An overview of the stages of
photosynthesis (Fig 6.19)
• light drives the
reactions in the
thylakoid membrane
producing ATP and
NADPH + H+
• the Calvin cycle uses
the ATP and NADPH +
H+ produced to produce
glucose
The products of the light reactions are
consumed in the dark reactions--these
reactions are coupled:
The Hill reactions (the light reactions):
12 H2O + 12 NADP+ + 18 ADP + 18 P---light---> 6O2 + 12 NADPH
+ 12 H+ + 18 ATP
The Calvin Cycle (the dark reactions):
6CO2 + 12 NADPH + 12 H+ +18 ATP---------> C6H12O6 + 12
NADP+ + 18 ADP +18 P (+ 6H2O)
____________________________________
The net equation:
6CO2 + 6H2O----light----------> C6H12O6 + 6O2
How is light absorbed
by the chloroplast?
(see Fig 6.5)
• the “primary”
photosynthetic
pigment is
chlorophyll
Lipid soluble tail
1
Action Spectrum
Reaction Centers
Transfer of Excitation Energy
2
Light energy causes chlorophyll oxidation at the reaction
centre
Molecular Biology of the Cell 4 ed.
Exciton Transfer
Lehninger Principles of Biochemistry 3rd Ed., Nelson and Cox, 2000
In thylakoid membranes, the photosystems are positioned between
electron transport proteins that donate electrons to them, and other
components that can accept electrons from them (ie option 3 on the
previous slide)
3
Electron Flow in Light Reactions
Photosystem II
Plastoquinone
4
Kinetics of O2 Release
Electron Transport between PSII and PSI
Photosystem I
5
An overview of the thylakoid electron transport chain shows how the
photosystems are positioned to: [1] split water; [2]cause electron flow(red
arrow) ; [3] pump H+ across the thylakoid membrane; [4] reduce NADP
Overview
Photophosphorylation
6