Aldolase cateysing steps in regeneration phase of calvin cycle are
A) `2G3P + 2DHAP rarr 2 F16P`
B) `F6P + G3P rarr XMP`
C) `SMP + G3P rarr XMP + RiMP`
D) `EMP + DHAP rarr SHBP`

Options

A. All the above
B. AB only
C. BC only
D. AD only

Answer

To determine which reactions in the regeneration phase of the Calvin cycle are catalyzed by aldolase, we will analyze each of the given options step by step.

### Step 1: Analyze Option A
- **Reaction**: \(2 \text{G3P} + 2 \text{DHAP} \rightarrow 2 \text{F16P}\)
- **Enzyme**: Aldolase
- **Explanation**: This reaction involves the combination of two molecules of glyceraldehyde 3-phosphate (G3P) and two molecules of dihydroxyacetone phosphate (DHAP) to form two molecules of fructose 1,6-bisphosphate (F16P). This reaction is indeed catalyzed by aldolase.

### Step 2: Analyze Option B
- **Reaction**: \( \text{F6P} + \text{G3P} \rightarrow \text{XMP}\)
- **Enzyme**: Transketolase
- **Explanation**: In this reaction, fructose 6-phosphate (F6P) reacts with glyceraldehyde 3-phosphate (G3P) to produce xylulose monophosphate (XMP). This reaction is catalyzed by transketolase, not aldolase.

### Step 3: Analyze Option C
- **Reaction**: \( \text{SMP} + \text{G3P} \rightarrow \text{XMP} + \text{RiMP}\)
- **Enzyme**: Transketolase
- **Explanation**: Here, sedoheptulose monophosphate (SMP) reacts with glyceraldehyde 3-phosphate (G3P) to yield xylulose monophosphate (XMP) and ribose monophosphate (RiMP). This reaction is also catalyzed by transketolase, not aldolase.

### Step 4: Analyze Option D
- **Reaction**: \( \text{EMP} + \text{DHAP} \rightarrow \text{SHBP}\)
- **Enzyme**: Aldolase
- **Explanation**: In this reaction, erythrose monophosphate (EMP) combines with dihydroxyacetone phosphate (DHAP) to form sedoheptulose 1,7-bisphosphate (SHBP). This reaction is catalyzed by aldolase.

### Conclusion
From the analysis:
- **Aldolase catalyzes**:
- Option A: \(2 \text{G3P} + 2 \text{DHAP} \rightarrow 2 \text{F16P}\)
- Option D: \( \text{EMP} + \text{DHAP} \rightarrow \text{SHBP}\)

Thus, the correct answer is **AD only**.

---