Question

In a "pulse chase" experiment under anaerobic conditions, ¹⁴C glucose is added to an ethanol-producing yeast cell extract just long enough that each intermediate in the ethanol fermentation is labeled with a ¹⁴C (pulse). The ¹⁴C label is then diluted so that no additional radioactivity is incorporated into the intermediates (chase).

1. What position in ethanol will be labeled with ¹⁴C if ¹⁴C-glucose labeled at position C-1 is used?

2. Where should the ¹⁴C label sit in glucose for it to be found in CO2?

3. Adding ¹⁴C-labeled glyceraldehyde 3-phosphate to a yeast extract can, after a short time, isolate ¹⁴C-labeled fructose 1,6-bisphophate. The isolated fructose 1,6-bisphosphate was found to be labeled at positions C-3 and C-4. At what position was the glyceraldehyde 3-phosphate ¹⁴C labeled? Why are two positions ¹⁴C labeled in fructose 1,6-bisphosphate?

4. What position in the resulting glucose - 6 phosphate molecule would be labeled with ¹⁴C if [¹⁴C] bicarbonate is added to a rat liver extract?

5.What if instead adding [1-¹⁴C] pyruvate?

Answer 1

Ans 1- If C-1 of glucose is labeled then in ethanol also C- 1 is labeled

Ans- 2 CO₂ evolved will be C-3 or C-4 of glucose

Ans 3 Glyceraldehyde 3-phosphate is labeled at C-3 position . In fructose 1,6 bisphosphate two positions are labeled because two three C containing molecules of which one is Glyceraldehyde -3 phosphate and another DHAP come together to form a six C containing molecule fructose 1,6 bisphosphate

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