Download Document

Chapter 5
The Structure and Function of
Macromolecules
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Edited by DR. Ziad W Jaradat
• Overview: The Molecules of Life
– Another level in the hierarchy of biological
organization is reached when small organic
molecules are joined together
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Macromolecules
– Are large molecules composed of smaller
molecules
– Are complex in their structures
Figure 5.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 5.1: Most macromolecules are
polymers, built from monomers
• Three of the classes of life’s organic
molecules are polymers
– Carbohydrates
– Proteins
– Nucleic acids
• The fourth class is not a polymer (the lipids)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A polymer (poly=many; mer=part)
– Is a long molecule consisting of many
similar building blocks called monomers
(mono=single)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Synthesis and Breakdown of Polymers
• Monomers form larger molecules by
condensation reactions called dehydration
(polymerization) reactions
• Requires energy
• Requires enzymes
HO
1
3
2
H
Unlinked monomer
Short polymer
Dehydration removes a water
molecule, forming a new bond
HO
Figure 5.2A
1
2
H
HO
3
H2O
4
H
Longer polymer
(a) Dehydration reaction in the synthesis of a polymer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Polymers can disassemble by
– Hydrolysis: (hydro= water; lysis= break)
HO
1
2
3
4
Hydrolysis adds a water
molecule, breaking a bond
HO
1
2
3
H
Figure 5.2B (b) Hydrolysis of a polymer
• Releases energy
• Enzymes speed up hydrolysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H
H2O
HO
H
The Diversity of Polymers
• Each class of polymer
– Is formed from a specific set of monomers
1
2
3
H
HO
• Although organisms share the same limited
number of monomer types, each organism is
unique based on the arrangement of
monomers into polymers
• An immense variety of polymers can be built
from a small set of monomers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•
Concept 5.2: Carbohydrates serve as fuel
and building material
•
Carbohydrates
–
Include both sugars and their polymers
–
Monomers of carbohydrates are simple
sugars called Monosaccharides
–
Polymers are formed by condensation
reaction
–
Are classified based on the number of
simple sugars
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Sugars
•
Monosaccharides
–
Mono=single, sacchar=sugar
–
Are the simple sugars in which C, H and O
are occur in the ratio of CH2O.
–
Are major nutrients for the cell
–
Can be produced by photosynthesis from
CO2, H2O and sunlight.
–
Store energy in their chemical bonds
which are harvested by cellular
respiration.
–
Can be incorporated as monomers into
disaccharides and polysaccharides
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Examples of monosaccharides
Triose sugars
(C3H6O3)
H
O
Pentose sugars
(C5H10O5)
H
Aldoses
C
O
Hexose sugars
(C6H12O6)
H
C
H
O
C
C
H
C
OH
H
C
OH
H
C
OH
H
C
OH
H
C
OH
HO
C
H
C
OH
H
H
C
OH
H
O
H
C
OH
H
HO
C
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
C
OH
Glyceraldehyde
H
Ribose
H
H
Ketoses
H
Glucose
Galactose
H
C OH
C
H
H
C OH
C
O
H
H
C OH
C
O
O
C OH
H
C OH
HO
H
H
C OH
H
C OH
Dihydroxyacetone
H
C OH
H
C OH
H
H
C OH
H
Ribulose
Figure 5.3
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C H
H
Fructose
• Monosaccharides
– May be linear
– Can form rings
O
H
1C
6CH OH
2
6CH OH
2
2
H
C
OH
C
H
OH
OH
C
OH
6
H
H
OH
4C
C
5
H
H
4
H
O
C
OH
5C
H
H
3
HO
5C
3
C
H
2C
O
O
H
H
4C
1C
CH2OH
OH
H
OH
3C
6
H
1C
H
2C
4
HO
H
OH
3
OH
H
1
OH
2
OH
OH
H
Figure 5.4 (a) Linear and ring forms. Chemical equilibrium between the linear and ring
structures greatly favors the formation of rings. To form the glucose ring,
carbon 1 bonds to the oxygen attached to carbon 5.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H
OH
H
H
O
5
• Disaccharides
– (Di=two; sacchar=sugar)
– consists of two monosaccharides joined by
glycosidic linkage
– Maltose (malt sugar) = glucose + glucose
– Lactose (milk sugar) = glucose + galactose
– Sucrose (table sugar) = glucose + fructose
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Examples of disaccharides
(a) Dehydration reaction
in the synthesis of
maltose. The bonding
of two glucose units
forms maltose. The
glycosidic link joins
the number 1 carbon
of one glucose to the
number 4 carbon of
the second glucose.
