Chapter 23 - Light-Dependent Reactions of Photosynthesis

photosystems

photosynthetic units in the thylakoid membrane, have two parts and are the location for light dependent reactions

light harvesting complex (LHC) and electron transport train (ETC)

the 2 parts of a photosystem

anthena complex and reaction center

the 2 parts of the LHC

antenna complex

pigment molecules and binding proteins, absorb and channel photon energy through resonance

reaction center

connects the LHC and ETC, mostly made of chlorophyll a, 2 special types transfer an excited e^- to the ETC through oxidation

electron transport chain (ETC)

chain of carriers where an energized e^- is passed along carriers where the primary e^- receptor takes an excited e^- from the reaction center

photosystem one (PSI)’s overall goal

to create NADPH

P700

PSI’s reaction center

ferredoxin

transfers e^- to make NADPH

PSI’s primary e^- receptor

modified chlorophyll at the start of the ETC, ferredoxin

NADP reductase

enzyme that reduces NADP+ and H+ to NADPH

P680

PSII’s reaction center

PSII’s primary e^- acceptor

pheophytin

z-scheme

energy levels fluctuate forming a “z” shape

step 1 of chemiosmotic photophosphorylation

e^- are passed along the ETC, a carrier series

step 2 of chemiosmotic photophosphorylation

each pass in a series results in an “energy spillover”

step 3 of chemiosmotic photophosphorylation

the energy spillover pushes H+ (protons) to the lumen side of the thylakoid membrane

step 4 of chemiosmotic photophosphorylation

a H+ gradient (proton motive force) is formed

step 5 of chemiosmotic photophosphorylation

the protein ATP synthase facilitates H+ diffusion, the proton flow causes the protein to turn like a water wheel

step 6 of chemiosmotic photophosphorylation

the turning of ATP synthase powers ATP production using kinetic energy from the OEC

oxygen evolving complex (OEC)

breaks water apart

how does chemiosmotic photophosphorylation replace e^- for the ETC?

4H atoms break into 4H+ to power ATP production and 4e^- which replace the e^- lost in the ETC