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How
did we discover the functions of the mitochondria?
We
know that mitochondria are energy factories, but how did scientists
figure that out? Some of the energy that mitochondria make produces
heat, much like how a burning match produces heat. Burning matches
consume oxygen. The human body also consumes oxygen when
it generates energy. So, scientists measured oxygen consumption
in pure preparations of mitochondria and found that they consume
much more oxygen and produce more heat than other organelles.
 Do
you know why the body needs oxygen?
In non-living systems, oxygen can release the trapped energy
of chemical bonds (as in wood and paper, for example).
Of course the energy released in burning wood is "lost" as light and heat. In a
living system, oxygen does a similar thing, helping to release
the stored chemical bond energy of foods. Except a living
system cannot afford to waste too much of the energy as heat.
Self-quiz
Scientists first discovered
that mitochondria were "energy factories" by measuring
their oxygen consumption and ______ .
A. glucose
B. membrane surface
C. size
D. heat
How
do scientists find out how organisms capture energy?
Scientists knew that the energy release in
mitochondria needed to be captured temporarily in some kind of
molecule. By testing the chemicals in mitochondria, they found
one that could take up or give up large amounts of energy. The
molecule that traps and stores energy is known as adenosine
triphosphate (ATP). Our body heat comes from the left over food
energy that is not captured in ATP.
When scientists measured oxygen consumption
and the build-up of ATP inside of cells, they found two
sets of reactions:
- One set of reactions
uses no oxygen and captures only a few molecules of ATP.
- The other set uses
lots of oxygen and captures a great deal of energy by
producing many molecules of ATP.
The first set of reactions breaks glucose into
a series of three-carbon molecules. This first step is called
glycolysis. The second set, where
oxygen is consumed, releases water and carbon dioxide as waste
products. These are the reactions that our Story-Time hero discovered
and which are named after him as the "Krebs' cycle."
Self-Quiz
Identify the pair that is
correct: A.
glycolysis--little energy produced
B. glycolysis--many
ATP molecules
C. Krebs
cycle--little energy
D. Krebs cycle--few
ATP molecules
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