Chapter 4
Carbon and the
Molecular Diversity of
Life
1
Carbon Chemistry
• Carbon is the backbone of biological
molecules (macromolecules)
• All living organisms are made up of chemicals
based mostly on the element carbon
Figure 4.1
2
Carbon Chemistry
• Organic chemistry is the study of carbon
compounds
• Carbon atoms can form diverse molecules by
bonding to four other atoms
• Carbon compounds range from simple
molecules to complex ones
• Carbon has four valence electrons and may
form single, double, or triple.
3
• The bonding versatility of carbon allows
it to form many diverse molecules,
including carbon skeletons
Name and
Comments
(a) Methane
Molecular Structural
Formula
Formula
Ball-andStick
Model
SpaceFilling
Model
H
CH4
H C
H
H
(b) Ethane
C2H
6
(c) Ethene
Figure 4.3 A-C (ethylene)
C2H4
H H
H C C H
H H
H
H
C C
H
H
4
• The electron configuration of carbon gives it
covalent compatibility with many different
elements
Hydrogen
Oxygen
Nitrogen
Carbon
(bonds = 1)
(bonds = 2)
(bonds = 3)
(bonds = 4)
H
O
N
C
Figure 4.4
5
• Carbon may bond to itself forming carbon
chains
• Carbon chains form the skeletons of most
organic molecules
• Carbon chains vary in length and shape
H H H H
H C C C C
H H H H
n-Butane
(b) Branching
(c) Double bonds
(d) Rings
Figure 4.5 A-D
H H H
H H
H C C H
H H
Ethane
(a) Length
H
H
H
H
H
H H H H
H C C C C
H H
1-Butene
H
H
H
C
C
C H
C
C H
H
C
Cyclohexane
H C C C H
H H H
Propane
H
H C H
H
H
H C C C H
H H H
isobutane
H
H H H H
H C C C C H
H
H
2-Butene
H
H
C C H
C
C
C
Benzene
6
Hydrocarbons
• Hydrocarbons are molecules consisting of only
carbon and hydrogen
• Hydrocarbons Are found in many of a cell’s organic
molecules
Fat droplets (stained red)
Figure 4.6 A, B
(a) A fat molecule
100 µm
(b) Mammalian adipose cells
7
Isomers
• Isomers are molecules with the same molecular
formula but different structures and properties
• Three types of isomers are
– Structural
H
– Geometric
H C H
H C H
H H H H H
H
H
– Enantiomers
H C C C C C H
H C C C H
(a) Structural isomers
H H H
H H H H H
(b) Geometric isomers
X
H
C C
X
H
H
X
CO2H
(c) Enantiomers
Figure 4.7 A-C
H
C
CH3
C
C
X
H
CO2H
NH2 NH2
C
CH3
H
8
• Enantiomers Are important in the
pharmaceutical industry
Figure 4.8
L-Dopa
D-Dopa
(effective against
Parkinson’s disease)
(biologically
inactive)
9
Functional Groups
• Functional groups are
the parts of
molecules involved in
chemical reactions
• They are the
chemically reactive
groups of atoms
within an organic
molecule
• They give organic
molecules distinctive
chemical properties
Estradiol
HO
Female lion
OH
CH3
CH3
O
Figure 4.9
OH
CH3
Testosterone
Male lion
10
• Seven functional groups are important in the chemistry
of life
–
–
–
–
–
–
–
Hydroxyl
Carboxyl
Amino
Phosphate
Carbonyl
Methyl
Sulfhydryl
11
Some important functional groups of organic
compounds
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
O
OH
(may be written HO
STRUCTURE
Figure 4.10
CARBOXYL
C
C
OH
)
In a hydroxyl group (—
OH), a hydrogen atom is
bonded to an oxygen atom,
which in turn is bonded to
the carbon skeleton of the
organic molecule. (Do not
confuse this functional
group with the hydroxide
ion, OH–.)
O
The carbonyl group
( CO) consists of a
carbon atom joined to
an oxygen atom by a
double bond.

When an oxygen atom is
double-bonded to a carbon
atom that is also bonded to a
hydroxyl group, the entire
assembly of atoms is called a
carboxyl group (—COOH).
12
Some important functional groups of
organic compounds
NAME OF
COMPOUNDS
Alcohols (their specific
names usually end in -ol)
Ketones if the carbonyl group
is within a carbon skeleton
Aldehydes if the carbonyl
Carboxylic acids, or organic
acids
group is at the end of the
carbon skeleton
EXAMPLE
H
H
H
C
C
H
H
H
OH
H
Ethanol, the alcohol
present in alcoholic
beverages
H
C
H
C
H
H
Acetone, the simplest ketone
H
Figure 4.10
C
H
H
O
H
H
C
C
H
H
C
H
O
C
OH
Acetic acid, which gives vinegar
its sour tatste
O
C
H
Propanal, an aldehyde
13