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Chapter 3
The Molecules of Cells
PowerPoint Lectures
Campbell Biology: Concepts & Connections, Eighth Edition
REECE • TAYLOR • SIMON • DICKEY • HOGAN
© 2015 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Introduction
• Most of the world’s population cannot digest milkbased foods.
• These people are lactose intolerant, because they
lack the enzyme lactase.
• This illustrates the importance of biological
molecules, such as lactase, in the daily functions of
living organisms.
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INTRODUCTION TO ORGANIC
COMPOUNDS
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3.1 Life’s molecular diversity is based on the
properties of carbon
• Almost all the molecules a cell makes are
composed of carbon bonded to
• other carbons and
• atoms of other elements.
• Carbon-based molecules are called organic
compounds.
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3.1 Life’s molecular diversity is based on the
properties of carbon
• By sharing electrons, carbon can
• bond to four other atoms and
• branch in up to four directions.
• Methane (CH4) is one of the simplest organic
compounds.
• Four covalent bonds link four hydrogen atoms to
the carbon atom.
• Each of the four lines in the formula for methane
represents a pair of shared electrons.
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Figure 3.1a
H
C
H
H
H
The four single bonds of carbon point
to the corners of a tetrahedron.
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3.1 Life’s molecular diversity is based on the
properties of carbon
• Methane and other compounds composed of only
carbon and hydrogen are called hydrocarbons.
• Carbon, with attached hydrogens, can form chains
of various lengths.
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3.1 Life’s molecular diversity is based on the
properties of carbon
• A carbon skeleton is a chain of carbon atoms that
can differ in length and be
• straight,
• branched, or
• arranged in rings.
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3.1 Life’s molecular diversity is based on the
properties of carbon
• Compounds with the same formula but different
structural arrangements are called isomers.
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Figure 3.1b-0
Double bond
Ethane
Propane
Length: Carbon skeletons vary
in length.
Butane
Isobutane
Branching: Carbon skeletons may
be unbranched or branched.
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1-Butene
2-Butene
Double bonds: Carbon skeletons may have
double bonds, which can vary in location.
Cyclohexane
Benzene
Rings: Carbon skeletons may be arranged in
rings. (In the abbreviated ring structures, each
corner represents a carbon and its attached
hydrogens.)
3.2 A few chemical groups are key to the
functioning of biological molecules
• The unique properties of an organic compound
depend on
• the size and shape of its carbon skeleton and
• the groups of atoms that are attached to that
skeleton.
• The sex hormones testosterone and estradiol (a
type of estrogen) differ only in the groups of atoms
highlighted in Figure 3.2.
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Figure 3.2-0
Testosterone
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Estradiol
3.2 A few chemical groups are key to the
functioning of biological molecules
• Table 3.2 illustrates six chemical groups important
in the chemistry of life.
• The first five groups are called functional groups;
they affect a molecule’s function in a characteristic
way.
• These five groups are polar, so compounds
containing them are typically hydrophilic (waterloving) and soluble in water.
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3.2 A few chemical groups are key to the
functioning of biological molecules
• A sixth group, a methyl group,
• consists of a carbon bonded to three hydrogen
atoms,
• is nonpolar and not reactive, but
• still affects molecular shape and thus function.
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Table 3.2-0
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3.2 A few chemical groups are key to the
functioning of biological molecules
• The functional groups are
• hydroxyl group—a hydrogen bonded to an
oxygen,
• carbonyl group—a carbon linked by a double
bond to an oxygen atom,
• carboxyl group—a carbon double-bonded to both
an oxygen and a hydroxyl group,
• amino group—a nitrogen bonded to two hydrogen
atoms and the carbon skeleton, and
• phosphate group—a phosphorus atom bonded to
four oxygen atoms.
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3.3 Cells make large molecules from a limited
set of small molecules
• There are four classes of molecules important to
organisms:
1.
2.
3.
4.
carbohydrates,
lipids,
proteins, and
nucleic acids.
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3.3 Cells make large molecules from a limited
set of small molecules
• The four classes of biological molecules contain
very large molecules.
• They are often called macromolecules because of
their large size.
• They are also called polymers because they are
made from identical or similar building blocks strung
together.
• The building blocks of polymers are called
monomers.
