Download Ch 5 Biomolc Strc & Fxn

Chapter 5
The Structure and Function of
Large Biological Molecules
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: The Molecules of Life
• Living things are made of four classes of large
biomolecules: carbohydrates, lipids, proteins,
and nucleic acids
• Macromolecules-large molecules made of
small organic molecules covalently bonded
together
• Molecular structure and function are
inseparable (form follows function)
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Concept 5.1: Macromolecules are polymers, built
from monomers
• Polymer- long molecule consisting of many
similar building blocks
• Monomers- small building-block molecules
• Three out of four classes of organic molecules
are polymers. They are:
– Carbohydrates
– Proteins
– Nucleic acids
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The Synthesis and Breakdown of Polymers
• Condensation reaction (also called
dehydration reaction)- when two monomers
bond together by losing a water molecule
• Hydrolysis- breaks down polymers to monomers
by adding a water molecule- (reverse process)
• Enzymes- macromolecules that speed up
chemical reactions
Animation: Polymers
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Fig. 5-2
HO
1
2
3
H
Short polymer
HO
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
HO
2
1
H
3
H2O
4
H
Longer polymer
(a) Dehydration reaction in the synthesis of a polymer
HO
1
2
3
4
Hydrolysis adds a water
molecule, breaking a bond
HO
1
2
3
(b) Hydrolysis of a polymer
H
H
H2O
HO
H
The Diversity of Polymers
• A variety of polymers can be built from a small
set of monomers
• So cells have thousands of different
macromolecules
• Macromolecules vary among cells in an
organism, vary more within a species, and even
more between species
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Concept 5.2: Carbohydrates serve as fuel and
building material
• Carbohydrates include sugars and polymers
of sugars
• Monosaccharides, or single sugars are the
simplest carbohydrates
• Polysaccharides are polymers composed of
many sugar building blocks or carbohydrate
macromolecules,
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Sugars
• Monosaccharide molecular formulas are
usually multiples of CH2O
• Glucose (C6H12O6) is the most common one
• Monosaccharides are classified by
– The location of the carbonyl group (as aldose
or ketose)
– The number of carbons in the carbon skeleton
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Fig. 5-3
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Glyceraldehyde
Ribose
Glucose
Galactose
Dihydroxyacetone
Ribulose
Fructose
• Aldose- has a carbonyl at the end
• Ketose- has a carbonyl in the middle
• Though drawn as linear skeletons, in aqueous
solutions many sugars form rings
• Monosaccharides are a major fuel for cells and
a raw material for building molecules
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Fig. 5-4
(a) Linear and ring forms
(b) Abbreviated ring structure
• Disaccharide- formed when a dehydration
reaction joins two monosaccharides
• Glycosidic linkage- a covalent bond between
two monosaccharides
• The structure and function of a polysaccharide
are determined by the sugar monomers in it
and the positions of glycosidic linkages
• Polysaccharides, the polymers of sugars,
have storage and structural roles
Animation: Disaccharides
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Fig. 5-5
1–4
glycosidic
linkage
Glucose
Glucose
Maltose
(a) Dehydration reaction in the synthesis of maltose
1–2
glycosidic
linkage
Glucose
Fructose
(b) Dehydration reaction in the synthesis of sucrose
Sucrose
Storage Polysaccharides
• Starch, a storage polysaccharide of plants,
made of glucose monomers only
• Plants store surplus starch as granules within
chloroplasts and other plastids
• Glycogen is a storage polysaccharide in
animals
• Humans and other vertebrates store glycogen
mainly in liver and muscle cells
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Fig. 5-6
Chloroplast
Mitochondria Glycogen granules
Starch
0.5 µm
1 µm
Glycogen
Amylose
Amylopectin
(a) Starch: a plant polysaccharide
(b) Glycogen: an animal polysaccharide
Structural Polysaccharides
• Cellulose is a structural polysaccharide, a
major component of tough plant cell walls
• Cellulose also is a polymer of glucose, but the
glycosidic linkages are different
• The difference is based on two ring forms for
glucose: alpha () and beta ()
Animation: Polysaccharides
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Fig. 5-7
(a) α and β
glucose
ring structures
α Glucose
(b) Starch: 1–4 linkage of α glucose
monomers
β Glucose
(b) Cellulose: 1–4 linkage of β glucose
monomers
• Polymers with  glucose are helical
• Polymers with  glucose are straight
• In straight, , structures, H atoms on one
strand bond with OH groups on other strands
• So, parallel cellulose molecules held together
group into microfibrils, which form strong
building materials for plants
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Fig. 5-8
Cell walls
Cellulose
microfibrils
