The Structure and Function of MacromoleculesOct 05, 2012 · LE 5-3 Triose sugars (C 3 H 6 O 3)...
Transcript of The Structure and Function of MacromoleculesOct 05, 2012 · LE 5-3 Triose sugars (C 3 H 6 O 3)...
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 5
The Structure and Function of
Macromolecules
PowerPoint lectures are originally from Campbell / Reece
Media Manager and Instructor Resources for BIOLOGY,
7th & 8th Edition by N. A. Campbell & J. B. Reece
Copyright 2005 & 2008 Pearson Education, Inc. Publishing
as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Molecules of Life
• The four classes of macromolecules that are
important to life are:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Most macromolecules are polymers, built from monomers
• Three of the four classes of life’s organic molecules are polymers:
– Carbohydrates
– Proteins
– Nucleic acids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Macromecules are made of monomers
• Carbohydrates, Proteins, and Nucleic Acids are all
polymers made from building blocks. Building blocks can
be called monomers
Macromolecule Type
Carbohydrate Protein Nucleic Acid (DNA and RNA)
Name of
Monomer
monosaccharide Amino acid nucleotides
monomer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Synthesis of Polymers by DEHYDRATION REACTIONS
• Monomers form larger
molecules called polymers
by condensation reactions
called dehydration
reactions.
• A dehydration reaction
occurs when two monomers
bond together through the
loss of a water molecule
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Dehydration removes a water molecule, forming a new bond
Short polymer Unlinked monomer
Longer polymer
Dehydration reaction in the synthesis of a polymer
HO
HO
HO
H2O
H
H H
4 3 2 1
1 2 3
(a)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Breakdown of Polymers by HYDOLYSIS REACTIONS
• Polymers are disassembled to monomers
by hydrolysis, a reaction that is essentially
the reverse of the dehydration reaction.
• In hydrolysis, bonds are broken by the
addition of water molecules.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fig. 5-2b
Hydrolysis adds a water
molecule, breaking a bond
Hydrolysis of a polymer
HO
HO HO
H2O
H
H
H 3 2 1
1 2 3 4
(b)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 5.2: Carbohydrates serve as fuel and building material
• Carbohydrates include single (simple) sugars and
their polymers
• Carbohydrates may be classified as:
– Monosaccharides (the simplest)
– Disaccharides
– Polysaccharides
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Monosaccharides
• Monosaccharides have molecular formulas that
are usually multiples of CH2O
(CH2O)n where n ranges from 1-7
• Glucose (C6H12O6) is the most common
monosaccharide.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Monosaccharides
• Monosaccharides have two
functional groups:
1- One carbonyl group that is either:
– An aldehyde group OR
– a ketone group
2- Many hydroxyl groups.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Monosaccharides
• Monosaccharides are classified by:
– The specific type of the carbonyl group:
• Aldoses
• ketoses
– and the number of carbons in the carbon skeleton:
• Trioses (3 Carbons)
• Tetroses (4 Carbons)
• Pentoses (5 Carbons)
• Hexoses (6 Carbons)
• Heptoses (7 Carbons)
LE 5-3 Triose sugars
(C3H6O3)
Glyceraldehyde
Pentose sugars
(C5H10O5)
Ribose
Hexose sugars
(C5H12O6)
Glucose Galactose
Dihydroxyacetone
Ribulose
Fructose
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Monosaccharides
• Functions of monosaccharides:
– major fuel (source of energy) for cells and
– raw material for building other molecules such
as fatty acids and amino acids.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Monosaccharides
• Though often drawn as a linear skeleton, in
aqueous solutions they form rings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
alpha and Beta Forms of Glucose
• There are two interconvertible forms of glucose
that differ in the placement of the hydroxyl
group attached to the number 1 carbon in the
ring form of glucose.
• These forms are α-glucose and β-glucose.
α-Glucose β-Glucose
Glucose
Maltose
Fructose Sucrose
Glucose Glucose
Dehydration
reaction in the
synthesis of maltose
Dehydration
reaction in the
synthesis of sucrose
1–4 glycosidic
linkage
1–2 glycosidic
linkage
• A disaccharide is formed when a dehydration reaction joins
two monosaccharides
• The covalent bond joining two monosaccharides is called a
glycosidic linkage
Disaccharides
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Polysaccharides
• Polymers of monosaccharides
• Based on their function, there are two types of
polysaccharides:
– Storage polysaccharides.
