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Light Independent Reactions

Light Independent Reactions

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Light Independent Reactions

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  1. Light Independent Reactions The path of carbon in photosynthesis

  2. The steps of the light-independent reactions • The experiments of Melvin Calvin’s team established the details of the path of carbon from carbon dioxide to glucose • Nobel Prize in 1961 • Occurs in the stroma (the fluid that surrounds the thylakoids) • They showed that …

  3. The steps • The first product of the fixation of carbon dioxide is glycerate 3-phosphate (GP). • This is the fixation step • The initial product is immediately reduced to the 3-carbon sugar phosphate, triosephosphate, using NADPH + H and ATP • This is the reduction step • 2 triose phosphate molecules can combine to form hexose phosphate which can combine to form starch

  4. The steps (continued) • Then the triose phosphate is further metabolized to produce carbohydrates (sugars, sugar phosphates, starch) and later lipids and amino acids • This is the product synthesis step • Some of the triose phosphate is metabolized to produce the molecule that first reacts with carbon dioxide (the acceptor molecule • This is the regeneration of acceptor step • The reactions of this regeneration process are known as the Calvin Cycle

  5. Which intermediate is the actual acceptor molecule? • The acceptor molecule for carbon dioxide is a 5-carbon acceptor (ribulose biphosphate or RuBP) • When carbon dioxide has combined the 6-carbon product immediately splits into two 3-carbon GP molecules • The enzyme involved is called ribulose biophosphate carboxylase (Rubisco) • Rubisco is the most common protein of green plant leaves

  6. Regeneration of RuBP • As RuBP is both consumed and produced, these reactions form a cycle • Calvin Cycle • For the Calvin cycle to continue indefinitely, as much RuBP must be produced as consumed • If 3 RuBP molecules are used, six triose phosphates are produced • Five of these are needed to regenerate the three RuBP molecules, leaving just one triose phosphate for the conversion of photosynthesis products • To produce one molecule of glucose, 6 turns of the cycle are needed

  7. The steps of carbon in photosynthesis

  8. Summary of light independent reactions

  9. Animations • http://www.sinauer.com/cooper/4e/animations0305.html • Glyceraldehyde 3 phosphate is the same as triose phosphate

  10. Chloroplast structure and function • Table 9.4 identifies how the structure of the chloroplast facilitates function