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Chapter 15 (part 2)

Chapter 15 (part 2). Photophosphorylation. 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

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Chapter 15 (part 2)

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  1. 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

  3. 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

  4. 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

  5. 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

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

  7. 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.

  8. Arrangement of photosystems in thylakoid membrane

  9. 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)

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