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Chapter 3
The Molecules of Life
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
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ORGANIC COMPOUNDS
• A cell is mostly water.
• The rest of the cell consists mainly of carbon-based molecules.
• Carbon forms large, complex, and diverse molecules necessary
for life’s functions.
• Organic compounds are carbon-based molecules.
•C H O N
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Organic Compounds?
 CH4
 CO2
 H2O
 C6H12O6
 HCl
 O3
 C12H22O11
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Carbon Chemistry
• Carbon is a versatile atom.
– It has four electrons in an outer shell that holds eight.
– Carbon can share its electrons with other atoms to form up to four
covalent bonds.
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• Carbon can use its bonds to
– Attach to other carbons
– Form an endless diversity of carbon skeletons
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• The simplest organic compounds are hydrocarbons, which are
organic molecules containing only carbon and hydrogen atoms.
• The simplest hydrocarbon is methane, consisting of a single
carbon atom bonded to four hydrogen atoms.
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Giant Molecules from Smaller Building Blocks
• On a molecular scale, many of life’s molecules are gigantic,
earning the name macromolecules.
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Short polymer
Monomer
Dehydration Reaction
or
Dehydration Synthesis
Longer polymer
a Building a polymer chain
Figure 3.4a
Take out the H’s and the O
That water molecule has to
go
To go from simple to
complex
It’s Dehydration Synthesis
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Hydrolysis
b Breaking a polymer chain
Figure 3.4b
LARGE BIOLOGICAL MOLECULES
• There are four categories of large molecules in cells:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
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Carbohydrates
• Carbohydrates are sugars or sugar polymers. They include
– Small sugar molecules in soft drinks
– Long starch molecules in pasta and potatoes
“ose”
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Sources of Carbs
Sugars are found in honey, fruit, soft drinks,
milk and sugar.
Starches are found in cereals, pasta, flour,
bread, potatoes, and vegetables.
Cellulose or Dietary Fiber is found in whole
cereals, whole meal bread, outer skins of fruit
and vegetables, brown rice and oatmeal
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Monosaccharides
• Monosaccharides are simple sugars that cannot be broken down
by hydrolysis into smaller sugars.
• Common examples are
– Glucose in sports drinks
– Fructose found in fruit
• Glucose and fructose are isomers, molecules that have the same
molecular formula but different structures.
• Monosaccharides are the main fuels for cellular work.
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Monosaccharides
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 C6H12O6
b Abbreviated
ring structure
a Linear and ring structures
Figure 3.6
Disaccharides
• A disaccharide is
– A double sugar
– Constructed from two monosaccharides
– Formed by a dehydration reaction
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Galactose
Glucose
Lactose
Figure 3.7
• Disaccharides include
– Lactose in milk
– Maltose in beer, malted milk shakes, and malted milk ball candy
– Sucrose in table sugar
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• Sucrose is
– The main carbohydrate in plant sap
– Rarely used as a sweetener in processed foods
• High-fructose corn syrup is made by a commercial process that
converts natural glucose in corn syrup to much sweeter fructose.
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processed to extract
Starch
broken down into
Glucose
converted to sweeter
Fructose
added to foods as
high-fructose corn syrup
Ingredients: carbonated water,
high-fructose corn syrup,
caramel color, phosphoric acid,
natural flavors
Figure 3.8
Polysaccharides
• Polysaccharides are
– Complex carbohydrates
– Made of long chains of sugar units and polymers of
monosaccharides
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Glucose
monomer
Starch granules
a Starch
Glycogen
granules
b Glycogen
Cellulose fibril
Cellulose
molecules
c Cellulose
Figure 3.9
Polysaccharides
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• Starch is
– A familiar example of a polysaccharide
– Used by plant cells to store energy
• Potatoes and grains are major sources of starch in the human diet.
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• Glycogen is
– Used by animals cells to store energy
– Converted to glucose when it is needed
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• Cellulose
– Is the most abundant organic compound on Earth
– Forms cable-like fibrils in the tough walls that enclose plants
– Cannot be broken apart by most animals
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Lipids
Oil (hydrophobic)
Vinegar (hydrophilic)
Figure 3.10
Fats
• A typical fat, or triglyceride, consists of a glycerol molecule
joined with three fatty acid molecules via a dehydration reaction.
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Fatty acid
triglyceride
Glycerol
(a) A dehydration reaction linking a fatty acid to glycerol
(b) A fat molecule with a glycerol “head” and three
energy-rich hydrocarbon fatty acid “tails”
Figure 3.11
• Fats perform essential functions in the human body including
– Energy storage
– Cushioning
– Insulation
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• If the carbon skeleton of a fatty acid has
– Fewer than the maximum number of hydrogens, it is unsaturated
– The maximum number of hydrogens, then it is saturated
• A saturated fat has no double bonds, and all three of its fatty acids
are saturated.
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• Most animal fats
– Have a high proportion of saturated fatty acids
– Can easily stack, tending to be solid at room temperature
– Contribute to atherosclerosis, a condition in which lipidcontaining plaques build up within the walls of blood vessels
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• Most plant oils tend to be low in saturated fatty acids and liquid at
room temperature.
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• Hydrogenation
– Adds hydrogen
– Converts unsaturated fats to saturated fats
– Makes liquid fats solid at room temperature
– Creates trans fat, a type of unsaturated fat that is even less healthy
than saturated fats
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TYPES OF FATS
Saturated Fats
Unsaturated Fats
Margarine
INGREDIENTS: SOYBEAN OIL, FULLY HYDROGENATED
COTTONSEED OIL, PARTIALLY HYDROGENATED
COTTONSEED OIL AND SOYBEAN OILS, MONO AND
DIGLYCERIDES, TBHO AND CITRIC ACID
Plant oils
Trans fats
ANTIOXIDANTS
Omega-3 fats
Figure 3.12
Steroids
• Steroids are very different from fats in structure and function.
