Plastocyanin: a small, soluble-copper protein

1 e-

Q cycle

Net reaction:

QH2 + 2 PC(ox)+ 2H+

Q + 2 PC(red) + 4H+

1st cycle:

QH2 + PC(ox) Q• + 2 H+ + PC(red)

2nd cycle:

QH2 + Q• + PC(ox) + 2 H+

QH2 + Q + 2 H+ + PC(red)

Cyclic Photosystem Ⅰ (cyclic photophosphorylation)

Only ATP formation, neither NADPH nor O2 is generated

2ATP / 4 photons

during high NADPH/NAD+ ratio

Herbicides: block e- flow

resistance

Superoxide formation,

damage lipid

malondialdehyde

between ferredoxin acceptor and NADP

reduced

Web Topic 7.10

Photophosphorylation: the captured light energy is used for light-dependent ATP synthesis

In the chloroplast oxidative phosphorylation in the mitochondrion

1960s Mitchell: chemiosmotic mechanism

Proton motive force [ p (mv)= E △ △ － 59 (pHi － pHo) ]

Jagendorf (1966): an incisive experiment

H2O oxidation

NADPH formation

ATP synthesis

NADH oxidation

H2O formation

ATP synthesis

orientation

The protective, scavenging, and repairing mechanisms of the photosynthetic machinery

Def: the inhibition of potosynthesis by excess light

Especially for PSⅠ

Easily damage the cellular components, especially lipids.

Carotenoids類胡蘿蔔素 : photoprotective agents, not only as accessory pigments

Photochemical quenching:

the energy stored in the excited chlorophylls葉綠素 is rapidly dissipated by photochemistry.

chlorophyll fluorescence

Non-photochemical quenching:

the quenching of chlorophyll fluorescence by

processing other than photochemistry, such as

excitation transfer, heat or photoinhibition.

Xanthophylls葉黃素 :

three carotenoids – violaxanthin, antheraxanthin,

zeaxanthin, involved in nonphotochemical

quenching.

Xanthophyll cycle: [Sapozhnikov et al., (1957) discovered]

an important avenue for dissipation of excess light energy

bind to light-harvesting antenna proteins, conformation change

quenching and heat dissipation

de-epoxidasecarotenoids

No. double bonds

The biosynthetic pathway of chlorophyll

1. Chlorophyllase: remove phytol

2. Mg de-chelatase

3. Oxygenase: open porphyrin

Stored in vacuole

Chloroplast

Maternal or non-Mendelian inheritance

(mitochondria)

Semiautonomous cell organelle

Chloroplast proteins are encoded by either chloroplastic or nuclear DNA

chloroplast: large subunit of rubisco

nucleus: small subunit of rubisco, plastocyanin

(transit peptide)

1. What is an absorption spectrum? What is the absorption spectrum of

chlorophyll? What is the relation between the electromagnetic spectrum

of solar radiation and the absorption spectrum of chlorophyll?

2. What is an action spectrum? What is the relationship between the action

spectrum for photosynthesis and the absorption spectrum of chlorophyll?

3. Photosynthesis in oxygen-evolving organisms is said to involve two distinct

photosystems. Describe the two photosystems and provide two lines of

experimental evidence that led to their discovery.

4. What is the role of electron transport in oxygen-evolving photosynthesis? Name

the final electron donor and final electron acceptor in photosynthesis. Describe

the path traveled by an electron in the electron transport process.

5. How are the major pigments and proteins involved in photosynthesis organized

in the thylakoid membrane?

6. Describe the process of ATP synthesis at the thylakoid membrane. Name the

reactants, the energy source and the role of light in the process. Can ATP

synthesis take place in thylakoid membranes kept in the dark? Explain your

answer.