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3.3 Cells make large molecules from a limited
set of small molecules
• Monomers are linked together to form polymers
through dehydration reactions, which remove
water.
• Polymers are broken apart by hydrolysis, the
addition of water.
• These reactions are mediated by enzymes,
specialized macromolecules that speed up
chemical reactions in cells.
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3.3 Cells make large molecules from a limited
set of small molecules
• A cell makes a large number of polymers from a
small group of monomers. For example,
• proteins are made from only 20 different amino
acids and
• DNA is built from just four kinds of monomers called
nucleotides.
• The monomers used to make polymers are
essentially universal.
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Figure 3.3-0
Unlinked
monomer
Short polymer
Dehydration reaction
forms a new bond
Longer polymer
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H2O
H2O
Hydrolysis
breaks a bond
CARBOHYDRATES
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3.4 Monosaccharides are the simplest
carbohydrates
• Carbohydrates range from small sugar molecules
(monomers) to large polysaccharides.
• Sugar monomers are monosaccharides, such as
those found in
• fructose,
• glucose, and
• honey.
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Figure 3.4a
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3.4 Monosaccharides are the simplest
carbohydrates
• Monosaccharides can be hooked together by
dehydration reactions to form
• more complex sugars and
• polysaccharides.
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3.4 Monosaccharides are the simplest
carbohydrates
• The carbon skeletons of monosaccharides vary in
length.
• Glucose and fructose are six carbons long.
• Others have three to seven carbon atoms.
• Monosaccharides are
• the main fuels for cellular work and
• used as raw materials to manufacture other organic
molecules.
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Figure 3.4b
Glucose
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Fructose
3.4 Monosaccharides are the simplest
carbohydrates
• Many monosaccharides form rings.
• The ring diagram may be
• abbreviated by not showing the carbon atoms at the
corners of the ring and
• drawn with different thicknesses for the bonds, to
indicate that the ring is a relatively flat structure with
attached atoms extending above and below it.
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Figure 3.4c
Structural
formula
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Abbreviated
structure
Simplified
structure
3.5 Two monosaccharides are linked to form
a disaccharide
• Two monosaccharides (monomers) can bond to
form a disaccharide in a dehydration reaction.
• The disaccharide sucrose is formed by combining
• a glucose monomer and
• a fructose monomer.
• The disaccharide maltose is formed from two
glucose monomers.
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Figure 3.5-2
Glucose
Glucose
H2O
Maltose
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3.6 CONNECTION: What is high-fructose corn
syrup, and is it to blame for obesity?
• Most sodas and fruit drinks contain high-fructose
corn syrup (HFCS).
• Fructose is sweeter than glucose.
• To make HFCS, glucose atoms are rearranged to
make the glucose isomer fructose.
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3.6 CONNECTION: What is high-fructose corn
syrup, and is it to blame for obesity?
• High-fructose corn syrup (HFCS)
• is used to sweeten many beverages,
• consists of about 55% fructose and 45% glucose,
and
• is a mixture with about the same proportions as in
sucrose.
• Most scientific studies have not shown health
consequences associated with replacing sucrose
with HFCS.
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3.6 CONNECTION: What is high-fructose corn
syrup, and is it to blame for obesity?
• Although HFCS consumption has declined
somewhat in recent years, obesity rates continue
to rise, with almost 36% of U.S. adults now
considered obese.
• Good health is promoted by
• a diverse diet of proteins, fats, vitamins, minerals,
complex carbohydrates, and
• exercise.
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3.7 Polysaccharides are long chains of sugar
units
• Polysaccharides are macromolecules, polymers
composed of thousands of monosaccharides.
• Polysaccharides may function as
• storage molecules or
• structural compounds.
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3.7 Polysaccharides are long chains of sugar
units
• Starch is
• a polysaccharide,
• composed of glucose monomers, and
• used by plants for energy storage.
• Glycogen is
• a polysaccharide,
• composed of glucose monomers, and
• used by animals for energy storage.
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3.7 Polysaccharides are long chains of sugar
units
• Cellulose
• is a polymer of glucose and
• forms plant cell walls.
• Chitin is
• a polysaccharide,
• used by insects and crustaceans to build an
exoskeleton, and
• found in the cell walls of fungi.
