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6 turn of calvin produce 1 glucose?

Discussion in 'DAT Discussions' started by vvvv, Jun 19, 2008.

  1. vvvv

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    I know this question had come up before but Im still confused. Destroyer said 6 turn of calvin cycle produce 1 glucose. but campbell said 2 turn. becasue calcin cycle start with 3 ribulose biphosphate and 3 CO3 is added to the cycle. each cycle consume 9 ATP and 6 NADPH. and produce 6 G3P, 1 G3P will get out of the cycle and 5 G3P will regenerate 3 molecule of RuBP. so in order to produce glucose, need 2 G3P which mean 2 cycle....

    any thought?
     
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  3. harrygt

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    It's good that you get the overall point. THis difference is just based on how you define each cycle.
    Some sources say : One cycle = consumption of 3 CO2
    Some other sources say : One cycle = consumption of 1 CO2 [This is the more frequent definition]

    Anyway, the important point is that for one molecule of glucose [or 2 molecules of G3p], 6 CO2, 18 ATP, and 12 NADPH are used. But you already knew that ! I would say we need 6* cycles for one molecule of glucose [based on the more frequent definition]'
    I hope this helps
     
  4. vvvv

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    woa...science can not clarify this?
     
  5. vvvv

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    so what is the product for 1 cycle if 1 CO2 enter the cycle? 1C molecule?
     
  6. harrygt

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    That is the point! Based on the second definition, you won't have any product until 3 cycles happen together. I just tried to clarify this for you buddy. The multiple choice questions usually use the second definition. Don't worry, you will be fine as long as you know the cycle very well.
     
  7. vvvv

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    thanks
     
  8. achilles2

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    I think you fix 1 CO2 per turn so to net a six carbon glucose you need 6 turns....remember you spend carbons regenerating materials for the calvin cycle
    The real product of the dark rxns is G3P, not glucose, you convert 2 G3P's to glucose I believe....

    let me wikipedia it real quick:

    I too am studying for the DATs going over questions and trying to help explain processes is a great way to study!!!


    "The cycle repeats continuously, each time making a carbon atom available for G3P. When three cycles are completed, one G3P can be removed for making glucose and other organic molecules.

    but you need 2 G3P's

    To make a molecule of glucose requires 6 turns of the cycle. Eighteen molecules of ATP will be dephosphorylated and 12 molecules of NADPH will be oxidized. Each molecule of NADPH can be considered to be roughly equivalent to 3 molecules of ATP in terms of energy. So, it requires approximately the equivalent of 54 ATPs to make a molecule of glucose. (3 x 12 NADPH = 36 ATP. 36 ATP + 18 ATP = 54ATP)"

    http://faculty.nl.edu/jste/calvin_cycle.htm
     

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