Download Outline Overview: The Molecules of Life Macromolecules are

Chapter 5 - The Structure and Function of
Large Biological Molecules
Outline
I. Macromolecules
II. Carbohydrates – simple and complex
III. Lipids – triglycerides (fats and oils),
phospholipids, carotenoids, steroids, waxes
IV. Proteins – enzymes, keratin,
V. Nucleotides – ATP, NAD+
VI. Nucleic Acids – DNA & RNA
Overview: The Molecules of Life
 All living things are made up of four classes of
large biological molecules: carbohydrates,
lipids, proteins, and nucleic acids
 Macromolecules are large molecules
composed of thousands of covalently
connected atoms
 Molecular structure and function are
inseparable
© 2011 Pearson Education, Inc.
Polymers
 Many biological molecules formed by linking a
chain of monomers
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
 Three of the four classes of life’s organic
molecules are polymers
 Carbohydrates
 Proteins
 Nucleic acids
© 2011 Pearson Education, Inc.
The Synthesis and Breakdown of Polymers
 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
© 2011 Pearson Education, Inc.
1
Figure 5.2a
(a) Dehydration reaction: synthesizing a polymer
2
1
3
Short polymer
Unlinked monomer
Dehydration removes
a water molecule,
forming a new bond.
1
2
3
4
Longer polymer
Animation: Polymers
Right-click slide / select
“Play”
© 2011 Pearson Education, Inc.
Figure 5.2b
Examples of Organic Compounds
(b) Hydrolysis: breaking down a polymer
1
2
3
Hydrolysis adds
a water molecule,
breaking a bond.
1
2
3
Simple Carbohydrates
1. Carbohydrates – sugars, polymers of sugars
4
2. Lipids – triglycerides (fats and oils),
phospholipids, steroids, waxes
3. Proteins – enzymes, keratin, actin
4. Nucleic Acids – DNA & RNA
Carbohydrates serve as fuel and building
material
 Carbohydrates include sugars and the polymers
of sugars
 The simplest carbohydrates are
monosaccharides, or single sugars
 Carbohydrate macromolecules are
polysaccharides, polymers composed of many
sugar building blocks
© 2011 Pearson Education, Inc.
2
Functions of Carbohydrates
Sugars
1. Rapidly Mobilized Source of Energy

Monosaccharides and disaccharides
 Monosaccharides have molecular formulas that
are usually multiples of CH2O
2. Energy storage


 Glucose (C6H12O6) is the most common
monosaccharide
Glycogen in animals
Starch in plants
3. Structural


In cell walls bacteria and plants (Cellulose).
In exoskeletons (Chitin).
4. Coupled with protein to form glycoproteins
 Important in cell membranes
 Monosaccharides are classified by
 The location of the carbonyl group (as aldose or
ketose)
 The number of carbons in the carbon skeleton
© 2011 Pearson Education, Inc.
Figure 5.3a
Figure 5.3b
Aldose (Aldehyde Sugar)
Aldose (Aldehyde Sugar)
Ketose (Ketone Sugar)
Ketose (Ketone Sugar)
Pentoses: 5-carbon sugars (C5H10O5)
Trioses: 3-carbon sugars (C3H6O3)
Glyceraldehyde
Dihydroxyacetone
Ribose
Ribulose
Figure 5.3c
Aldose (Aldehyde Sugar)
Ketose (Ketone Sugar)
Hexoses: 6-carbon sugars (C6H12O6)
 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
Glucose
Galactose
Fructose
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3
Figure 5.4
Disaccharide
1
2
6
6
5
5
3
4
4
5
1
3
2
4
1
3
2
 A disaccharide is formed when a dehydration
reaction joins two monosaccharides
6
 This covalent bond is called a glycosidic
linkage
(a) Linear and ring forms
6
5
4
1
3
2
(b) Abbreviated ring structure
© 2011 Pearson Education, Inc.
Figure 5.5
1
Glucose
Glucose
1–4
glycosidic
linkage 4
Maltose
(a) Dehydration reaction in the synthesis of maltose
1
Glucose
Fructose
1–2
glycosidic
linkage 2
Sucrose
(b) Dehydration reaction in the synthesis of sucrose
Animation: Disaccharide
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
4
Reactions where two molecules are linked together
and water is removed is …
ro
ly
si
yd
H
de
ns
at
io
n
C
on
50%
s
50%
1. Condensation or
dehydration
2. Hydrolysis
Complex Carbohydrates
Polysaccharides
Complex
carbohydrates - Polysaccharide
 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
 Types
1.
2.
3.
4.
Starch
Glycogen
Cellulose
Chitin
© 2011 Pearson Education, Inc.
Structure of Complex Carbohydrates
 Polysaccharides - Long chains of saccharides
(sugars) – 100s to 1000s
 Cellulose, starch and glycogen consist of chains
of only glucose.
 Chitin consists of chains of glucose with N-acetyl
groups
Animation: Polysaccharides
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Structure of Complex Carbohydrates
 The differences between the complex
carbohydrates is in the structure – branched,
unbranched, spiral, hydrogen-bonded.
 Cellulose is tightly packed and hard to digest
 Starch is coiled and may be branched and is easier
to digest
 Glycogen is coiled with extensive branching and is
even easier to digest.
5
Functions of Carbohydrates
Figure 5.6
Chloroplast
Starch granules
Amylopectin
1. Rapidly Mobilized Source of Energy

