monday’s topics 1.overview of photosynthesis 2.key early photosynthesis experiments 3....

Monday’s Topics

1.Overview of photosynthesis2.Key early photosynthesis experiments3. Photosynthesis: light reactions

From which molecule does the O2 released by plants come from?

What happens to H20 during photosynthesis? (more than one answer might be correct)

a. Oxidizedb. Reducedc. Activatedd. Looses electronse. Gains electrons

Which are the energy rich compounds generated during the light reactions?

Today’s Topics

1.Electron transfer during the light reactions2.Regulation of photosynthesis3.Evolution of photosynthetic systems

Ener

gy

H20

2 H+ + ½ O2

The Electron Transfer Process

Oxidized State

Reduced State

PSI Light

PSI + PSII Light

PSI Light

Darkness

Time

Duysens & Amesz (1962)

Cytochrome

Z-Scheme: Electron transfers (redox reactions)

Photosynthesis: Light Reactions

Reactions of Plastoquinones

Photosynthesis: Light Reactions

Electron Transfer in the Cytochrome b6f Complex

Electron Transfer in the Cytochrome b6f Complex

Photosynthesis: Light Reactions

Herbicides and the study of photosynthesis

Blocks electron transfer to plastoquinone

Blocks electron transfer in PSI

Excercises

What will the status of the plastoquinone pool in DCMU treated plants?a. Reducedb. Oxidiced

What will the status of the plastocyanin pool be in Paraquot treated plants?a. Reducedb. Oxidiced

Photosynthesis: Light Reactions

Today’s Topics

1.Electron transfer during the light reactions2.Regulation of photosynthesis3.Evolution of photosynthetic systems

Problems with the electron transfer process

A. Excess energy absorbanceB. Electron balances between PSI and PSII

Ener

gy

H20

2 H+ + ½ O2

Problems with the electron transfer process

PHOTOPROTECTION

Nonphotochemical Quenching

a. Reorganization of antenna complexes

b. Special carotenoids: xantophylls

c. Thylakoid lumen pH

Problems with the electron transfer process

A. Excess energy absorbanceB. Electron balances between PSI and PSII

Energy partitioning between photosystems

LHCII LHCII-P

Topics

1.Electron transfer during the light reactions2.Regulation of photosynthesis3.Evolution of photosynthetic systems

How does a plant make more chloroplasts?

Where do the chloroplasts come from?

Do all chloroplasts in all algae and plants have the same origin?

Where are chloroplast proteins made?

What are the main open questions about the origin of oxygenic photosynthesis?

Which are the current hypothesis to explain the beginning of oxygenic photosynthesis?

Next lecture:-Carbon reactions of photosynthesis

Light ReactionsLight ReactionsATP

NADPHCarbon

ReactionsCarbon

Reactions

H20 O2 CO2 CH20