Chemical Composition of the Body
39
The products of the reaction are
adenosine diphosphate
(ADP),
inorganic phosphate (P
i
) and H
+
.
The energy derived from the hydrolysis of ATP is used
by the cells for (1) the production of force and movement, as
in muscle contraction; (2) active transport of molecules across
membranes; and (3) synthesis of the organic molecules used
in cell structures and functions.
We must emphasize that cells use ATP not to
store
energy
but rather to
transfer
it. ATP is an energy-carrying molecule
that transfers relatively small amounts of energy from fuel
molecules to the cells for processes that require energy.
SUMMARY
Atoms
I. Atoms are composed of three subatomic particles: positive
protons and neutral neutrons, both located in the nucleus, and
negative electrons revolving around the nucleus.
II. The atomic number is the number of protons in an atom, and
because atoms are electrically neutral, it is also the number of
electrons.
III. The atomic weight of an atom is the ratio of the atom’s mass
relative to that of a carbon-12 atom.
IV. One gram atomic mass is the number of grams of an element
equal to its atomic weight. One gram atomic mass of any
element contains the same number of atoms—6
×
10
23
.
Molecules
I. Molecules are formed by linking atoms together.
II. A covalent bond forms when two atoms share a pair of
electrons. Each type of atom can form a characteristic number
of covalent bonds: hydrogen forms one; oxygen, two; nitrogen,
three; and carbon, four.
III. Molecules have characteristic shapes that can be altered
within limits by the rotation of their atoms around covalent
bonds.
Ions
I. When an atom gains or loses one or more electrons, it acquires
a net electric charge and becomes an ion.
Free Radicals
I. Free radicals are atoms or molecules that contain atoms having
an unpaired electron in their outer electron orbital.
H
2
O
NH
2
HC
C
OH
C
N
C
H
H
C
H
OH
H
C
CH
C
N
C
N
N
O
P
O
O
OP
O
P
O
O
HH
O
O
O
CH
2
NH
2
HO
C
OH
C
N
C
H
H
C
OH
C
CH
C
N
C
N
N
O
P
O
P
O
P
O
OO
O
HH
O
O
O
CH
2
O
HC
O
Energy
ATP
ADP
H
+
P
i
+
++
+
O
ATP
+
H
2
O
ADP
+
P
i
+
H
+
+
energy
Adenine
Ribose
Figure 2–26
Chemical structure of ATP. Its breakdown to ADP and P
i
is accompanied by the release of energy.
previous page 67 Vander's Human Physiology The Mechanisms of Body Function read online next page 69 Vander's Human Physiology The Mechanisms of Body Function read online Home Toggle text on/off