5.4.2 The Calvin Cycle: RuBP Regeneration Flashcards

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1
Q

note

A
  • In the Calvin cycle, carbon dioxide is fixed onto ribulose bisphosphate (RuBP) by the enzyme rubisco to form 3-phosphoglycerate. 3-phosphoglycerate is then phosphorylated and reduced to eventually give rise to
    glyceraldehyde 3-phosphate (G3P). RuBP is then regenerated through a complex series of reactions in order to continue the cycle.
    • For the synthesis of one glyceraldehyde 3-phosphate the Calvin cycle must make three turns.
  • In order to produce one glyceraldehyde 3-phosphate, the cycle must make three turns. Let’s follow the numbers of carbons throughout the cycle.
  • Starting in phase one of the diagram, if three carbon dioxide (CO2) molecules enter the cycle, they must be fixed to three five-carbon ribulose bisphosphate molecules (RuBP). The three new six-carbon molecules that result from this addition then split apart to make six three-carbon molecules called 3-phosphoglycerate.
  • In phase two of the Calvin cycle, the 3-phosphoglycerate molecules get reduced to form
    glyceraldehyde 3-phosphate (G3P). One G3P molecule is released from the cycle for use by the plant cell, leaving five behind. Through a complex series of reactions, in phase three of the cycle, five three-carbon G3P molecules are used to regenerate three five-carbon RuBP molecules. And the cycle continues….
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2
Q

The reactions of the Calvin cycles are referred to as light-independent reactions, yet in most plants they occur during daylight hours. Why?

A
  • The Calvin cycle depends on ATP and NADPH from the light-dependent reactions
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3
Q

In the Calvin cycle, _______ ATP’s and ________ NADPH’s are required for a net output of two molecules of glyceraldehyde 3-phosphate.

A
  • 18; 12
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4
Q

Which of the following molecules represents the end-product of the Calvin cycle?

A
  • glyceraldehyde 3-phosphate
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5
Q

In the regeneration phase of the Calvin cycle 10 glyceraldehyde 3-phosphates will be regenerated into __________ RuBP.

A
  • 6
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6
Q

Which of the following is not a stage in the Calvin cycle?

A
  • carbon regeneration
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