– The carbon skeleton is bent to form four fused rings.
– Steroids vary in the functional groups attached to this core set of
rings.
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• Cholesterol is
– A key component of cell membranes
– The “base steroid” from which your body produces other steroids,
such as estrogen and testosterone
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Cholesterol
Testosterone
A type of estrogen
Figure 3.13
• Synthetic anabolic steroids
– Resemble testosterone
– Mimic some of its effects
– Can cause serious physical and mental problems
– Are abused by athletes to enhance performance
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Proteins
• Proteins
– Are polymers constructed from amino acid monomers
– Perform most of the tasks the body needs to function
– Form enzymes, chemicals that change the rate of a chemical
reaction without being changed in the process
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Enzymes
help chemical
reactions
Contractile Proteins
help movement
Structural Proteins
provide support
MAJOR TYPES OF PROTEINS
Structural Proteins
Storage Proteins
Storage Proteins
provide amino acids
for growth
Contractile Proteins
Transport Proteins
Enzymes
Transport Proteins
help transport
substances
Figure 3.15
The Monomers of Proteins: Amino Acids
• All proteins are constructed from a common set of 20 kinds of
amino acids.
• Each amino acid consists of a central carbon atom bonded to four
covalent partners in which three of those attachment groups are
common to all amino acids.
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Amino
group
Carboxyl
group
Side
group
a The general structure of an amino acid
Hydrophobic
side group
Hydrophilic
side group
Leucine
Serine
b Examples of amino acids with hydrophobic and hydrophilic
side groups
Figure 3.16
Proteins as Polymers
• Cells link amino acids together by dehydration reactions, forming
peptide bonds and creating long chains of amino acids called
polypeptides.
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Carboxyl
group
Side
group
Amino acid
Amino
group
Side
group
Amino acid
Figure 3.17-1
Carboxyl
group
Amino
group
Side
group
Side
group
Amino acid
Amino acid
Dehydration reaction
Side
group
Side
group
Peptide bond
Figure 3.17-2
• Your body has tens of thousands of different kinds of protein.
• Proteins differ in their arrangement of amino acids.
• The specific sequence of amino acids in a protein is its primary
structure.
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15
5
1
10
30
35
20
25
45
40
50
55
65
60
70
75
Amino acid
85
80
95
100
90
110
115
105
125
120
129
Figure 3.18
• A slight change in the primary structure of a protein affects its
ability to function.
• The substitution of one amino acid for another in hemoglobin
causes sickle-cell disease.
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SEM
1
2
Normal red blood cell
3
4
5
6
7. . . 146
Normal hemoglobin
SEM
a Normal hemoglobin
1
Sickled red blood cell
2
3
4
5
6
7. . . 146
Sickle-cell hemoglobin
b Sickle-cell hemoglobin
Figure 3.19
What Determines Protein Shape?
• A protein’s shape is sensitive to the surrounding environment.
• Unfavorable temperature and pH changes can cause
denaturation of a protein, in which it unravels and loses its
shape.
• High fevers (above 104º F) in humans can cause some proteins to
denature.
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Nucleic Acids
• Nucleic acids
– Are macromolecules that provide the directions for building
proteins
– Include DNA and RNA
– Are the genetic material that organisms inherit from their parents
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• DNA resides in cells in long fibers called chromosomes.
• A gene is a specific stretch of DNA that programs the amino acid
sequence of a polypeptide.
• The chemical code of DNA must be translated from “nucleic acid
language” to “protein language.”
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Gene
DNA
Nucleic acids
RNA
Amino acid
Protein
Figure 3.22
•
Nucleic acids are polymers of nucleotides.
•
Each nucleotide has three parts:
–
A five-carbon sugar
–
A phosphate group
–
A nitrogenous base
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• Each DNA nucleotide has one of the following bases:
– Adenine (A)
– Guanine (G)
– Thymine (T)
– Cytosine (C)
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Nitrogenous base
A, G, C, or T
Thymine T
Phosphate
group
Phosphate
Base
Sugar
deoxyribose
a Atomic structure
Sugar
b Symbol used in this book
Figure 3.23
Sugar-phosphate
backbone
Base
Nucleotide
pair
Hydrogen
bond
Bases
a DNA strand
polynucleotide
b Double helix
two polynucleotide strands
Figure 3.25
• Two strands of DNA join together to form a double helix.
• Bases along one DNA strand hydrogen-bond to bases along the
other strand.
• The functional groups hanging off the base determine which bases
pair up:
– A only pairs with T.
– G can only pair with C.
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• RNA, ribonucleic acid, is different from DNA.
– RNA is usually single-stranded but DNA usually exists as a double
helix.
– RNA uses the sugar ribose and the base uracil (U) instead of
thymine (T).
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Nitrogenous base
A, G, C, or U
Uracil U
Phosphate
group
Sugar ribose
Figure 3.26
Large biological
molecules
Carbohydrates
Functions
Components
Examples
Monosaccharides:
glucose, fructose
Disaccharides:
lactose, sucrose
Polysaccharides:
starch, cellulose
Dietary energy;
storage; plant
structure
Monosaccharide
Lipids
Long-term
energy storage
fats;
hormones
steroids
Fatty acid
Glycerol
Components of
a triglyceride
Amino
group
Proteins
Enzymes, structure,
storage, contraction,
transport, and others
Fats triglycerides;
Steroids
testosterone,
estrogen
Carboxyl
group
Side
group
Lactase
an enzyme,
hemoglobin
a transport protein
Amino acid
Phosphate
Base
Nucleic acids
Information
storage
DNA, RNA
Sugar
Nucleotide
Figure UN3-2