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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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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 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


I carbon fixation

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.


Ii reduction reactions

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.


Iii rubp regeneration

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.


End result

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)


Summary

SUMMARY

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


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