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BIOLOGY Life on Earth
WITH PHYSIOLOGY Tenth Edition
Audesirk Audesirk Byers
3
Biological
Molecules
Lecture Presentations by
Carol R. Anderson
Westwood College, River Oaks Campus
© 2014 Pearson Education, Inc.
Chapter 3 At a Glance
 3.1 Why Is Carbon So Important in Biological
Molecules?
 3.2 How Are Organic Molecules Synthesized?
 3.3 What Are Carbohydrates?
 3.4 What Are Lipids?
 3.5 What Are Proteins?
 3.6 What Are Nucleotides and Nucleic Acids?
© 2014 Pearson Education, Inc.
3.1 Why Is Carbon So Important in Biological
Molecules?
 Organic refers to molecules containing a carbon
skeleton bonded to hydrogen atoms
 Inorganic refers to carbon dioxide and all molecules
without carbon
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3.1 Why Is Carbon So Important in Biological
Molecules?
 The unique bonding properties of carbon are key to
the complexity of organic molecules
– The carbon atom is versatile because it has four
electrons in an outermost shell that can accommodate
eight electrons
– Therefore, a carbon atom can become stable by
forming up to four bonds (single, double, or triple)
– As a result, organic molecules can assume complex
shapes, including branched chains, rings, sheets, and
helices
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Figure 3-1 Bonding patterns
H
hydrogen
carbon
nitrogen
oxygen
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C
C
N
C
N
O
C
N
O
3.1 Why Is Carbon So Important in Biological
Molecules?
 The unique bonding properties of carbon are key to
the complexity of organic molecules (continued)
– Functional groups in organic molecules determine
the characteristics and chemical reactivity of the
molecules
– Functional groups are less stable than the carbon
backbone and are more likely to participate in
chemical reactions
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Table 3-1
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3.2 How Are Organic Molecules Synthesized?
 Small organic molecules (called monomers) are
joined to form longer molecules (called polymers)
 Biomolecules are joined or broken through
dehydration synthesis or hydrolysis
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3.2 How Are Organic Molecules Synthesized?
 Biological polymers are formed by removing water
and split apart by adding water
– Monomers are joined together through dehydration
synthesis, at the site where an H and an OH are
removed, resulting in the loss of a water molecule
(H2O)
– The openings in the outer electron shells of the two
subunits are filled when the two subunits share
electrons, creating a covalent bond
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Figure 3-2 Dehydration synthesis
dehydration
synthesis
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3.2 How Are Organic Molecules Synthesized?
 Biological polymers are formed by removing water
and split apart by adding water (continued)
– Polymers are broken apart through hydrolysis
(“water cutting”)
– Water is broken into H and OH and is used to break the
bond between monomers
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Animation: Dehydration Synthesis and Hydrolysis
Figure 3-3 Hydrolysis
hydrolysis
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3.2 How Are Organic Molecules Synthesized?
 Biological polymers are formed by removing water
and split apart by adding water (continued)
– All biological molecules fall into one of four categories
– Carbohydrates
– Lipids
– Proteins
– Nucleotides/nucleic acids
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Table 3-2
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3.3 What Are Carbohydrates?
 Carbohydrate molecules are composed of C, H, and O
in the ratio of 1:2:1
– If a carbohydrate consists of just one sugar molecule, it is
a monosaccharide
– Two linked monosaccharides form a disaccharide
– A polymer of many monosaccharides is a polysaccharide
– Carbohydrates are important energy sources for most
organisms
– Most small carbohydrates are water-soluble due to the
polar OH functional group
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3.3 What Are Carbohydrates?
 There are several monosaccharides with slightly
different structures
– The basic monosaccharide structure is a backbone of
3–7 carbon atoms
– Most of the carbon atoms have both a hydrogen
(-H) and a hydroxyl group (-OH) attached to them
– Most carbohydrates have the approximate chemical
formula (CH2O)n where “n” is the number of carbons in
the backbone
– When dissolved in the cytoplasmic fluid of a cell, the
carbon backbone usually forms a ring
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3.3 What Are Carbohydrates?
