The Calvin-Benson cycle is a series of biochemical reactions that occur in the chloroplasts of plants during photosynthesis. It is the primary pathway by which carbon dioxide is fixed and converted into carbohydrates. The cycle consists of three phases: carboxylation, reduction, and regeneration.
1. Carboxylation phase:
In this phase, carbon dioxide is fixed and added to a five-carbon molecule called ribulose-1,5-bisphosphate (RuBP). The enzyme that catalyzes this reaction is called ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The substrate for this reaction is RuBP and the product is a six-carbon molecule called 3-phosphoglycerate (3PGA). This reaction is often referred to as carbon fixation because it is the first step in converting inorganic carbon dioxide into organic compounds.
2. Reduction phase:
In this phase, 3PGA is reduced to form a three-carbon sugar called glyceraldehyde-3-phosphate (G3P). This reduction is achieved through a series of enzymatic reactions. The key enzymes involved are phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, and transketolase. The reduction reactions require energy in the form of ATP and NADPH (which is produced during the light-dependent reactions of photosynthesis). The substrate for these reactions is 3PGA, and the products are G3P and other intermediate compounds. Some of the G3P is used to regenerate RuBP, while the rest is used to synthesize other carbohydrates and molecules necessary for plant growth.
Overall, the Calvin-Benson cycle is responsible for converting carbon dioxide into usable energy in the form of carbohydrates. It is an essential process for sustaining life on Earth, as it is the primary means by which plants generate organic compounds and oxygen through photosynthesis.
DISCUSS THE TWO REACTIONS (CARBOXYLATION AND REDUCTION PHASES) INVOLVED INTHE CALVIN-BENSON CYCLE. INDICATE THE SUBSTRATE, ENZYMES AND THE PRODUCTS OF THESE TWO REACTIONS
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