Question

14C-Labeled glyceraldehyde 3-phosphate was added to a yeast extract. After a short time, fructose 1,6-bisphosphate labeled with 14C at C-3 and C-4 was isolated. What was the location of the 14C label in the starting glyceraldehyde 3-phosphate

Answer 1

The 14C label in the starting molecule of glyceraldehyde 3-phosphate used in the experiment was at the C-1 position, as this carbon becomes C-3 in fructose 1,6-bisphosphate after it is metabolically converted.

Step-by-step explanation:

The student asked where the 14C label was located in the starting molecule of glyceraldehyde 3-phosphate used in the yeast extract experiment, which after a short time produced fructose 1,6-bisphosphate labeled with 14C at C-3 and C-4. In the glycolytic pathway, glyceraldehyde 3-phosphate is an intermediate which is metabolic converted into fructose 1,6-bisphosphate. Glyceraldehyde 3-phosphate has three carbon atoms: C-1, C-2, and C-3. Since fructose 1,6-bisphosphate was labeled at C-3 and C-4 after conversion, this indicates that the 14C label in the glyceraldehyde 3-phosphate was at C-1. During the conversion, C-1 of glyceraldehyde 3-phosphate becomes C-3 of fructose 1,6-bisphosphate, and C-2 of glyceraldehyde 3-phosphate becomes C-4 of fructose 1,6-bisphosphate, explaining the location of the 14C label.

Answer 2

The 14C label in the starting glyceraldehyde 3-phosphate is located at carbon-1.

Step-by-step explanation:

The 14C label in the starting glyceraldehyde 3-phosphate (G3P) was most likely located on the carbonyl carbon (carbon 1). This can be explained by the following steps:

Triose Phosphate Isomerase (TIM) reaction: 14C-labeled G3P enters the glycolytic pathway and undergoes the TIM reaction. This reaction converts G3P into its isomer, dihydroxyacetone phosphate (DHAP). The label on carbon 1 of G3P migrates to the carbon 3 position of DHAP.

Aldolase reaction: DHAP and unlabeled G3P condense into fructose 1,6-bisphosphate (FBP) through the aldolase reaction. The aldolase reaction forms a carbon-carbon bond between the carbon 1 of G3P and the carbon 3 of DHAP.

Therefore, the final FBP molecule will have 14C labels at carbon 3 and carbon 4, indicating that the initial G3P label was on carbon 1.