 There are several monosaccharides with slightly
different structures (continued)
– Glucose (C6H12O6) is the most common
monosaccharide in living organisms
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Figure 3-4 Sugar dissolving in water
water
hydrogen
bond
hydroxyl
group
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Figure 3-5 Depictions of glucose structure
5
6
Chemical formula
1
2
6
5
5
4
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3
Linear, ball and stick
6
1
3
4
2
Ring, ball and stick
1
4
3
2
Ring, simplified
3.3 What Are Carbohydrates?
 There are several monosaccharides with slightly
different structures (continued)
– Additional monosaccharides are
– Fructose (“fruit sugar” found in fruits, corn syrup, and
honey)
– Galactose (“milk sugar” found in lactose)
– Ribose and deoxyribose (found in RNA and DNA,
respectively)
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Figure 3-6 Some six-carbon monosaccharides
6
6
5
2
5
4
3 1
fructose
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4
1
3
2
galactose
Figure 3-7 Some five-carbon monosaccharides
5
5
4
1
3
ribose
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2
4
3
1
2
deoxyribose
Note “missing”
oxygen atom
3.3 What Are Carbohydrates?
 Disaccharides consist of two monosaccharides
linked by dehydration synthesis
– The fate of monosaccharides inside a cell can be
– Some are broken down to free their chemical energy
– Some are linked together by dehydration synthesis
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3.3 What Are Carbohydrates?
 Disaccharides consist of two monosaccharides
linked by dehydration synthesis (continued)
– Disaccharides are two-part sugars
– They are used for short-term energy storage
– When energy is required, they are broken apart into
their monosaccharide subunits by hydrolysis
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Figure 3-8 Synthesis of a disaccharide
glucose
sucrose
fructose
dehydration
synthesis
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3.3 What Are Carbohydrates?
 Disaccharides consist of two monosaccharides
linked by dehydration synthesis (continued)
– Examples of disaccharides include
– Sucrose (table sugar)  glucose  fructose
– Lactose (milk sugar)  glucose  galactose
– Maltose (malt sugar)  glucose  glucose
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3.3 What Are Carbohydrates?
 Polysaccharides are chains of monosaccharides
– Storage polysaccharides include
– Starch, an energy-storage molecule in plants, formed
in roots and seeds
– Glycogen, an energy-storage molecule in animals,
found in the liver and muscles
– Both starch and glycogen are polymers of glucose
molecules
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Figure 3-9 Starch structure and function
starch grains
Potato cells
A starch molecule
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Detail of a starch molecule
3.3 What Are Carbohydrates?
 Polysaccharides are chains of monosaccharides
(continued)
– Many organisms use polysaccharides as a structural
material
– Cellulose (a polymer of glucose) is one of the most
important structural polysaccharides
– It is found in the cell walls of plants
– It is indigestible for most animals due to the orientation
of the bonds between glucose molecules
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Animation: Carbohydrate Structure and Function
Figure 3-10 Cellulose structure and function
Cellulose is a major
component of wood
Hydrogen bonds
cross-linking
cellulose molecules
A plant cell with
a cell wall
A close-up of
cellulose fibers
in a cell
wall
bundle of
cellulose
molecules
Alternating bond
configuration differs
from starch
Detail of a cellulose molecule
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cellulose fiber
3.3 What Are Carbohydrates?
 Polysaccharides are chains of monosaccharides
(continued)
– Chitin (a polymer of modified glucose units) is found
in
– The outer coverings of insects, crabs, and spiders
– The cell walls of many fungi
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Figure 3-11 Chitin structure and function
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3.4 What Are Lipids?
 Lipids are a diverse group of molecules that contain
regions composed almost entirely of hydrogen and
carbon
– All lipids contain large chains of nonpolar
hydrocarbons
– Most lipids are therefore hydrophobic and water
insoluble
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Animation: Lipids
3.4 What Are Lipids?
 Lipids are diverse in structure and serve a variety
of functions
– They are used for energy storage
– They form waterproof coverings on plant and animal
bodies
– They serve as the primary component of cellular
membranes
– Still others are hormones
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3.4 What Are Lipids?
