Which of the following statements about RuBisCO is true? 

The correct answer is It catalyzes the carboxylation of RuBP.

Concept:

• RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the most abundant enzyme in the world (Do
• It plays a critical role in the process of photosynthesis by catalyzing the first major step of carbon fixation, where atmospheric carbon dioxide is converted into organic compounds.
• RuBisCO facilitates the reaction between ribulose-1,5-bisphosphate (RuBP), a 5-carbon compound, and carbon dioxide, leading to the formation of two molecules of 3-phosphoglycerate (3-PGA).

Explanation:

It catalyzes the carboxylation of RuBP:

• RuBisCO catalyzes the carboxylation (adding CO₂) of ribulose-1,5-bisphosphate (RuBP), which is the initial and crucial step in the Calvin cycle of photosynthesis.
• This reaction produces two molecules of 3-phosphoglycerate (3-PGA), which are then further processed in the Calvin cycle to form glucose and other carbohydrates that are essential for plant growth and energy storage.

Other Options:

 It is active only in the dark:

• This statement is incorrect because RuBisCO is active during the light phase of photosynthesis.
• Although RuBisCO itself does not directly depend on light, its activity is regulated by factors influenced by light, such as the presence of ATP and NADPH, which are generated during the light-dependent reactions of photosynthesis.

It has higher affinity for oxygen than carbon dioxide:

• RuBisCO can bind both oxygen and carbon dioxide, it has a higher affinity for carbon dioxide under normal physiological conditions.

It is an enzyme involved in the photolysis of water:

• This statement is incorrect because RuBisCO is not involved in the photolysis of water. Photolysis of water occurs during the light-dependent reactions of photosynthesis and is catalyzed by the oxygen-evolving complex (OEC) in photosystem II, not RuBisCO.