Joining the glucose
monomers in a
different way would
result in a different
disaccharide.
CH2OH
CH2OH
H
O
H
OH H
OH
HO
H
H
H
HO
O
H
OH
H
OH
H
CH2OH
H
OHOH
H
O
H
OH H
CH2OH
H
1–4
1 glycosidic
linkage
HO
4
O
H
H
OH H
OH
O
H
OH
H
H
OH
OH
H2O
Glucose
Glucose
CH2OH
H
(b) Dehydration reaction
in the synthesis of
HO
sucrose. Sucrose is
a disaccharide formed
from glucose and fructose.
Notice that fructose,
though a hexose like
glucose, forms a
five-sided ring.
O
H
OH
H
H
CH2OH
H
OH
HO
CH2OH
O
H
H
H
HO
CH2OH
OH
OH
Maltose
H
O
H
OH
H
1–2
glycosidic
1
linkage
H
Fructose
Figure 5.5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2
H
H
CH2OH
OH H
OH
Sucrose
H
HO
O
HO
H2O
Glucose
CH2OH
O
Polysaccharides
•
Polysaccharides
–
Macromolecules that are polymers of a
few hundred or thousand of
monosaccharides.
–
Formed by linking monomers in
condensation reaction
–
Have two important biological functions:
i. energy storage (starch and glycogen)
ii. structural support (cellulose and chitin).
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Storage Polysaccharides
•
Starch
–
Is a polymer consisting entirely of
glucose monomers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Starch
– Is the major storage
form of glucose in
plants
Chloroplast
Starch
– Stored as granules
within plant
organelles called
plastids
– Amylose the
simplest form is an
unbranched polymer.
– Amylopectin is
branched polymer
1 m
Amylose
Amylopectin
– Most animals have
digestive enzymes to Figure 5.6 (a) Starch: a plant polysaccharide
hydrolyse starch
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glycogen
Large glucose polymer that is more highly
branched than amylopectin
Mitochondria
Is the major storage form of
Giycogen granules
glucose in animals
Stored in the muscles and
0.5 m
liver of humans and other
vertebrates
Glycogen
Figure 5.6
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) Glycogen: an animal polysaccharide
Structural Polysaccharides
•
Cellulose
–
Linear unbranched polymer of glucose
–
Differ from starch in its glycosidic
linkages
–
Cellulose and starch have different threedimensional shapes and properties as a
result of differences in glycosidic
linkages.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Has different glycosidic linkages than
starch
H
CH2O
H
O
H
OH H
H
4
H
OH
HO
H
O
CH2O
H
H
O OH
H
4
1
OH H
HO
H
C
OH
 glucose
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
OH
 glucose
(a)  and  glucose ring structures
CH2O
H
O
CH2O
H
O
HO
4
1
OH
O
1
OH
4
O
1
OH
OH
OH
CH2O
H
O
CH2O
H
O
O
4
1
OH
O
OH
OH
(b) Starch: 1– 4 linkage of  glucose monomers
CH2O
H
O
HO
Figure 5.7 A–C
OH
CH2O
H
O
OH
O
1
4
OH
O
OH
OH
O
OH
O
O
CH2O
CH2O
OH
OH
H
H
(c) Cellulose: 1– 4 linkage of  glucose monomers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
OH
– Is a major component of the tough walls
that enclose plant cells
Cell walls
Cellulose microfibrils
in a plant cell wall
Microfibril
About 80 cellulose
molecules associate
to form a microfibril, the
main architectural unit
of the plant cell wall.
0.5 m
Plant cells
Parallel cellulose molecules are
held together by hydrogen
bonds between hydroxyl
groups attached to carbon
atoms 3 and 6.