Monosaccharides and disaccharides
2. Energy storage - Polysaccharides


Glycogen in animals
Starch in plants
3. Structural


In cell walls bacteria and plants (Cellulose).
In exoskeletons (Chitin).
Amylose
(a) Starch:
a plant polysaccharide
Mitochondria
1 m
Glycogen granules
4. Coupled with protein to form glycoproteins
 Important in cell membranes
Glycogen
(b) Glycogen:
0.5 m
an animal polysaccharide
Polysaccharides in Plants for Energy Storage
 Starch, a storage polysaccharide of plants,
consists entirely of glucose monomers
 Plants store surplus starch as granules within
chloroplasts and other plastids
Starch
 Starch – form stored in plants, coiled, mainly α
1-4 glycosidic linkage. If branched then will
also have 1-6 glycosidic linkage, stored in
amyloplasts. Plants used for energy storage,
easy to digest
 Potatoes, rice, carrots, corn
 The simplest form of starch is amylose
 Types of starches:
 Amylose – not branched
 Amylopectin – branched, more common
© 2011 Pearson Education, Inc.
Glycogen
 Glycogen – form stored in animals for energy,
coiled, mainly α 1-4 glycosidic linkage. It is
branched therefore also has 1-6 glycosidic
linkage, easy to digest
 Found in animals: stored mainly in liver and
muscle
Functions of Carbohydrates
1. Rapidly Mobilized Source of Energy

