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Molecular Diversity of Life
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Overview: Carbon: The Backbone of Life
Living organisms consist mostly of carbon-basedcompounds
Carbon is unparalleled in its ability to form large,
complex, and diverse molecules Proteins, DNA, carbohydrates, and other
molecules that distinguish living matter are all
composed of carbon compounds
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Figure 4.1
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Concept 4.1: Organic chemistry is the study
of carbon compounds
Organic chemistryis the study of compoundsthat contain carbon
Organic compounds range from simplemolecules to colossal ones
Most organic compounds contain hydrogenatoms in addition to carbon atoms
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Vitalism, the idea that organic compoundsarise only in organisms, was disproved when
chemists synthesized these compounds
Mechanism
is the view that all naturalphenomena are governed by physical and
chemical laws
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Organic Molecules and the Origin of Life
on Earth
Stanley Millers classic experiment
demonstrated the abiotic synthesis of
organic compounds Experiments support the idea that abiotic
synthesis of organic compounds, perhaps
near volcanoes, could have been a stage in
the origin of life
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Figure 4.2EXPERIMENT
Atmosphere
Electrode
Condenser
CH4Water vapor
Cooled raincontainingorganicmolecules
Coldwater
Sample for chemical analysis
H2Osea
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Concept 4.2: Carbon atoms can form diverse
molecules by bonding to four other atoms
Electron configuration is the key to an atoms
characteristics
Electron configuration determines the kindsand number of bonds an atom will form with
other atoms
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The Formation of Bonds with Carbon
With four valence electrons, carbon can formfour covalent bonds with a variety of atoms
This ability makes large, complex moleculespossible
In molecules with multiple carbons, each carbonbonded to four other atoms has a tetrahedralshape
However, when two carbon atoms are joined bya double bond, the atoms joined to the carbonsare in the same plane as the carbons
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Figure 4.3
Name and
CommentMolecular
Formula
(a) Methane
(b) Ethane
CH4
Ball-and-
Stick Model
Space-Filling
Model
(c) Ethene
(ethylene)
C2H6
C2H4
Structural
Formula
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The electron configuration of carbon gives itcovalent compatibility with many different
elements
The valences of carbon and its most frequent
partners (hydrogen, oxygen, and nitrogen) are
the building code that governs the
architecture of living molecules
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Figure 4.4
Hydrogen
(valence 1)Oxygen
(valence 2)Nitrogen
(valence 3)Carbon
(valence 4)
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Carbon atoms can partner with atoms other thanhydrogen; for example:
Carbon dioxide: CO2
Urea: CO(NH2)2
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Molecular Diversity Arising from Carbon
Skeleton Variation
Carbon chains form the skeletons of most
organic molecules
Carbon chains vary in length and shape
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Animation: Carbon Skeletons
Fi 4 5
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Figure 4.5
(a) Length
Ethane 1-Butene
(c) Double bond position
2-ButenePropane
(b) Branching (d) Presence of rings
Butane 2-Methylpropane
(isobutane)Cyclohexane Benzene
Fig re 4 5a
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Figure 4.5a
(a) Length
Ethane Propane
Figure 4 5b
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Figure 4.5b
(b) Branching
Butane 2-Methylpropane
(commonly called isobutane)
Figure 4 5c
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Figure 4.5c
1-Butene
(c) Double bond position
2-Butene
Figure 4 5d
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Figure 4.5d
(d) Presence of rings
Cyclohexane Benzene
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Hydrocarbons
Hydrocarbonsare organic moleculesconsisting of only carbon and hydrogen
Many organic molecules, such as fats, have
hydrocarbon components
Hydrocarbons can undergo reactions that
release a large amount of energy
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Figure 4 6
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Figure 4.6
Nucleus
Fat droplets
(b) A fat molecule(a) Part of a human adipose cell
10 m
Figure 4 6a
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Figure 4.6a
Nucleus
Fat droplets
10 m
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I somers
Isomersare compounds with the samemolecular formula but different structures and
properties
Structural isomershave different covalent
arrangements of their atoms
Cis-transisomershave the same covalent
bonds but differ in spatial arrangements
Enantiomersare isomers that are mirrorimages of each other
2011 Pearson Education, Inc.
Animation: Isomers
Figure 4.7( ) St t l i
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Figure 4.7(a) Structural isomers
(b) Cis-transisomers
(c) Enantiomers
c isisomer: The two Xs
are on the same side.t ransisomer: The two Xs
are on opposite sides.