Figure 5.8
OH CH2OH
OH
CH2OH
O O
O O
OH
OH
OH
OH
O
O O
O O
O CH OH
OH
CH2OH
2
H
CH2OH
OH CH2OH
OH
O O
O O
OH
OH
OH
OH
O
O O
O O
O CH OH
OH CH2OH
2
H
CH2OH
OH
OH CH2OH
O O
O O
OH
OH
OH O
O OH
O O
O
O CH OH
OH CH2OH
2
H
 Glucose
monomer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cellulose
molecules
A cellulose molecule
is an unbranched 
glucose polymer.
• Cellulose is difficult to digest
– Cows have microbes in their stomachs to
facilitate this process
Figure 5.9
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Chitin, another important structural
polysaccharide
– Is found in the exoskeleton of arthropods
– Can be used as surgical thread
CH2O
H
O OH
H
H
OH H
OH
H
H
NH
C
O
CH3
(a) The structure of the (b) Chitin forms the exoskeleton
of arthropods. This cicada
chitin monomer.
is molting, shedding its old
exoskeleton and emerging
Figure 5.10 A–C
in adult form.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(c) Chitin is used to make a
strong and flexible surgical
thread that decomposes after
the wound or incision heals.
• Concept 5.3: Lipids are a diverse group of
hydrophobic molecules
• Lipids
– Are the one class of large biological
molecules that do not consist of polymers
– Share the common trait of being
hydrophobic
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fats
– Are constructed from two types of smaller
molecules
– a single glycerol (a three carbon alcohol)
and usually three fatty acids (carboxylic
acid)
Fats are formed by a
condensation reaction
which links glycerol to
fatty acids by an Ester
linkage.
H
H
C
O
C
OH
HO
H
C
OH
H
C
OH
H
C
H
C
H
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
Fatty acid
(palmitic acid)
H
Glycerol
(a) Dehydration reaction in the synthesis of a fat
Ester linkage
O
H
H
C
O
C
H
C
H
O
H
C
O
C
O
H
C
O
H
Figure 5.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C
H
C
H
H
C
H
C
H
H
H
C
H
C
H
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H
C
C
H
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
(b) Fat molecule (triacylglycerol)
H
C
H
H
H
C
H
H
H
C
H
H
H
C
H
H
•
Fatty acids
–
composed of a carboxyl group at one end
(head) and an attached hydrocarbon (C-H)
chain (tail)
–
Nonpolar C-H bonds make the chain
hydrophobic (not water soluble)
–
Vary in the length and number and
locations of double bonds they contain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Saturated fatty acids
– Have the maximum number of hydrogen
atoms possible
– Have no double bonds
Stearic acid
Figure 5.12 (a) Saturated fat and fatty acid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Unsaturated fatty acids
– Have one or more double bonds
Oleic acid
Figure 5.12
(b) Unsaturated fat and fatty acid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
cis double bond
causes bending
Saturated fatty acids
Unsaturated fatty acids
- No double bonds
between carbons of fatty
acid tail.
- Carbon skeleton of
fatty acid is bonded to
maximum number of
hydrogens
-Usually a solid at room
temperature
-Most animal fats
- One or more double bonds
between carbons of fatty acid
tail
-Tail kinks at each C=C, so
molecules do not pack enough
to solidify at room temperature.
-Usually a liquid
temperature
- Most plant fats
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
at
room
Phospholipids
• Phospholipids
– Have only two fatty acids
– Have a phosphate group instead of a third
fatty acid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Phospholipid structure
– Consists of a hydrophilic “head” and
hydrophobic “tails” → it’s amphiphatic
CH2
+
N(CH )
Choline
3 3
CH2
O
O
P
O–
Phosphate
O
CH2
CH
O
O
C
O C
CH2
Glycerol
O
Fatty acids
Hydrophilic
head
Hydrophobic
tails
Figure 5.13
(a) Structural formula
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) Space-filling model
(c) Phospholipid
symbol
• The structure of phospholipids
– Results in a bilayer arrangement found in
cell membranes
WATER
Hydrophilic
head
WATER
Hydrophobic
tail
Figure 5.14
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Steroids
• Steroids
– Are lipids characterized by a carbon
skeleton consisting of four fused rings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• One steroid, cholesterol
– Is found in cell membranes
– Is a precursor for some hormones
H3C
CH3
CH3
Figure 5.15
HO
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH3
CH3
• Concept 5.4: Proteins have many structures,
resulting in a wide range of functions
– Proteins
• Have many roles inside the cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of protein functions
- Are abundant, forming about 50% of cellular dry weight
- Have important functions in the cell:
1.structural support
2.storage (of amino acids)
3.transport (e.g. hemoglobin)
4. signaling (chemical messengers)
5.cellular response (receptor proteins)
6.movement (contractile proteins)
7.defense (antibodies)
8.catalysts of biochemical reactions (enzymes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Enzymes
– Are a type of protein that acts as a catalyst,
speeding up chemical reactions
1 Active site is available for
a molecule of substrate, the
reactant on which the enzyme acts.