in a plant
cell wall
Microfibril
10 µm
0.5 µm
Cellulose
molecules
b Glucose
monomer
• Enzymes that digest starch by hydrolyzing 
linkages can’t hydrolyze  linkages in cellulose
• So, cellulose in human food passes through
the digestive tract as insoluble fiber
• Many herbivores, like cows, have symbiotic
relationships with microbes that use enzymes
to digest cellulose
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• Chitin is a structural polysaccharide found in
the exoskeleton of arthropods and the cell
walls of fungi
(a) The structure of
the chitin monomer
(b) Chitin forms the exoskeleton of arthropods
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(c) Chitin used as strong
flexible surgical
thread
Concept 5.3: Lipids are a diverse group of
hydrophobic molecules
• Lipids- the only large biomolecule class that
can’t form polymers
• ALL lipids have little or no affinity for water
• Lipids are made of hydrocarbons which form
nonpolar covalent bonds, making lipids
hydrophobic
• The most important lipids are fats,
phospholipids, and steroids
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Fats
• Fats- made from glycerol and fatty acids
• Glycerol- three-carbon alcohol with a hydroxyl
group attached to each carbon
• Fatty acid- carboxyl group attached to a long
carbon skeleton
• Fats separate from water because water
molecules form hydrogen bonds & exclude fats
• Fats are three fatty acids joined to glycerol by an
ester linkage, making a triacylglycerol or
triglyceride
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Fig. 5-11
Fatty acid
(palmitic acid)
Glycerol
(a) Dehydration reaction in the synthesis of a fat
Ester linkage
(b) Fat molecule (triacylglycerol)
• An ester linkage is a Carbon-to-Oxygen-toCarbon series of covalent bonds
• Fatty acids vary in length (number of carbons)
and 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
Animation: Fats
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-12a
Structural
formula of a
saturated fat
molecule
Stearic acid, a
saturated fatty
acid
(a) Saturated fat
Fig. 5-12b
Structural formula
of an unsaturated
fat molecule
Oleic acid, an
unsaturated
fatty acid
(b) Unsaturated fat
cis double
bond causes
bending
• Saturated fats- made from saturated fatty acids;
solid at room temperature
– Most animal fats are saturated
• Unsaturated fats (oils)- made from unsaturated
fatty acids; liquid at room temperature
– Plant fats and fish fats are usually unsaturated
• Diets rich in saturated fats may cause
cardiovascular disease through plaque deposits
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• Hydrogenation adds hydrogen to unsaturated fats
– changes unsaturated fats to saturated fats
– makes unsaturated fats with trans double bonds
• These trans fats may contribute more than
saturated fats to cardiovascular disease!!
• Humans & mammals store fat in adipose cells
• The major function of fats is energy storage
• Adipose tissue also cushions vital organs and
insulates the body
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Phospholipids
• Phospholipid- two fatty acids and a
phosphate group attached to glycerol
• The two fatty acid tails are hydrophobic, but the
phosphate group and its attachments form a
hydrophilic head
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Hydrophobic tails
Hydrophilic head
Fig. 5-13
(a) Structural formula
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic
head
Hydrophobic
tails
(b) Space-filling model
(c) Phospholipid symbol
• Phospholipids are the major component of all
cell membranes
– Added to water, they self-assemble into a
bilayer, with hydrophobic tails pointing inward.
– Thus the structure results in the bilayer
arrangement seen in cell membranes
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Fig. 5-14
Hydrophilic
head
Hydrophobic
tail
WATER
WATER
Steroids
• Steroids- lipids having a carbon skeleton
consisting of four fused rings
• Cholesterol- important steroid component in
animal cell membranes; stabilizes membranes
• Cholesterol is essential in animals, but high
levels in the blood may contribute to
cardiovascular disease
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Fig. 5-15
Notice the similarity in ring structure between cholesterol and the
hormones estradiol & testosterone.
Concept 5.4: Proteins have many structures,
resulting in a wide range of functions
• Proteins are more than 50% of the dry mass of
most cells
• Protein functions include
–
–
–
–
–
–
structural support
storage
transport
cellular communications
movement
defense against foreign substances
• A protein consists of one or more polypeptides
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Animation: Structural Proteins
Animation: Storage Proteins
Animation: Transport Proteins
Animation: Receptor Proteins
Animation: Contractile Proteins
Animation: Defensive Proteins
Animation: Hormonal Proteins
Animation: Sensory Proteins
Animation: Gene Regulatory Proteins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Polypeptides are polymers built from a set of
20 amino acids.