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Figure 3.7-0
Starch granules in
a potato tuber cell
Glycogen granules
in muscle
tissue
Cellulose microfibrils
in a plant cell wall
Cellulose
molecules
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Starch
Glucose
monomer
Glycogen
Cellulose
Hydrogen bonds
3.7 Polysaccharides are long chains of
sugar units
• Polysaccharides are usually hydrophilic (waterloving).
• Bath towels, for example, are often made of
cotton, which is mostly cellulose, and therefore
water absorbent.
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LIPIDS
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3.8 Fats are lipids that are mostly energystorage molecules
• Lipids
• are water insoluble (hydrophobic, or water-fearing)
compounds,
• are important in long-term energy storage,
• contain twice as much energy as a polysaccharide,
and
• consist mainly of carbon and hydrogen atoms
linked by nonpolar covalent bonds.
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3.8 Fats are lipids that are mostly energystorage molecules
• Lipids differ from carbohydrates, proteins, and
nucleic acids in that they are
• not huge molecules and
• not built from monomers.
• Lipids vary a great deal in structure and function.
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3.8 Fats are lipids that are mostly energystorage molecules
• We will consider three types of lipids:
1. fats,
2. phospholipids, and
3. steroids.
• A fat is a large lipid made from two kinds of smaller
molecules:
• glycerol and
• fatty acids.
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3.8 Fats are lipids that are mostly energystorage molecules
• A fatty acid can link to glycerol by a dehydration
reaction.
• A fat contains one glycerol linked to three fatty
acids.
• Fats are often called triglycerides because of their
structure.
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3.8 Fats are lipids that are mostly energystorage molecules
• Some fatty acids contain one or more double
bonds, forming unsaturated fatty acids.
• These have one fewer hydrogen atom on each
carbon of the double bond.
• These double bonds cause kinks or bends in the
carbon chain, preventing them from packing
together tightly and solidifying at room temperature.
• Fats with the maximum number of hydrogens are
called saturated fatty acids.
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3.8 Fats are lipids that are mostly energystorage molecules
• Unsaturated fats are referred to as oils.
• Most animal fats are saturated fats.
• Hydrogenated vegetable oils are unsaturated fats
that have been converted to saturated fats by
adding hydrogen.
• This hydrogenation creates trans fats, which are
associated with health risks.
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3.9 SCIENTIFIC THINKING: Scientific studies
document the health risks of trans fats
• In the 1890s, the process of adding hydrogen
atoms to unsaturated oils was developed to
• reduce spoilage of oils,
• help oils withstand repeated heating for frying, and
• reduce consumption of animal fats, thought to be
less healthy than partially hydrogenated vegetable
oils.
• By the 1990s, partially hydrogenated oils were
common in cookies, crackers, snacks, baked
goods, and fried foods.
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3.9 SCIENTIFIC THINKING: Scientific studies
document the health risks of trans fats
• Recent research has shown that trans fats pose an
even greater health risk than saturated fats.
• One study estimated that eliminating trans fats from the
food supply could prevent up to one in five heart
attacks!
• In 2006, the U.S. Food and Drug Administration
required the listing of trans fat on food labels.
• Many cities and states have passed laws to eliminate
trans fats in unlabeled foods served in restaurants and
schools.
• An increasing number of countries have banned trans
fats.
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3.9 SCIENTIFIC THINKING: Scientific studies
document the health risks of trans fats
• Experimental studies have tested the health risks
of consuming trans fats.
• In experimental controlled feeding trials, the diets of
participants contained different proportions of
saturated, unsaturated, and partially hydrogenated
fats.
• For ethical and practical reasons, controlled feeding
trials are usually fairly short in duration, involve only
limited dietary changes, generally use healthy
individuals, and measure intermediary risk factors,
such as changes in cholesterol levels, rather than
actual disease outcomes.
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3.9 SCIENTIFIC THINKING: Scientific studies
document the health risks of trans fats
• Observational scientific studies on dietary health
effects can
• extend over a longer time period,
• use a more representative population, and
• measure disease outcomes and risk factors.
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3.9 SCIENTIFIC THINKING: Scientific studies
document the health risks of trans fats
• The Nurses’ Health Study
• began in 1976 with more than 120,000 female
nurses and
• is an example of an observational study on dietary
health.
