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CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
3
Carbon and
the Molecular
Diversity of Life
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
Overview: Carbon Compounds and Life
 Aside from water, living organisms consist mostly
of carbon-based compounds
 Carbon is unparalleled in its ability to form large,
complex, and diverse molecules
 A compound containing carbon is said to be an
organic compound
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 Critically important molecules of all living things fall
into four main classes
 Carbohydrates
 Lipids
 Proteins
 Nucleic acids
 The first three of these can form huge molecules
called macromolecules
© 2014 Pearson Education, Inc.
Figure 3.1
© 2014 Pearson Education, Inc.
Concept 3.1: Carbon atoms can form diverse
molecules by bonding to four other atoms
 An atom’s electron configuration determines the
kinds and number of bonds the atom will form with
other atoms
 This is the source of carbon’s versatility
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The Formation of Bonds with Carbon
 With four valence electrons, carbon can form four
covalent bonds with a variety of atoms
 This ability makes large, complex molecules
possible
 In molecules with multiple carbons, each carbon
bonded to four other atoms has a tetrahedral shape
 However, when two carbon atoms are joined by a
double bond, the atoms joined to the carbons are in
the same plane as the carbons
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 When a carbon atom forms four single covalent
bonds, the bonds angle toward the corners of an
imaginary tetrahedron
 When two carbon atoms are joined by a double bond,
the atoms joined to those carbons are in the same
plane as the carbons
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Figure 3.2
Name
Methane
Ethane
Ethene
(ethylene)
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Molecular
Formula
Structural
Formula
Ball-and-Stick
Model
Space-Filling
Model
 The electron configuration of carbon gives it covalent
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 3.3
Hydrogen
(valence  1)
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Oxygen
(valence  2)
Nitrogen
(valence  3)
Carbon
(valence  4)
 Carbon atoms can partner with atoms other than
hydrogen; for example:
 Carbon dioxide: CO2
 Urea: CO(NH2)2
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Figure 3.UN01
Estradiol
Testosterone
© 2014 Pearson Education, Inc.
Molecular Diversity Arising from Variation in
Carbon Skeletons
 Carbon chains form the skeletons of most organic
molecules
 Carbon chains vary in length and shape
Animation: Carbon Skeletons
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Figure 3.4
(a) Length
Ethane
(c) Double bond position
Propane
(b) Branching
Butane
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1-Butene
2-Butene
(d) Presence of rings
2-Methylpropane
(isobutane)
Cyclohexane
Benzene
Figure 3.4a
(a) Length
Ethane
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Propane
Figure 3.4b
(b) Branching
Butane
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2-Methylpropane
(isobutane)
Figure 3.4c
(c) Double bond position
1-Butene
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2-Butene
Figure 3.4d
(d) Presence of rings
Cyclohexane
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Benzene
 Hydrocarbons are organic molecules consisting
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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The Chemical Groups Most Important to Life
 Functional groups are 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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 The seven functional groups that are most important
in the chemistry of life:
 Hydroxyl group
 Carbonyl group
 Carboxyl group
 Amino group
 Sulfhydryl group
 Phosphate group
 Methyl group
© 2014 Pearson Education, Inc.
Figure 3.5
Chemical Group
Hydroxyl group (
Compound Name
Examples
OH)
Alcohol
Carbonyl group (
C
O)
Ethanol
Ketone
Aldehyde
Acetone
Carboxyl group (
Propanal
COOH)
Carboxylic acid,
or organic acid
Acetic acid
Amino group (
NH2)
Amine
Glycine
Sulfhydryl group (
SH)
Thiol
Phosphate group (
OPO32–)
Organic
phosphate
Methyl group (
Glycerol
phosphate
CH3)
Methylated
compound
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Cysteine
5-Methyl cytosine
Figure 3.5a
Chemical Group
Hydroxyl group (
Compound Name
Examples
OH)
Alcohol
Carbonyl group ( C
O)
Ethanol
Ketone
Aldehyde
Acetone
Carboxyl group (
COOH)
Carboxylic acid,
or organic acid
Acetic acid
Amino group (
NH2)
Amine
Glycine
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Propanal
Figure 3.5aa
Hydroxyl group (
OH)
(may be written HO
)
Alcohol
(The specific name
usually ends in -ol.)