Monosaccharides and disaccharides
2. Energy storage - Polysaccharides


Glycogen in animals
Starch in plants
3. Structural - Polysaccharides


Cellulose in cell walls bacteria and plants
Chitin in exoskeletons
4. Coupled with protein to form glycoproteins
 Important in cell membranes
6
Structural Polysaccharides in Plants - Starch
Cellulose
 Cellulose – straight chains of glucose, -OH
groups H-bond to stabilize chains into tight
bundles, β 1-4 glycosidic linkage, hard to
digest
 The polysaccharide cellulose is a major
component of the tough wall of plant cells
 Like starch, cellulose is a polymer of glucose,
but the glycosidic linkages differ
 Used by plants for structure and in cell walls.
 The difference is based on two ring forms for
glucose: alpha () and beta ()
© 2011 Pearson Education, Inc.
Figure 5.7a
Figure 5.7b
1
1
4
 Glucose
1
4
4
(b) Starch: 1–4 linkage of  glucose monomers
 Glucose
1
4
(a)  and  glucose ring structures
(c) Cellulose: 1–4 linkage of  glucose monomers
Figure 5.8
Cellulose
microfibrils in a
plant cell wall
Cell wall
 Polymers with  glucose are helical
 Polymers with  glucose are straight
Microfibril
10 m
0.5 m
 In straight structures, H atoms on one strand can
bond with OH groups on other strands
 Parallel cellulose molecules held together this way
are grouped into microfibrils, which form strong
building materials for plants
Cellulose
molecules
 Glucose
monomer
© 2011 Pearson Education, Inc.
7
Why do we care?
Structural Polysaccharides - Chitin
 Enzymes that digest starch by hydrolyzing 
linkages can’t hydrolyze  linkages in cellulose
 Chitin, another structural polysaccharide, is found
in the exoskeleton of arthropods.
 Cellulose in human food passes through the
digestive tract as insoluble fiber
 Contains N-acetyl group which hydrogen bond. Is
cross-linked with protein to form a strong
exoskeleton for insects and crustaceans
 Some microbes use enzymes to digest cellulose
 Chitin also provides structural support for the cell
walls of many fungi
 Many herbivores, from cows to termites, have
symbiotic relationships with these microbes
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Figure 5.9
Glycoproteins
The structure
of the chitin
monomer
Chitin forms the exoskeleton
of arthropods.
 Glycoproteins – carbohydrate + protein on
outer surface of cell membranes – we will
return to this when we study cell membranes
Chitin is used to make a strong and flexible
surgical thread that decomposes after the
wound or incision heals.
25% 25% 25%
25%
in
h it
C
ly
G
ell
ul
os
co
ge
n
e
Starch
Cellulose
Glycogen
Chitin
ch
1.
2.
3.
4.
C
lo
s
el
lu
ly
G
C
ch
ta
r
S
33%
e
33%
co
ge
n
33%
1. Starch
2. Glycogen
3. Cellulose
Which carbohydrate contains nitrogen?
St
ar
The form of carbohydrate stored in animals is?
8
Starch is composed of glucose molecules
joined by what kind of covalent bond?
50%
Lipids

Like carbohydrates, lipids are mainly made of
carbon, hydrogen and oxygen

They are not soluble in water, they are soluble
in nonpolar solvents
50%
1. β 1-4 Glycosidic
linkage
2. α 1-4 Glycosidic
linkage

