Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

48 Chapter 2: Cell Chemistry and Bioenergetics
H
C
HO
H
H C
H
CH 2 OH
C O OH
H
OH H
C
H 3 N +
C C H
H
C COO
CH 3
H OH
A SUGAR
AN AMINO ACID
H H
C C
H H
H
C
H
H
C
H
H
C
H
H H
C C
H H
H H
C C
H H
H H H H
C C C C
H H H H
A FATTY ACID
N
O O O
–
N
O P O P O P O CH 2
O – O – O –
O
O
C
O _
NH 2
N
N
building blocks
of the cell
SUGARS
FATTY ACIDS
AMINO ACIDS
NUCLEOTIDES
larger units
of the cell
POLYSACCHARIDES
FATS, LIPIDS, MEMBRANES
PROTEINS
NUCLEIC ACIDS
Figure 2–6 The four main families of small organic molecules in
cells. These small molecules form the monomeric building blocks, or
subunits, for most of the macromolecules and other assemblies of the
cell. Some, such as the sugars and the fatty acids, are also energy
sources. Their structures are outlined here and shown in more detail in
the Panels at the end of this chapter and in Chapter 3.
A NUCLEOTIDE
OH
OH
long chains (Figure 2–8). They have remarkable properties that could not have
been predicted from their simple constituents.
Proteins are abundant and spectacularly versatile, performing thousands of
distinct functions in cells. Many proteins serve as enzymes, the catalysts that facilitate
the many covalent bond-making and bond-breaking reactions that the cell
needs. Enzymes catalyze all of the reactions whereby cells extract energy from
food molecules, for example, and an enzyme called ribulose bisphosphate carboxylase
helps to convert CO 2 to sugars in photosynthetic organisms, producing
most of the organic matter needed for life on Earth. Other proteins are used to
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build structural components, such as tubulin, a protein that self-assembles to
make the cell’s long microtubules, or histones, proteins that compact the DNA in
chromosomes. Yet other proteins act as molecular motors to produce force and
bacterial
cell
30%
chemicals
inorganic ions (1%)
small molecules (3%)
phospholipid (2%)
DNA (1%)
RNA (6%)
CELL
VOLUME OF
2 × 10 –12 cm 3
70%
H 2 O
protein (15%)
MACROMOLECULES
polysaccharide (2%)
Figure 2–7 The distribution of molecules in cells. The approximate composition of a bacterial cell
is shown by weight. The composition of an animal cell is similar, even though its volume is roughly
1000 times greater. Note that macromolecules dominate. The major inorganic ions include Na + , K + ,
Mg 2+ , Ca 2+ , and Cl – .