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18. Photosynthesis: antennas and reaction centers

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18. Photosynthesis: antennas and reaction centers

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    1. 18. Photosynthesis: antennas and reaction centers

    2. Synthesizing carbohydrates from CO2 and water presents a formidable thermodynamic problem:

    3. When light raises a molecule to an excited electronic state, the molecule becomes a stronger reductant

    4. The photochemically reactive pigments are chlorins or bacteriochlorins, which are structurally related to hemes

    5. The photochemical reactions of photosynthesis take place in integral membrane proteins

    6. Most of the pigments in photosynthetic cells do not participate in the electron-transfer reactions of photosynthesis. Instead, they serve as an antenna that increases the absorption of light.

    7. The antenna system of purple photosynthetic bacteria has circular pigment-protein complexes

    8. When the antenna is excited with light, excitations are transferred to the reaction center within ~40 ps

    9. The LHC-II (light-harvesting complex II) antenna protein of plants is a trimer with 14 chlorophylls and 3 carotenoids per protein subunit

    10. The reaction center of purple photosynthetic bacteria has 3 to 4 subunits, depending on the species

    11. The electron carriers in the bacterial reaction center are arranged around an axis of approximate rotational symmetry

    12. The sequence and kinetics of the initial electron-transfer reactions can be studied by exciting RCs with short pulses of light

    13. When the complex is excited with light, an electron moves from the BChl dimer (P870) to a BPh and then to a quinone

    14. The photosynthetic electron-transfer system in purple bacteria is cyclic

    15. Plants have two photosystems that work in series to move electrons from water to NADP

    16. The reaction center of Photosystem II has 20 subunits

    17. The core of the Photosystem II reaction center is very similar to that of purple bacteria

    18. Electron carriers in the Photosystem II reaction center

    19. The Photosystem I reaction center has 12 subunits

    20. Two of the Fe-S centers in Photosystem I are in subunit C, on the stromal side of the membrane

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