Ethanol, the alcohol present
in alcoholic beverages
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Figure 3.5ab
Carbonyl group (
C
O)
Ketone if the carbonyl
group is within a carbon
skeleton
Aldehyde if the carbonyl
group is at the end of a
carbon skeleton
Acetone, the simplest ketone
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Propanal, an aldehyde
Figure 3.5ac
Carboxyl group (
COOH)
Carboxylic acid, or
organic acid
Acetic acid, which gives
vinegar its sour taste
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Ionized form of
COOH
(carboxylate ion),
found in cells
Figure 3.5ad
Amino group (
NH2)
Amine
Glycine, an amino acid
(note its carboxyl group)
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Ionized form of
found in cells
NH2
Figure 3.5b
Chemical Group
Sulfhydryl group (
Compound Name
SH)
Thiol
Phosphate group (
Glycerol
phosphate
CH3)
Methylated
compound
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Cysteine
OPO32–)
Organic
phosphate
Methyl group (
Examples
5-Methyl cytosine
Figure 3.5ba
Sulfhydryl group (
SH)
Thiol
(may be written HS
)
Cysteine, a sulfurcontaining amino acid
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Figure 3.5bb
Phosphate group (
OPO32–)
Organic phosphate
Glycerol phosphate, which
takes part in many important
chemical reactions in cells
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Figure 3.5bc
Methyl group (
CH3)
Methylated compound
5-Methyl cytosine, a
component of DNA that has
been modified by addition of
a methyl group
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ATP: An Important Source of Energy for Cellular
Processes
 One organic phosphate molecule, adenosine
triphosphate (ATP), is the primary energytransferring 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 3.UN02
Adenosine
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Figure 3.UN03
Reacts
with H2O
Adenosine
Adenosine
ATP
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Inorganic
phosphate
ADP
Energy
Concept 3.2: Macromolecules are polymers, built
from monomers
 A polymer is a long molecule consisting of many
similar building blocks
 These small building-block molecules are called
monomers
 Some molecules that serve as monomers also have
other functions of their own
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The Synthesis and Breakdown of Polymers
 Cells make and break down polymers by the same
process
 A dehydration reaction occurs when two monomers
bond together through the loss of a water molecule
 Polymers are disassembled to monomers by
hydrolysis, a reaction that is essentially the reverse
of the dehydration reaction
 These processes are facilitated by enzymes, which
speed up chemical reactions
Animation: Polymers
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Figure 3.6
(a) Dehydration reaction: synthesizing a polymer
Short polymer
Longer polymer
(b) Hydrolysis: breaking down a polymer
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Unlinked monomer
Figure 3.6a
(a) Dehydration reaction: synthesizing a polymer
Short polymer
Dehydration removes
a water molecule,
forming a new bond.
Longer polymer
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Unlinked monomer
Figure 3.6b
(b) Hydrolysis: breaking down a polymer
Hydrolysis adds
a water molecule,
breaking a bond.
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The Diversity of Polymers
 Each cell has thousands of different macromolecules
HO
 Macromolecules vary among cells of an organism,
vary more within a species, and vary even more
between species
 An immense variety of polymers can be built from a
small set of monomers
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Concept 3.3: Carbohydrates serve as fuel and
building material
 Carbohydrates include sugars and the polymers of
sugars
 The simplest carbohydrates are monosaccharides,
or simple sugars
 Carbohydrate macromolecules are polysaccharides,
polymers composed of many sugar building blocks
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Sugars
 Monosaccharides have molecular formulas that
are usually multiples of CH2O
 Glucose (C6H12O6) is the most common
monosaccharide
 Monosaccharides are classified by the number of
carbons in the carbon skeleton and the placement
of the carbonyl group
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Figure 3.7
Triose: 3-carbon sugar (C3H6O3)
Pentose: 5-carbon sugar (C5H10O5)
Glyceraldehyde
An initial breakdown
product of glucose in cells
Ribose
A component of RNA
Hexoses: 6-carbon sugars (C6H12O6)
Glucose
Fructose
Energy sources for organisms
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Figure 3.7a
Triose: 3-carbon sugar (C3H6O3)
Glyceraldehyde
An initial breakdown
product of glucose in cells
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Figure 3.7b
Pentose: 5-carbon sugar (C5H10O5)
Ribose
A component of RNA
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Figure 3.7c
Hexoses: 6-carbon sugars (C6H12O6)
Glucose
Fructose
Energy sources for organisms
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 Though often drawn as linear skeletons, in aqueous
solutions many sugars form rings
 Monosaccharides serve as a major fuel for cells and
as raw material for building molecules
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Figure 3.8
(a) Linear and ring forms
(b) Abbreviated ring structure
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 A disaccharide is formed when a dehydration
reaction joins two monosaccharides
 This covalent bond is called a glycosidic linkage
Animation: Disaccharides
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Figure 3.9-1
Glucose
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Fructose
Figure 3.9-2
Glucose
Fructose
1–2
glycosidic
linkage
Sucrose
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Polysaccharides
 Polysaccharides, the polymers of sugars, have
storage and structural roles
 The structure and function of a polysaccharide are
determined by its sugar monomers and the positions
of glycosidic linkages
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Storage Polysaccharides
 Starch, a storage polysaccharide of plants, consists
entirely of glucose monomers
 Plants store surplus starch as granules
 The simplest form of starch is amylose
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 Glycogen is a storage polysaccharide in animals
 Humans and other vertebrates store glycogen
mainly in liver and muscle cells
Animation: Polysaccharides
© 2014 Pearson Education, Inc.