Types:
1.
2.
3.
4.
5.
Lipids are a diverse group of hydrophobic
molecules
 Lipids are the one class of large biological
molecules that do not form polymers
Triglycerides (Fats)
Phospholipids
Carotenoids
Steroids
Waxes
I. Lipid - Triglycerides
 Function
 Energy storage, insulation, protection
 The unifying feature of lipids is having little or no
affinity for water
 Triglycerides (triacylglycerol) are three fatty
acids joined to glycerol
 Lipids are hydrophobic because they consist
mostly of hydrocarbons, which form nonpolar
covalent bonds
 The fatty acids are covalently linked by an
ester linkage through a condensation reaction
 The most biologically important lipids are fats,
phospholipids, and steroids
© 2011 Pearson Education, Inc.
Figure 5.10a
Figure 5.10b
Ester linkage
Fatty acid
(in this case, palmitic acid)
Glycerol
(a) One of three dehydration reactions in the synthesis of a fat
(b) Fat molecule (triacylglycerol)
9
Ester vs Ether
Triglycerides
 Butter, lard (animal fat), and vegetable oils
are all triglycerides
 Differences are in the structure of the fatty
acids
Fatty Acids
Fatty Acids
 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
 Saturated fatty acids – carbon chain has no
double bonds CH3-(CH2-CH2)n-COOH
 Unsaturated fatty acids – carbon chain has a
double bond
 Monounsaturated fatty acids have one double
bond
 Polyunsaturated fatty acids – more than one
double bond
© 2011 Pearson Education, Inc.
Figure 5.11
(a) Saturated fat
Structural
formula of a
saturated fat
molecule
Space-filling
model of stearic
acid, a saturated
fatty acid
Animation: Fats
Right-click slide / select “Play”
(b) Unsaturated fat
Structural
formula of an
unsaturated fat
molecule
Space-filling model
of oleic acid, an
unsaturated fatty
acid
Cis double bond
causes bending.
© 2011 Pearson Education, Inc.
10
Figure 5.11a
Figure 5.11b
(a) Saturated fat
Structural
formula of a
saturated fat
molecule
(b) Unsaturated fat
Structural
formula of an
unsaturated fat
molecule
Space-filling model
of oleic acid, an
unsaturated fatty
acid
Space-filling
model of stearic
acid, a saturated
fatty acid
Cis double bond
causes bending.
 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 are called
unsaturated fats or oils, and are liquid at room
temperature
 Plant fats and fish fats are usually unsaturated
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Trans fat
 A diet rich in saturated fats may contribute to
cardiovascular disease through plaque deposits
 Hydrogenation is the process of converting
unsaturated fats to saturated fats by adding
hydrogen
 Hydrogenated oils – unsaturated oils that
have been chemically saturated so they will
be solid at room temperature (Crisco)
 Hydrogenating vegetable oils also creates
unsaturated fats with trans double bonds
 These trans fats may contribute more than
saturated fats to cardiovascular disease
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11
Trans Fats
 Hydrogenation is the process of adding
hydrogen to the unsaturated and
polyunsaturated oils to saturate them.
 This process can also create unsaturated fats
that now have a different configuration than the
original oil
 Labeled “partially hydrogenated oil”
Fats and Health
 Heart disease is caused by plaque collecting
in the blood vessels leading to the heart.
 Cholesterol in the blood leads to more plaque
building up in the vessels.
 LDL (bad cholesterol) – transports cholesterol to
the heart
 HDL (good cholesterol) – transports cholesterol
away from the heart
Fatty acids and Cholesterol
 Trans fats – worst type of fat, raise the bad
cholesterol (LDL) and lower the good cholesterol
(HDL)
 Saturated fats raise the bad cholesterol
 Sources = animal fats, dairy products, and some plant
oils (palm and coconut)
 Polyunsaturated fats – do not raise the bad
cholesterol but slightly lower good cholesterol
 Sources – many vegetable oils (corn and
safflower)
 Monounsaturated fats – do not increase either
 Sources – olive, canola and peanut oils;
avocado
Essential fatty acids
 Certain unsaturated fatty acids are not synthesized
in the human body
 These must be supplied in the diet
 These essential fatty acids include the omega-3
fatty acids, required for normal growth, and thought
to provide protection against cardiovascular
disease
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12
Omega-3 Fats
Function of Triglycerides
 Omega-3s are a type of unsaturated fat
 This fat has a carbon double bond located
three carbons from the end (end = omega)
 This is the healthiest type of fat
 Protect against heart disease by reducing bad
cholesterol
 Sources – fatty fish (salmon, tuna), walnuts
 The major function of fats is energy storage
 Humans and other mammals store their fat in
adipose cells
 Adipose tissue also cushions vital organs and
insulates the body
© 2011 Pearson Education, Inc.
Which of these fats are the least healthy?
25% 25% 25% 25%
25% 25% 25% 25%
 Function
ed
t
fa
tu
ra
t
Sa
ra
te
d
3
Tr
an
s
ra
te
d
un
sa
tu
Po
ly
O
m
eg
a
m
O
II. Lipid - Phospholipids
un
sa
tu
ed
t
fa
tu
ra
t
Sa
ra
te
d
Tr
an
s
Polyunsaturated
Omega 3 unsaturated
Trans fat
Saturated
3
Po
ly
un
sa
tu
ra
te
d
1.
2.
3.
4.
eg
a
Polyunsaturated
Omega 3 unsaturated
Trans fat
Saturated
un
sa
tu
1.
2.
3.
4.
Which type of fatty acid does not contain a double
bond?
II. Lipid - Phospholipids
 Phospholipids are amphiphathic
 Backbone of cell membranes
 Similar structure as triglycerides but have:




Glycerol
2 fatty acids
Phosphate group (negatively charged)
R group
 Phosphate end of molecule soluble in water hydrophilic.
 Lipid (fatty acid) end is not soluble in water hydrophobic.
13
Figure 5.12
Hydrophilic head
Phospholipid’s role in memebranes
Choline
Phosphate
Hydrophobic tails
Glycerol
Fatty acids
Hydrophilic
head
 When phospholipids are added to water, they
self-assemble into a bilayer, with the
hydrophobic tails pointing toward the interior
 The structure of phospholipids results in a
bilayer arrangement found in cell membranes
 Phospholipids are the major component of all
cell membranes
Hydrophobic
tails
(a) Structural formula
(b) Space-filling model
(c) Phospholipid symbol
© 2011 Pearson Education, Inc.
Figure 5.13
III. Lipid - Carotenoids
 Consist of isoprene units
Hydrophilic
head
Hydrophobic
tail
Isoprene-derived
compounds
WATER




