1 chapter 2 the structure and function of macromolecules
TRANSCRIPT
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Chapter 2
The Structure and Function of
Macromolecules
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The Molecules of Life
• Overview:– Another level in the hierarchy
of biological organization is reached when small organic molecules are joined together
– Atom ---> molecule --- compound
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Macromolecules– Are large molecules composed of
smaller molecules– Are complex in their structures
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Macromolecules
•Most macromolecules are polymers, built from monomers• Four classes of life’s organic molecules are polymers
– Carbohydrates– Proteins– Nucleic acids– Lipids
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• A polymer– Is a long molecule consisting of many
similar building blocks called monomers– Specific monomers make up each
macromolecule– E.g. amino acids are the monomers for
proteins
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The Synthesis and Breakdown of Polymers
• Monomers form larger molecules by condensation reactions called dehydration synthesis
HO H1 2 3 HO
HO H1 2 3 4
H
H2O
Short polymer Unlinked monomer
Longer polymer
Dehydration removes a watermolecule, forming a new bond
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The Synthesis and Breakdown of Polymers
• Polymers can disassemble by– Hydrolysis (addition of water
molecules)
(
HO 1 2 3 H
HO H1 2 3 4
H2O
HHO
Hydrolysis adds a watermolecule, breaking a bond
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• 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
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Carbohydrates
• Serve as fuel and building material
• Include both sugars and their polymers (starch, cellulose, etc.)
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Sugars
• Monosaccharides– Are the simplest sugars– Can be used for fuel– Can be converted into other
organic molecules– Can be combined into polymers
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• Disaccharides–Consist of two monosaccharides
–Are joined by a glycosidic linkage
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Polysaccharides
• Polysaccharides– Are polymers of sugars– Serve many roles in organisms
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Storage Polysaccharides
• Starch– Is a polymer
consisting entirely of glucose monomers
– Is the major storage form of glucose in plants
Chloroplast Starch
Amylose Amylopectin
1 m
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• Glycogen– Consists of glucose monomers– Is the major storage form of glucose in
animals Mitochondria Giycogen granules
0.5 m
Glycogen
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Structural Polysaccharides
• Cellulose– Is a polymer of glucose
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Plant cells
0.5 m
Cell walls
Cellulose microfibrils in a plant cell wall
Microfibril
CH2OH
CH2OH
OH
OH
OO
OHOCH2OH
O
OOH
OCH2OH OH
OH OHO
O
CH2OH
OO
OH
CH2OH
OO
OH
O
O
CH2OHOH
CH2OHOHOOH OH OH OH
O
OH OH
CH2OH
CH2OH
OHO
OH CH2OH
OO
OH CH2OH
OH
Glucose monomer
O
O
O
O
O
O
Parallel cellulose molecules areheld together by hydrogenbonds between hydroxyl
groups attached to carbonatoms 3 and 6.
About 80 cellulosemolecules associate
to form a microfibril, themain architectural unitof the plant cell wall.
A cellulose moleculeis an unbranched glucose polymer.
OH
OH
O
OOH
Cellulosemolecules
– Is a major component of the tough walls that enclose plant cells
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• Cellulose is difficult to digest– Cows have microbes in their stomachs
to facilitate this process
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• Chitin, another important structural polysaccharide– Is found in the exoskeleton of
arthropods– Can be used as surgical thread
(a) The structure of the chitin monomer.
O
CH2OH
OHHH OH
H
NH
CCH3
O
H
H
(b) Chitin forms the exoskeleton of arthropods. This cicada is molting, shedding its old exoskeleton and emergingin adult form.
(c) Chitin is used to make a strong and flexible surgical
thread that decomposes after the wound or incision heals.
OH
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Lipids
• 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
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Fats– Are constructed from two types of smaller
molecules, a single glycerol and usually three fatty acids
– Vary in the length and number and locations of double bonds they contain
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• Saturated fatty acids– Have the maximum number of
hydrogen atoms possible– Have no double bonds
(a) Saturated fat and fatty acid
Stearic acid
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• Unsaturated fatty acids– Have one or more double bonds
(b) Unsaturated fat and fatty acidcis double bondcauses bending
Oleic acid
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• Phospholipids– Have only two fatty acids– Have a phosphate group instead of
a third fatty acid
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• The structure of phospholipids– Results in a bilayer arrangement found
in cell membranes
Hydrophilichead
WATER
WATER
Hydrophobictail
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Steroids
• Steroids– Are lipids characterized by a carbon
skeleton consisting of four fused rings
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• One steroid, cholesterol– Is found in cell membranes– Is a precursor for some hormones
HO
CH3
CH3
H3C CH3
CH3
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Proteins
• Proteins have many structures, resulting in a wide range of functions
• Proteins do most of the work in cells and act as enzymes
• Proteins are made of monomers called amino acids
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• Enzymes– Are a type of protein that acts as a
catalyst, speeding up chemical reactions
Substrate(sucrose)
Enzyme (sucrase)
Glucose
OH
H O
H2O
Fructose
3 Substrate is convertedto products.
1 Active site is available for a molecule of substrate, the
reactant on which the enzyme acts.