• Enzymes are a type of protein (polypeptide)
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
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Fig. 5-16
Substrate
(sucrose)
Glucose
OH
Fructose
HO
Enzyme
(sucrase)
H2O
Amino Acid Monomers
• Amino acids- organic molecules with carboxyl
and amino groups
• Their properties differ due to differing side
chains, called R groups
• There are 20 amino acids
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Fig. 5-UN1
α carbon
Amino
group
Carboxyl
group
Fig. 5-17a
Nonpolar
Glycine
(Gly or G)
Methionine
(Met or M)
Alanine
(Ala or A)
Valine
(Val or V)
Phenylalanine
(Phe or F)
Leucine
(Leu or L)
Tryptophan
(Trp or W)
Isoleucine
(Ile or I)
Proline
(Pro or P)
Fig. 5-17b
Polar
Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Tyrosine
(Tyr or Y)
Asparagine Glutamine
(Asn or N) (Gln or Q)
Fig. 5-17c
Electrically
charged
Acidic
Aspartic acid Glutamic acid
(Glu or E)
(Asp or D)
Basic
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)
Amino Acid Polymers
• Amino acids are linked by peptide bonds to
make polypeptides
• Polypeptide- polymer of amino acids, range in
length from few to over a thousand monomers
• Each has a unique linear amino acid sequence
• All proteins are polypeptides
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Fig. 5-18
Peptide
bond
(a)
Side chains
Peptide
bond
Backbone
(b)
Amino end
(N-terminus)
Carboxyl end
(C-terminus)
Protein Structure and Function
• Functional proteins are one or more polypeptides
twisted, folded, and coiled into a unique shape
• A protein’s amino acid sequence determines its
three-dimensional structure
• The structure determines its function (form follows
function)
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Fig. 5-19
Groove
Groove
(a) A ribbon model of lysozyme
(b) A space-filling model of lysozyme
Fig. 5-20
Antibody protein
Protein from flu virus
Four Levels of Protein Structure
• Primary- the unique sequence of amino acids
• Secondary- coils & folds in polypeptide chain
• Tertiary- due to interactions among various
side chains (R groups)
• Quaternary- seen when a protein is made of
multiple polypeptide chains
• Primary structure is like the order of letters in
a long word and is due to inherited genetic
information
Animation: Protein Structure Introduction
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Animation: Primary Protein Structure
Fig. 5-21a
Primary Structure
1
+H
5
3N
Amino end
10
Amino acid
subunits
15
20
25
• Secondary structure coils and folds result
from hydrogen bonds between repeating parts
of the polypeptide backbone
Examples:
–  helix- a coil
–  pleated sheet- a folded structure
Animation: Secondary Protein Structure
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-21c
Secondary Structure
β pleated sheet
Examples of
amino acid
subunits
α helix
• Tertiary structure is due to interactions
between R groups (not backbone constituents)
– R group interactions include hydrogen and
ionic bonds, also hydrophobic and van der
Waals interactions
– Disulfide bridges are strong covalent bonds
that reinforce the protein’s structure
• Quaternary structure- two or more
polypeptide chains form one macromolecule
Animation: Tertiary Protein Structure
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Fig. 5-21e
Tertiary Structure
Quaternary Structure
Coils or sheets due to Rgroup interactions
Protein subunits of an enzyme held
together by hydrogen bonds,
disulfide,Van der Waals forces, etc.
Fig. 5-21f
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Ionic bond
Fig. 5-21g
Polypeptide
chain
α Chains
Iron
Heme
β Chains
Hemoglobin
Collagen
Collagen- fibrous protein
made of three polypeptides
coiled like a rope
Hemoglobin- globular protein made
of four polypeptides: two alpha and
two beta chains
Animation: Quaternary Protein Structure
Sickle-Cell Disease: A Change in Primary Structure
• Small changes in primary structure can affect
protein structure and ability to function
• Sickle-cell disease, an inherited blood disorder,
results from a single amino acid substitution in
the protein hemoglobin
10 µm
10 µm
Normal red blood
cells are full of
individual
hemoglobin
molecules, each
carrying oxygen.
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Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.
Normal hemoglobin
Primary
structure
Sickle-cell hemoglobin
Primary
structure
Val His Leu Thr Pro Glu Glu
1
2
3
Secondary
and tertiary
structures
4
5
6
7
subunit
Secondary
and tertiary
structures
Val His Leu Thr Pro Val Glu
1
2
3
Exposed
hydrophobic
region
Quaternary
structure
Normal
hemoglobin
(top view)
Quaternary
structure
Sickle-cell
hemoglobin
Function
Molecules do
not associate
with one
another; each
carries oxygen.
Function
Molecules
interact with
one another and
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.
10 µm
Red blood
cell shape
Normal red blood
cells are full of
individual
hemoglobin
moledules, each
carrying oxygen.