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3.9 SCIENTIFIC THINKING: Scientific studies
document the health risks of trans fats
• The results indicate that
• for each 5% increase in saturated fat, there was a
17% increase in the risk of heart disease and
• for each 2% increase in trans fat, there is a 93%
increase in risk.
• Trans fats are indeed a greater health risk than
saturated fats.
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Table 3.9-1
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3.10 Phospholipids and steroids are
important lipids with a variety of functions
• Phospholipids are the major component of all cell
membranes.
• Phospholipids are structurally similar to fats.
• Fats contain three fatty acids attached to glycerol.
• Phospholipids contain two fatty acids attached to
glycerol.
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Figure 3.10
Phosphate
group
Glycerol
Water
Hydrophilic heads
Hydrophobic tails
Symbol for phospholipid
Water
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3.10 Phospholipids and steroids are
important lipids with a variety of functions
• Phospholipids cluster into a bilayer of
phospholipids.
• The hydrophilic heads are in contact with
• the water of the environment and
• the internal part of the cell.
• The hydrophobic tails cluster together in the center
of the bilayer.
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Figure 3.10b
Water
Hydrophilic heads
Hydrophobic tails
Symbol for phospholipid
Water
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3.10 Phospholipids and steroids are
important lipids with a variety of functions
• Steroids are lipids in which the carbon skeleton
contains four fused rings.
• Cholesterol is
• a common component in animal cell membranes
and
• a starting material for making steroids, including
sex hormones.
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Figure 3.10c
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3.11 CONNECTION: Anabolic steroids pose
health risks
• Anabolic steroids are synthetic variants of the
male hormone testosterone that are abused by
some athletes with serious consequences,
including
•
•
•
•
•
•
violent mood swings,
depression,
liver damage,
cancer,
high cholesterol, and
high blood pressure.
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PROTEINS
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3.12 Proteins have a wide range of functions
and structures
• Proteins are
• involved in nearly every dynamic function in your
body and
• very diverse, with tens of thousands of different
proteins, each with a specific structure and function,
in the human body.
• Proteins are composed of differing arrangements
of a common set of just 20 amino acid monomers.
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3.12 Proteins have a wide range of functions
and structures
• Probably the most important role for proteins is as
enzymes, proteins that
• serve as catalysts and
• regulate virtually all chemical reactions within cells.
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3.12 Proteins have a wide range of functions
and structures
• Other types of proteins include
• transport proteins embedded in cell membranes,
which move sugar molecules and other nutrients
into your cells,
• defensive proteins, such as antibodies of the
immune system,
• signal proteins such as many hormones and other
chemical messengers that help coordinate body
activities,
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3.12 Proteins have a wide range of functions
and structures
• Other types of proteins include (continued)
• receptor proteins, built into cell membranes, which
receive and transmit signals into your cells,
• contractile proteins found within muscle cells,
• structural proteins such as collagen, which form the
long, strong fibers of connective tissues, and
• storage proteins, which serve as a source of amino
acids for developing embryos in eggs and seeds.
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3.12 Proteins have a wide range of functions
and structures
• The functions of different types of proteins depend
on their individual shapes.
• A polypeptide chain contains hundreds or
thousands of amino acids linked by peptide bonds.
• The amino acid sequence causes the polypeptide
to assume a particular shape.
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Figure 3.12a
Groove
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Figure 3.12c
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3.12 Proteins have a wide range of functions
and structures
• If a protein’s shape is altered, it can no longer
function.
• In the process of denaturation, a protein
• unravels,
• loses its specific shape, and
• loses its function.
• Proteins can be denatured by changes in salt
concentration, changes in pH, or high heat.
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3.13 Proteins are made from amino acids
linked by peptide bonds
• Amino acids all have
• an amino group and
• a carboxyl group (which makes it an acid).
• Also bonded to the central carbon is
• a hydrogen atom and
• a chemical group symbolized by R, which
determines the specific properties of each of the 20
amino acids used to make proteins.
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Figure 3.13a
Amino
group
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Carboxyl
group
3.13 Proteins are made from amino acids
linked by peptide bonds
• Amino acids are classified as either
• hydrophobic or
• hydrophilic.
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Figure 3.13b
Hydrophobic
Leucine (Leu)
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Hydrophilic
Serine (Ser)
Aspartic acid (Asp)
3.13 Proteins are made from amino acids
linked by peptide bonds
• Amino acid monomers are linked together in a
dehydration reaction,
• joining the carboxyl group of one amino acid to the
amino group of the next amino acid, and
• creating a peptide bond.