 Lipids are classified into three major groups
– Oils, fats, and waxes
– Phospholipids
– Steroids containing rings of carbon, hydrogen, and
oxygen
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3.4 What Are Lipids?
 Oils, fats, and waxes are lipids containing only
carbon, hydrogen, and oxygen
– Oils, fats, and waxes are made of one or more fatty
acid subunits
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3.4 What Are Lipids?
 Oils, fats, and waxes are lipids containing only
carbon, hydrogen, and oxygen (continued)
– Fats and oils
– Are used primarily as energy-storage molecules,
containing twice as many calories per gram as
carbohydrates and proteins
– Are formed by dehydration synthesis
– Three fatty acids  glycerol  triglyceride
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Figure 3-12 Synthesis of a triglyceride
glycerol
fatty acids
triglyceride
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Figure 3-13a Fat
Fat
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3.4 What Are Lipids?
 Oils, fats, and waxes are lipids containing only
carbon, hydrogen, and oxygen (continued)
– Fats that are solid at room temperature are saturated
(the carbon chain has as many hydrogen atoms as
possible, and mostly or all C–C bonds); for example,
beef fat
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Figure 3-14a A fat
A fat
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3.4 What Are Lipids?
 Oils, fats, and waxes are lipids containing only
carbon, hydrogen, and oxygen (continued)
– Fats that are liquid at room temperature are
unsaturated (with fewer hydrogen atoms, and many
CC bonds); for example, corn oil
– Unsaturated trans fats have been linked to heart
disease
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Figure 3-14b An oil
An oil
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3.4 What Are Lipids?
 Oils, fats, and waxes are lipids containing only
carbon, hydrogen, and oxygen (continued)
– Waxes are highly saturated and solid at room
temperature
– Waxes form waterproof coatings such as on
– Leaves and stems in plants
– Fur in mammals
– Insect exoskeletons
– Waxes are also used to build honeycomb structures
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Figure 3-13b Wax
Wax
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3.4 What Are Lipids?
 Phospholipids have water-soluble “heads” and
water-insoluble “tails”
– These form plasma membranes around all cells
– Phospholipids consist of two fatty acids  glycerol  a
short polar functional group
– They have hydrophobic and hydrophilic portions
– The polar functional groups form the “head” and are
water soluble
– The nonpolar fatty acids form the “tails” and are water
insoluble
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Figure 3-15 Phospholipids
variable
functional phosphate
group
group
polar head
(hydrophilic)
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glycerol
backbone
fatty acid tails
(hydrophobic)
3.4 What Are Lipids?
 Steroids contain four fused carbon rings
– Steroids are composed of four carbon rings fused
together with various functional groups protruding
from them
– Examples of steroids include cholesterol
– Found in the membranes of animal cells
– Component of male and female sex hormones
– Makes up 2% of human brain
– Excessive cholesterol contributes to cardiovascular
disease
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Figure 3-16 Steroids
Estrogen
Cholesterol
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Testosterone
3.5 What Are Proteins?
– Proteins are molecules composed of chains of amino
acids
– Proteins have a variety of functions
– Enzymes are proteins that promote specific
chemical reactions
– Structural proteins (e.g., elastin) provide support
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Table 3-3
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Figure 3-17 Structural proteins
Hair
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Horn
Silk
3.5 What Are Proteins?
 Proteins are molecules composed of chains of amino acids
(continued)
– Proteins are polymers of amino acids joined by peptide bonds
– All amino acids have a similar structure
– All contain amino and carboxyl groups
– All have a variable “R” group
– Some R groups are hydrophobic
– Some are hydrophilic
– Cysteine R groups can form disulfide bonds
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Figure 3-18 Amino acid structure
variable
group (R)
amino
group
carboxylic
acid group
hydrogen
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Figure 3-19 Amino acid diversity
glutamic acid (glu)
aspartic acid (asp)
Hydrophilic functional groups
phenylalanine (phe)
leucine (leu)
Hydrophobic functional groups
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cysteine (cys)
