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Biology 1202B Lecture Notes - Light-Dependent Reactions, Chlorophyll, Photosynthetic Reaction Centre

Course Code
BIOL 1202B
Richard Gardiner

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- Electron acceptor/carrier in removal of H ions
- Antenna molecule absorbs a photon, moves through molecules until it reaches a specific chlorophyll A molecule,
the reaction center
- At RC, is a primary electron receptor that removes an excited electron from the reaction center chlorophyll A (light
reactions start)
- Each photosystem functions in the chloroplast as a light harvesting unit
Photosystem I
- Absorption peak = 700 nm
Photosystem II
- Absorption peak = 680 nm
*Differences of these reaction centers (peaks of RC) lie in the proteins associated with each RC
* These two photosystem work together to use light energy to generate ATP and NADPH
Light Reactions
- 2 routes for electron flow:
- Cyclic = produces ATP and NADPH
- Non-cyclic = Absorbs light, excited electron captured by PEA, leaves RC oxidized
- Photoexcited electrons pass along the ETC before ending up at an oxidized photosystem I RC
- As these electrons pass along the transport chain, their energy is harnessed to produce ATP
- At the bottom of the ETC, electrons fill an electron 'hole' in an oxidized P700 center
- This hole is created when photons excite electrons on the photosystem I complex
- These electrons make NADP+ to NADPH (glycolosis)
- LR use solar power of photons, absorbed by the photosystems, to provide ATP and reduces power in the form of
the electrons carried by NADPH
- Non-cyclic = 1 H2O splits, get 1 ATP and 1 NADPH
- Produces ATP and NADPH in roughly equal quantities
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