126
UNIT ONE
A DNA molecule is sleek and symmetrical because
the bases pair in only two combinations, which maintains
a constant width of the overall structure. In a DNA nucle-
otide, the base may be one of four types: adenine (A), thy-
mine (T), cytosine (C), or guanine (G). A and G are
purines
(pu
re
¯nz), and they consist of two organic ring structures.
T and C are
pyrimidines
(pe-rimi-denz), and they have a
High energy
electrons carried
by NADH and FADH
2
Complete oxidation
of acetyl coenzyme A
to H
2
O and CO
2
produces
high energy electrons
(carried by NADH and
FADH
2
), which yield much
ATP via the electron
transport chain
Breakdown of simple
molecules to acetyl
coenzyme A
accompanied by
production of limited
ATP and high energy
electrons
H
2
O
2e
and 2H
+
Waste products
1
/
2
O
2
–NH
2
CO
2
CO
2
Citric
acid
cycle
Electron
transport
chain
Amino acids
Acetyl coenzyme A
Simple sugars
(glucose)
Glycerol
Fatty acids
Proteins
(egg white)
Carbohydrates
(toast, hashbrowns)
Food
Fats
(butter)
Pyruvic acid
ATP
ATP
ATP
Breakdown of large
macromolecules
to simple molecules
Glycolysis
1
2
3
FIGURE 4.15
A summary of the breakdown (catabolism) of proteins, carbohydrates, and fats.
S
P
B
FIGURE 4.16
Each nucleotide of a nucleic acid consists of a
5-carbon sugar (S); a phosphate group (P); and an organic, nitrogenous
base (B).
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