A suspension of photosynthetic green algae was illuminated in the presence of \(^{14}\)CO\(_2\) for few seconds. The first metabolite in the Calvin cycle to be radiolabeled will be 3-phosphoglycerate (3-PGA).
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- glyceraldehyde
- 1,3-bisphosphoglycerate
- 3-phosphoglycerate
- ribulose 1,5-bisphosphate
The Correct Option is C
Solution and Explanation
Step 1: Calvin cycle CO$_2$ fixation.
- CO$_2$ first reacts with ribulose 1,5-bisphosphate (RuBP) in the Calvin cycle.
- This reaction is catalyzed by the enzyme Rubisco.
Step 2: First stable product.
- The unstable 6-carbon intermediate immediately splits into two molecules of 3-phosphoglycerate (3-PGA).
- Therefore, 3-PGA is the first stable compound to incorporate the radioactive carbon.
Therefore, the first radiolabeled metabolite is 3-phosphoglycerate.
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