Photosynthesis consists of light-dependent and light-independent reactions
- photoactivation of photosystem II:
- at 680 nm photons absorbed by pigments
- chlorophyll a reduced (since gains energy)
- chlorophyll a oxidized (excited electrons are moving to electron transport systems)
- photolysis of water:
- oxidized chlorophyll a lacks electrons
- replaced as H20, split
- remains in thylakoid interior (lowers pH)
- contributes to chemiosmotic gradient
- used in phosphorylation of ATP
- 2 3l3ctrons
- 1/2 O2: lost in environment
- Electron transport system: proteins in thylakoid membrane transfer energy along a pathway in a series of redox reactions:
- from PsI to NADP+
- some used to pump H+s from stroma –> thylakoid interior (lower pH)
- contributes to chemiosmotic gradient (in phosphorlyation of ATP
- Photoactivation of photosystem I:
- at 700nm, photons absorbed by pigments
- chlorophyll a reduced (gains energy)
- chlorophyll a oxidized
- Reduction of NADP+ —> NADPH + H+
- gain of 2 electrons from ETS
- reduces NADP+ –> NADPH + H+
- Non-cyclic Photophosphorylation:
- one way flow of 2 electrons
- 2 main products: NADPH + H+ and ATP
- Cyclic Photophosphorylation
- cyclic flow of electron PsI –> ETS —> PsI
- Main product: ATP
Evidence for Chemiosmosis (p. 110)
1 a) The rate of ATP production is faster as the pH of the ADP solution is higher. At the same time, the rate of ATP production is higher at a lower pH as well.
b) This is due to the fact the magnitude of the concentration gradient (between the inside, outside) in increasing.
2) At a lower incubation pH, the concentration gradient increases as well as the yield of ATP.
3) The concentration difference is decreased once any change is made and thus results in a decrease in ATP production. The ATP production is generated with the help of the H movement, and goes down the concentration gradient, too.
4) The concentration gradient is affected because of the occurrence of photolysis with the help of light, which produces H.