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06- Photosynthesis

06- Photosynthesis - Photosynthesis Photosynthesis In...

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Photosynthesis Photosynthesis - In simple terms: photosynthesis uses light energy (photons) to make organic compounds (sugars) - 6CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6O 2 - Endergonic reaction - energy comes from photons from sun - capturing light energy, using energy to drive endergonic reactions - It is the most important set of chemical reactions in the biosphere, everything depends on photosynthesis - Revisit some basic chemistry: - Loss and gain of electrons → Redox reactions (revisited) - Oxidation: the loss of electrons - In biological systems: often dehydrogenation - Often, when electrons are lost, hydrogen is lost. - Reduction: the gain of electrons - When molecule gains electrons, hydrogen is often gained as well - When something looses an electron, something else will gain - Usually coupled so: thus called a redox reaction - The same molecule can be: - Oxidized by one molecule - Reduced by different molecule - Affinity for electrons: controls direction of electron flow - how much a molecule is able to attract an electron - high affinity for electrons: reduced - low affinity for electrons: oxidized Electron carriers - electron carriers : molecules that can be reversibly oxidized and reduced - without being damaged - can donate/accept electrons depending on what's around them - Vary in their affinity for electrons - Arrange by increasing affinity for electrons: electron transport chain - low → high - one oxidized, other reduced - Gradual release of energy that can be captured - When we transfer an electron, energy can be given off and then captured - Allows maximal synthesis of ATP - 3 molecules – electron carriers: - A – electron affinity 10 - B – electron affinity 1
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- C – 5 - If B gives off electron, it can go to A or C because electron affinity is higher - If we rearrange them: B, C, A - Electron will go B → C → A because of the electron affinities (1 → 5 → 10) - Every time electron is transferred, a small amount of energy is released. What does this have to do with photosynthesis? - We are going to oxidize H 2 O to O 2 and H + during part of photosynthesis - Endergonic – energy input required - We are going to reduce CO 2 to glucose during part of photosynthesis - Also endergonic - 6CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6O 2 - Endergonic energy input: the sun! Site of photosynthesis - Occurs within cells, usually in the leaf - Organelle involved is the chloroplast - chloroplast stores chlorophyll - Structure of chloroplast is important - Thylakoid membranes: - Create enclosed compartment within disks - important because it stores protons - membrane is an effective barrier - Must be intact for photosynthesis to occur - Must maintain H +
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