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The light reactions of photosynthesis and the Calvin cycle (Photosynthesis…
The light reactions of photosynthesis and the Calvin cycle
Photosynthesis
Converts light energy to chemical energy
light reaction
Energy + 6H2O +6CO2 --> C6H12O6 + 6O2
Synthesize glucose to CO2
Boost electrons from low energy to high energy state
Takes place in Chloroplasts
Membranes
Inner (impermeable)
thylakoid (impermeable)
Outer
Spaces
Outer
Inner (impermeable)
Thylakoid lumen (impermeable)
Contain DNA that aren't autonomous
Absorb light by photoreceptor (can absorb energy of light of specific wave length, pigment)
light energy excites electrons from the ground energy level to excited level
Fluoresces : excited electrons move to ground state and the absorbed energy turns to heat or light
Resonance energy transfer : excitation energy release with 1 electron returns to ground state, then accepted by an electron from neighbour molecule which then jump to higher energy state.
Excited electron itself move to nearby molecules with lower excited state (electron transfer)
Chlorophyll is primary light acceptor in the photosynthesis system
light harvesting complexes enhance the efficiency of photosynthesis
PSI PSII generate a proton gradient and NADPH
Photosystem I
NADPH (electron carrier for biosynthesis)
Photosystem II
20 subunits
Chlorophyll a
Cytochrome b6f links PSI to PSII
The Calvin Cycle
Dark reaction
No light needed
Stage 1 : Fixation of CO2 by ribose 1,5-bisphosphate to form 2 molecules of 3-phosphoglycerate
Rubisco (catalyzes a wasteful oxygenate reaction)
Stage 2 : 3-phospoglycerate products are converted to hexose phosphate
Stage 3 : Regeneration of ribulose 1,5-bisphosphate (acceptor of CO2 in the 1st stage)
6CO2 + 18ATP + 12NADPH + 12H2O --> C6H12O6 + 18ADP + 18Pi + 12NADP+ + 6H+
The synthesis of starch and sucrose
Thioredoxin plays a main role in the Calvin cycle
Oxygenase activity of rubisco increase with temperature
The C4 pathway
Crassulacean acid metabolism permits growth in arid ecosystem