Sulfur-containing
functional group
3.5 What Are Proteins?
 Amino acids are joined by dehydration synthesis
– An amino group reacts with a carboxyl group, and
water is lost
– The covalent bond resulting after the water is lost is a
peptide bond, and the resulting chain of two amino
acids is called a peptide
– Long chains of amino acids are known as
polypeptides, or just proteins
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Figure 3-20 Protein synthesis
amino acid
amino
group
dehydration
amino acid synthesis
carboxylic amino
acid group group
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peptide
peptide
bond
water
3.5 What Are Proteins?
 A protein can have as many as four levels of
structure
– Primary structure is the sequence of amino acids
linked together in a protein
– Secondary structure is a helix, or a pleated sheet
– Tertiary structure refers to complex foldings of the
protein chain held together by disulfide bridges,
hydrophobic/hydrophilic interactions, and other bonds
– Quaternary structure occurs where multiple protein
chains are linked together
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Animation: Protein Structure
Figure 3-21 The four levels of protein structure
Primary structure:
Secondary structure:
The sequence of amino
acids linked by peptide
bonds
Usually maintained by
hydrogen bonds, which
shape this helix
leu
val
heme group
lys
lys
gly
his
hydrogen
ala bond
lys
val
Quaternary structure:
Tertiary structure:
lys
helix
pro
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Folding of the helix results
from hydrogen bonds with
surrounding water molecules
and disulfide bridges between
cysteine amino acids
Individual polypeptides are
linked to one another by
hydrogen bonds or disulfide
bridges
Figure 3-22 The pleated sheet and the structure of silk protein
hydrogen
bond
stack of pleated sheets
Pleated sheet
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Structure of silk
disordered
segment
strand
of silk
3.5 What Are Proteins?
 The functions of proteins are related to their threedimensional structures
– Precise positioning of amino acid R groups leads to
bonds that determine secondary and tertiary structure
– Disruption of secondary and tertiary bonds leads to
denatured proteins and loss of function
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3.6 What Are Nucleotides and Nucleic Acids?
 Nucleotides are the monomers of nucleic acid
chains and fall into two general classes
– Deoxyribose nucleotides
– Ribose nucleotides
 All nucleotides are made of three parts
– Phosphate group
– Five-carbon sugar
– Nitrogen-containing base
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Figure 3-23 Deoxyribose nucleotide
phosphate
base
sugar
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3.6 What Are Nucleotides and Nucleic Acids?
 Nucleotides act as energy carriers and intracellular
messengers
– Adenosine triphosphate (ATP) is a deoxyribose
nucleotide with three phosphate functional groups
– Ribose nucleotide cyclic adenosine monophosphate
(cAMP) acts as a messenger molecule in cells
– Electron carriers are those nucleotides (NAD and
FAD) transporting energy in the form of high-energy
electrons
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Figure 3-24 The energy-carrier molecule adenosine triphosphate (ATP)
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3.6 What Are Nucleotides and Nucleic Acids?
 DNA and RNA, the molecules of heredity, are nucleic
acids
– Nucleic acids are polymers formed by monomers
strung together in long chains by dehydration
synthesis
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3.6 What Are Nucleotides and Nucleic Acids?
 DNA and RNA, the molecules of heredity, are nucleic
acids (continued)
– There are two types of polymers of nucleic acids
– DNA (deoxyribonucleic acid) is found in
chromosomes and carries genetic information needed
for protein construction
– Each DNA molecule consists of two chains of nucleotides
that form a double helix linked by hydrogen bonds
– RNA (ribonucleic acid) makes copies of DNA and is
used directly in the synthesis of proteins
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Figure 3-25 Deoxyribonucleic acid
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hydrogen
bond