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LIGHT INDEPENDENT REACTIONS (The CALVIN CYCLE) ‏

LIGHT INDEPENDENT REACTIONS (The CALVIN CYCLE) ‏. Melvin Calvin in the early 1960's; Nobel Prize in 1961; died in 1997. Occurs in the stroma of the chloroplast. ATP and NADPH from the light reactions go into the stroma and are used to create carbohydrate from atmospheric carbon.

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LIGHT INDEPENDENT REACTIONS (The CALVIN CYCLE) ‏

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  1. LIGHT INDEPENDENT REACTIONS (The CALVIN CYCLE)‏ • Melvin Calvin in the early 1960's; Nobel Prize in 1961; died in 1997. • Occurs in the stroma of the chloroplast. • ATP and NADPH from the light reactions go into the stroma and are used to createcarbohydrate from atmospheric carbon. • Glucose is created from water and carbon dioxide. Carbon Fixation: the attachment of atmospheric carbon dioxide to an organic molecule. • Requires no light energy. • 3 phases: http://courses.cm.utexas.edu/emarcotte/ch339k/fall2005/Lecture-Ch19-3/SlideCalvinCycle.jpg

  2. I: CARBON FIXATION • Calvin Cycle begins and ends with a 5C molecule called Ribulose 1,5-Bisphosphate (RuBP) • 3RuBP capture 3 atmospheric carbon dioxides to form 3 six carbon compounds. • This reaction is catalyzed by rubisco, a slow enzyme that catalyzes 3 molecules per second. To make up for its slow speed, it makes up 20-50% of the protein in a chloroplast…it may be the most abundant protein in the planet! • Each of the 3 - 6C compounds immediately react with water to form 2 – 3C molecules of phosphoglyceric acid (PGA). Therefore 6 PGA in total. • For 3 carbon dioxide molecules you would get 6 PGA molecules, therefore a total of 12 are created for 6 CO2 in one chemical reaction of photosynthesis.

  3. II: REDUCTION REACTIONS • (essentially the reverse of glycolysis)‏ • Energy (6 ATP) and reducing power (6 NADPH) are used to convert 6 PGA into 6 G3P (also known as phosphoglyceraldehyde (PGAL) ). • Each of the 6 molecules of PGA are phosphorylated by an ATP to form six molecules of 1,3-bisphosphoglycerate (1,3-BPG). • A pair of electrons from each of the six NADPH molecules reduces six molecules of 1,3-BPG to 6 molecules of glyceraldehyde-3-phosphate (G3P or PGAL), a sugar. • One PGAL leaves the cycle at this point.

  4. III: RuBP REGENERATION • The remaining molecules of PGAL go through a series of reactions to regenerate 3 molecules of RuBP. • This uses 3 ATP in the process.

  5. END RESULT • The overall equation for the Calvin Cycle (per G3P produced) is: 3 RuBP + 3 CO2 + 9 ATP + 6 NADPH + 5 H2O --> 9 ADP + 9 P + 6 NADP + G3P + 3 RuBP • The G3P can be: • combined with another G3P to form glucose. (requires 6 turns – hence 6 CO2) • converted to starch and stored in the chloroplast as a reserve for when light is not present. • converted into sucrose and translocated to other parts of the plant. • Both glucose and sucrose can be made into many things essential for the plant (cellulose, lipids, amino acids...) 6 CO2 (g) + 12 H2O (I) + light energy ---------> C6 H12 O6 (aq) + 6O2 (g)

  6. SUMMARY http://www.ualr.edu/botany/photosynthesis.gif

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