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Question
Name the two important enzymes of C4 pathway, and explain their role in fixing CO2?
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Solution
The two important enzymes of C3 and C4 pathways are RuBisCO and PEPcase respectively. RuBisCO is the primary CO2 acceptor in C3 plants, while PEPcase is the primary CO2 acceptor in C4 plants.
Role of RuBisCO: RuBisCO is also called RUBP Carboxylase Oxygenase. As the name indicates; it has both carboxylase and oxygenase actions. This enzyme has more affinity toward carbon dioxide than oxygen. However, some of these enzymes fix oxygen in C3 plants through a process called photorespiration. Photorespiration is an inefficient process because it does not create any beneficial product for the plants. Moreover, it also reduces carbon fixation in C3 plants.
Role of PEP case: This is the major carbon dioxide acceptor in C4 plants. However, RuBisCO is also present in these plants. PEPcase binds with carbon dioxide to produce a 4-carbon compound oxaloacetic acid (OAA). OAA is eventually converted into carbon dioxide. Carbon dioxide eventually enters the Calvin cycle and carbohydrates are generated. It is crucial to memorize that the Calvin Cycle is mutual in both C3 and C4 plants.
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