Figure 3.10
Starch granules
in a potato tuber cell
Starch (amylose)
Glucose
monomer
Glycogen granules
in muscle
tissue
Cellulose microfibrils
in a plant cell wall
Cellulose
molecules
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Glycogen
Cellulose
Hydrogen bonds
between —OH groups
(not shown) attached to
carbons 3 and 6
Figure 3.10a
Starch granules
in a potato tuber cell
Starch (amylose)
Glucose
monomer
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Figure 3.10aa
Starch granules
in a potato
tuber cell
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Figure 3.10b
Glycogen granules
in muscle
tissue
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Glycogen
Figure 3.10ba
Glycogen
granules
in muscle
tissue
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Figure 3.10c
Cellulose microfibrils
in a plant cell wall
Cellulose
molecules
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Cellulose
Hydrogen bonds
between —OH
groups on
carbons 3 and 6
Figure 3.10ca
Cellulose
microfibrils
in a plant
cell wall
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Structural Polysaccharides
 The polysaccharide cellulose is a major component
of the tough wall of plant cells
 Like starch and glycogen, cellulose is a polymer of
glucose, but the glycosidic linkages in cellulose differ
 The difference is based on two ring forms for
glucose
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Figure 3.11
(a)  and  glucose
ring structures
 Glucose
 Glucose
(b) Starch: 1–4 linkage of  glucose monomers
(c) Cellulose: 1–4 linkage of  glucose monomers
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Figure 3.11a
(a)  and  glucose
ring structures
 Glucose
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 Glucose
 In starch, the glucose monomers are arranged in
the alpha () conformation
 Starch (and glycogen) are largely helical
 In cellulose, the monomers are arranged in the beta
() conformation
 Cellulose molecules are relatively straight
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Figure 3.11b
(b) Starch: 1–4 linkage of  glucose monomers
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Figure 3.11c
(c) Cellulose: 1–4 linkage of  glucose monomers
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 In straight structures (cellulose), H atoms on one
strand can form hydrogen bonds with OH groups on
other strands
 Parallel cellulose molecules held together this way
are grouped into microfibrils, which form strong
building materials for plants
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 Enzymes that digest starch by hydrolyzing  linkages
can’t hydrolyze  linkages in cellulose
 Cellulose in human food passes through the
digestive tract as insoluble fiber
 Some microbes use enzymes to digest cellulose
 Many herbivores, from cows to termites, have
symbiotic relationships with these microbes
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 Chitin, another structural polysaccharide, is found in
the exoskeleton of arthropods
 Chitin also provides structural support for the cell
walls of many fungi
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Concept 3.4: Lipids are a diverse group of
hydrophobic molecules
 Lipids do not form true polymers
 The unifying feature of lipids is having little or no
affinity for water
 Lipids are hydrophobic because they consist mostly
of hydrocarbons, which form nonpolar covalent bonds
 The most biologically important lipids are fats,
phospholipids, and steroids
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Fats
 Fats are constructed from two types of smaller
molecules: glycerol and fatty acids
 Glycerol is a three-carbon alcohol with a hydroxyl
group attached to each carbon
 A fatty acid consists of a carboxyl group attached
to a long carbon skeleton
Animation: Fats
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Figure 3.12
Fatty acid
(in this case, palmitic acid)
Glycerol
(a) One of three dehydration reactions in the synthesis of a fat
Ester linkage
(b) Fat molecule (triacylglycerol)
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Figure 3.12a
Fatty acid
(in this case, palmitic acid)
Glycerol
(a) One of three dehydration reactions in the synthesis of a fat
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 Fats separate from water because water molecules
hydrogen-bond to each other and exclude the fats
 In a fat, three fatty acids are joined to glycerol by an
ester linkage, creating a triacylglycerol, or
triglyceride
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Figure 3.12b
Ester linkage
(b) Fat molecule (triacylglycerol)
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 Fatty acids vary in length (number of carbons) and
in the number and locations of double bonds
 Saturated fatty acids have the maximum number
of hydrogen atoms possible and no double bonds
 Unsaturated fatty acids have one or more double
bonds
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Figure 3.13
(a) Saturated fat
Structural
formula of a
saturated fat
molecule
Space-filling
model of
stearic acid,
a saturated
fatty acid
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(b) Unsaturated fat
Structural
formula
of an
unsaturated
fat molecule
Space-filling
model of oleic
acid, an
unsaturated
fatty acid
Double bond
causes bending.
