(Lodish)

lumen

1. Reduction of NADP+---proton consumption (dog elimination!) on the stromal side

2. Pumping from the stroma to the lumen by cytochrome b6f

3. Plastiquinone- translocation of protons from stroma to lumen

4. The splitting of water in the lumen—proton production on lumen side (new dogs in the doghouse!)

Figure 6.15 (Cell View):

Contributions to the proton gradient

Now have ATP and NADPH for Calvin cycle.

Photophosphorylation produces NADPH and ATP. Why?

Light Reactions of Photosynthesis

To give to the Dark Reactions to help make carbohydrates

1. The energy from the sun is used to set up a H+ gradient with high H+

inside thylakoids

2. When H+ flow out (through the CFo/CF1), ATP is made in the stroma

The initial e- donor is H2O and the final e- acceptor is NADP+

In both mitochondria and chloroplasts, H+ flux is coupled to ATP synthesis

H+

H+H+

H+H+

H+

H+H+

H+

H+H+

Membrane

ADP + Pi

ATP

High [H+]

Low pH

Low [H+]

High pH

F1 of mitochondria

CF1 of chloroplasts

In both, ATP is made when H+ flow from the low pH side to high pH side

The CF1/CFo can make ATP in vitro

pH 7

pH 4

All of this is done in the dark

Step 1. Put thylakoids in pH =4.0

CF1 faces outside. Lower [H+] inside

Which direction is the pmf?

inward

pH 4

pH 4

pH 4

pH 7

Step 2. Wait until pH=4.0 inside. Load up H+ inside.

ADP+ Pi

ATP

Step 3. Move thylakoids to pH=7.0 and add ADP+Pi. High [H+] in, low [H+] out

pH = 4 is high [H+] inside

Which direction is the pmf now?

outward

What provides the energy for ATP synthesis?

The H+ gradientIs e- transport necessary for ATP synthesis in vitro?

How do thylakoid membranes harvest light to make NADPH and ATP?

pigmentLight

Transmitted

No change in

wavelength

Passed along to another

energy carrier

Emitted Heat Fluorescence

Pigment

Emitted at a longer

wavelength

Five different things that can happen to light after it hits a pigment

1. 2.

3.

4.

Why are isolated pigments (like chlorophyll) fluorescent but chloroplasts aren’t?

Reflected5.

The “Z-scheme” for electron transport in thylakoidsLow

Reduction Potential

High Reduction Potential P680 is part of PSII

P700 is part of PSI

*Excited State P680

*Excited State P700

Ground State P680

Ground State P700

1. The excited state of P680 now has a low enough Eo value to pass electrons to PQ and the rest of the electron transport chain but the ground state of P700 is too high to pass e- further

2. Light energy at PSI is needed to lower the Eo value of P700 so that it can pass electrons to the rest of the e- transport chain and, ultimately, to NADP+

3. Light provides energy to split water and lower Eo value of P680 (to P680*)

Remember: In a redox couple, electrons can only be passed to a compound with a higher (more positive) reduction potential (Eo value).

Summary of Light Reactions1. PSII (P680) uses light energy to split water by

photolysis: H2O H+ + O2 + e-A. The H+ contribute to the H+ gradient in the lumenB. The electrons are passed to the e- transport chain and provide energy for more H+ pumping

2. Electrons passed to PQ and H+ go to the lumen to increase [H+] in lumen

3. Cytb6/f complex accepts e- (GER) and pumps some more H+ into the lumen

4. Electrons passed to PC and PSI (P700)5. Electrons passed to NADP+ to make NADPH6. The pmf of the H+ gradient is used to make ATP in the

stroma

Why do plants need water, light and CO2 to grow?

Some inhibitors of photosynthesis (see p.231)

1. DCMU. We will use it in our lab to block electron transport from PSII to PQ

2. Atrazine (herbicide): Blocks e- transport from PSII to PQ. Why doesn’t it kill us?

3. DCIP: Artificial electron acceptor that “steals” electrons from PQ. We will use this in our labs too.

4. Paraquat: “Steals” electrons from PSI so that NADP+ doesn’t get reduced to NADPH. It is another herbicide

Chloroplasts

H2O oxidized to O2

Energy required (light)

Makes sugars from CO2

H+ high inside thylakoids

CF1 faces out (into the stroma)

H+ efflux during ATP synthesis (into the stroma)

Mitochondria

O2 reduced to H2O

Energy produced (ATP)

Makes CO2 from sugars

H+ high outside inner membrane

F1 faces in (into the matrix)

H+ influx during ATP synthesis (into the matrix)

The Circle of Life

SUN

Photosynthetic Cells

O2Carbohydrates

Heterotrophic Cells (us)

H2OCO2

From another book: “Solar energy is the ultimate source of

all biological energy.”

Chloroplasts use energy from light to make carbohydrates and generate O2

Mitochondria produce water and CO2 from carbohydrates and O2

In mitochondria

In chloroplasts