Organization of the Body
ATP phosphorylates transport
proteins, activating them to transport solutes
(ions, for example) across cell membranes.
contractile proteins in muscle cells so the cells
ATP phosphorylates key
reactants, providing energy to drive energy-
absorbing chemical reactions.
Three examples of cellular work driven by
energy from ATP.
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Deﬁnition of Concepts: Matter and Energy
Matter is anything that takes up space and has mass.
Energy is the capacity to do work or put matter into motion.
Energy exists as potential energy (stored energy or
energy of position) and kinetic energy (active or working
Forms of energy involved in body functioning are chemical,
electrical, radiant, and mechanical. Of these, chemical (bond)
energy is most important.
Energy may be converted from one form to another, but
some energy is always unusable (lost as heat) in such
Composition of Matter: Atoms and Elements
Elements are unique substances that cannot be decomposed into
simpler substances by ordinary chemical methods. Four elements
(carbon, hydrogen, oxygen, and nitrogen) make up 96% of body
)—and an inorganic phosphate group, indicated by P
accompanied by a transfer of energy:
As ATP is hydrolyzed to provide energy for cellular needs, ADP
accumulates. Cleavage of the terminal phosphate bond of ADP
liberates a similar amount of energy and produces adenosine
±e cell’s ATP supplies are replenished as glucose and other
fuel molecules are oxidized and their bond energy is released.
±e same amount of energy that is liberated when ATP’s ter-
minal phosphates are cleaved oﬀ must be captured and used
to reverse the reaction to reattach phosphates and re-form the
energy-transferring phosphate bonds. Without ATP, molecules
cannot be made or degraded, cells cannot transport substances
across their membrane boundaries, muscles cannot shorten to
tug on other structures, and life processes cease
Check Your Understanding
Glucose is an energy-rich molecule. So why do body cells
What change occurs in ATP when it releases energy?
For answers, see Appendix H.