Figure 3.13a
(a) Saturated fat
Structural
formula of a
saturated fat
molecule
Space-filling
model of
stearic acid,
a saturated
fatty acid
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Figure 3.13aa
© 2014 Pearson Education, Inc.
Figure 3.13b
(b) Unsaturated fat
Structural
formula
of an
unsaturated
fat molecule
Space-filling
model of
oleic acid, an
unsaturated
fatty acid
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Double bond
causes bending.
Figure 3.13ba
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 Fats made from saturated fatty acids are called
saturated fats and are solid at room temperature
 Most animal fats are saturated
 Fats made from unsaturated fatty acids, called
unsaturated fats or oils, are liquid at room
temperature
 Plant fats and fish fats are usually unsaturated
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 The major function of fats is energy storage
 Fat is a compact way for animals to carry their
energy stores with them
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Phospholipids
 In a phospholipid, two fatty acids and a phosphate
group are attached to glycerol
 The two fatty acid tails are hydrophobic, but the
phosphate group and its attachments form a
hydrophilic head
 Phospholipids are major constituents of cell
membranes
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Hydrophobic tails
Hydrophilic head
Figure 3.14
Choline
Phosphate
Glycerol
Fatty acids
(a) Structural formula
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Hydrophilic
head
Hydrophobic
tails
(b) Space-filling model
(c) Phospholipid
symbol
(d) Phospholipid
bilayer
Hydrophobic tails
Hydrophilic head
Figure 3.14ab
Choline
Phosphate
Glycerol
Fatty acids
(a) Structural formula
© 2014 Pearson Education, Inc.
(b) Space-filling model
 When phospholipids are added to water, they selfassemble into a bilayer, with the hydrophobic tails
pointing toward the interior
 This feature of phospholipids results in the bilayer
arrangement found in cell membranes
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Figure 3.14cd
Hydrophilic
head
Hydrophobic
tails
(c) Phospholipid
symbol
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(d) Phospholipid
bilayer
Steroids
 Steroids are lipids characterized by a carbon
skeleton consisting of four fused rings
 Cholesterol, an important steroid, is a component in
animal cell membranes
 Although cholesterol is essential in animals, high
levels in the blood may contribute to cardiovascular
disease
Video: Cholesterol Space Model
Video: Cholesterol Stick Model
© 2014 Pearson Education, Inc.
Figure 3.15
© 2014 Pearson Education, Inc.
Concept 3.5: Proteins include a diversity of
structures, resulting in a wide range of functions
 Proteins account for more than 50% of the dry mass
of most cells
 Protein functions include defense, storage, transport,
cellular communication, movement, and structural
support
Animation: Contractile Proteins
Animation: Defensive Proteins
Animation: Enzymes
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Animation: Gene Regulatory Proteins
Animation: Hormonal Proteins
Animation: Receptor Proteins
Animation: Sensory Proteins
Animation: Storage Proteins
Animation: Structural Proteins
Animation: Transport Proteins
© 2014 Pearson Education, Inc.
Figure 3.16
Enzymatic proteins
Defensive proteins
Function: Protection against disease
Function: Selective acceleration of chemical reactions
Example: Digestive enzymes catalyze the hydrolysis of bonds in food Example: Antibodies inactivate and help destroy viruses and bacteria.
molecules.
Antibodies
Enzyme
Bacterium
Virus
Storage proteins
Transport proteins
Function: Storage of amino acids
Examples: Casein, the protein of milk, is the major source of amino
acids for baby mammals. Plants have storage proteins in their seeds.
Ovalbumin is the protein of egg white, used as an amino acid source
for the developing embryo.
Function: Transport of substances
Examples: Hemoglobin, the iron-containing protein of vertebrate
blood, transports oxygen from the lungs to other parts of the body.
Other proteins transport molecules across cell membranes.
Transport
protein
Ovalbumin
Amino acids
for embryo
Cell membrane
Hormonal proteins
Receptor proteins
Function: Coordination of an organism’s activities
Example: Insulin, a hormone secreted by the pancreas, causes other
tissues to take up glucose, thus regulating blood sugar
concentration.
Function: Response of cell to chemical stimuli
Example: Receptors built into the membrane of a nerve cell detect
signaling molecules released by other nerve cells.
Insulin
secreted
High
blood sugar
Receptor
protein
Normal
blood sugar
Signaling molecules
Contractile and motor proteins
Structural proteins
Function: Movement
Examples: Motor proteins are responsible for the undulations of cilia
and flagella. Actin and myosin proteins are responsible for the
contraction of muscles.