Substrate
(sucrose)
2 Substrate binds to
enzyme.
Glucose
OH
Enzyme
(sucrase)
H2O
Fructose
H O
4 Products are released.
Figure 5.16
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3 Substrate is converted
to products.
Polypeptides
• Polypeptides
– Are polymers of amino acids
• A protein
– Consists of one or more polypeptides
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Amino Acid Monomers
• Amino acids
– Are organic molecules possessing both
carboxyl and amino groups
– Differ in their properties due to differing
side chains, called R groups
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 20 different amino acids make up proteins
CH3
CH3
H
H3N+
C
CH3
O
H3N+
C
H
Glycine (Gly)
O–
C
H3N+
C
H
Alanine (Ala)
O–
CH
CH3
CH3
O
C
CH2
CH2
O
H3N+
C
H
Valine (Val)
CH3
CH3
O–
C
O
H3N+
C
H
Leucine (Leu)
H3C
O–
CH
C
O
C
O–
H
Isoleucine (Ile)
Nonpolar
CH3
CH2
S
NH
CH2
CH2
H3N+
C
H
CH2
O
H3N+
C
O–
Methionine (Met)
C
H
H3 N+
C
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C
O–
Phenylalanine (Phe)
Figure 5.17
CH2
O
H
O
H2C
CH2
H2N
C
O
C
O–
H
C
O–
Tryptophan (Trp)
Proline (Pro)
OH
OH
Polar
CH2
H3N+
C
CH
O
H3N+
C
O–
H
Serine (Ser)
C
CH2
O
H3N+
C
O–
H
C
CH2
O
C
H
O–
H3N+
C
O
H3N+
C
O–
H
Electrically
charged
H3N+
CH2
C
H3N+
O–
C
NH3+
O
C
CH2
C
CH2
CH2
CH2
CH2
CH2
CH2
O
CH2
C
O–
H
H3N+
C
O
CH2
C
H
O–
H3N+
C
H
O–
H
Glutamic acid
(Glu)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
NH+
C
O–
Lysine (Lys)
NH2+
H3N+
CH2
O
CH2
H3N+
C
H
Aspartic acid
(Asp)
O
C
Glutamine
(Gln)
NH2
C
C
C
Basic
O–
O
O
Asparagine
(Asn)
Acidic
–O
CH2
CH2
H
Tyrosine
(Tyr)
Cysteine
(Cys)
Threonine (Thr)
C
NH2 O
C
SH
CH3
OH
NH2 O
NH
CH2
O
C
C
O–
H
O
C
O–
Arginine (Arg)
Histidine (His)
Amino Acid Polymers
• Amino acids
– Are linked by peptide bonds
Peptide
bond
OH
CH2
SH
CH2
H
N
H
OH
CH2
H
C C
H
N C C OH H N C
H O
H O
H
(a)
C OH
O DESMOSOMES
H2O
OH
DESMOSOMES
DESMOSOMES
SH
OH
Peptide
CH2 bond CH2
CH2
H
H N C C
H O
Figure 5.18
(b)
Amino end
(N-terminus)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H
H
N C C
H O
N C C OH
H O
Carboxyl end
(C-terminus)
Side
chains
Backbone
Determining the Amino Acid Sequence of a Polypeptide
• The amino acid sequences of polypeptides
– Were first determined using chemical
means
– Can now be determined by automated
machines
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Protein Conformation and Function
• A protein’s specific conformation
– Determines how it functions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Two models of protein conformation
Groove
(a) A ribbon model
Groove
Figure 5.19
(b) A space-filling model
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Four Levels of Protein Structure
•
Primary structure
Gly Pro Thr Gly
Thr
+H N
3
Amino end
–
Is the unique
sequence of amino
acids in a polypeptide
–
determined by genes
