LIGHT INDEPENDENT REACTIONS (The CALVIN CYCLE)?

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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.
• 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/fall
2005/Lecture-Ch19-3/SlideCalvinCycle.jpg
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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 chloroplastit 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.

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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.

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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.

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END RESULT

• The overall equation for the Calvin Cycle (per
  G3P produced) is
• 3 RuBP 3 CO2 9 ATP 6 NADPH 5 H2O --gt
  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
  ---------gt C6 H12 O6 (aq) 6O2 (g)

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