CO2HCO2H
CH3
H NH2
L isomer
NH2
CH3
H
D isomer
Figure 4.7a
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Figure 4.7a
(a) Structural isomers
Figure 4.7b
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g
(b) Cis-transisomers
c isisomer: The two Xs
are on the same side.t ransisomer: The two Xs
are on opposite sides.
Figure 4.7c
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g
(c) Enantiomers
CO2HCO2H
CH3
H NH2
L isomer
NH2
CH3
H
D isomer
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Enantiomers are important in thepharmaceutical industry
Two enantiomers of a drug may have different
effects
Usually only one isomer is biologically active
Differing effects of enantiomers demonstrate
that organisms are sensitive to even subtle
variations in molecules
2011 Pearson Education, Inc.
Animation: L-Dopa
Figure 4.8
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g
Drug
Ibuprofen
Albuterol
Condition
Effective
Enantiomer
Ineffective
Enantiomer
Pain;inflammation
Asthma
S-Ibuprofen R-Ibuprofen
R-Albuterol S-Albuterol
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Concept 4.3: A few chemical groups are key
to the functioning of biological molecules
Distinctive properties of organic molecules
depend on the carbon skeleton and on the
molecular components attached to it
A number of characteristic groups can
replace the hydrogens attached to skeletons
of organic molecules
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The Chemical Groups Most Important in
the Processes of Life
Functional groupsare the components of
organic molecules that are most commonly
involved in chemical reactions
The number and arrangement of functional
groups give each molecule its unique
properties
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Figure 4.UN02
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Estradiol
Testosterone
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The seven functional groups that are mostimportant in the chemistry of life:
Hydroxyl group
Carbonyl group
Carboxyl group
Amino group
Sulfhydryl group
Phosphate group Methyl group
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Figure 4.9-a
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STRUCTURE
CHEMICALGROUP Hydroxyl
NAME OF
COMPOUND
EXAMPLE
Ethanol
Alcohols (Their specific names
usually end in -ol.)
(may be written HO)
Carbonyl
Ketones if the carbonyl group is
within a carbon skeleton
Aldehydes if the carbonyl group
is at the end of the carbon skeleton
Carboxyl
Acetic acidAcetone
Propanal
Carboxylic acids, or organic acids
FUNCTIONAL
PROPERTIES
Is polar as a result of the
electrons spending more timenear the electronegative oxygen
atom.
Can form hydrogen bonds with
water molecules, helping dissolve
organic compounds such as
sugars.
A ketone and an aldehyde may be
structural isomers with differentproperties, as is the case for
acetone and propanal.
Ketone and aldehyde groups are
also found in sugars, giving rise
to two major groups of sugars:
ketoses (containing ketone
groups) and aldoses (containing
aldehyde groups).
Found in cells in the ionized form
with a charge of 1 and called acarboxylate ion.
Nonionized Ionized
Acts as an acid; can donate an
H+because the covalent bondbetween oxygen and hydrogen
is so polar:
Figure 4.9-b
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Amino Sulfhydryl Phosphate Methyl
Methylated compoundsOrganic phosphates
(may be
written HS)
ThiolsAmines
Glycine Cysteine
Acts as a base; can
pick up an H+ from the
surrounding solution
(water, in living
organisms):
Nonionized Ionized
Found in cells in the
ionized form with a
charge of 1+.
