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Question
RuBisCo is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCo carries out more carboxylation in C4 plants?
Solution
- RuBisCO is an enzyme that functions as an oxygenase (during photorespiration) and carboxylase (during photosynthesis). However, in C4 plants, RuBisCO performs greater carboxylation. Mesophyll cells in C4 plants are where carbon dioxide is first fixed.
- Phosphoenol pyruvate, or PER, is the main absorber of carbon dioxide. When PEP carboxylase or PEP case, is present, it reacts with carbon dioxide to produce oxaloacetic acid or oxaloacetate. Through plasmodesmata, malic or aspartic acid is translocated to bundle sheath cells.
- They undergo decarboxylation (or, in the case of aspartic acid, deamination) inside the bundle sheath cells to produce pyruvate and CO2. Through the Calvin cycle, CO2 is once again trapped inside the bundle sheath cells. In C4 plants, RuBP of the Calvin cycle is referred to as the secondary or ultimate acceptor of CO2. Pyruvate returns to the cells of the mesophyll
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