Expert: Florence M Rollwagen - 5/6/2008

Question
What is a simple definition of a radioactive isotopes and how can we use them to determine if oxygen in CO2 comes from sugar or oxygen gas

Answer
What is a simple definition of a radioactive isotopes and how can we use them to determine if oxygen in CO2 comes from sugar or oxygen gas.

Hi Bill and thanks for your question.

Radioactive isotopes are atoms that have unstable nuclei and some may give off (small or large) amounts of radiation.  Because they are “labeled” we can find them after a chemical reaction.  I think the question you are asking was determined by using nonradioactive isotopes of O2, called “heavy” oxygen.  

In cellular respiration, carbon containing molecules are broken down by glycolysis and the Krebs cycle.  During the Krebs cycle, CO2 is released from pyruvate, a sugar breakdown product.  This was determined by providing sugar synthesized with heavy oxygen, and looking for the label in products of the Krebs cycle.

In the mitochondrion, the electron transport chain captures the energy collected from breaking the molecular bonds in the Krebs cycle.  This energy is stepped down a series of energy collecting molecules until all the energy is exhausted.  Then the electron is captured by oxygen and protons to form water.  

Here is a good movie:

http://vcell.ndsu.nodak.edu/animations/etc/movie.htm

I hope this answer has helped you.  Please write back if you have more questions.

FM Rollwagen, PhD