Function: Support
Examples: Keratin is the protein of hair, horns, feathers, and other skin
appendages. Insects and spiders use silk fibers to make their cocoons
and webs, respectively. Collagen and elastin proteins provide a fibrous
framework in animal connective tissues.
Actin
Myosin
Collagen
Muscle tissue
© 2014 Pearson Education, Inc.
30 m
Connective tissue
60 m
Figure 3.16a
Enzymatic proteins
Defensive proteins
Function: Selective acceleration of
chemical reactions
Function: Protection against disease
Example: Digestive enzymes catalyze the
hydrolysis of bonds in food molecules.
Example: Antibodies inactivate and help
destroy viruses and bacteria.
Antibodies
Enzyme
Virus
Bacterium
Storage proteins
Transport proteins
Function: Storage of amino acids
Function: Transport of substances
Examples: Casein, the protein of milk, is
the major source of amino acids for baby
mammals. Plants have storage proteins
in their seeds. Ovalbumin is the protein
of egg white, used as an amino acid
source for the developing embryo.
Examples: Hemoglobin, the iron-containing
protein of vertebrate blood, transports
oxygen from the lungs to other parts of the
body. Other proteins transport molecules
across cell membranes.
Transport
protein
Ovalbumin
© 2014 Pearson Education, Inc.
Amino acids
for embryo
Cell membrane
Figure 3.16aa
Enzymatic proteins
Function: Selective acceleration of
chemical reactions
Example: Digestive enzymes catalyze the
hydrolysis of bonds in food molecules.
Enzyme
© 2014 Pearson Education, Inc.
Figure 3.16ab
Defensive proteins
Function: Protection against disease
Example: Antibodies inactivate and help
destroy viruses and bacteria.
Antibodies
Virus
© 2014 Pearson Education, Inc.
Bacterium
Figure 3.16ac
Storage proteins
Function: Storage of amino acids
Examples: Casein, the protein of milk, is
the major source of amino acids for baby
mammals. Plants have storage proteins
in their seeds. Ovalbumin is the protein
of egg white, used as an amino acid
source for the developing embryo.
Ovalbumin
© 2014 Pearson Education, Inc.
Amino acids
for embryo
Figure 3.16aca
© 2014 Pearson Education, Inc.
Figure 3.16ad
Transport proteins
Function: Transport of substances
Examples: Hemoglobin, the iron-containing
protein of vertebrate blood, transports
oxygen from the lungs to other parts of the
body. Other proteins transport molecules
across cell membranes.
Transport
protein
Cell membrane
© 2014 Pearson Education, Inc.
Figure 3.16b
Hormonal proteins
Receptor proteins
Function: Coordination of an organism’s
activities
Function: Response of cell to chemical
stimuli
Example: Insulin, a hormone secreted by
the pancreas, causes other tissues to
take up glucose, thus regulating blood
sugar concentration.
Example: Receptors built into the
membrane of a nerve cell detect signaling
molecules released by other nerve cells.
Receptor
protein
High
blood sugar
Insulin
secreted
Signaling molecules
Normal
blood sugar
Contractile and motor proteins
Function: Movement
Examples: Motor proteins are responsible
for the undulations of cilia and flagella.
Actin and myosin proteins are
responsible for the contraction of
muscles.
Actin
Structural proteins
Function: Support
Examples: Keratin is the protein of hair,
horns, feathers, and other skin appendages.
Insects and spiders use silk fibers to make
their cocoons and webs, respectively.
Collagen and elastin proteins provide a
fibrous framework in animal connective
tissues.
Myosin
Collagen
Muscle tissue
30 m
© 2014 Pearson Education, Inc.
Connective tissue 60 m
Figure 3.16ba
Hormonal proteins
Function: Coordination of an organism’s
activities
Example: Insulin, a hormone secreted by
the pancreas, causes other tissues to
take up glucose, thus regulating blood
sugar concentration.
High
blood sugar
© 2014 Pearson Education, Inc.
Insulin
secreted
Normal
blood sugar
Figure 3.16bb
Receptor proteins
Function: Response of cell to chemical
stimuli
Example: Receptors built into the
membrane of a nerve cell detect signaling
molecules released by other nerve cells.
Receptor
protein
Signaling molecules
© 2014 Pearson Education, Inc.
Figure 3.16bc
Contractile and motor proteins
Function: Movement
Examples: Motor proteins are responsible
for the undulations of cilia and flagella.
Actin and myosin proteins are
responsible for the contraction of
muscles.
Actin
Muscle tissue
© 2014 Pearson Education, Inc.
30 m
Myosin
Figure 3.16bca
Muscle tissue
© 2014 Pearson Education, Inc.
30 m
Figure 3.16bd
Structural proteins
Function: Support
Examples: Keratin is the protein of hair,
horns, feathers, and other skin appendages.