Orange and yellow plant pigments
Classified with lipids
Some play a role in photosynthesis
Animals convert to vitamin A
WATER
IV. Lipids - Steroids
 Structure: Four fused rings
 Examples: cholesterol, bile salts, reproductive
hormones, cortisol
14
Steroids - Functions
IV. Lipids - Steroids
 Unlike triglycerides and phospholipids, steroids
have no fatty acids
 Functions include
 Hormones - Signaling within and between cells
(estrogen, testosterone, cortisol)
 Structure is a four ring backbone, with side chains
attached
 Cholesterol – Important part of cell membrane
 Bile salts - Emulsify fat in small intestine
Figure 5.14 Cholesterol
V. Lipids - Waxes
 Covers surface of leaves of plants.
 Functions
 Minimizes water loss from leaves to air.
 Barrier against entrance of bacteria and
parasites into leaves of plants.
This type of lipid is an important component of
membranes
1. Triglycerides
2. Phospholipids
3. Waxes
33%
33%
33%
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
ax
es
W
li p
id
s
ho
sp
ho
P
Tr
ig
ly
c
er
id
es
 Protein functions include structural support,
storage, transport, cellular communications,
movement, and defense against foreign
substances
© 2011 Pearson Education, Inc.
15
Proteins
Protein Functions - Enzymes
 Functions – numerous and varied – Page 78









