1 / 23

Photosynthesis: The Details

Photosynthesis: The Details. Photosynthesis is a two stage process. Stage one :. The Light Reactions. The Light Reactions. Aka light-dependent reactions Occur in the thylakoid membrane involve photosystems and protein complexes. The Players...take out some colours.

hope
Download Presentation

Photosynthesis: The Details

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Photosynthesis: The Details

  2. Photosynthesis is a two stage process

  3. Stage one: The Light Reactions

  4. The Light Reactions Aka light-dependent reactions Occur in the thylakoid membrane involve photosystems and protein complexes

  5. The Players...take out some colours

  6. The Light Reactions STEP 1 Photon of light hits PS II and excites an e- of chlorophyll P680 (e- goes to the e- acceptor) P680 is now missing an e- and has a positive charge (P680+ )

  7. Pg 160

  8. The Light Reactions Note: this e- will end up in PS I further down the chain (in order to replace PS I’s e-)

  9. The Light Reactions Water-splitting enzyme holds H20 in place • P680+ pulls e- from water Enzyme splits Water into • O2 gas (released to atmosphere) • H+ (released to lumen, to be used later) • e- (used to replace the e- from PS 680)

  10. Pg 161

  11. Light Reactions STEP 2 • Energized e- continue through the ETC • At the b6-F complex, the E from the e- is used to pump H+ from the stroma into the thylakoid lumen. • H+ accumulate in the thylakoid lumen & contribute to the electrochemical gradient

  12. Light Reactions STEP 3(occurs while steps 1 & 2 are taking place) • A photon strikes PSI, and excites an e- of chlorophyll P700 • e- is passed to a high-E e- acceptor • lost e- from PSI are replaced by those that have reached the end of the ETC from PSII

  13. Light Reactions STEP 4 (occurs while steps 1 & 2 are taking place) • NADP reductase uses the e- from PSI and H+ ions from the stroma to reduce NADP+ to NADPH

  14. Light Reactions Chemiosmosis • H+ in thylakoid space cannot diffuse back across the membrane (bc the membrane is impermeable to ions) • ATP synthase is embedded in the membrane and provides the only pathway for hydrogen ions to move down their [gradient]

  15. Light Reactions Chemiosmosis • H+ moving through the ATP synthase complex drives the phosphorylation of ADP to ATP called Photophosphorylation

  16. Light Reactions • **The ATP and NADPH produced in the light reactions go to fuel the Calvin Cycle. • This series of reactions is called non-cyclic photophosphorylation http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::Photosynthetic%20Electron%20Transport%20and%20ATP%20Synthesis

  17. Soooo…what about when we are low on water or there is not enough NADP+???

  18. Cyclic Photophosphorylation • Occurs when plants are low in water or NADP+ • e- in PS I, pass backwards to cytochrome b6 -F

  19. Cyclic Photophosphorylation • Still produces a PMF, pumping H+ ions across the membrane • produces a [gradient] that can be used to power ATP synthase during chemiosmosis • BUT neither O2 nor NADPH are produced.

  20. Pg 162

More Related