Substrate binds toenzyme.
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4 Products are released.
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Polypeptides
• Polypeptides– Are polymers (chains) of amino
acids
• A protein– Consists of one or more
polypeptides
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Protein Conformation and Function
• A protein’s specific conformation (shape) determines how it functions
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Four Levels of Protein Structure
• Primary structure– Is the unique
sequence of amino acids in a polypeptide
–
Amino acid
subunits
+H3NAmino
end
oCarboxyl end
oc
GlyProThrGlyThr
Gly
GluSeuLysCysProLeu
MetVal
Lys
ValLeu
AspAlaValArgGly
SerPro
Ala
Gly
lle
SerProPheHisGluHis
Ala
GluValValPheThrAla
Asn
AspSer
GlyProArg
ArgTyrThr
lleAla
Ala
Leu
LeuSer
ProTyrSerTyrSerThr
Thr
Ala
ValVal
ThrAsnProLysGlu
ThrLys
SerTyrTrpLysAlaLeu
GluLleAsp
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O C helix
pleated sheetAmino acid
subunitsNCH
C
O
C N
H
CO H
R
C NH
C
O H
C
R
N
HH
R C
O
R
C
H
NH
C
O H
NCO
R
C
H
NH
H
C
R
C
O
C
O
C
NH
H
R
C
C
ON
HH
C
R
C
O
NH
R
C
H C
ON
HH
C
R
C
O
NH
R
C
H C
ON
HH
C
R
C
O
N H
H C R
N HO
O C N
C
RC
H O
CHR
N HO C
RC
H
N H
O CH C R
N H
CC
N
R
H
O C
H C R
N H
O C
RC
H
H
C
RN
H
CO
C
NH
R
C
H C
O
N
H
C
• Secondary structure– Is the folding or coiling of the
polypeptide into a repeating configuration
– Includes the helix and the pleated sheet
H H
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• Tertiary structure– Is the overall three-dimensional shape
of a polypeptide– Results from interactions between
amino acids and R groups
CH2CH
OH
O
CHO
CH2
CH2 NH3+ C-O CH2
O
CH2SSCH2
CH
CH3
CH3
H3C
H3C
Hydrophobic interactions and van der Waalsinteractions Polypeptid
ebackbone
Hyrdogenbond
Ionic bond
CH2
Disulfide bridge
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• Quaternary structure– Is the overall protein structure that
results from the aggregation of two or more polypeptide subunits
Polypeptidechain
Collagen
Chains
ChainsHemoglobin
IronHeme
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Review of Protein Structure
+H3NAmino end
Amino acidsubunits
helix
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Sickle-Cell Disease: A Simple Change in Primary Structure
• Sickle-cell disease– Results from a single amino
acid substitution in the protein hemoglobin
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What Determines Protein Conformation?
• Protein conformation Depends on the physical and chemical conditions of the protein’s environment
• Temperature, pH, etc. affect protein structure
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•Denaturation is when a protein unravels and loses its native conformation(shape)
Denaturation
Renaturation
Denatured protein
Normal protein
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Nucleic Acids
• Nucleic acids store and transmit hereditary information
• Genes– Are the units of inheritance– Program the amino acid
sequence of polypeptides– Are made of nucleotide
sequences on DNA
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The Roles of Nucleic Acids
• There are two types of nucleic acids– Deoxyribonucleic acid (DNA)– Ribonucleic acid (RNA)
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Deoxyribonucleic Acid
• DNA– Stores information for the
synthesis of specific proteins– Found in the nucleus of cells
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• Each polynucleotide– Consists of monomers called nucleotides– Sugar + phosphate + nitrogen base
Nitrogenousbase
Nucleoside
O
O
O
O P CH2
5’C
3’CPhosphate
group Pentosesugar
(b) NucleotideFigure 5.26
O
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Gene
• The sequence of bases along a nucleotide polymer– Is unique for each gene
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The DNA Double Helix
• Cellular DNA molecules– Have two polynucleotides that spiral
around an imaginary axis– Form a double helix
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A,T,C,G
• The nitrogenous bases in DNA– Form hydrogen bonds in a
complementary fashion (A with T only, and C with G only)