Question

Which of the following enzymes is used for carboxylation of RuBP?
A. Ribulose transaminase
B. Ribulose bisphosphatase transaminase
C. Ribulose diphosphate carboxylase
D. Peroxidase

Answer 1

Hint: Carboxylation of RuBP is the initial step of the Calvin cycle of photosynthesis. This step occurs in the initial stage of dark reactions. Carboxylation of RuDP is done by the most abundant plant enzyme which is also called Rubisco.

Complete answer: The photosynthesis process consists of two major stages called light reactions and dark reactions. The light reactions are independent of light and result in the formation of carbon dioxide. The carbon dioxide needs to be fixed for energy production. The carbon dioxide fixation process occurs in dark reactions. Dark reactions are required for the formation of final energy products which are food to plants. These are in the form of glucose, starch, etc. The dark reaction occurs in the stroma of the chloroplast and is also called the Calvin cycle. The products of a Calvin cycle are 2 G3P or glyceraldehyde$-3-$phosphate, 2 \[NAD{{P}^{+}}\], and 3 ADP molecules. The 2 G3P molecules are further used for regeneration of RuBP or they are used to make starch or glucose. The first step of the Calvin cycle which is called carbon fixation involves Ribulose diphosphate carboxylase or Rubisco enzyme. It causes the association of carbon dioxide with ribulose $-1,5-$ bisphosphate. This results in the formation of a sex carbon compound which splits into two 3 carbon compounds. Thus, we can say that Ribulose diphosphate carboxylase catalyzes the attachment of carbon dioxide.
Hence, option C is the correct answer.

Note: The last stage of the Calvin cycle is called regeneration. This stage involves the regeneration of RuBP. This allows the cycle to continue again. Thus, this cycle is important for cell function and metabolism of plants. The final energy comes from dark reactions.