Question about the Calvin cycle?

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In the Calvin cycle, describe the initial step of CO2 uptake/fixation. What are the 2 reactants? What is the name of the enzyme that catalyzes this step? What are the products? ...show more
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The second stage of photosynthesis, which takes place in the stroma of the chloroplast, can occur without the presence of sunlight. In this stage, known as the Calvin Cycle, carbon molecules from CO2 are fixed into glucose (C6H12O2). The reactions of the Calvin Cycle is as follows:



1. A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2 dissolved in the stroma. This process, called CO2 fixation, is catalyzed by the enzyme RuBP carboxylase, forming an unstable six-carbon molecule. This molecule quickly breaks down to give two molecules of the three-carbon 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA).

2. The two 3PG molecules are converted into glyceraldehyde 3-phosphate (G3P, a.k.a. phosphoglyceraldehyde, PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADPH + H+.

3. Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose.

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  • aa answered 5 years ago
    CO2 joins into the process by coupling with RuBP a five carbon compound called ribulose Biphosphate forming an unstable six carbon molecule that immediately slpits into two three carbon molecules called (PGA) 3-phosphoglycerate
    the busy enzyme that catalyses this is called RUBISCO (ribulose biphosphate carboxylase/oxygenase)
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  • NJJ answered 5 years ago
    6 molecules of ribulose bisphosphate react with 6 molecules of CO2, making 12 PGAs. They are now fixed. The enzyme used is rubisco, or ribulose bisphosphate oxygenase/carboxylase
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  • Justin answered 5 years ago
    yes, 6 molecules of ribulose bisphosphate react with 6 molecules of CO2, making 12 PGAs that are now fixed. CO2 joins into the process by coupling with RuBP a five carbon compound called ribulose Biphosphate forming an unstable six carbon molecule that immediately slpits into two three carbon molecules called (PGA) 3-phosphoglycerate. The enzyme used is ribulose bisphosphate oxygenase/carboxylase (RUBISCO)

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