Glucose is led with radioactive carbon 14 C at its C2 positi

Glucose is led with radioactive carbon (^14 C at its C2 position. How many turns of the TCA cycle are needed to release^14C as CO_2?

Solution

Answer:

When a Glucose is labeled with radioactive carbon (¹⁴C) at its C2 position. To resease this ¹⁴C as CO_2, one turn of TCA cycles is needed.

Explaination: The initial one molecule of 3C pyruvate which is the end product of Glycolysis (where one molecule of 6C glucose is converted to 2 molecules of 3C pyruvate), is ultimately converted into 3 molecules of CO₂. As one molecule of CO₂, released during the transformation step (from Pyruvate to Acetyl CoA) and the two CO₂ are made during intermediate steps of the TCA cycle. Thus, if a Glucose is labeled with radioactive carbon (¹⁴C) at its C2 position, it will be converted into two molecules of pyruvate. Out of these two, initial pyruvate which contain the ¹⁴C would be released as CO₂ in a single TCA cycle.