Facilitate chemical reactions (enzymes)
Transport
Movement of muscles
Structure
Cell signaling - Hormones (insulin)
Nutrition
Defense
Components of cell membrane
Immune response
 Enzymes are a type of protein that acts as a
catalyst to speed up chemical reactions
 Enzymes can perform their functions
repeatedly, functioning as workhorses that carry
out the processes of life
© 2011 Pearson Education, Inc.
Enzymes
Substrate = the
thing that is being
changed in the
reaction
 Enzymes are proteins that catalyze reactions =
help reactions to happen – they speed up
chemical reactions
Active site = Place
in the enzyme
where the substrate
binds.
Product = The
end result
 They can only speed up reactions that would
happen eventually (may take years)
 They are usually specific for their substrates
 They are not consumed (destroyed) in the
process
 Some enzymes need cofactors to function.
Example = iron
Figure 5.15-a
Figure 5.15-b
Enzymatic proteins
Defensive proteins
Function: Selective acceleration of chemical reactions
Example: Digestive enzymes catalyze the hydrolysis
of bonds in food molecules.
Function: Protection against disease
Example: Antibodies inactivate and help destroy
viruses and bacteria.
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.
Antibodies
Enzyme
Virus
Bacterium
High
blood sugar
Insulin
secreted
Normal
blood sugar
Receptor
protein
Signaling
molecules
Storage proteins
Transport proteins
Contractile and motor proteins
Structural 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.
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.
Transport
protein
Actin
Myosin
Collagen
Ovalbumin
Amino acids
for embryo
Cell membrane
Muscle tissue
100 m
Connective
tissue
60 m
16
Polypeptides
Amino Acids
 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, each folded
and coiled into a three dimensional shape
 Proteins are made up of amino acids
 Amino acids are organic molecules with carboxyl
and amino groups
 There are 20 amino acids, each with a different
substitution for R.
© 2011 Pearson Education, Inc.
Figure 5.UN01
Ionized amino acid
Side chain (R group)
 carbon
Amino
group
Figure 5.16
Carboxyl
group
Ionized form
Figure 5.16a
Nonpolar side chains; hydrophobic
Side chain
(R group)
Glycine
(Gly or G)
Alanine
(Ala or A)
Methionine
(Met or M)
Valine
(Val or V)
Phenylalanine
(Phe or F)
Isoleucine
(Ile or I)
Leucine
(Leu or L)
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)
Electrically charged side chains; hydrophilic
Asparagine
(Asn or N)
Nonpolar side chains; hydrophobic
Side chain
Glycine
(Gly or G)
Alanine
(Ala or A)
Valine
(Val or V)
Leucine
(Leu or L)
Isoleucine
(Ile or I)
Glutamine
(Gln or Q)
Basic (positively charged)
Acidic (negatively charged)
Methionine
(Met or M)
Aspartic acid
(Asp or D)
Glutamic acid
(Glu or E)
Lysine
(Lys or K)
Arginine
(Arg or R)
Phenylalanine
(Phe or F)
Tryptophan
(Trp or W)
Proline
(Pro or P)
Histidine
(His or H)
17
Figure 5.16b
Figure 5.16c
Polar side chains; hydrophilic
Electrically charged side chains; hydrophilic
Basic (positively charged)
Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Acidic (negatively charged)
Aspartic acid
(Asp or D)
Tyrosine
(Tyr or Y)
Asparagine
(Asn or N)
Glutamic acid
(Glu or E)
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)
Glutamine
(Gln or Q)
Amino Acid Polymers
Figure 5.17
 Amino acids are linked by peptide bonds
 A polypeptide is a polymer of amino acids
Peptide bond
 Polypeptides range in length from a few to more
than a thousand monomers
New peptide
bond forming
Side
chains
 Each polypeptide has a unique linear sequence of
amino acids, with a carboxyl end (C-terminus) and
an amino end (N-terminus)
Backbone
Amino end
(N-terminus)
Peptide Carboxyl end
bond (C-terminus)
© 2011 Pearson Education, Inc.
Protein Structure and Function
Figure 5.18
 A functional protein consists of one or more
polypeptides precisely twisted, folded, and
coiled into a unique shape
Groove
Groove
(a) A ribbon model
(b) A space-filling model
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18
Protein Structure and Function
 The sequence of amino acids determines a
protein’s three-dimensional structure
 A protein’s structure determines its function
Four Levels of Protein Structure
 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 when a protein consists
of multiple polypeptide chains
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Figure 5.20a
Primary structure
Amino
acids
Amino end
Primary structure of transthyretin
Animation: Protein Structure Introduction
Right-click slide / select “Play”
Carboxyl end
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Primary Structure of Proteins
 Primary structure, the sequence of amino
acids in a protein, is like the order of letters in
a long word
 Primary structure is determined by inherited
genetic information
Animation: Primary Protein Structure
Right-click slide / select “Play”
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19
Secondary Structure of Proteins
 The coils and folds of secondary structure result
from hydrogen bonds between repeating
constituents of the polypeptide backbone
 Typical secondary structures are a coil called an 
helix and a folded structure called a  pleated
sheet
Animation: Secondary Protein Structure Rightclick slide / select “Play”
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Figure 5.20c
© 2011 Pearson Education, Inc.
Tertiary Structure of Proteins
Secondary structure
 Tertiary structure is determined by interactions
between R groups, rather than interactions
between backbone constituents
 helix
Hydrogen bond
 pleated sheet
 strand, shown as a flat
arrow pointing toward
the carboxyl end
Hydrogen bond
 These interactions between R groups include
hydrogen bonds, ionic bonds, hydrophobic
interactions, and van der Waals interactions
 Strong covalent bonds called disulfide bridges
may reinforce the protein’s structure
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Figure 5.20e
Tertiary structure
Animation: Tertiary Protein Structure
Right-click slide / select “Play”
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20
Figure 5.20f
Quaternary Structure of Proteins
 Quaternary structure results when two or more
polypeptide chains form one macromolecule
Hydrogen
bond
Hydrophobic
interactions and
van der Waals
interactions
Disulfide
bridge
Ionic bond
 Collagen is a fibrous protein consisting of three
polypeptides coiled like a rope
 Hemoglobin is a globular protein consisting of four
polypeptides: two alpha and two beta chains
Polypeptide
backbone
© 2011 Pearson Education, Inc.
Figure 5.20g
Figure 5.20i
Heme
Iron
 subunit
Quaternary structure
 subunit
four identical
polypeptides
 subunit
 subunit
Hemoglobin
Figure 5.20j
Animation: Quaternary Protein Structure
Right-click slide / select “Play”
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21
 A slight change in primary structure can affect a
protein’s structure and ability to function
Primary
Structure
Sickle-cell hemoglobin
 Sickle-cell disease, an inherited blood disorder,
results from a single amino acid substitution in the
protein hemoglobin
Figure 5.21
Normal hemoglobin
Sickle-Cell Disease: A Change in Primary Structure
1
2
3
4
5
6
7
Secondary
and Tertiary
Structures
Quaternary
Structure
Function
Normal
hemoglobin
 subunit

Red Blood
Cell Shape
Molecules do not
associate with one
another; each carries
oxygen.

