75. The Carbon (C1) of glucose is labelled with 14C (specific activity of 10 mCi/mmole). After one round of
glycolysis, the specific activity of radiolabelled pyruvate is:
1. 0
2. 10
3. 5
4. 20

Introduction to Radiolabeling in Glycolysis

Radiolabeling is a powerful technique used to track the movement and transformation of specific molecules in biochemical processes. In this context, we focus on the radiolabeling of the carbon (C1) of glucose with 14C and how this label behaves during glycolysis. Specifically, we will look at how the specific activity of pyruvate changes after one round of glycolysis when glucose is labeled at the C1 position.

Radiolabeling in Glycolysis

Glucose (C6H12O6) is a six-carbon sugar that undergoes glycolysis, a metabolic pathway that breaks down glucose into two molecules of pyruvate (C3H4O3). If the C1 carbon of glucose is labeled with 14C (specific activity of 10 mCi/mmole), this carbon will eventually be incorporated into one of the two pyruvate molecules produced.

Since glycolysis splits one molecule of glucose into two molecules of pyruvate, and the 14C label is attached to the C1 carbon of glucose, only one of the two pyruvates will inherit this labeled carbon. This means that half of the pyruvate molecules will contain the 14C label.

How the Specific Activity of Pyruvate is Affected

To calculate the specific activity of the labeled pyruvate, we need to understand how the radioactivity is distributed:

• The initial specific activity of glucose is 10 mCi/mmole.

• After glycolysis, one of the two pyruvates will contain the labeled carbon, and the other will not.

• Since only half of the pyruvates will have the labeled carbon, the specific activity of the labeled pyruvate will be half of that of glucose.

Thus, the specific activity of the radiolabeled pyruvate is 5 mCi/mmole.

Answer Explanation

The correct answer is 3. 5 because after one round of glycolysis, the labeled carbon from glucose will be split equally between the two pyruvate molecules, resulting in a specific activity of 5 mCi/mmole for the radiolabeled pyruvate.

Conclusion

Radiolabeling of glucose provides insights into the biochemical pathways of cellular metabolism. In the case of glycolysis, when the C1 carbon of glucose is labeled with 14C, the specific activity of the resulting pyruvate is 5 mCi/mmole after one round of glycolysis. Understanding these calculations can be helpful in tracing metabolic pathways and studying the fate of molecules in biological systems.

By presenting the information in a clear, structured format, the article provides valuable insights into the concept of radiolabeling in glycolysis and how specific activity is transferred to pyruvate, enhancing understanding for students and researchers in the field.