Lect17_PS2 - Summary to date (biosynthesis or anabolism)...

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1 Using sun energy to make fuels (Photosynthesis) Day 17 Summary to date (biosynthesis or anabolism) • ATP and high-energy electrons from NADH can be used to construct organic molecules – ATP can drive uphill reactions – NADH (and its cousin NADPH) can reduce organic molecules (transfer high-energy electrons onto them) • Thus, cells can use energy (e.g., from food or light) to construct the organic molecules necessary for life Phototrophs • Some organisms can use light energy to help construct organic molecules – Such organisms have less (photo- heterotrophs) or no (photo-autotrophs) need for external sources of organic molecules (fuel, food) • What’s necessary to fix carbon dioxide and make your own organic ‘food’? The Problem Making fuel from scratch Requires: 1. Carbon dioxide 2. An energy source (such as light , reduced compounds ) 3. A source of Electrons (such as hydrogen sulfide, H 2 S; or water, H 2 O , or reduced compounds ) 4. A way to store captured energy for the long run – that is, formation of a stable fuel that waits for a match (has a high activation energy) (Biosynthesis). Chemo autotrophs and photo autotrophs do similar things but use different energy sources – we’ll look at photoautotrophs here A summary of photosynthesis: A Redox reaction run “uphill” or in reverse (CH 2 O) n + X 2 CO 2 + H 2 X Light, chll X could be Sulfur for nonoxygenic PS, and is Oxygen for oxygenic PS Adding electrons to a molecule this way requires energy input The product has more bond energy that the reactants did Photosynthesis: reducing carbon using energy from light Photosynthesis converts light energy into chemical energy through a multi-step process: I. Light reactions – 1. Energy captured from the sun is used to excite electrons – 2. High energy electrons are transferred to NADPH (cousin of NADH) – 3. Electrons that leave on NADPH must be replaced from some electron source.
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2 Photosynthesis: Capturing energy from the Sun Photosynthesis converts light energy into chemical energy through a multi-step process: II. Light-independent Reactions – 4. Carbon is “fixed” onto organic molecules and reduced with high energy electrons (from NADPH) -- forming new aviation fuel! The energy (and carbon) can then be released again as needed, through fermentation and / or respiration NAD is used as an electron acceptor for the (oxidative) degradative reactions but NADP - another electron carrier - is used to drive (reductive) synthetic reactions BUT WAIT! What is NADP? The original electron acceptor used in oxidative reactions NAD + NAD + NADP + NADP + ….by adding PO 4 The second universal electron carrier is made…. O-P-O - O O nicotinamide 2e - and 2H + (2e - , 1H + and 1H + ) NADP + Oxidized Reduced NADP + works just like NAD + -- same business end -- only difference PO 4 • Why is it advantageous for a photosynthetic cell to have both NADH and NADPH?
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This note was uploaded on 03/08/2011 for the course BIS 2A taught by Professor Grossberg during the Fall '08 term at UC Davis.

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Lect17_PS2 - Summary to date (biosynthesis or anabolism)...

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