10 m


1
2
3
4
5
6
7
Exposed
hydrophobic
region
Sickle-cell
hemoglobin
Molecules crystallize
into a fiber; capacity
to carry oxygen is
reduced.


 subunit
10 m


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What Determines Protein Structure?
Figure 5.22
 In addition to primary structure, physical and
chemical conditions can affect structure
tu
 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
Denatured protein
Normal protein
 A denatured protein is biologically inactive
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Protein Folding in the Cell
Figure 5.23
 It is hard to predict a protein’s structure from its
primary structure
Polypeptide
 Most proteins probably go through several stages on
their way to a stable structure
 Chaperonins or chaperones are protein molecules
that assist the proper folding of other proteins
 Diseases such as Alzheimer’s, Parkinson’s, and
mad cow disease are associated with misfolded
proteins
Correctly
folded
protein
Cap
Hollow
cylinder
Steps of Chaperonin2
Chaperonin
(fully assembled) Action:
1 An unfolded polypeptide enters the
cylinder from
one end.
3 The cap comes
The cap attaches, causing
the cylinder to change
off, and the
shape in such a way that properly folded
it creates a hydrophilic
protein is
environment for the
released.
folding of the polypeptide.
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22
Determining the Structure of Proteins
Figure 5.24
EXPERIMENT
Diffracted
X-rays
 Scientists use X-ray crystallography to determine
a protein’s structure
X-ray
source
X-ray
beam
Crystal
 Another method is nuclear magnetic resonance
(NMR) spectroscopy, which does not require
protein crystallization
Digital detector
X-ray diffraction
pattern
RESULTS
DNA
RNA
 Bioinformatics uses computer programs to predict
protein structure from amino acid sequences
RNA
polymerase II
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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
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
 Protein synthesis occurs on ribosomes
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Figure 5.25-1
Figure 5.25-2
DNA
1 Synthesis of
mRNA
DNA
1 Synthesis of
mRNA
mRNA
NUCLEUS
mRNA
NUCLEUS
CYTOPLASM
CYTOPLASM
mRNA
2 Movement of
mRNA into
cytoplasm
23
Figure 5.25-3
The Components of Nucleic Acids
DNA
1 Synthesis of
mRNA
 Nucleic acids are polymers called
polynucleotides
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into
cytoplasm
Ribosome
 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
3 Synthesis
of protein
Polypeptide
 Each polynucleotide is made of monomers called
nucleotides
Amino
acids
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Nucleotides
 Their functions include:
 Energy (ATP)
 Coenzymes that aid enzyme function (NAD+)
 Messengers within cells (GTP)
 Nucleotides consists of a sugar, phosphate
groups, and a base.
 There are 5 nucleotide bases:
 Adenine, Thymine, Uracil, Guanine, Cytosine
Nucleic Acids
Figure 5.26
Sugar-phosphate backbone
5 end
Nitrogenous bases
Pyrimidines
5 C
 Nucleic Acids are a chain or chains of
nucleotides
 The nucleotides are covalently bonded by
phosphodiester linkage between the
phosphates and sugars
3 C
Nucleoside
Nitrogenous
base
Cytosine (C)
Thymine (T, in DNA) Uracil (U, in RNA)
Purines
5 C
1 C
5 C
3 C
Phosphate
group
3 C
Sugar
(pentose)
Guanine (G)
Adenine (A)
(b) Nucleotide
Sugars
3 end
(a) Polynucleotide, or nucleic acid
Deoxyribose (in DNA)
Ribose (in RNA)
(c) Nucleoside components
24
Figure 5.26ab
Figure 5.26c
Sugar-phosphate backbone
5 end
Nitrogenous bases
5C
Pyrimidines
3C
Nucleoside
Nitrogenous
base
Cytosine
(C)
Thymine
(T, in DNA)
Uracil
(U, in RNA)
5C
Sugars
Purines
1C
5C
3C
Phosphate
group
3C
Sugar
(pentose)
(b) Nucleotide
3 end
Adenine (A)
Guanine (G)
Deoxyribose
(in DNA)
Ribose
(in RNA)
(c) Nucleoside components
(a) Polynucleotide, or nucleic acid
The Components of Nucleotides
