Lect_11__Photosynthesis-I

Lect_11__Photosynthesis-I - Lecture 11 Photosynthesis light...

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Introduction and history Chloroplasts, chlorophyll, pigments Photosystems I and II Z-scheme for production of NADPH and ATP Cyclic and non-cyclic flow of electrons in the Z-scheme Quantum requirement for PS Lecture 11 - Photosynthesis light reactions
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Photosynthesis (PS) is the ultimate source of biological energy! Photosynthesis is the process by which the CO 2 of the atmosphere is reduced to living cell compounds. The energy for the process is provided by sunlight. PS organisms trap solar energy and form ATP and NADPH which are used to form carbohydrate from CO 2 and H 2 O. If the photosynthetic organism is a green plant, O 2 is released simultaneously into the atmosphere.
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Not all organisms can carry out PS. Green plants and various algae are photosynthetic. About 50% of photosynthesis is carried out by microorganisms such as blue green algae, green sulfur bacteria and purple bacteria. Animals cannot carry out PS and are totally dependent on plants and microorganisms for their supply of biological energy, i.e. food. A large amount of energy is trapped per year by PS - about 10 17 kJ of free energy is trapped and used for PS. This is about 10 times more energy than the fossil fuel energy used every year by people all over the world.
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CO 2 + H 2 O CH 2 O + O 2 sunlight chloroplasts G’ = +480 kJ 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 G’ = +2,880 kJ sunlight chloroplasts Energy requirement to fix CO 2 glucose The basic reaction of photosynthesis (PS) for making glucose by green plants: CO 2 is the electron acceptor H 2 O is the electron donor Sunlight provides energy A PS apparatus is required - chloroplast The products are reduced CO 2 plus the oxidized electron donor
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H 2 O is a poor electron donor; recall its standard reduction potential is +0.82 V. NADH is a good electron donor; its redox potential was -0.32 V. A crucial difference between oxidative phosphorylation and photo- phosphorylation (ATP synthesis during photosynthesis) is that ox phos starts with a good electron donor (NADH), while photophosphorylation requires the input of energy to create a good electron donor.
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Higher green plants CO 2 + 2 H 2 O 18 CH 2 O + O 2 18 + H 2 O Green sulfur bacteria (anaerobic) CO 2 + 2 H 2 S CH 2 O + 2 S + H 2 O Non-sulfur purple bacteria CO 2 + 2 CH 3 CHOHCH 3 CH 2 O + 2CH 3 COCH 3 + H 2 O propanol acetone CO 2 + 2 CH 3 CHOHCOOH CH 2 O + 2 CH 3 COCOOH + H 2 O lactate pyruvate History - Pattern of CO 2 fixation by various organisms (O 2 is derived from H 2 O)
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CO 2 + 2 H 2 D CH 2 O + 2 D + H 2 O General pattern emerges -H 2 D is any H or e- donor -D is the oxidized form of the donor -CO 2 is reduced to the carbohydrate state
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Light and dark reactions of photosynthesis (PS) Rate of PS Light intensity Rate of PS is proportional to intensity of light only at relatively low intensities. At higher intensities, the rate of
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This note was uploaded on 04/19/2008 for the course BIS 103 taught by Professor Abel during the Spring '08 term at UC Davis.

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Lect_11__Photosynthesis-I - Lecture 11 Photosynthesis light...

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