Life and Chemistry:
Large Molecules
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Macromolecules: Giant Polymers
• There are four major types of biological
macromolecules:
 Proteins
 Carbohydrates
 Lipids
 Nucleic acids
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Macromolecules: Giant Polymers
• Macromolecules are giant polymers.
• Polymers are formed by covalent linkages of
smaller units called monomers.
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Condensation and Hydrolysis Reactions
• Macromolecules are made from smaller
monomers by means of a condensation or
dehydration reaction in which an OH from one
monomer is linked to an H from another
monomer.
• The reverse reaction, in which polymers are
broken back into monomers, is a called a
hydrolysis reaction.
Figure 3.3 Condensation and Hydrolysis of Polymers (Part 1)
Figure 3.3 Condensation and Hydrolysis of Polymers (Part 2)
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Proteins: Polymers of Amino Acids
• Proteins are polymers of amino acids. They are
molecules with diverse structures and functions.
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Proteins: Polymers of Amino Acids
• An amino acid has four
groups attached to a central
carbon atom:
 A hydrogen atom
 An amino group (NH3+)
 The acid is a carboxyl
group (COO–).
 Differences in amino
acids come from the side
chains, or the R groups.
Table 3.2 The Twenty Amino Acids Found in Proteins (Part 1)
Table 3.2 The Twenty Amino Acids Found in Proteins (Part 2)
Table 3.2 The Twenty Amino Acids Found in Proteins (Part 3)
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Proteins: Polymers of Amino Acids
• Proteins are synthesized by condensation
reactions between the amino group of one amino
acid and the carboxyl group of another. This forms
a peptide linkage.
• Forms a polypeptide.
Figure 3.5 Formation of Peptide Linkages
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Proteins: Polymers of Amino Acids
• There are four levels of protein structure: primary,
secondary, tertiary, and quaternary.
• The precise sequence of amino acids is called its
primary structure.
• The peptide backbone consists of repeating units of
atoms: N—C—C—N—C—C.
• Enormous numbers of different proteins are possible.
Figure 3.6 The Four Levels of Protein Structure (Part 1)
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Proteins: Polymers of Amino Acids
• A protein’s secondary structure consists of
regular, repeated patterns in different regions in
the polypeptide chain.
• This shape is influenced primarily by hydrogen
bonds arising from the amino acid sequence
(the primary structure).
• The two common secondary structures are the
a helix and the b pleated sheet.
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Proteins: Polymers of Amino Acids
• The a helix is a right-handed coil.
• The R groups point away from the
peptide backbone.
Figure 3.6 The Four Levels of Protein Structure (Part 2)
β pleated sheets form from
peptide regions that lie parallel
to each other.
Stabilized by hydrogen
bonds between N-H groups
on one chain with the C=O
group on the other.
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Proteins: Polymers of Amino Acids
• Tertiary structure is the three-dimensional shape of the
completed polypeptide.
• Interaction between R groups.
• Includes the location of disulfide bridges, which form
between cysteine residues.
Figure 3.4 A Disulfide Bridge
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Proteins: Polymers of Amino Acids
• Other factors determining tertiary structure:
 The nature and location of secondary
structures
 Hydrophobic side-chain aggregation and van
der Waals forces, which help stabilize them
 The ionic interactions between the positive
and negative charges deep in the protein,
away from water
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Proteins: Polymers of Amino Acids
• It is now possible to determine the complete description
of a protein’s tertiary structure.
• The location of every atom in the molecule is specified in
three-dimensional space.
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Proteins: Polymers of Amino Acids
• Quaternary structure results from the ways in
which multiple polypeptide subunits bind together
and interact.
• This level of structure adds to the threedimensional shape of the finished protein.
Figure 3.8 Quaternary Structure of a Protein
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Proteins: Polymers of Amino Acids
• Shape is crucial to the functioning of some
proteins.
• The combination of attractions, repulsions, and
interactions determines the right fit.
Figure 3.9 Noncovalent Interactions between Proteins and Other Molecules
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Proteins: Polymers of Amino Acids
• Changes in temperature, pH, salt concentrations,
and oxidation or reduction conditions can change
the shape of proteins.
• This loss of a protein’s normal three-dimensional
structure is called denaturation.
Figure 3.11 Denaturation Is the Loss of Tertiary Protein Structure and Function
Figure 3.12 Chaperonins Protect Proteins from Inappropriate Folding
Chaperonins are specialized proteins that help keep
other proteins from interacting inappropriately with one
another.
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Carbohydrates: Sugars and Sugar Polymers
• Carbohydrates are carbon molecules with
hydrogen and hydroxyl groups.
• They act as energy storage and transport
molecules.
• They also serve as structural components.
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Carbohydrates: Sugars and Sugar Polymers
• There are four major categories of carbohydrates:
 Monosaccharides
 Disaccharides, which consist of two
monosaccharides
 Oligosaccharides, which consist of between
3 and 20 monosaccharides
 Polysaccharides, which are composed of
hundreds to hundreds of thousands of
monosaccharides
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Carbohydrates: Sugars and Sugar Polymers
• The general formula for a carbohydrate monomer
is multiples of CH2O, maintaining a ratio of 1
carbon to 2 hydrogens to 1 oxygen.
• During the polymerization, which is a
condensation reaction, water is removed.
• Carbohydrate polymers have ratios of carbon,
hydrogen, and oxygen that differ somewhat from
the 1:2:1 ratios of the monomers.
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Carbohydrates: Sugars and Sugar Polymers
• All living cells contain the monosaccharide
glucose (C6H12O6).
• Glucose exists as a straight chain and a ring, with
the ring form predominant.
• The two forms of the ring, a-glucose and bglucose, exist in equilibrium when dissolved in
water.