Insects and spiders use silk fibers to make
their cocoons and webs, respectively.
Collagen and elastin proteins provide a
fibrous framework in animal connective
tissues.
Collagen
Connective tissue
© 2014 Pearson Education, Inc.
60 m
Figure 3.16bda
Connective tissue 60 m
© 2014 Pearson Education, Inc.
 Life would not be possible without enzymes
 Enzymatic proteins act as catalysts, to speed up
chemical reactions without being consumed by the
reaction
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 Polypeptides are unbranched polymers built from
the same set of 20 amino acids
 A protein is a biologically functional molecule that
consists of one or more polypeptides
© 2014 Pearson Education, Inc.
Amino Acids
 Amino acids are organic molecules with carboxyl
and amino groups
 Amino acids differ in their properties due to differing
side chains, called R groups
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Figure 3.UN04
Side chain (R group)
 carbon
Amino
group
© 2014 Pearson Education, Inc.
Carboxyl
group
Figure 3.17
Nonpolar side chains; hydrophobic
Side chain
(R group)
Glycine
(Gly or G)
Alanine
(Ala or A)
Phenylalanine
(Phe or F)
Methionine
(Met or M)
Leucine
(Leu or L)
Valine
(Val or V)
Isoleucine
(le or )
Tryptophan
(Trp or W)
Proline
(Pro or P)
Polar side chains; hydrophilic
Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Tyrosine
(Tyr or Y)
Asparagine
(Asn or N)
Glutamine
(Gln or Q)
Electrically charged side chains; hydrophilic
Basic (positively charged)
Acidic (negatively charged)
Aspartic acid
(Asp or D)
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Glutamic acid
(Glu or E)
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)
Figure 3.17a
Nonpolar side chains; hydrophobic
Side chain
(R group)
Glycine
(Gly or G)
Methionine
(Met or M)
© 2014 Pearson Education, Inc.
Alanine
(Ala or A)
Valine
(Val or V)
Phenylalanine
(Phe or F)
Leucine
(Leu or L)
Tryptophan
(Trp or W)
Isoleucine
(le or )
Proline
(Pro or P)
Figure 3.17b
Polar side chains; hydrophilic
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Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Tyrosine
(Tyr or Y)
Asparagine
(Asn or N)
Glutamine
(Gln or Q)
Figure 3.17c
Electrically charged side chains; hydrophilic
Basic (positively charged)
Acidic (negatively charged)
Aspartic acid Glutamic acid
(Asp or D)
(Glu or E)
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Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)
Polypeptides
 Amino acids are linked by peptide bonds
 A polypeptide is a polymer of amino acids
 Polypeptides range in length from a few to more
than a thousand monomers
 Each polypeptide has a unique linear sequence of
amino acids, with a carboxyl end (C-terminus) and
an amino end (N-terminus)
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Figure 3.18
Peptide bond
New peptide
bond forming
Side
chains
Backbone
Amino end
(N-terminus)
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Peptide
bond
Carboxyl end
(C-terminus)
Figure 3.18a
Peptide bond
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Figure 3.18b
Side
chains
Backbone
Amino end
(N-terminus)
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Peptide
bond
Carboxyl end
(C-terminus)
Protein Structure and Function
 A functional protein consists of one or more
polypeptides precisely twisted, folded, and coiled
into a unique shape
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Figure 3.19
Groove
Groove
(a) A ribbon model
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(b) A space-filling model
Figure 3.19a
Groove
(a) A ribbon model
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Figure 3.19b
Groove
(b) A space-filling model
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 The sequence of amino acids, determined
genetically, leads to a protein’s three-dimensional
structure
 A protein’s structure determines its function
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Figure 3.20
Antibody protein
© 2014 Pearson Education, Inc.
Protein from flu virus
Four Levels of Protein Structure
 Proteins are very diverse, but share three
superimposed levels of structure called primary,
secondary, and tertiary structure
 A fourth level, quaternary structure, arises when a
protein consists of more than one polypeptide chain
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 The primary structure of a protein is its unique
sequence of amino acids
 Secondary structure, found in most proteins,
consists of coils and folds in the polypeptide chain
 Tertiary structure is determined by interactions
among various side chains (R groups)
 Quaternary structure results from interactions
between multiple polypeptide chains
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Video: Alpha Helix with No Side Chain
Video: Alpha Helix with Side Chain
Video: Beta Pleated Sheet
Video: Beta Pleated Stick
Animation: Introduction to Protein Structure
Animation: Primary Structure
Animation: Secondary Structure
Animation: Tertiary Structure
Animation: Quaternary Structure
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Figure 3.21a
Primary structure
Amino
acids
1
10
5
Amino end
30
35
15
20
25
45
40
50
Primary structure of transthyretin
65
70
55
60
75
80
90
85
95
115
120
110
105
100
125
Carboxyl end
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Figure 3.21aa
Primary structure
Amino
acids
1
5
10
Amino end
30
© 2014 Pearson Education, Inc.