Two sulfhydryl groups can
react, forming a covalent
bond. This cross-linking
helps stabilize protein
structure.
Cross-linking of cysteines
in hair proteins maintains
the curliness or straightness
of hair. Straight hair can be
permanently curled by
shaping it around curlers
and then breaking and
re-forming the cross-linking
bonds.
Contributes negative charge to
the molecule of which it is a part
(2when at the end of a molecule,
as above; 1when located
internally in a chain of
phosphates).
Molecules containing phosphate
groups have the potential to react
with water, releasing energy.
Arrangement of methyl
groups in male and femalesex hormones affects their
shape and function.
Addition of a methyl group
to DNA, or to molecules
bound to DNA, affects the
expression of genes.
Glycerol phosphate 5-Methyl cytidine
Figure 4.9a
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STRUCTURE
EXAMPLE
Alcohols(Their specific
names usually
end in -o l.)
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
(may be written
HO)
Ethanol
Is polar as a result
of the electrons
spending more
time near the
electronegative
oxygen atom.
Can form hydrogen
bonds with watermolecules, helping
dissolve organic
compounds such
as sugars.
Hydroxyl
Figure 4.9b
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Carbonyl
STRUCTURE
EXAMPLE
Ketones if the carbonyl
group is within a
carbon skeleton
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Aldehydes if the carbonyl
group is at the end of the
carbon skeleton
A ketone and an
aldehyde may be
structural isomers
with different properties,
as is the case for
acetone and propanal.
Acetone
Propanal
Ketone and aldehyde
groups are also found
in sugars, giving riseto two major groups
of sugars: ketoses
(containing ketone
groups) and aldoses
(containing aldehyde
groups).
Figure 4.9c
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Carboxyl
STRUCTURE
EXAMPLE
Carboxylic acids, or organic
acids
NAME OFCOMPOUND
FUNCTIONAL
PROPERTIES
Acetic acid
Acts as an acid; can
donate an H+
because thecovalent bond between
oxygen and hydrogen is so
polar:
Found in cells in the ionizedform with a charge of 1and
called a carboxylate ion.
Nonionized Ionized
Figure 4.9d
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Amino
Amines
Glycine
STRUCTURE
EXAMPLE Acts as a base; can
pick up an H+
from thesurrounding solution
(water, in living
organisms):
NAME OFCOMPOUND
FUNCTIONAL
PROPERTIES
Found in cells in theionized form with a
charge of 1.
Nonionized Ionized
Figure 4.9e
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Sulfhydryl
Thiols
(may be
written HS)
STRUCTURE
EXAMPLE Two sulfhydryl groups can
react, forming a covalentbond. This cross-linking
helps stabilize protein
structure.
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Cross-linking of cysteinesin hair proteins maintains
the curliness or straightnessof hair. Straight hair can be
permanently curled by
shaping it around curlers
and then breaking and
re-forming the cross-linking
bonds.
Cysteine
Figure 4.9f
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Phosphate
STRUCTURE
EXAMPLE
NAME OF
COMPOUND
FUNCTIONAL
PROPERTIES
Organic phosphates
Glycerol phosphate
Contributes negativecharge to the moleculeof which it is a part(2when at the end ofa molecule, as at left;1when locatedinternally in a chain ofphosphates).
Molecules containingphosphate groups havethe potential to reactwith water, releasingenergy.
Figure 4.9g
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Methyl
STRUCTURE
EXAMPLE
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Methylated compounds
5-Methyl cytidine
Addition of a methyl groupto DNA, or to moleculesbound to DNA, affects theexpression of genes.
Arrangement of methylgroups in male and femalesex hormones affects theirshape and function.
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ATP: An Important Source of Energy for
Cellular Processes
One phosphate molecule, adenosine
triphosphate(ATP), is the primary energy-
transferring molecule in the cell
ATP consists of an organic molecule called
adenosine attached to a string of three
phosphate groups
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Figure 4.UN03
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a. b.
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