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and other groups of acids that contain six carbon atoms each—that were created when sugars are oxidized (combined with oxygen). He also noted that this process created carbon dioxide, water, and energy.
These results were confusing. What did all these chemicals have to do with simple metabolism of sugars into energy? Krebs saw citric acid being broken down and yet at the same
time, citric acid was being produced. The same was true for a number of other acids.
Slowly Krebs realized that the process worked in a circle—a circle with seven separate
chemical steps. It started with citric acid. Each step produced the chemicals and acids that
were needed for the next step in the cycle. In the last step, citric acid was produced to start
the cycle all over again.
The cycle continues endlessly in each of our cells. Along the way, glucose molecules
(sugars) supplied by the blood are consumed. Two waste products were produced by this
seven-step cycle: carbon dioxide and free hydrogen atoms. These hydrogen atoms then
combine with oxygen and a form of high-energy phosphate to create water and ATP, the
chemical that stores energy for cells just like a battery.
Sugar molecules enter the cycle, and carbon dioxide, water, and ATP to power the
cells exit the cycle. By 1938 Krebs had unraveled this amazingly complex and yet amazingly efficient seven-step chemical cycle—specifically designed to accomplish a seemingly
simple task: convert sugars in the blood into energy for muscle cells. Amazingly, each muscle cell in our bodies creates these seven sequential reactions, each sparked by a different
enzyme, every minute of every day. And Hans Krebs discovered how it works.
Fun Facts: The average person’s body could theoretically generate 100
watts of electricity using a bio-nano generator, a nano-scale electrochemical fuel cell that draws power from blood glucose much the same way
the body generates energy using the Krebs Cycle.
More to Explore
Bailey, Donna. Energy for Our Bodies. New York: Steck-Vaughn, 1999.
Curran, Christina. Metabolic Processes and Energy Transfers: An Anthology of Current Though. Cherry Hill, NJ: Rosen Central, 2005.
Hewitt, Sally. Full of Energy. New York: Scholastic Library Publishing, 1998.
Holmes, Frederick. Hans Krebs: Architect of Intermediary Metabolism. New York:
Oxford University Press, 1999.
Nichols, Peter. Biology of Oxygen. Jefferson, NC: McFarland, 1997.