25
20
15
Figure 3.21b
Secondary
structure
Tertiary
structure
Quaternary
structure
Transthyretin
polypeptide
Transthyretin
protein
 helix
 pleated sheet
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Figure 3.21ba
Secondary structure
 helix
 pleated sheet
Hydrogen bond
 strand
Hydrogen
bond
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Figure 3.21bb
Tertiary structure
Transthyretin
polypeptide
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Figure 3.21bc
Quaternary structure
Transthyretin
protein
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Figure 3.21c
© 2014 Pearson Education, Inc.
Figure 3.21d
Hydrogen
bond
Hydrophobic
interactions and
van der Waals
interactions
Disulfide
bridge
Ionic bond
Polypeptide
backbone
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Figure 3.21e
Collagen
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Figure 3.21f
Heme
Iron
 subunit
 subunit
 subunit
 subunit
Hemoglobin
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Sickle-Cell Disease: A Change in Primary Structure
 Primary structure is the sequence of amino acids
on the polypeptide chain
 A slight change in primary structure can affect a
protein’s structure and ability to function
 Sickle-cell disease, an inherited blood disorder,
results from a single amino acid substitution in the
protein hemoglobin
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Figure 3.22
Secondary
and Tertiary
Structures
Sickle-cell
Normal
Primary
Structure
Function
Normal
hemoglobin
1
2
3
4
5
6
7
1
2
3
4
5
6
7
Quaternary
Structure
 subunit

Molecules do not
associate with one
another; each carries
oxygen.


5 m

Exposed hydrophobic region
Sickle-cell
hemoglobin

 subunit
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
Red Blood Cell
Shape
Molecules crystallized
into a fiber; capacity to
carry oxygen is reduced.


5 m
Figure 3.22a
Normal
Primary
Structure
1
2
3
4
5
6
7
© 2014 Pearson Education, Inc.
Secondary
and Tertiary
Structures
Quaternary
Structure
Normal
hemoglobin
 subunit




Function
Molecules do not
associate with one
another; each carries
oxygen.
Figure 3.22aa
5 m
© 2014 Pearson Education, Inc.
Figure 3.22b
Sickle-cell
Primary
Structure
1
2
3
4
5
6
7
© 2014 Pearson Education, Inc.
Secondary
and Tertiary
Structures
Quaternary
Structure
Exposed hydrophobic region
Sickle-cell
hemoglobin

 subunit

Function


Molecules crystallized
into a fiber; capacity to
carry oxygen is reduced.
Figure 3.22ba
5 m
© 2014 Pearson Education, Inc.
What Determines Protein Structure?
 In addition to primary structure, physical and
chemical conditions can affect structure
 Alterations in pH, salt concentration, temperature, or
other environmental factors can cause a protein to
unravel
 This loss of a protein’s native structure is called
denaturation
 A denatured protein is biologically inactive
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Figure 3.23-1
Normal protein
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Figure 3.23-2
Normal protein
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Denatured protein
Figure 3.23-3
Normal protein
© 2014 Pearson Education, Inc.
Denatured protein
Protein Folding in the Cell
 It is hard to predict a protein’s structure from its
primary structure
 Most proteins probably go through several
intermediate structures on their way to their final,
stable shape
 Scientists use X-ray crystallography to determine
3-D protein structure based on diffractions of an
X-ray beam by atoms of the crystalized molecule
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Figure 3.24
Experiment
Diffracted
X-rays
X-ray
source X-ray
beam
Crystal
Digital detector
X-ray diffraction
pattern
Results
RNA
DNA
RNA
polymerase 
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Figure 3.24a
Experiment
Diffracted
X-rays
X-ray
source
X-ray
beam
Crystal
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Digital detector
X-ray diffraction
pattern
Figure 3.24b
Results
RNA
DNA
RNA
polymerase 
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Concept 3.6: Nucleic acids store, transmit, and
help express hereditary information
 The amino acid sequence of a polypeptide is
programmed by a unit of inheritance called a gene
 Genes are made of DNA, a nucleic acid made of
monomers called nucleotides
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The Roles of Nucleic Acids
 There are two types of nucleic acids
 Deoxyribonucleic acid (DNA)
 Ribonucleic acid (RNA)
 DNA provides directions for its own replication
 DNA directs synthesis of messenger RNA (mRNA)
and, through mRNA, controls protein synthesis
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Figure 3.25-1
DNA
1 Synthesis
of mRNA
mRNA
NUCLEUS
CYTOPLASM
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Figure 3.25-2
DNA
1 Synthesis
of mRNA
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into
cytoplasm
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Figure 3.25-3
DNA
1 Synthesis
of mRNA
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into
cytoplasm
Ribosome
3 Synthesis
of protein
Polypeptide
© 2014 Pearson Education, Inc.