4
5
6
7
subunit
10 µm
Red blood
cell shape
Fig. 5-22
Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.
What Determines Protein Structure?
• Denaturation- loss of a protein’s native structure
– Changes in pH, salt concentration, temperature,
or other environmental factors can cause a
protein to unravel
– A denatured protein is biologically inactive
Denaturation
Normal
protein
Denatured
protein
Renaturation
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Fig. 5-23
Protein Folding in the Cell
• Chaperonins are protein molecules that assist the proper
folding of other proteins
Correctly
folded
protein
Cap
Polypeptide
Hollow
cylinder
Chaperonin
(fully assembled)
Fig. 5-24
Steps of Chaperonin
Action:
1
An unfolded
poly-peptide
enters the
cylinder
from one end.
2
The cap attaches,
causing the cylinder
to change shape in
such a way that it
creates a hydrophilic
environment for
the folding of the
polypeptide.
3
The cap comes
off, and the
properly
folded protein
Is released.
Determining Shapes in the Cell
• To determine protein structure, scientists use:
– X-ray crystallography
– nuclear magnetic resonance (NMR)
spectroscopy, (doesn’t require protein
crystallization)
– Bioinformatics- uses computer programs to
predict structure from amino acid sequences
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Fig. 5-25
EXPERIMENT
Diffracted
X-rays
X-ray
source X-ray
beam
Crystal
Digital detector
X-ray diffraction
pattern
RESULTS
RNA
polymerase II
DNA
RNA
Concept 5.5: Nucleic acids store and transmit
hereditary information
• Genes program the amino acid sequence of a
polypeptide
• Genes are made of DNA, a nucleic acid
• 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 in ribosomes
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Fig. 5-26-3
DNA
1 Synthesis of
mRNA in the
nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into cytoplasm
via nuclear pore
Ribosome
3 Synthesis
of protein
Polypeptide
Amino
acids
The Structure of Nucleic Acids
• Nucleic acids- polymers called polynucleotides
• Polynucleotides are made of monomers called
nucleotides which consist of:
– nitrogenous base
– pentose sugar
– a phosphate group
• Nucleoside- a nucleotide lacking the phosphate
group (base & sugar, only)
• Nucleoside = nitrogenous base + sugar
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Fig. 5-27
5
end
Nitrogenous bases
Pyrimidines
5 C
3 C
Nucleoside
Nitrogenous
base
Cytosine (C)
Thymine (T, in DNA) Uracil (U, in RNA)
Purines
Phosphate
group
5 C
Sugar
(pentose)
Adenine (A)
Guanine (G)
(b) Nucleotide
3 C
Sugars
3
end
(a) Polynucleotide, or nucleic acid
Deoxyribose (in DNA)
Ribose (in RNA)
(c) Nucleoside components: sugars
Nucleotide Monomers
• Nucleotide = nucleoside + phosphate group
• There are two families of nitrogenous bases:
– Pyrimidines (cytosine, thymine, and uracil)
have a single six-membered ring
– Purines (adenine and guanine) have a sixmembered ring fused to a five-membered ring
• In DNA, the sugar is deoxyribose
• In RNA, the sugar is ribose
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Nucleotide Polymers
• Nucleotide polymers link up to make
polynucleotides
• Nucleotides join by covalent bonds between the
–OH group on the 3 carbon of one nucleotide
and the phosphate on the 5 carbon of the next
• The links make a backbone of sugar-phosphate
units with nitrogen bases as appendages
• The sequence of bases on DNA or mRNA
polymers is unique to each gene
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The DNA Double Helix
• A DNA molecule has two polynucleotide strands
spiraling around each other, making a double helix
• The backbones of the two strands run in opposite
5 → 3 directions from each other, or antiparallel
• One DNA molecule has many genes
• Nitrogen bases in DNA pair up forming hydrogen
bonds:
– adenine (A) with thymine (T)
– guanine (G) with cytosine (C)
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Fig. 5-28
5' end
3' end
Sugar-phosphate
backbones
Base pair (joined by
hydrogen bonding)
Old strands
Nucleotide
about to be
added to a
new strand
3' end
5' end
New
strands
5' end
3' end
5' end
3' end
DNA and Proteins as Tape Measures of Evolution
• DNA nucleotide sequences are passed from
parents to offspring
• Two closely related species have more similar
DNA than more distantly related species
• Molecular biology can be used to assess
evolutionary kinship
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Emergent Properties in the Chemistry of Life
• Higher levels of organization cause the
emergence of new properties
• Organization is the key to the chemistry of life
• Form follows function- as seen in the shapes of
the macromolecules seen here
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