Ribulose diphosphate carboxylase enzyme catalyses the carboxylation reaction between

Options

A. Oxaloacetic acid and acetyl CoA
B. `CO_2` and ribulose 1,5 diphosphate
C. Ribulose diphosphate and phosphoglyceraldehyde
D. PGA and dihydroxyacetone phosphate

Answer

To solve the question regarding the enzyme ribulose diphosphate carboxylase, also known as Rubisco, we will analyze the options given and identify the correct reaction that it catalyzes.

### Step-by-Step Solution:

1. **Understanding the Enzyme**:
- Ribulose diphosphate carboxylase (Rubisco) is an enzyme that plays a crucial role in the process of photosynthesis. It catalyzes the carboxylation of ribulose 1,5-bisphosphate (RuBP).

**Hint**: Remember that Rubisco is primarily involved in the Calvin cycle of photosynthesis.

2. **Analyzing the Options**:
- **Option 1**: Oxaloacetic acid and acetyl coenzyme A.
- This reaction is part of the Krebs cycle and involves the enzyme citrate synthase. Thus, it is not related to Rubisco.

**Hint**: Identify the metabolic pathways associated with each option.

3. **Option 2**: CO2 and ribulose 1,5-bisphosphate (RuBP).
- This is the correct reaction. Rubisco catalyzes the reaction between CO2 and RuBP to form 3-phosphoglycerate (3-PGA).

**Hint**: Look for the direct involvement of CO2 in the Calvin cycle.

4. **Option 3**: Ribulose diphosphate and phosphoglyceraldehyde (PGAL).
- This reaction does not occur in living systems as there is no known enzyme that catalyzes this reaction.

**Hint**: Consider the validity of the reactions in biological systems.

5. **Option 4**: Phosphoglyceric acid (PGA) and dihydroxyacetone phosphate (DHAP).
- Similar to option 3, there is no enzyme that catalyzes this reaction in living organisms.

**Hint**: Verify if the reactions are catalyzed by known enzymes.

6. **Conclusion**:
- The only valid reaction that Rubisco catalyzes is the carboxylation of ribulose 1,5-bisphosphate with CO2, leading to the formation of 3-PGA. Therefore, the correct answer is **Option 2: CO2 and ribulose 1,5-bisphosphate**.

### Final Answer:
The ribulose diphosphate carboxylase enzyme catalyzes the carboxylation reaction between CO2 and ribulose 1,5-bisphosphate (RuBP).