Amino
acids
The Components of Nucleic Acids
 Nucleic acids are polymers called polynucleotides
 Each polynucleotide is made of monomers called
nucleotides
 Each nucleotide consists of a nitrogenous base, a
pentose sugar, and one or more phosphate groups
 The portion of a nucleotide without the phosphate
group is called a nucleoside
Animation: DNA and RNA Structure
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Figure 3.26
5 end
Sugar-phosphate backbone
(on blue background)
Nitrogenous bases
Pyrimidines
5C
3C
Nucleoside
Nitrogenous
base
Cytosine (C)
Thymine
(T, in DNA)
Uracil
(U, in RNA)
Purines
5C
Phosphate
group
3C
Sugar
(pentose)
Adenine (A)
Guanine (G)
(b) Nucleotide
3 end
Sugars
(a) Polynucleotide, or nucleic acid
Deoxyribose (in DNA)
(c) Nucleoside components
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Ribose (in RNA)
Figure 3.26a
5 end
Sugar-phosphate backbone
(on blue background)
5C
3C
Nucleoside
Nitrogenous
base
5C
Phosphate
group
3C
(b) Nucleotide
3 end
(a) Polynucleotide, or nucleic acid
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Sugar
(pentose)
Figure 3.26b
Nucleoside
Nitrogenous
base
Phosphate
group
(b) Nucleotide
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Sugar
(pentose)
Figure 3.26c
Nitrogenous bases
Pyrimidines
Cytosine (C)
Thymine
(T, in DNA)
Uracil
(U, in RNA)
Purines
Adenine (A)
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Guanine (G)
Figure 3.26d
Sugars
Deoxyribose (in DNA)
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Ribose (in RNA)
 Each nitrogenous base has one or two rings that
include nitrogen atoms
 The nitrogenous bases in nucleic acids are called
cytosine (C), thymine (T), uracil (U), adenine (A),
and guanine (G)
 Thymine is found only in DNA, and uracil only in
RNA; the rest are found in both DNA and RNA
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 The sugar in DNA is deoxyribose; in RNA it is
ribose
 A prime () is used to identify the carbon atoms in the
ribose, such as the 2 carbon or 5 carbon
 A nucleoside with at least one phosphate attached is
a nucleotide
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Nucleotide Polymers
 Adjacent nucleotides are joined by covalent bonds
that form between the —OH group on the 3 carbon
of one nucleotide and the phosphate on the 5
carbon of the next
 These links create a backbone of sugar-phosphate
units with nitrogenous bases as appendages
 The sequence of bases along a DNA or mRNA
polymer is unique for each gene
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The Structures of DNA and RNA Molecules
 RNA molecules usually exist as single polypeptide
chains
 DNA molecules have two polynucleotides spiraling
around an imaginary axis, forming a double helix
 In the DNA double helix, the two backbones run in
opposite 5→ 3 directions from each other, an
arrangement referred to as antiparallel
 One DNA molecule includes many genes
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 The nitrogenous bases in DNA pair up and form
hydrogen bonds: adenine (A) always with thymine
(T), and guanine (G) always with cytosine (C)
 This is called complementary base pairing
 Complementary pairing can also occur between
two RNA molecules or between parts of the same
molecule
 In RNA, thymine is replaced by uracil (U), so A and
U pair
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Animation: DNA Double Helix
Video: DNA Stick Model
Video: DNA Surface Model
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Figure 3.27
5
3
Sugar-phosphate
backbones
Hydrogen bonds
Base pair joined
by hydrogen
bonding
3
5
(a) DNA
Base pair joined
by hydrogen bonding
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(b) Transfer RNA
Figure 3.27a
5
3
3
5
(a) DNA
© 2014 Pearson Education, Inc.
Sugar-phosphate
backbones
Hydrogen bonds
Base pair joined
by hydrogen bonding
Figure 3.27b
Sugar-phosphate
backbones
Hydrogen bonds
Base pair joined
by hydrogen
bonding
(b) Transfer RNA
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DNA and Proteins as Tape Measures of Evolution
 The linear sequences of nucleotides in DNA
molecules are passed from parents to offspring
 Two closely related species are more similar in DNA
than are more distantly related species
 Molecular biology can be used to assess
evolutionary kinship
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Figure 3.UN05
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Figure 3.UN06
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Figure 3.UN06a
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Figure 3.UN06b
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Figure 3.UN07
© 2014 Pearson Education, Inc.