–
slight change can
effect the protein
conformation and
function (e.g. sicklecell hemoglobin)
Amino acid
subunits
Gly
Glu
Leu
Met
Seu
Pro Cys Lys
Val
Lys
Val
Leu
Asp
Ala Val Arg
Gly
Ser
Pro
Ala
Glu Lle
Asp
Thr
Lys
Ser
Gly
Lys
Leu Ala
Trp Tyr
lle
Ser
Pro Phe
His Glu
His
Ala
Glu
Ala Thr Phe Val
Val
Asn
Asp
Arg
Ser
Gly Pro
Tyr
Thr
lle
Ala
Ala
Arg
Leu
Leu
Thr
Ser Tyr
Ser
Tyr Pro
Ser
Thr
Ala
o
Val
Val
Thr
Figure 5.20
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Asn Pro
Lys Glu
c
o–
Carboxyl end
• Hemoglobin structure and sickle-cell disease
Primary
structure
Normal hemoglobin
Val
His Leu Thr
Val
His
Leu Thr


Molecules do
not associate
with one
another, each
carries oxygen.


Quaternary
structure
Figure 5.21
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Val Glu
...




10 m
Red blood
cell shape
Exposed
hydrophobic
region
 subunit
Function
10 m
Normal cells are
full of individual
hemoglobin
molecules, each
carrying oxygen
Pro
structure 1 2 3 4 5 6 7
Secondary
 subunit and tertiary
structures
Quaternary Hemoglobin A
structure
Red blood
cell shape
Sickle-cell hemoglobin
. . . Primary
1 2 3 4 5 6 7
Secondary
and tertiary
structures
Function
Pro Glul Glu
Hemoglobin S
Molecules
interact with
one another to
crystallize into a
fiber, capacity to
carry oxygen is
greatly reduced.
Fibers of abnormal
hemoglobin
deform cell into
sickle shape.
• Secondary structure
–
Is the folding or coiling of the polypeptide into a repeating
configuration
–
Includes the  helix and the  pleated sheet
–
Stabilized by hydrogen bonding
 pleated sheet
O H H
C C N
Amino acid
subunits
C N
H
R
R
O H H
C C N
C C N
O H H
R
R
O H H
C C N
C C N
OH H
R
R
R
O
R
C
H
H
R
O C
O C
N H
N H
N H
O C
O C
H C R H C R
H C R H C
R
N H O C
N H
O C
O C
H
C
O
N H
N
C
C
H
R
H
R
N
C
C
H
H
 helix
Figure 5.20
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
O H H
C C N
C C N
OH H
R
O
C
H
H
H C N HC
C N HC N
C
N
H
H
C
O
C
C
O
R
R
O
R
O
C
H
H
NH C N
C
H
O C
R
C C
O
R
R
H
C
N HC N
H
O C
• Tertiary structure
– Is the overall three-dimensional shape of a
polypeptide
– Results from interactions between amino
acids and R groups
Hydrophobic
Hyrdogen
bond
CH22
CH
O
H
O
CH
H3C
CH3
H3C
CH3
CH
interactions and
van der Waals
interactions
Polypeptide
backbone
HO C
CH2
covalent
Non-covalent
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH2 S S CH2
Disulfide bridge
O
CH2 NH3+ -O C CH2
Ionic bond
• Quaternary structure
– Is the overall protein structure that results
from the aggregation of two or more
polypeptide subunits
Polypeptide
chain
Collagen
 Chains
Iron
Heme
 Chains
Hemoglobin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The four levels of protein structure
+H
3N
Amino end
Amino acid
subunits
helix
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
What Determines Protein Conformation?
