G3P

Calvin Cycle

© ClydeH. Smith/Peter Arnold Inc.

17

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Inner membrane Chloroplast Outer membrane€¦ · ADP + NADP+ NADP NADPH ADP + P i ATP Calvin Cycle Photon Photon H O 2e– 2e– 2e– Fd PC PQ 1. Photosystem II absorbs photons,