 Nucleoside = nitrogenous base + sugar
 There are two families of nitrogenous bases
Nucleotide Polymers
 Nucleotides are linked together to build a
polynucleotide polymer
 Purines (adenine and guanine) have a sixmembered ring fused to a five-membered ring
 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 on the next
 In DNA, the sugar is deoxyribose; in RNA, the
sugar is ribose
 These links create a backbone of sugar-phosphate
units with nitrogenous bases as appendages
 Nucleotide = nucleoside + phosphate group
 The sequence of bases along a DNA or mRNA
polymer is unique for each gene
 Pyrimidines (cytosine, thymine, and uracil) have a
single six-membered ring
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The Structures of DNA and RNA Molecules
 RNA molecules usually exist as single polynucleotides
chains
 DNA molecules have two polynucleotides spiraling
around an imaginary axis, forming a double helix
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The Structures of DNA and RNA Molecules
 The nitrogenous bases in DNA pair up and form
hydrogen bonds: adenine (A) always with thymine
(T), and guanine (G) always with cytosine (C)
 Called complementary base pairing
 In the DNA double helix, the two backbones run in
opposite 5→ 3 directions from each other, an
arrangement referred to as antiparallel
 Complementary pairing can also occur between
two RNA molecules or between parts of the same
molecule
 One DNA molecule includes many genes
 In RNA, thymine is replaced by uracil (U) so A and
U pair
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
25
Figure 5.27
5
3
DNA and Proteins as Measures of Evolution
Sugar-phosphate
backbones
 The linear sequences of nucleotides in DNA
molecules are passed from parents to offspring
Hydrogen bonds
Base pair joined
by hydrogen
bonding
 Two closely related species are more similar in DNA
than are more distantly related species
 Molecular biology can be used to assess
evolutionary kinship
3
5
(a) DNA
Base pair joined
by hydrogen bonding
(b) Transfer RNA
© 2011 Pearson Education, Inc.
Fatty acids are joined to glycerol by what
kind of linkage?
25% 25% 25% 25%
te
r
Es
st
er
os
ph
od
ie
Ph
yc
os
i
di
c
Peptide
Gycosidic
Phosphodiester
Ester
pt
id
e
1.
2.
3.
4.
G
Figure 5.UN02b
Figure 5.UN02a
Pe
Figure 5.UN02
26
Important Concepts
Important Concepts
 Know the vocabulary of the lecture and reading
 What are the types of starches and what structure
stores starch?
 What are the different types of lipids and their
biological functions
 What are the different types of biological
molecules, their functions and be able to identify
their structures
 What are the types of carbohydrates and what
types of organisms they are found in, what are
their functions, identify their structures
 Be able to describe the differences in the
carbohydrates’ structures and the implications
these difference have on our ability to digest them
Important Concepts
 Be able to describe protein structure including
primary, secondary etc. Know what forces hold
alpha helixes and beta sheets together, know
the forces that help shape tertiary structure.
 Know examples of steroids and functions of
each type of steroids.
 What are enzymes, what is their function, what
are their properties, what are the active site, the
substrates, and the products.
 What are the types of dietary triglycerides and
which are healthy – know the order from healthiest
to least healthy
 What is the structure of amino acids, what bond
links amino acids together, how they link together.
Be able to draw and amino acid structure.
Important Concepts
 What is the structure of nucleotides, you should
be able to identify the bases but you don’t need
to draw their structure. What are nucleic acids
what are their functions. Know the examples of
nucleic acids and nucleotides
 Which molecules join together to form what
molecules (monomer and polymers) what are the
linkages called
27