•
Protein conformation
–
A proteins three-dimensional shape is a
consequence of the interactions
responsible for the secondary and tertiary
structures.
–
This conformation is influenced by
physical & chemical environmental
conditions.
–
If a protein’s environment is changed, it
may become denatured and lose its
conformation.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•
Denaturation
–
Is when a protein unravels and loses its native conformation
–
A protein can be denatured by:
•
transfer to organic solution.
•
Chemical agent that disrupt hydrogen bonds.
•
Excessive heat that disrupt weak interactions
Denaturation
Normal protein
Figure 5.22
Denatured protein
Renaturation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 5.5: Nucleic acids store and
transmit hereditary information
• Genes
– Are the units of inheritance
– Program the amino acid sequence of
polypeptides
– Are made of nucleic acids
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)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•
DNA
–
Stores information for the synthesis of specific
proteins
–
contains genes that program all cell activity.
–
Contain directions for its own replication
–
Is copied and passed from one generation to
another.
–
In eukaryotic cells, is found in the nucleus.
–
Makes up genes that contain instructions for
protein synthesis.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Directs RNA synthesis
– Directs protein synthesis through RNA
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
Figure 5.25
Polypeptide
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Amino
acids
RNA
•
function in the actual synthesis of proteins
•
Sites of protein synthesis are on ribosomes
in the cytoplasm.
•
Messenger RNA (mRNA) carries encoded
message from the nucleus to the cytoplasm
•
The flow of genetic information goes from
DNA  RNA protein (central dogma)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Structure of Nucleic Acids
• Nucleic acids
– Exist as polymers called polynucleotides
5’ end
5’C
O
3’C
O
O
5’C
O
3’C
OH
Figure 5.26
3’ end
(a) Polynucleotide,
or nucleic acid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Each polynucleotide
– Consists of monomers called nucleotides
Nucleoside
Nitrogenous
base
5’C
O

O
P
O
CH2
O
O
Phosphate
group
Figure 5.26
(b) Nucleotide
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3’C
Pentose
sugar
Nucleotide Monomers
Are made up of nucleosides and
phosphate groups
Purine: Characterized by a fivemembered ring fused to a sixmembered ring.
Nitrogenous bases
Pyrimidines
NH2
O
O
C
C
CH
C
3
N
CH
C
CH HN
HN
CH
C
CH
C
C
CH
N
N
O
N
O
O
H
H
H
Cytosine Thymine (in DNA) Uracil
(in
RNA)
Uracil (in RNA)
U
C
U
T
Examples
- Adenine (A)
- Guanine (G)
Pyrimidine: Characterized
by a six-membered ring
made up of carbon and
nitrogen atoms.
Purines
O
NH2
N C C
N CC
NH
N
HC
HC
C
CH
N C
N
NH2
N
N
H
H
Adenine
Guanine
A
G
Examples:
- Cytosine (C)
5”
HOCH2 O OH
- Thymine (T); found
only in DNA
- Uracile (U); found only
in RNA
Pentose sugars
4’
H H
1’
5”
HOCH2 O OH
4’
H H
1’
H
H
H 3’ 2’ H
3’ 2’
OH H
OH OH
Deoxyribose (in DNA) Ribose (in RNA)
Figure 5.26
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(c) Nucleoside components
Nucleotide Polymers
• Nucleotide polymers
– Are made up of nucleotides linked by the
–OH group on the 3´ carbon of one nucleotide
and the phosphate on the 5´ carbon on the
next → phosphodiester linkages
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The sequence of bases along a nucleotide
polymer
– Is unique for each gene
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The DNA Double Helix
• Cellular DNA molecules
– Have two polynucleotides that spiral
around an imaginary axis
– Form a double helix
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The DNA double helix
– Consists of two antiparallel nucleotide
strands
3’ end
5’ end
Sugar-phosphate
backbone
Base pair (joined by
hydrogen bonding)
Old strands
A 3’ end
Nucleotide
about to be
added to a
new strand
5’ end
3’ end
Figure 5.27
5’ end
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
New
strands
3’ end
• The nitrogenous bases in DNA
– Form hydrogen bonds in a complementary
fashion (A with T only, and C with G only)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings