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An introduction to
(The Encylpedia of Earth, 2006)
Adenosine Triphosphate
• The primary source of free energy in living
• Structure: nitrogenous base adenine
attached to the 5-carbon sugar Ribose
which is attached (bound) to a chain of 3
phosphate groups. (see p65)
Image taken from:
How is energy obtained from ATP?
• Enzyme ATPase catalyzes the hydrolysis of the
phosphate on the terminal end of the molecule
making ADP
• One Pi (inorganic phosphate) molecule is
released with a ton of energy! (p65)
• But the energy isn’t always freely released: the
Pi can go on to PHOSPHORYLATE (add a
phosphate to) other molecules changing their
shape and making them more active (like in
active transport)
ATP cycle
The Big Picture of Cellular respiration:
• Photoautotrophs, like green plants, transform light
energy into chemical potential energy (glucose and other
• Heterotrophs (animals, fungi, bacteria…) rely on
autotrophs for energy.
• Glucose is the primary energy source for (almost) all
organisms. The energy is extracted by enzymes doing
redox reactions
• When the bonds are broken, more stable compounds
are formed and so energy is released
• Released energy is “trapped” and stored as ATP (34% of
it anyways)
Aerobic cellular respiration:
C6H12O6 + 6O2  6CO2 + 6H2O
• Aerobic means oxygen is used
• Accomplished by 20 chemical reactions (not by
breathing)… the equation above is a summary!
(initial reactants and final products only)
• Glucose and oxygen don’t just react together
spontaneously… the activation energy barrier
must be overcome!
• This is done by enzymes….lots of enzymes