Figure 3.13 Glucose: From One Form to the Other
Figure 3.14 Monosaccharides Are Simple Sugars (Part 1)
Figure 3.14 Monosaccharides Are Simple Sugars (Part 2)
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Carbohydrates: Sugars and Sugar Polymers
• Monosaccharides are bonded together covalently
by condensation reactions. The bonds are called
glycosidic linkages.
Figure 3.15 Disaccharides Are Formed by Glycosidic Linkages
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Carbohydrates: Sugars and Sugar Polymers
• Oligosaccharides contain
more than two
monosaccharides.
• Many proteins found on the
outer surface of cells have
oligosaccharides attached to
the R group of certain amino
acids, or to lipids.
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Carbohydrates: Sugars and Sugar Polymers
• Polysaccharides are giant
polymers of
monosaccharides
connected by glycosidic
linkages.
Structure of cellulose as it occurs in a
plant cell wall.
• Cellulose is a giant polymer
of glucose joined by b-1,4
linkages.
• Starch is a polysaccharide
of glucose with a-1,4
linkages.
Cellulose Fibers from Print Paper (SEM x1,080).
Figure 3.16 Representative Polysaccharides (Part 1)
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Carbohydrates: Sugars and Sugar Polymers
• Starches vary by amount of branching.
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Carbohydrates: Sugars and Sugar Polymers
• Carbohydrates are modified by the addition of
functional groups.
Figure 3.17 Chemically Modified Carbohydrates (Part 1)
Figure 3.17 Chemically Modified Carbohydrates (Part 2)
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Nucleic Acids: Informational Macromolecules
That Can Be Catalytic
• Nucleic acids, composed of many nucleotides,
are polymers that are specialized for storage and
transmission of information.
• Two types of nucleic acid are DNA
(deoxyribonucleic acid) and RNA (ribonucleic
acid).
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Nucleic Acids: Informational Macromolecules
That Can Be Catalytic
• Nucleic acids are polymers of nucleotides.
• A nucleotide consists of a pentose sugar, a
phosphate group, and a nitrogen-containing base.
• In DNA, the pentose sugar is deoxyribose; in RNA
it is ribose.
Figure 3.24 Nucleotides Have Three Components
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Nucleic Acids: Informational Macromolecules
That Can Be Catalytic
• DNA typically is double-stranded.
• The two separate polymer chains are held
together by hydrogen bonding between their
nitrogenous bases.
• The base pairing is complementary.
• Purines have a double-ring structure – Adenine
and Guanine.
• Pyrimidines have one ring – Cytosine and
Thymine.
• A pairs with T, G pairs with C.
Figure 3.25 Distinguishing Characteristics of DNA and RNA
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Nucleic Acids: Informational Macromolecules
That Can Be Catalytic
• The linkages that hold the nucleotides in RNA and
DNA are called phosphodiester linkages.
• These linkages are formed between carbon 3 of
the sugar and a phosphate group that is
associated with carbon 5 of the sugar.
• The backbone consists of alternating sugars and
phosphates.
• In DNA, the two strands are antiparallel.
• The DNA strands form a double helix, a molecule
with a right-hand twist.
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Nucleic Acids: Informational Macromolecules
That Can Be Catalytic
• Most RNA molecules consist of only a single
polynucleotide chain.
• Instead of the base thymine, RNA uses the base
uracil; DNA has deoxyribose sugar, RNA has
ribose.
Figure 3.26 Hydrogen Bonding in RNA
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Nucleic Acids: Informational Macromolecules
That Can Be Catalytic
• DNA is an information molecule. The information
is stored in the order of the four different bases.
• This order is transferred to RNA molecules, which
are used to direct the order of the amino acids in
proteins.
DNA
RNA
PROTEIN
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Lipids: Water-Insoluble Molecules
• Lipids are insoluble in water.
• This insolubility results from the many nonpolar
covalent bonds of hydrogen and carbon in lipids.
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Lipids: Water-Insoluble Molecules
• Roles for lipids in organisms include:
 Energy storage (fats and oils)
 Cell membranes (phospholipids)
 Capture of light energy (carotinoids)
 Hormones and vitamins (steroids and modified
fatty acids)
 Thermal insulation
 Electrical insulation of nerves
 Water repellency (waxes and oils)
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Lipids: Water-Insoluble Molecules
• Fats and oils store energy.
• Fats and oils are triglycerides, composed of
three fatty acid molecules and one glycerol
molecule.
Figure 3.18 Synthesis of a Triglyceride
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Lipids: Water-Insoluble Molecules
• Saturated fatty acids have only single carbon-tocarbon bonds and are said to be saturated with
hydrogens.
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Lipids: Water-Insoluble Molecules
• Unsaturated fatty acids have at least one
double-bonded carbon in one of the chains —the
chain is not completely saturated with hydrogen
atoms.
Figure 3.19 Saturated and Unsaturated Fatty Acids
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Lipids: Water-Insoluble Molecules
• Phospholipids have two hydrophobic fatty acid
tails and one hydrophilic phosphate group
attached to the glycerol.
Figure 3.20 Phospholipid Structure
Figure 3.21 Phospholipids Form a Bilayer
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Lipids: Water-Insoluble Molecules
• Carotenoids are light-absorbing pigments found
in plants and animals.
Figure 3.22 b –Carotene is the Source of Vitamin A
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Lipids: Water-Insoluble Molecules
• Steroids are signaling molecules.
• Steroids are organic compounds with a series of
fused rings.
Figure 3.23 All Steroids Have the Same Ring Structure
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Lipids: Water-Insoluble Molecules
• Waxes are highly nonpolar molecules consisting
of saturated long fatty acids bonded to long fatty
alcohols.
• A fatty alcohol is similar to a fatty acid, except for
the last carbon, which has an —OH group instead
of a —COOH group.