Which type of reaction does RuBisCO primarily facilitate in the Calvin Cycle?

RuBisCO primarily facilitates carboxylation and decarboxylation reactions within the Calvin Cycle. This enzyme catalyzes the first major step of carbon fixation, where it catalyzes the reaction of ribulose-1,5-bisphosphate (RuBP) with carbon dioxide (CO2), resulting in an unstable six-carbon intermediate that quickly splits into two molecules of 3-phosphoglycerate (3-PGA). This specific process of adding CO2 to RuBP is known as carboxylation.

The latter part of RuBisCO's role involves the decarboxylation activity, where the enzyme can also catalyze the reaction in the presence of oxygen in a less efficient pathway, leading to the production of a three-carbon compound and a release of CO2. However, in the context of the Calvin Cycle and its primary function, the focus is on the carboxylation reaction that enables carbon fixation, which is essential for synthesizing sugars used by plants for energy and growth.

The other reaction types, while important in biochemistry, do not represent the primary function of RuBisCO in the context of the Calvin Cycle.