GENERAL BOTANY Lecture 10 - goes back to the original...

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GENERAL BOTANY Lecture 10 - Photosynthesis (Part II) IV. (Continued from last time) Dark reactions A. Major purpose - use energy from light reactions to fix CO 2 into organic molecules B. Reagents of dark reactions 1. ATP and NADPH 2. CO 2 3. Ribulose bisphosphate 4. Enzymes (especially RUBISCO - Ribulose bisphosphate carboxylase / oxygenase) C. Why fix CO 2 ? 1. Store and use chemical energy in the form of organic compounds D. Steps of CO 2 fixation: 1. CO 2 and H 2 O (1 carbon) are added to ribulose bisphosphate (5 carbons) to form two molecules of 3-phosphoglyceric acid (3-PGA) (total of 6 carbons) 2. Catalysis of this reaction by RUBISCO 3. 3-PGA is reduced to 3-PGAL with the help of NADPH and ATP 4. 3-PGAL is converted to either fructose diphosphate or, eventually ribulose bisphosphate 5. Fructose diphosphate goes to other aspects of metabolism and ribulose bisphosphate
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Unformatted text preview: goes back to the original cycle of CO 2 fixation. E. Overall reaction of photosynthesis 12H 2 O + 6CO 2 ==== light ====> 6O 2 + C 6 H 12 O 6 + 6H 2 O F. Other types of CO 2 fixation - under hot conditions (to prevent O 2 competition) 1. C4 plants - fix CO 2 by combining it with PEP to form OAA (PEP carboxylase) 2. OAA (Malate after reduction) from mesophyll releases CO 2 to bundle sheath where RUBISCO carries on its usual process) 3. Recyclization occurs when Malate is converted to pyruvate and, subsequently PEP for another round of CO 2 fixation. G. Now what happens? 1. We have carbohydrate - a principle form of organic energy a) Respiration will harvest energy and convert it to the universal currency - ATP...
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This note was uploaded on 01/30/2012 for the course BSC BSC1085 taught by Professor Sharonsimpson during the Fall '10 term at Broward College.

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