– Structural polysaccharides.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Storage Polysaccharides
• Store glucose and are hydrolyzed as needed to
provide sugar for cells.
• Examples on storage polysaccharides:
– Starch in Plants
– Glycogen in animals
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.6b
Mitochondria Glycogen granules
0.5 m
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Starch (A Storage Polysaccharides in Plants)
• Starch is a carbohydrate polymer consists
entirely of α-glucose monomers.
• Starch is a storage polysaccharide in plants.
• Two types of starch:
– Amylose is the unbranched polymer.
– Amylopectin is the branched polymer.
LE 5-6a Chloroplast Starch
1 µm
Amylose
Starch: a plant polysaccharide
Amylopectin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glycogen (A Storage Polysaccharides in Animals)
• Glycogen is a storage polysaccharide in
animals
• Humans and other vertebrates store
glycogen mainly in liver and muscle cells
Glycogen: an animal polysaccharide
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Structural Polysaccharides
• 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
• The difference is based on two ring forms for
glucose: alpha () and beta ()
© 2011 Pearson Education, Inc.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cell wall
Microfibril
Cellulose microfibrils in a plant cell wall
Cellulose molecules
Glucose monomer
10 m
0.5 m
Figure 5.8
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Enzymes that digest starch by hydrolyzing alpha
linkages can’t hydrolyze beta linkages in cellulose
• Humans can’t digest cellulose. Cellulose in
human food passes through the digestive tract as
insoluble fiber
• Some microbes use enzymes to digest cellulose
• Many herbivores, from cows to termites, have symbiotic relationships with these
microbes
Cellulose Digestion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chitin (A Structural Polysaccharides)
• Chitin is found in the
exoskeleton of
arthropods
• Chitin also provides structural support for the cell walls of many fungi
• Chitin can be used as
surgical thread
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.9b
Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 5.3: Lipids are a diverse group of hydrophobic molecules
• Lipids are the one class of large biological
molecules that do not form polymers
• The unifying feature of lipids is having little or
no affinity for water (Hydrophobic)
• Lipids are hydrophobic becausethey consist
mostly of hydrocarbons, which form nonpolar
covalent bonds
© 2011 Pearson Education, Inc.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Lipids
• The most biologically important lipids are:
– fats
– Phospholipids
– steroids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fats
• Fats are constructed from one glycerol
and three fatty acid molecules
• Glycerol is a three-carbon alcohol with a
hydroxyl group attached to each carbon
• A fatty acid consists of a carboxyl group
attached to a long hydrocarbon skeleton
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.10
(a) One of three dehydration reactions in the synthesis of a fat
(b) Fat molecule (triacylglycerol)
Fatty acid (in this case, palmitic acid)
Glycerol
Ester linkage
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Fatty Acids
Alpha linolenic acid (ALA) An Omega-3
f.a. and the parent of other omega-3 f.as
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fats (Saturated fats)
• Fats made from saturated fatty acids are called saturated fats
• Most animal fats are saturated
• Saturated fats are solid at room temperature
• A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fats (Unsaturated fats)
• Fats made from unsaturated fatty acids are called
unsaturated fats
• Plant fats and fish fats are usually unsaturated
• Plant fats and fish fats are liquid at room
temperature and are called oils
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fats
• Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Trans Fatty Acids
• Hydrogenation is the process of
converting unsaturated fats to
saturated fats by adding
hydrogen
• Hydrogenating vegetable oils
also creates unsaturated fats
with trans double bonds
• These trans fats may contribute
more than saturated fats to
cardiovascular disease
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Major Functions of Fats
• 1- Good source of energy. One gram of fat
stores more than twice as much energy as one
gram of a polysaccharide, such as starch.
