Fig 7.22

In the light, acidification of the lumen creates a pH gradient across thylakoid membranes.

ATP-synthase is a protein motor

Driving force is chemiosmotic

gradient(Mitchell 1960s)

Fig 7.33

Jagendorf experiment:

Acidified lumen drives ATP synthesis in dark

Fig 7.32

I. Overview

How do herbicides that are inhibitors of electron transport activity work?

Some herbicides are inhibitors of electron transport

Blocks electron flow Intercepts electrons

Fig 7.31

Some herbicides are inhibitors of electron transport

Fig 7.31

-4

-2

0

2

4

6

8

10

12

14

0 500 1000 1500 2000

PAR, µmol photons m -2 s-1

Net CO

2 uptake, µmol m

-2 s

-1

Light response of photosynthesis in redwood, Sequoia sempervirens.

Summary of photophosphorylation

Fig 7.34

The use of a proton gradient to produce ATP is common theme in biology.

Purple bacteria have only PSI and ATPsynthase

But they do have ATP-ase

Fig 7.34

Mitochondria also have electron transport chain and ATP synthase

Oxidative phosphorylation

Fig 7.34

Products and substrates of Light and Dark reactions

Substrate Energy source

Products Location

Light reactions

H2O light NADPH

ATP

Thylakoids

Dark reactions

CO2 NADPH ATP

Sugars Stroma

Summary of the Light Reactions

The Carbon Reaction of photosynthesisUsing ATP and NADPH to produce carbohydratesfrom CO2.

Products and substrates of Light and Dark reactions

Substrate Energy source

Products Location

Light reactions

H2O light NADPH

ATP

Thylakoids

Dark reactions

CO2 NADPH ATP

Carbo-hydrates

Stroma

The “dark” or Carbon Reduction Reactions

Products and substrates of Light and Dark reactions

Substrate Energy source

Products Location

Light reactions

H2O light NADPH

ATP

Thylakoids

Dark reactions

CO2 NADPH ATP

Carbo-hydrates

Stroma

Relating the Light and Dark Reactions

Photosynthesis: Carbon Reactions (Chapter 8)

Photosynthetic CO2 uptake uses the products of thelight reactions to enable the “dark” or carbon reductionreactions.

-4

-2

0

2

4

6

8

10

12

14

0 500 1000 1500 2000

PAR, µmol photons m -2 s-1

Net CO

2 uptake, µmol m

-2 s

-1

Light response of photosynthesis in redwood, Sequoia sempervirens.

Conceptual linkage between the light and carbon

reactions of photosynthesis.

Fig. 8.1

I. Basics of the carbon reactionsthe Calvin cycle and C3 photosynthesis

II. Photorespiration - a process of O2 reduction thatcompetes with CO2 reduction and reduces the rateof carbon fixation.

III. CO2 concentrating mechanisms - variation on the “C3” photosynthetic metabolism.

C4 photosynthesis - an adaptation to warm and dry environments

CAM metabolism - an adaptation that greatly increaseswater use efficiency.

Fig. 8.2

The Calvin Cycle(reductivepentose phosphatecycle)

3 Stages•Carboxylation•Reduction•Regeneration

A 3 carbon molecule

An outline of C3 photosynthesis

Carboxylation•The key initial step in C3 photosynthesis•RUBP + CO2 ---> 3-PGA •Catalyzed by “Rubisco”: ribulose 1,5-bisphosphate carboxylase-oxygenase• binds the 5C RUBP molecule and 1C CO2, making two 3C molecules.

5 C + 1 C -----> 2 x 3C molecules

Fig. 8.3 (partial)

Fig. 8.2

•Carboxylation•Reduction•Regeneration

Reduction steps of the Calvin Cycle use ATP and NADPH to produce a carbohydrate, glyceraldehyde 3 phosphate.

3PGA + ATP + NADPH --> G3P

G3P can be used to make sucrose or starch

Reduction

Fig. 8.3 (partial) - the reduction steps

Fig. 8.2

•Carboxylation•Reduction•Regeneration

RegenerationThe regeneration steps of the Calvin Cycleuse ATP to regenerate RUBP from some ofthe glyceraldehyde-3-P so the cyclecan continue.

Some of the carbohydrate is converted backinto ribulose 1,5 bisphosphate, the initial CO2

receptor molecule.

Fig. 8.3 (partial) - the regeneration steps

Height (m)-related variation in foliar structure in redwood.

“shade” leaves

“sun” leaves