• Additional amino acids can be added by the same
process to create a chain of amino acids called a
polypeptide.
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3.14 VISUALIZING THE CONCEPT: A protein’s
functional shape results from four levels of
structure
• A protein can have four levels of structure:
1.
2.
3.
4.
primary structure,
secondary structure,
tertiary structure, and
quaternary structure.
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Figure 3.14-0
PRIMARY STRUCTURE
+H N
3
Amino end
Peptide bonds
connect amino
acids.
Amino
acids
Two types of
SECONDARY STRUCTURES
Alpha
helix
Secondary structures
are maintained by
hydrogen bonds
between atoms
of the
backbone.
Beta pleated sheet
TERTIARY STRUCTURE
Tertiary structure is
stabilized by interactions
between R groups.
QUATERNARY
STRUCTURE
Polypeptides are associated
into a functional protein.
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NUCLEIC ACIDS
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3.15 DNA and RNA are the two types of
nucleic acids
• The amino acid sequence of a polypeptide is
programmed by a discrete unit of inheritance
known as a gene.
• Genes consist of DNA (deoxyribonucleic acid), a
type of nucleic acid.
• DNA is inherited from an organism’s parents.
• DNA provides directions for its own replication.
• DNA programs a cell’s activities by directing the
synthesis of proteins.
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3.15 DNA and RNA are the two types of
nucleic acids
• DNA does not build proteins directly.
• DNA works through an intermediary, RNA
(ribonucleic acid).
• DNA is transcribed into RNA in a cell’s nucleus.
• RNA is translated into proteins in the cytoplasm.
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Figure 3.15-3
Gene
DNA
Nucleic acids
Transcription
RNA
Translation
Amino
acid
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Protein
3.16 Nucleic acids are polymers of
nucleotides
• DNA (deoxyribonucleic acid) and RNA (ribonucleic
acid) are composed of monomers called
nucleotides.
• Nucleotides have three parts:
1. a five-carbon sugar called ribose in RNA and
deoxyribose in DNA,
2. a phosphate group, and
3. a nitrogenous base.
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Figure 3.16a
Nitrogenous
base
(adenine)
Phosphate
group
Sugar
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3.16 Nucleic acids are polymers of
nucleotides
• DNA nitrogenous bases are
•
•
•
•
adenine (A),
thymine (T),
cytosine (C), and
guanine (G).
• RNA also has A, C, and G, but instead of T, it has
uracil (U).
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3.16 Nucleic acids are polymers of
nucleotides
• A nucleic acid polymer, a polynucleotide, forms
from the nucleotide monomers when the
phosphate of one nucleotide bonds to the sugar of
the next nucleotide by dehydration reactions.
• This produces a repeating sugar-phosphate
backbone with protruding nitrogenous bases.
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Figure 3.16b
A
T
C
G
T
Sugar-phosphate
backbone
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Nucleotide
3.16 Nucleic acids are polymers of
nucleotides
• RNA is usually a single polynucleotide strand.
• DNA is a double helix, in which two
polynucleotide strands wrap around each other.
• The two strands are associated because particular
bases always hydrogen-bond to one another.
• A pairs with T, and C pairs with G, producing base
pairs.
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Figure 3.16c
C
C
G
G
T
A
C
G
A
Base
pair
T
A
T
G
C
A
A
T
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A
T
T
3.17 EVOLUTION CONNECTION: Lactose
tolerance is a recent event in human evolution
• The majority of people
• stop producing the enzyme lactase in early
childhood and
• do not easily digest the milk sugar lactose after
childhood.
• Lactose tolerance represents
• a relatively recent mutation in the human genome
and
• a survival advantage for human cultures with milk
and dairy products available year-round.
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3.17 EVOLUTION CONNECTION: Lactose
tolerance is a recent event in human evolution
• Researchers identified three new mutations in 43
ethnic groups in East Africa that keep the lactase
gene permanently turned on.
• The mutations
• are all different from each other and from the
European mutation,
• appear to have occurred about 7,000 years ago,
and
• occurred about the same time as the domestication
of cattle in these regions.
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Figure 3.17
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