1. Photophosphorylation
Chapter 15 (part 2)
Photophosphorylation

2. Photophosphorylation
Light-Driven ATP Synthesis
Electron transfer through the proteins of the Z scheme drives the generation of a proton gradient across the thylakoid membrane
Protons pumped into the lumen of the thylakoids flow back out, driving the synthesis of ATP
CF1-CFo ATP synthase is similar to the mitochondrial ATP synthase

4. Chloroplast CF1CFo ATPase
Similar in structure to mitochondrial F1Fo ATPase
CF1 domain (ATP synthesis) extends into the stroma.
Many of the protein subunits are encoded by the chloroplast genome

5. Chloroplast Proton Motive Force (Dp)
What contributes more to PMF, DY or DpH?
In the light DpH=3
DY is negligible due to counter ion movement in and out of the lumen
DG for export of one mole H+ across thylakoid membrane = -17 kJ/mole
DGo’ for ATP formation = 30.5 kJ/mole
Since 12 moles of protons gives –200 kJ of energy
Experiment show that 3 ATPs are generated per mole of O2 produced

6. Energy Balance Sheet 8 photons (4 e-) generate 1 oxygen and 2 NADPH
Photosynthetic ETC pumps between 8 and 12 protons across thylakoid membrane to generate proton gradient (DpH ~3.5).
Photophosphorylation produces 3 ATPs per O2 produced

7. Non-cyclic photosynthetic ETC
NADPH and ATP produced
Involves both PSI and PSII
cyclic photosynthetic ETC
only ATP produced
Involves only PSI

8. Cyclic Photosynthetic ETC
Involves only PSI
Reduced ferredoxin transfers e- to Cytobf complex which then re-reduces Plastocyanin and finally the oxidized P700 of PSI
No NADPH produce.Only ATP
Levels of NADP+ thought to regulated this process.
Low NADP+ activates cyclic ETC
Observed in vitro.

9. Arrangement of photosystems in thylakoid membrane

10. Arrangement of photosystems in thylakoid membrane
PSII primarily present in granal lamellae
Light harvesting antennae complexes (LHC) are also present in the granal lamellae.
Under low light conditions LHCs are closely associated with PSII, Under high light condition the 2 disassociate.
PSI and ATPase are in the stroma lamellae.
Physical separation suggest that mobile electron carrier must be involved (i.e. PQ and Plastocyanin)