• 2- Adipose tissue (the tissue that stores fats in
the body) also functions to cushion vital organs
such as the kidneys, and a layer of fat beneath
the skin insulates the body. The subcutaneous
layer is especially thick in whales, seals, and
most other marine mammals.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Phospholipids
• In a phospholipid, two fatty acids and a phosphate
group are attached to glycerol
• The two fatty acid tails are hydrophobic, but the
phosphate group and its attachments form a
hydrophilic head
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.12
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic head
Hydrophobic tails
(c) Phospholipid symbol (b) Space-filling model (a) Structural formula
Hyd
rop
hil
ic h
ead
H
yd
rop
ho
bic
tail
s
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Phospholipids in water (a micelle formation)
WATER Hydrophilic
head
Hydrophobic
tails
WATER
Phospholipids in water (a bilayer formation)
The structure of phospholipids in water results also in a
bilayer arrangement found in cell membranes
Phospholipids are the major component of all cell membranes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Steroids
• Steroids are lipids characterized by a carbon
skeleton consisting of four fused rings
• Different steroids are created by varying functional
groups attached to the rings.
Estradiol
Testosterone
Female lion
Male lion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cholerterol (A Steroid)
• Cholesterol, an important
steroid, is a component
in animal cell
membranes
• Although cholesterol is
essential in animals, high
levels in the blood may
contribute to
cardiovascular disease
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Lipid Summary
Type of Lipid Structure of Lipid Function of Lipid
Triglycerides
Made out of one glycerol
molecule (blue part below)
with three fatty acids
attached (black parts
below).
These are entirely
hydrophobic. The "tri"
prefix of the name comes
from having three fatty
acids.
These are the "fats" and
also the "oils." They are
used for long-term sugar
storage or for insulation of a
multicellular organism.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Lipid summary cont’d
Phospholipids
Phospholipids have the special
property of having both
hydrophobic and hydrophilic
parts, although they are still
mostly hydrophobic. A molecule
that is both hydrophilic and
hydrophobic is called amphipathic.
Phospholipids help to make up the
basis of cellular membranes-- you
will learn much more about these
when we study membranes.
Type of Lipid Structure of Lipid Function of Lipid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Lipid summary cont’d
Steroids (a sterol derivative) They are entirely hydrophobic, and
have their own special structure that
does NOT include fatty acids.
These molecules are all ringed
structures, with 4 carbon rings.
This group includes cholesterol,
estrogen, testosterone, progesterone,
and cortisone. Most steroids are used
as hormones.
Type of Lipid Structure of Lipid Function of Lipid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 5.4: Proteins have many structures, resulting in a wide range of functions
• Proteins account for more than 50% of the dry
mass of most cells
• Protein functions include structural support,
storage, transport, cellular communications,
movement, and defense against foreign
substances
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.15-a
Enzymatic proteins Defensive proteins
Storage proteins
Transport proteins
Enzyme Virus
Antibodies
Bacterium
Ovalbumin Amino acids for embryo
Transport protein
Cell membrane
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.
Function: Storage of amino acids Function: Transport of substances
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.
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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.15-b
Hormonal 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
High blood sugar
Normal blood sugar
Insulin secreted
Signaling molecules
Receptor protein
Muscle tissue
Actin Myosin
100 m 60 m
Collagen
Connective tissue
Receptor proteins
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.
Contractile and motor 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.
Structural proteins 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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Polypeptides
• 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
© 2011 Pearson Education, Inc.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Polypeptide vs Protein
Lysozyme: an
antibacterial
enzyme found
in human
tears. It is
made of one
polypeptide
chain which is
folded into the
functioning
lysozyme
protein.
Hemoglobin (folded
protein) is made of
four polypeptides
Unfolded polypeptide
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.UN01
Side chain (R group)
Amino group
Carboxyl group
carbon
• Amino acids are
organic molecules
with carboxyl and
amino groups
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Amino Acids
• Cells use 20 amino acids to make thousands of proteins
• Amino acids differ in their properties due to differing side
chains, called R groups.
• According to the properties of their side chains, amino
acids are grouped into:
– Nonpolar
– Polar
– Electrically charged.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.16 Nonpolar side chains; hydrophobic
Side chain (R group)
Glycine (Gly or G)
Alanine (Ala or A)
Valine (Val or V)
Leucine (Leu or L)
Isoleucine (Ile or I)
Methionine (Met or M)
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)
Tyrosine (Tyr or Y)
Asparagine (Asn or N)
Glutamine (Gln or Q)
Electrically charged side chains; hydrophilic
Acidic (negatively charged)
Basic (positively charged)
Aspartic acid (Asp or D)
Glutamic acid (Glu or E)
Lysine (Lys or K)
Arginine (Arg or R)
Histidine (His or H)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.16a
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)
Methionine (Met or M)
Phenylalanine (Phe or F)
Tryptophan (Trp or W)
Proline (Pro or P)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.16b
Polar side chains; hydrophilic
Serine (Ser or S)
Threonine (Thr or T)
Cysteine (Cys or C)
Tyrosine (Tyr or Y)
Asparagine (Asn or N)
Glutamine (Gln or Q)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.16c
Electrically charged side chains; hydrophilic
Acidic (negatively charged)
Basic (positively charged)
Aspartic acid (Asp or D)
Glutamic acid (Glu or E)
Lysine (Lys or K)
Arginine (Arg or R)
Histidine (His or H)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Peptide
bond
Amino end (N-terminus)
Peptide
bond
Side chains
Backbone
Carboxyl end (C-terminus)
(a)
(b)
Amino acids are linked by peptide bonds formed by
dehydration reactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Amino Acid Polymers
• A polypeptide is a polymer of amino acids
• Polypeptides range in length from a few
monomers to more than a thousand
• Each polypeptide has a unique linear sequence of
amino acids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Protein Conformation and Function
• A functional protein consists of one or more
polypeptides twisted, folded, and coiled into a
unique shape
• The sequence of amino acids determines a
protein’s three-dimensional conformation
• A protein’s conformation determines its function
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.18
(a) A ribbon model (b) A space-filling model
Groove
Groove
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The sequence of amino acids determines a
protein’s three-dimensional structure
• A protein’s structure determines its function
© 2011 Pearson Education, Inc.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.19
Antibody protein Protein from flu virus
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Many proteins are globular ( semi-spherical ) in shape, while others are fibrous.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
LE 5-20
Amino acid subunits
pleated sheet
+H3N Amino end
helix
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Primary structure, the sequence of amino
acids in a protein, is like the order of letters in a
long word
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The coils and folds of secondary structure
result from hydrogen bonds between the repeating
constituents of the polypeptide backbone (NOT
the amino acid side chain).
• Typical secondary structures are a coil called an alpha helix and a folded structure called a beta pleated sheet.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fig. 5-21c
Secondary Structure
-pleated sheet
Examples of
amino acid
subunits
- helix
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fig. 5-21d
Abdominal glands of the
spider secrete silk fibers
made of a structural protein
containing -pleated sheets.
The radiating strands, made
of dry silk fibers, maintain
the shape of the web.
The spiral strands (capture
strands) are elastic, stretching
in response to wind, rain,
and the touch of insects.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Tertiary structure is determined by interactions
between R groups, rather than interactions
between backbone constituents
• 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 conformation
LE 5-20d
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Disulfide bridge
Ionic bond
Hydrogen
bond
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.20f
Hydrogen bond
Disulfide bridge
Polypeptide backbone
Ionic bond
Hydrophobic
interactions and
van der Waals
interactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Quaternary structure results when two or more
polypeptide chains form one macromolecule
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Sickle-Cell Disease: A Change in Primary Structure
• A slight change in primary structure can affect
a protein’s structure and ability to function
• Sickle-cell disease, an inherited blood
disorder, results from a single amino acid
substitution in the protein hemoglobin
© 2011 Pearson Education, Inc.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.21
Primary Structure
Secondary and Tertiary Structures
Quaternary Structure
Function Red Blood Cell Shape
subunit
subunit
Exposed hydrophobic region
Molecules do not associate with one another; each carries oxygen.
Molecules crystallize into a fiber; capacity to carry oxygen is reduced.
Sickle-cell hemoglobin
Normal hemoglobin
10 m
10 m
Sic
kle
-cell
he
mo
glo
bin
N
orm
al h
em
og
lob
in
1
2
3
4
5
6
7
1
2
3
4
5
6
7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.21a
10 m
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.21b
10 m
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
What Determines Protein Conformation?
