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Chapter 5:
The Structure and
Function of Large
Biological Molecules
Four classes of organic molecules:
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids
Organic molecules exhibit emergent properties
Macromolecules are polymers
• Polymers = large molecule consisting of smaller,
nearly identical molecules joined together
• Monomer = the small molecules used to build a
polymer
Figure 5.2
(a) Dehydration reaction: synthesizing a polymer
1
2
3
Short polymer
Unlinked monomer
Dehydration removes
a water molecule,
forming a new bond.
1
2
3
4
Longer polymer
(b) Hydrolysis: breaking down a polymer
1
2
3
Hydrolysis adds
a water molecule,
breaking a bond.
1
2
3
4
Carbohydrates
• Group includes sugars and polymers of sugars
• Monomer = monosaccharide
• Polymer = polysaccharide
Monosaccharides
• Simple sugars
• Usually a multiple of a general molecular formula CH2O
(e.g. C6H12O6)
• Contain hydroxyl and carbonyl functional groups
• Carbon skeletons vary in length from 3 to 7 carbons
• Important as fuel for cells
Figure 5.3
Aldoses (Aldehyde Sugars)
Ketoses (Ketone Sugars)
Trioses: 3-carbon sugars (C3H6O3)
Glyceraldehyde
Dihydroxyacetone
Pentoses: 5-carbon sugars (C5H10O5)
Ribose
Ribulose
Hexoses: 6-carbon sugars (C6H12O6)
Glucose
Galactose
Fructose
Figure 5.4
1
2
6
6
5
5
3
4
4
5
1
3
6
(a) Linear and ring forms
6
5
4
1
3
2
(b) Abbreviated ring structure
2
4
1
3
2
Disaccharides
• Two monosaccharides joined together
• Dehydration reaction
• Examples:
• Maltose (glucose + glucose)
• Sucrose (glucose + fructose)
Figure 5.5
1–4
glycosidic
1 linkage 4
Glucose
Glucose
Maltose
(a) Dehydration reaction in the synthesis of maltose
1–2
glycosidic
1 linkage 2
Glucose
Fructose
(b) Dehydration reaction in the synthesis of sucrose
Sucrose
Polysaccharides
• Long chains of monosaccharides
• Function in energy storage and/or structure
• Starch: energy storage in plants
• Glycogen: energy storage in animals
• Cellulose: structural in plants
Figure 5.6
Chloroplast
Starch granules
Amylopectin
Amylose
(a) Starch:
1 m
a plant polysaccharide
Mitochondria
Glycogen granules
Glycogen
(b) Glycogen:
0.5 m
an animal polysaccharide
Figure 5.7
(a)  and  glucose
ring structures
4
1
4
 Glucose
 Glucose
1 4
(b) Starch: 1–4 linkage of  glucose monomers
1
1 4
(c) Cellulose: 1–4 linkage of  glucose monomers
Figure 5.8
Cellulose
microfibrils in a
plant cell wall
Cell wall
Microfibril
10 m
0.5 m
Cellulose
molecules
 Glucose
monomer
Lipids
• Not a true polymer
• Three categories
1. Fats/Oils (triglycerides)
2. Phospholipids
3. Waxes
Figure 5.10
Fatty acid
(in this case, palmitic acid)
Glycerol
(a) One of three dehydration reactions in the synthesis of a fat
Ester linkage
(b) Fat molecule (triacylglycerol)
Figure 5.11
(a) Saturated fat
Structural
formula of a
saturated fat
molecule
Space-filling
model of stearic
acid, a saturated
fatty acid
(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.
Hydrophobic tails
Hydrophilic head
Figure 5.12
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic
head
Hydrophobic
tails
(a) Structural formula
(b) Space-filling model
(c) Phospholipid symbol
Fig. 5-14
Lipid Bilayer
Hydrophilic
head
Hydrophobic
tail
WATER
WATER
Waxes
• One fatty acid connected to a glycerol
• More hydrophobic than fats
Fig. 5-15
Cholesterol: The steroid precursor
Proteins
• Function determined by 3-D shape (important!)
• Monomer = amino acid
• Polymer = polypeptide (protein = functional)
Figure 5.15_a
