What is the first step of carbon dioxide reduction during the Calvin Cycle?

• A. Carbon fixation by ribulose bisphosphate
• B. Regeneration of ribulose bisphosphate
• C. Reduction of 3-phosphoglycerate to glyceraldehyde-3-phosphate
• D. Conversion of glyceraldehyde-3-phosphate to glucose

Answer: (A)

Verified step by step guidance

1. Understand the Calvin Cycle: The Calvin Cycle is a series of biochemical reactions that occur in the chloroplasts of photosynthetic organisms. It is part of the process of photosynthesis and is responsible for carbon fixation, which converts carbon dioxide into organic compounds.
2. Identify the phases of the Calvin Cycle: The Calvin Cycle consists of three main phases: carbon fixation, reduction, and regeneration. Each phase plays a crucial role in the conversion of carbon dioxide into glucose.
3. Focus on carbon fixation: The first step in the Calvin Cycle is carbon fixation. During this step, carbon dioxide is incorporated into an organic molecule. This is achieved by the enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO), which catalyzes the reaction between carbon dioxide and ribulose bisphosphate (RuBP).
4. Recognize the role of ribulose bisphosphate: Ribulose bisphosphate (RuBP) is a 5-carbon sugar that acts as the substrate for RuBisCO. When carbon dioxide is fixed, it combines with RuBP to form an unstable 6-carbon intermediate, which quickly splits into two molecules of 3-phosphoglycerate (3-PGA).
5. Connect carbon fixation to the rest of the cycle: After carbon fixation, the Calvin Cycle proceeds to the reduction phase, where 3-phosphoglycerate is converted into glyceraldehyde-3-phosphate (G3P). Eventually, G3P can be used to form glucose, and RuBP is regenerated to continue the cycle.