5.4.2 The Calvin Cycle: RuBP Regeneration Flashcards
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….
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
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
4
Q
Which of the following molecules represents the end-product of the Calvin cycle?
A
- glyceraldehyde 3-phosphate
5
Q
In the regeneration phase of the Calvin cycle 10 glyceraldehyde 3-phosphates will be regenerated into __________ RuBP.
A
- 6
6
Q
Which of the following is not a stage in the Calvin cycle?
A
- carbon regeneration