Proteins: Categorized based on function
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.
Antibodies
Enzyme
Virus
Bacterium
Storage proteins
Transport proteins
Function: Storage of amino acids
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.
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.
Transport
protein
Ovalbumin
Amino acids
for embryo
Cell membrane
Figure 5.15_b
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.
High
blood sugar
Insulin
secreted
Normal
blood sugar
Receptor
protein
Signaling
molecules
Contractile and motor proteins
Structural proteins
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.
Actin
Myosin
Collagen
Muscle tissue
100 m
Connective
tissue
60 m
Figure 5.UN01
Generic Amino Acid Structure
Side chain (R group)
 carbon
Amino
group
Carboxyl
group
Figure 5.16
Nonpolar side chains; hydrophobic
Side chain
(R group)
Glycine
(Gly or G)
R group
(side chain)
properties
Alanine
(Ala or A)
Methionine
(Met or M)
Isoleucine
(Ile or I)
Leucine
(Leu or L)
Valine
(Val or V)
Phenylalanine
(Phe or F)
Tryptophan
(Trp or W)
Proline
(Pro or P)
Polar side chains; hydrophilic
Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Electrically charged side chains; hydrophilic
Tyrosine
(Tyr or Y)
Asparagine
(Asn or N)
Glutamine
(Gln or Q)
Basic (positively charged)
Acidic (negatively charged)
Aspartic acid
(Asp or D)
Glutamic acid
(Glu or E)
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)
Figure 5.17
Peptide Bond
Formation
Peptide bond
New peptide
bond forming
Side
chains
Backbone
Amino end
(N-terminus)
Peptide
bond
Carboxyl end
(C-terminus)
Four levels of protein structure
• Primary
• Secondary
• Tertiary
• Quaternary
Figure 5.20a
Primary structure
Amino
acids
Amino end
Primary structure of transthyretin
Carboxyl end
Figure 5.20c
Secondary structure
 helix
 pleated sheet
Hydrogen bond
 strand, shown as a flat
arrow pointing toward
the carboxyl end
Hydrogen bond
Figure 5.20b
Tertiary
structure
Secondary
structure
Quaternary
structure
 helix
Hydrogen bond
 pleated sheet
 strand
Hydrogen
bond
Transthyretin
polypeptide
Transthyretin
protein
Figure 5.20f
Hydrogen
bond
Hydrophobic
interactions and
van der Waals
interactions
Disulfide
bridge
Ionic bond
Polypeptide
backbone
Fig. 5-21g
Polypeptide
chain
 Chains
Iron
Heme
 Chains
Hemoglobin
Collagen
Fig. 5-23
Denaturation
Normal protein
Renaturation
Denatured protein
Proteins can denature (lose shape)
• High temperature
• High/Low pH
• Variation in salt
concentration
Figure 5.21
Sickle-cell hemoglobin
Normal hemoglobin
Primary
Structure
1
2
3
4
5
6
7
Secondary
and Tertiary
Structures
Quaternary
Structure
Function
Molecules do not
associate with one
another; each carries
oxygen.
Normal
hemoglobin
 subunit

Red Blood
Cell Shape

10 m


1
2
3
4
5
6
7
Exposed
hydrophobic
region
Sickle-cell
hemoglobin

 subunit

Molecules crystallize
into a fiber; capacity
to carry oxygen is
reduced.


10 m
Nucleic Acids
• Monomer = nucleotide
• Polymer = polynucleotide (nucleic acid)
• Blueprints for proteins
• 2 types
• DNA – Deoxyribonucleic Acid
• RNA – Ribonucleic Acid
Figure 5.25-3
DNA
1 Synthesis of
mRNA
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into
cytoplasm
Ribosome
3 Synthesis
of protein
Polypeptide
Amino
acids
Figure 5.26
5 end
Sugar-phosphate backbone
Nitrogenous bases
Pyrimidines
5C
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)
(c) Nucleoside components
Ribose (in RNA)
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
Figure 5.UN02