web_L30_08BIO311C

web_L30_08BIO311C - BIO 311C April 4 2008 The Location of...

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BIO 311C April 4, 2008
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Several hundred chlorophyll molecules occur as an organized array within a cluster of several transmembrane proteins. Thylakoid membrane Complex of several transmembrane proteins Chlorophyll molecule The Location of Chlorophyll Molecules Within Thylakoid Membranes *
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Chlorophyll Molecule Space-filling model (different kinds of atoms are shown in different colors) Chemical structure * The ring structure (head) of chlorophyll is polar and projects from the hydrophobic interior of thylakoid membranes. It is the portion of the molecule that absorbs light energy. The magnesium ion is required for its function. The tail of chlorophyll is nonpolar. It anchors the chlorophyll in place within transmembrane proteins by hydrophobic bonding. tail head Textbook Fig. 10.10, p. 188 Mg 2+
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Light Harvesting in a Thylakoid Membrane 1. A photon of light is absorbed by any one of the chlorophyll molecules within an array. 2. The energy content of the light is transferred rapidly among the chlorophyll molecules within the array. 3. The energy eventually becomes "trapped" in a special pair of chlorophyll molecules. 4. Energized special-pair chlorophyll loses an electron to another molecule called a primary electron acceptor. This is an oxidation-reduction reaction. * Energy transfer among chlorophyll molecules does not involve any chemical reaction. Electron transfer from the special pair” chlorophyll molecules to the primary electron acceptor is the first chemical reaction of photosynthesis. Textbook Fig. 10.12, p. 189
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Three Steps in Primary Electrical Charge Separation in a Reaction Center * Chl : any chorophyll molecule that absorbs light energy P : special-pair chlorophyll A: electron acceptor D: electron donor
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A D Final Result of Primary Charge Separation in a Reaction Center *
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primary electron acceptor primary electron donor e - e - A - D + Primary charge separation in a reaction center makes the lumen of the thylakoid more positively charged and the stroma of the chloroplast more negatively charged. thylakoid lumen chloroplast stroma * Slightly modified from Fig. 10.12, p. 189.
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The Two Photosystems of Photosynthesis Two photosystems are embedded in the same thylakoid membrane. They are somewhat separated from each other, but are connected through an electron transport chain. * P700 and P680 are the names of the special-pair chlorophyll of
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web_L30_08BIO311C - BIO 311C April 4 2008 The Location of...

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