56
UNIT 1
Organization of the Body
2
Solute
Membrane
protein
Relaxed smooth
muscle cell
Contracted smooth
muscle cell
P
P
P
i
P
i
P
i
ATP
ADP
ATP
ATP
+
P
i
ADP
+
P
i
ADP
A
B
+
Transport work:
ATP phosphorylates transport
proteins, activating them to transport solutes
(ions, for example) across cell membranes.
Mechanical work:
ATP phosphorylates
contractile proteins in muscle cells so the cells
can shorten.
Chemical work:
ATP phosphorylates key
reactants, providing energy to drive energy-
absorbing chemical reactions.
A
B
(a)
(b)
(c)
Figure 2.24
Three examples of cellular work driven by
energy from ATP.
Chapter Summary
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PART 1
Basic Chemistry
Definition of Concepts: Matter and Energy
(pp. 23–25)
Matter
(p. 24)
1.
Matter is anything that takes up space and has mass.
Energy
(pp. 24–25)
2.
Energy is the capacity to do work or put matter into motion.
3.
Energy exists as potential energy (stored energy or
energy of position) and kinetic energy (active or working
energy).
4.
Forms of energy involved in body functioning are chemical,
electrical, radiant, and mechanical. Of these, chemical (bond)
energy is most important.
5.
Energy may be converted from one form to another, but
some energy is always unusable (lost as heat) in such
transformations.
Composition of Matter: Atoms and Elements
(pp. 25–28)
1.
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
weight.
(
ADP
)—and an inorganic phosphate group, indicated by P
i
,
accompanied by a transfer of energy:
H
2
O
H
2
O
ATP
ADP
energy
p
p
P
i
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
monophosphate (AMP).
±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
(Figure 2.24)
.
Check Your Understanding
31.
Glucose is an energy-rich molecule. So why do body cells
need ATP?
32.
What change occurs in ATP when it releases energy?
For answers, see Appendix H.
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