• In addition to primary structure, physical and
chemical conditions can affect conformation
• Alternations in pH, salt concentration,
temperature, or other environmental factors can
cause a protein to unravel
• This loss of a protein’s native conformation is
called denaturation
• A denatured protein is biologically inactive
Denaturation
Renaturation
Denatured protein Normal protein
Good for cake Not good for cake
Heat
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Protein Folding in the Cell
• It is hard to predict a protein’s structure from
its primary structure
• Most proteins probably go through several
stages on their way to a stable structure
• Chaperonins 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
© 2011 Pearson Education, Inc.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.23
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.
Cap
Polypeptide
Correctly folded protein
Chaperonin (fully assembled)
Steps of Chaperonin Action:
An unfolded poly- peptide enters the cylinder from one end.
Hollow cylinder
The cap comes off, and the properly folded protein is released.
1
2 3
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Scientists use X-ray crystallography to
determine a protein’s structure
• Another method is nuclear magnetic
resonance (NMR) spectroscopy, which does
not require protein crystallization
• Bioinformatics uses computer programs to
predict protein structure from amino acid
sequences
© 2011 Pearson Education, Inc.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.24a
Diffracted X-rays
X-ray source X-ray
beam
Crystal Digital detector X-ray diffraction pattern
EXPERIMENT
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.24b
RNA DNA
RNA polymerase II
RESULTS
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 5.5: Nucleic acids store and transmit 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Roles of Nucleic Acids
• There are two types of nucleic acids:
– Deoxyribonucleic acid (DNA)
– Ribonucleic acid (RNA)
• DNA replicates in order for the cells to divide
• DNA directs synthesis of messenger RNA (mRNA)
and, through mRNA, controls protein synthesis
• Protein synthesis occurs in ribosomes
LE 5-25
NUCLEUS
DNA
CYTOPLASM
mRNA
mRNA
Ribosome
Amino
acids
Synthesis of
mRNA in the nucleus
Movement of
mRNA into cytoplasm
via nuclear pore
Synthesis
of protein
Polypeptide
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Structure of Nucleic Acids
• Nucleic acids are polymers called polynucleotides
• Each polynucleotide is made of monomers called
nucleotides
• Each nucleotide consists of:
– a nitrogenous base
– a pentose sugar
– and a phosphate group
LE 5-26a 5 end
3 end
Nucleoside
Nitrogenous
base
Phosphate
group
Nucleotide
Polynucleotide, or
nucleic acid
Pentose
sugar
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Nitrogenous bases
• There are two families of nitrogenous bases:
– Pyrimidines have a single six-membered ring
– Purines have a six-membered ring fused to a five-membered ring.
Nitrogenous bases
Pyrimidines
Purines
Cytosine
C
Thymine (in DNA)
T
Uracil (in RNA)
U
Adenine
A
Guanine
G
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Pentose sugar
• In DNA, the sugar is deoxyribose
• In RNA, the sugar is ribose.
Pentose sugars
Deoxyribose (in DNA) Ribose (in RNA)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The DNA Double Helix
• A DNA molecule has two
polynucleotides spiraling around
an imaginary axis, forming a
double helix
• The nitrogenous bases in DNA
form hydrogen bonds in a
complementary fashion: A always
pairs with T, and G always pairs
with C
Sugar-phosphate
backbone
3 end 5 end
Base pair (joined by
hydrogen bonding)
Old strands
Nucleotide
about to be
added to a
new strand
5 end
New strands
3 end
5 end 3 end
5 end
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
RNA
• RNA is made of one
polynucleotide (one strand of
nucleotides)
• The nucleotide of RNA is made
of:
– A nitrogenous bases,
Adenine (A), Uracil (U),
Guanine (G), or Cytosine
(C).
– A ribose sugar.
– A phosphate group.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Differences between DNA and RNA
DNA RNA
Composed of two strands
of polynucleotides twisted
together helically to form a
double helix
Composed of one strand
of polynucleotides.
Contains the 5-carbon
sugar Deoxyribose
Contains the 5-carbon
sugar Ribose
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Differences between DNA and RNA
DNA RNA
Contains the nitrogenous
bases Adenine (A),
Thymine (T), Guanine (G),
and Cytosine (C)
Adenine pairs with Thymine
and Guanine pairs with
Cytosine.
Contains the nitrogenous
bases Adenine (A),
Uracil (U), Guanine (G),
and Cytosine (C)
Larger molecule. Shorter than DNA
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.UN02