Question

Carboxylation in $C_3$ plants requires the following enzyme:

• A. Kinase
• B. RuBisCo
• C. Nitrogenase
• D. $\alpha$ - ketoglutarate dehydrogenase

Answer 1

The correct option is B RuBisCo

Plants have the ability to fix carbon dioxide and thereby synthesise glucose. All the detailed reactions that occur during synthesis of glucose were given by Calvin. Hence it is also called the Calvin cycle. Calvin cycle occurs in the stroma of chloroplast and does not require light. Hence, it is also called a light independent reaction. It includes three stages - carboxylation, reduction and regeneration.

Carboxylation or carbon dioxide fixation is the first step in the Calvin cycle. RuBP (ribulose-1,5-bisphosphate) acts as the primary acceptor of carbon dioxide. RuBP combines with carbon dioxide and forms into an unstable 6 carbon compound. This reaction is catalysed by the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase). The unstable 6 carbon compound splits into two molecules of 3-PGA (3-phosphoglycerate).

Kinase is an enzyme that catalyzes the reaction in which phosphate groups from high energy phosphate donating molecules are added to specific substrates.

Nitrogenase enzyme is a Fe-Mo protein involved during biological nitrogen fixation.

$\alpha$ - ketoglutarate dehydrogenase complex is an enzyme known for its role in the citric acid cycle (Krebs cycle).