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Chapter 4Chapter 4
Carbon and the MolecularDiversity of Life
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Overview: CarbonThe Backbone of BiologicalMolecules
All living organisms
Are made up of chemicals based mostly on the
element carbon
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Organic chemistry is the study of carboncompounds
Organic compounds
Range from simple molecules to colossal ones
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The concept of vitalism
Is the idea that organic compounds arise only within living
organisms
Was disproved when chemists synthesized the compounds in thelaboratory
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.
A variety of organic compounds that play key roles in living cells were
synthesized in Millers apparatus.
EXPERIMENT
RESULTS
CONCLUSIONOrganic compounds may have been synthesized abiotically on the
early Earth, setting the stage for the origin of life.
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Carbon atoms can form diverse molecules bybonding to four other atoms
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The Formation of Bonds with Carbon
Carbon has four valence electrons
This allows it to form four covalent bonds with a
variety of atoms
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The bonding versatility of carbon
Allows it to form many diverse molecules,
including carbon skeletons
(a) Methane
(b) Ethane
(c) Ethene
(ethylene)
Molecular
Formula
Structural
Formula
Ball-and-
Stick Model
Space-
Filling
Model
HH
H
H
H
HH
H
HH
H H
HH
C
C C
C C
CH4
C2H
6
C2H4
Name and
Comments
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The electron configuration of carbon
Gives it covalent compatibility with many
different elements
H O N C
Hydrogen
(valence = 1)
Oxygen
(valence = 2)
Nitrogen
(valence = 3)
Carbon
(valence = 4)
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Molecular Diversity Arising from Carbon Skeleton
Variation
Carbon chains
Form the skeletons of most organic molecules
Vary in length and shape
H
HH
H
H
H H H
H
H
H
H H H
H H H
H H
H
H
H
H
H
H
HH
H
H
HH H
H H
H H
H H H H
H H
H H
HH
HH
H
H
H
C C C C C
C C C C C C C
CCCCCCCC
C
CC
CC
C
C
CCC
C
C
H
H
H
HH
H
H
(a) Length
(b) Branching
(c) Double bonds
(d) Rings
Ethane Propane
Butane 2-methylpropane
(commonly called isobutane)
1-Butene 2-Butene
Cyclohexane Benzene
H H H HH
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Hydrocarbons
Hydrocarbons
Are molecules consisting of only carbon and
hydrogen
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Hydrocarbons
Are found in many of a cells organic
molecules
(a) A fat molecule (b) Mammalian adipose cells
100 m
Fat droplets (stained red)
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Isomers
Isomers
Are molecules with the same molecular
formula but different structures and properties
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Three types of isomers are
Structural
Geometric
Enantiomers
H H H H HH
H H H H HH
H
HHHH
H
H
H
H
HHH
H
H
H
H
CO2H
CH3
NH2C
CO2H
HCH3
NH2
X X
X
X
C C C C C
CC
C C C
C C C C
C
(a) Structural isomers
(b) Geometric isomers
(c) Enantiomers
H
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Enantiomers
Are important in the pharmaceutical industry
L-Dopa
(effective against
Parkinsons disease)
D-Dopa
(biologically
inactive)
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Thalidomide
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Functional groups are the parts of moleculesinvolved in chemical reactions
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The Functional Groups Most Important in theChemistry of Life
Functional groups
Are the chemically reactive groups of atomswithin an organic molecule
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Six functional groups are important in thechemistry of life
Hydroxyl Carbonyl
Carboxyl
Amino
Sulfhydryl
Phosphate
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Some important functional groups of organiccompounds
FUNCTIONALGROUP
STRUCTURE
(may be written HO )
HYDROXYL CARBONYL CARBOXYL
OH
In a hydroxyl group (OH),
a hydrogen atom is bonded
to an oxygen atom, which inturn is bonded to the carbon
skeleton of the organic
molecule. (Do not confuse
this functional group with the
hydroxide ion, OH.)
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).
C
O O
C
OH
The carbonyl group
( CO) consists of a
carbon atom joined toan oxygen atom by a
double bond.
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Some important functional groups of organiccompounds
Acetic acid, which gives vinegar
its sour tatste
NAME OFCOMPOUNDS
Alcohols (their specificnames usually end in -ol)
Ketones if the carbonyl group is
within a carbon skeleton
Aldehydes if the carbonyl group
is at the end of the carbon
skeleton
Carboxylic acids, or organicacids
EXAMPLE
Propanal, an aldehyde
Acetone, the simplest ketone
Ethanol, the alcohol
present in alcoholic
beverages
H
H
H
H H
C C OH
H
H
H
HH
H
H
C C H
C
C C
C C C
O
H OH
O
H
H
H H
HO
H
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Some important functional groups of organiccompounds
FUNCTIONAL
PROPERTIES
Is polar as a result of the
electronegative oxygen atom
drawing electrons toward
itself.
Attracts water molecules,
helping dissolve organic
compounds such as sugars
A ketone and an
aldehyde may be
structural isomers with
different properties, as
is the case for acetone
and propanal.
Has acidic properties because
it is a source of hydrogen ions.
The covalent bond between
oxygen and hydrogen is so polar
that hydrogen ions (H+) tend to
dissociate reversibly; for
example,
In cells, found in the ionic
form, which is called a
carboxylate group.
H
H
C
H
H
C
O
OH
H
H
C
O
C
O
+ H+
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Some important functional groups of organiccompounds
The amino group (NH2)
consists of a nitrogen atom
bonded to two hydrogen
atoms and to the carbon
skeleton.
AMINO SULFHYDRYL PHOSPHATE
(may be written HS )
The sulfhydryl group
consists of a sulfur atom
bonded to an atom of
hydrogen; resembles a
hydroxyl group in shape.
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).
N
H
H
SH
O P
O
OH
OH
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Some important functional groups of organiccompounds
Because it also has a carboxyl
group, glycine is both an amineand a carboxylic acid;
compounds with both groups
are called amino acids.
Glycine EthanethiolGlycerol phosphate
O
C
HO
C
HH
N
H
H
H
C C SH
H
H H
H
H
OH
C C C O P O
O
HHH
OH OH
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Some important functional groups of organiccompounds
Acts as a base; can pick
up a proton from the
surrounding solution:
Ionized, with a charge
of 1+, under cellular
conditions.
(nonionized) (ionized)
N
H
H H
+N H
H
Two sulfhydryl groups can
interact to help stabilize
protein structure (see
Figure 5.20).
Makes the molecule of which
it is a part an anion (negatively
charged ion).
Can transfer energy between
organic molecules.
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