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Unformatted text preview: 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- 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 + concentration gradient...
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This note was uploaded on 03/25/2010 for the course BIO 11000 taught by Professor Friedman during the Spring '10 term at Purdue University-West Lafayette.
- Spring '10