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Multiple Choice
Which of the following best describes the carboxylation phase of the Calvin cycle?
A
The conversion of to .
B
The reduction of to .
C
The addition of to to form .
D
The regeneration of from .
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Verified step by step guidance
1
Understand the Calvin cycle: The Calvin cycle is a series of biochemical reactions that take place in the chloroplasts of photosynthetic organisms. It is divided into three main phases: carboxylation, reduction, and regeneration.
Identify the carboxylation phase: This phase involves the addition of carbon dioxide (CO2) to a 5-carbon sugar, ribulose-1,5-bisphosphate (RuBP), catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO).
Recognize the product of carboxylation: The reaction between CO2 and RuBP results in an unstable 6-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA), a 3-carbon compound.
Differentiate from other phases: The reduction phase involves the conversion of 3-phosphoglycerate to glyceraldehyde-3-phosphate (G3P) using ATP and NADPH. The regeneration phase involves the conversion of G3P back into RuBP, allowing the cycle to continue.
Conclude the correct description: The carboxylation phase is best described as the addition of carbon dioxide to ribulose-1,5-bisphosphate to form 3-phosphoglycerate, which aligns with the correct answer provided.