Linear electron flow

• LDR (light-dependent reaction)


  Linear electron flow, process results in photophosphorylation
• 1st Step

  • photon strikes pigment in LHC (light-harvesting complex)
  • electron is excited because it encompasses the photon
  • this electron excites another e-
  • process continues until the e- reaches P680 in PSII, both e- here are excited. (remember, P680 has 2 chlorophyll a molecules which have e-)
• 2nd step

  • one of the electrons that was excited in P680 is transferred from
  • P680 -> Primary e- acceptor
  • P680 is oxidized to P680+ (OIL RIG)
• 3rd Step

  • Because it just lost an e-, P680+ will do anything to gain that electron back
  • P680+ EXTREMELY STRONG oxidizing agent
  • REALLY wants to get reduced (gain an e- and go back to P680)
  • Takes e- away
  • P680+ splits H2O into 2 e-, 2 protons (H+), & Oxygen (O)
  • This is called photolysis
  • Now, there is a free e- which is supplied to P680+ turning it back into P680 :)
• 3rd Step cont.

  • Photolysis happens constantly in many cells
  • why plants need lots of water
  • H+ released into TM (increasing H+ amount in TM, eventually will cause disruption)
  • O combines with another O, O2 is released
• 4th Step

  • e- goes from primary electron acceptor of PSII down ETC to PSI
  • PSII ---ETC-----> PSI
  • High energy e- is captured by e- acceptor, go down ETC, and to PSI
  • ETC has plasto-quinone (e- acceptor that helps go down ETC) (basically a complex on ETC)
  • Cytochrome complex on ETC
  • Plastocyanin (complex on ETC)
• PSI

  • Has LHC and Reaction centers
  • Reaction centers are formed by chlorophyll a molecules named P700 because it absorbs light at wavelength of 700 nm
  • LHC has chlorophyll b + carotenoids, photon strikes here first.
• PSII

  • Reaction center has chlorophyll molecules called P680
  • LHC has carotenoids + chlorophyll b