Transcript Document

Chapter 4: Carbon and the
molecular diversity of life
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Living organisms are made up of chemicals based
on carbon
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 4.2 Inquiry Could organic compounds have
been synthesized abiotically on the early Earth?
EXPERIMENT
In 1953, Stanley Miller simulated what were thought to be environmental conditions on
the lifeless, primordial Earth. As shown in this recreation, Miller used electrical
discharges (simulated lightning) to trigger reactions in a primitive “atmosphere” of
H2O, H2, NH3 (ammonia), and CH4 (methane)—some of the gases released by
volcanoes
.
RESULTS
A variety of organic compounds that play key roles in living cells were synthesized in
Miller’s apparatus.
CONCLUSION
Organic compounds may have been synthesized abiotically on the early Earth,
setting the stage for the origin of life. (We will explore this hypothesis in more
detail in Chapter 26.)
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The Formation of Bonds with Carbon
• Carbon has four valence electrons
•  forms four covalent bonds with a variety of
atoms
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• Bonding versatility of carbon
 diverse molecules
Name and
Comments
Molecular Structural
Formula
Formula
H
(a) Methane
CH4
H C
H
H
H H
(b) Ethane
C2H
H C C H
6
(c) Ethene
Figure 4.3 A-C (ethylene)
H H
H
C2H4
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H
C C
H
H
Ball-andStick Model
SpaceFilling
Model
Carbon Skeleton Variation
• Carbon chains
(a)
Length
H
H
H
C
C
H
H
H H
Ethane
H
H
H
C
C
C
H
H
H
H
Propane
H
H
(b) Branching
H
H
H
H
H
C
C
C
C
H
H
H
H
H
H
H
bonds
H
H
H
H
H
C
C
C
C
H
H
H
(d) Rings
Figure 4.5 A-D
H
C
C
C
C
C
C
H
H
H
H
Cyclohexane
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H
C
C
C
H
H
H
H
H
H
H
H
H
C
C
C
C
H
1-Butene
H
H
H
H
H
H
2-methylpropane
(commonly called isobutane)
Butane
(c) Double
C
H
2-Butene
H
H
C
C
C
C
C
Benzene
H
H
• Hydrocarbons
– Found in many of a cell’s organic molecules
Fat droplets (stained red)
100 µm
Figure 4.6 A, B
(a) A fat molecule
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(b) Mammalian adipose cells
Isomers
• Molecules with the same molecular formula but
different structures and properties
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• 3 types of isomers
H
(a)
Structural isomers
H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
X
(b)
Geometric isomers
H
H
Enantiomers
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C
C
H
H
H
X
H
CO2H
C
H
C
X
H
C
H
NH2 NH2
CH3
Figure 4.7 A-C
C
C
C
CO2H
(c)
C
H
H
H
C
H
X
C
H
H
H
H
CH3
H
• Enantiomers
– important in the pharmaceutical industry
Figure 4.8
L-Dopa
D-Dopa
(effective against
Parkinson’s disease)
(biologically
inactive)
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Functional Groups
• Chemically reactive groups of atoms within an
organic molecule
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– Give organic molecules distinctive chemical
properties
Estradiol
OH
CH3
HO
Female lion
OH
CH3
CH3
O
Figure 4.9
Male lion
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Testosterone
• Functional groups
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
CARBOXYL
O
OH
(may be written HO
STRUCTURE
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.
Figure 4.10
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When an oxygen atom is doublebonded to a carbon atom that is
also bonded to a hydroxyl group,
the entire assembly of atoms is
called a carboxyl group (—
COOH).
• Functional groups
NAME OF
COMPOUNDS
Alcohols (their
Ketones if the carbonyl
specific names usually
end in -ol)
group is within a carbon
Carboxylic acids, or organic
skeleton
acids
EXAMPLE
H
H
H
C
C
H
H
Aldehydes if the carbonyl
group is at the end of the carbon
skeleton
H
OH
H
C
H
C
H
H
Ethanol, the alcohol
present in alcoholic
beverages
C
C
H
O
C
OH
H
H
Acetone, the simplest ketone
H
Figure 4.10
H
O
H
H
C
C
H
H
O
C
Propanal, an aldehyde
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H
Acetic acid, which gives vinegar
its sour tatste
• Functional groups
AMINO
SULFHYDRYL
H
(may be written HS
H
The amino group (—NH2)
consists of a nitrogen atom
bonded to two hydrogen
atoms and to the carbon
skeleton.
O
SH
N
PHOSPHATE
)
O P OH
OH
The sulfhydryl group
consists of a sulfur atom
bonded to an atom of
hydrogen; resembles a
hydroxyl group in shape.
Figure 4.10
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In a phosphate group, a
phosphorus atom is bonded to four
oxygen atoms; one oxygen is
bonded to the carbon skeleton; two
oxygens carry negative charges;
abbreviated P . The phosphate
group (—OPO32–) is an ionized
form of a phosphoric acid group (—
OPO3H2; note the two hydrogens).