Carbon fixation involves the addition of carbon dioxide to _.
A. Rubisco B. NADPH C. G3P D. RuBP E. 3-PGA
The Correct Answer and Explanation is :
The correct answer is D. RuBP (Ribulose bisphosphate).
Explanation
Carbon fixation is a critical process in photosynthesis, specifically occurring during the Calvin cycle in plants, algae, and some bacteria. This process is the initial step that allows carbon dioxide (CO₂) from the atmosphere to be incorporated into organic molecules.
The key enzyme that catalyzes the carbon fixation reaction is Rubisco (ribulose bisphosphate carboxylase/oxygenase), which facilitates the reaction between carbon dioxide and RuBP (ribulose bisphosphate). RuBP is a five-carbon sugar that serves as the carbon dioxide acceptor in the Calvin cycle. When CO₂ is added to RuBP, it forms a six-carbon intermediate, which is highly unstable and immediately splits into two molecules of 3-PGA (3-phosphoglycerate), a three-carbon compound.
The significance of this reaction lies in its role in the biosynthesis of glucose and other carbohydrates, which are crucial for the energy needs of the plant and, subsequently, for the organisms that consume these plants. This incorporation of atmospheric carbon into organic molecules not only fuels plant growth but also contributes to the global carbon cycle, helping to regulate atmospheric CO₂ levels.
Furthermore, the fixation of carbon through RuBP is part of a broader series of reactions in the Calvin cycle, where ATP and NADPH (produced in the light-dependent reactions of photosynthesis) are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), another three-carbon sugar. G3P can then be utilized to synthesize glucose and other carbohydrates, demonstrating the centrality of RuBP in the entire process of carbon fixation and the subsequent formation of organic compounds essential for life on Earth.