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Chapter 5 - The Structure and Function of Large Biological Molecules
Outline
I. MacromoleculesII. Carbohydrates – simple and complexIII. Lipids – triglycerides (fats and oils),
phospholipids, carotenoids, steroids, waxesIV. Proteins – enzymes, keratin, V. Nucleotides – ATP, NAD+
VI. Nucleic Acids – DNA & RNA
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
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Macromolecules are polymers, built from monomers
A polymer is a long molecule consisting of many similar building blocks
These small building-block molecules are called monomers
Three of the four classes of life’s organic molecules are polymers Carbohydrates Proteins Nucleic acids
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Polymers
Many biological molecules formed by linking a chain of monomers
A dehydration reaction occurs when two monomers bond together through the loss of a water molecule
Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction
The Synthesis and Breakdown of Polymers
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Animation: Polymers
Right-click slide / select “Play”
Figure 5.2a
(a) Dehydration reaction: synthesizing a polymer
Short polymer Unlinked monomer
Dehydration removesa water molecule,forming a new bond.
Longer polymer
1 2 3 4
1 2 3
Figure 5.2b
(b) Hydrolysis: breaking down a polymer
Hydrolysis addsa water molecule,breaking a bond.
1 2 3 4
1 2 3
Examples of Organic Compounds
1. Carbohydrates – sugars, polymers of sugars
2. Lipids – triglycerides (fats and oils), phospholipids, steroids, waxes
3. Proteins – enzymes, keratin, actin
4. Nucleic Acids – DNA & RNA
Simple Carbohydrates Carbohydrates serve as fuel and building material
Carbohydrates include sugars and the polymers of sugars
The simplest carbohydrates are monosaccharides, or single sugars
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks
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Functions of Carbohydrates
1. Rapidly Mobilized Source of Energy Monosaccharides and disaccharides
2. Energy storage Glycogen in animals Starch in plants
3. Structural In cell walls bacteria and plants (Cellulose). In exoskeletons (Chitin).
4. Coupled with protein to form glycoproteins Important in cell membranes
Sugars
Monosaccharides have molecular formulas that are usually multiples of CH2O
Glucose (C6H12O6) is the most common monosaccharide
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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Figure 5.3a
Aldose (Aldehyde Sugar) Ketose (Ketone Sugar)
Glyceraldehyde
Trioses: 3-carbon sugars (C3H6O3)
Dihydroxyacetone
Figure 5.3b
Pentoses: 5-carbon sugars (C5H10O5)
Ribose Ribulose
Aldose (Aldehyde Sugar) Ketose (Ketone Sugar)
Figure 5.3c
Aldose (Aldehyde Sugar) Ketose (Ketone Sugar)
Hexoses: 6-carbon sugars (C6H12O6)
Glucose Galactose Fructose
Though often drawn as linear skeletons, in aqueous solutions many sugars form rings
Monosaccharides serve as a major fuel for cells and as raw material for building molecules
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Figure 5.4
(a) Linear and ring forms
(b) Abbreviated ring structure
12
3
4
5
6
6
5
4
32
1 1
23
4
5
6
123
4
56
A disaccharide is formed when a dehydration reaction joins two monosaccharides
This covalent bond is called a glycosidiclinkage
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Disaccharide
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Animation: DisaccharideRight-click slide / select “Play”
Figure 5.5
(a) Dehydration reaction in the synthesis of maltose
(b) Dehydration reaction in the synthesis of sucrose
Glucose Glucose
Glucose
Maltose
Fructose Sucrose
1–4glycosidic
linkage
1–2glycosidic
linkage
1 4
1 2
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Reactions where two molecules are linked together and water is removed is …
1. Condensation or dehydration
2. Hydrolysis
Conde
nsatio
n
Hydro
lysis
50%50%
Complex Carbohydrates
Polysaccharides
Polysaccharides, the polymers of sugars, have storage and structural roles
The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages
Types
1. Starch2. Glycogen3. Cellulose 4. Chitin
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Complex carbohydrates - Polysaccharide
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Animation: PolysaccharidesRight-click slide / select “Play”
Structure of Complex Carbohydrates
Polysaccharides - Long chains of saccharides (sugars) – 100s to 1000s
Cellulose, starch and glycogen consist of chains of only glucose.
Chitin consists of chains of glucose with N-acetyl groups
Structure of Complex Carbohydrates
The differences between the complex carbohydrates is in the structure – branched, unbranched, spiral, hydrogen-bonded.
Cellulose is tightly packed and hard to digest Starch is coiled and may be branched and is easier
to digest Glycogen is coiled with extensive branching and is
even easier to digest.
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Functions of Carbohydrates
1. Rapidly Mobilized Source of Energy Monosaccharides and disaccharides
2. Energy storage - Polysaccharides Glycogen in animals Starch in plants
3. Structural In cell walls bacteria and plants (Cellulose). In exoskeletons (Chitin).
4. Coupled with protein to form glycoproteins Important in cell membranes
Figure 5.6
(a) Starch:a plant polysaccharide
(b) Glycogen:an animal polysaccharide
Chloroplast Starch granules
Mitochondria Glycogen granules
Amylopectin
Amylose
Glycogen
1 m
0.5 m
Polysaccharides in Plants for Energy Storage
Starch, a storage polysaccharide of plants, consists entirely of glucose monomers
Plants store surplus starch as granules within chloroplasts and other plastids
The simplest form of starch is amylose
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Starch
Starch – form stored in plants, coiled, mainly α1-4 glycosidic linkage. If branched then will also have 1-6 glycosidic linkage, stored in amyloplasts. Plants used for energy storage, easy to digest Potatoes, rice, carrots, corn
Types of starches: Amylose – not branched Amylopectin – branched, more common
Glycogen
Glycogen – form stored in animals for energy, coiled, mainly α 1-4 glycosidic linkage. It is branched therefore also has 1-6 glycosidiclinkage, easy to digest
Found in animals: stored mainly in liver and muscle
Functions of Carbohydrates
1. Rapidly Mobilized Source of Energy Monosaccharides and disaccharides
2. Energy storage - Polysaccharides Glycogen in animals Starch in plants
3. Structural - Polysaccharides Cellulose in cell walls bacteria and plants Chitin in exoskeletons
4. Coupled with protein to form glycoproteins Important in cell membranes
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Structural Polysaccharides in Plants - Starch
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 ()
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Cellulose
Cellulose – straight chains of glucose, -OH groups H-bond to stabilize chains into tight bundles, β 1-4 glycosidic linkage, hard to digest
Used by plants for structure and in cell walls.
Figure 5.7a
(a) and glucose ring structures
Glucose Glucose
4 1 4 1
Figure 5.7b
(b) Starch: 1–4 linkage of glucose monomers
(c) Cellulose: 1–4 linkage of glucose monomers
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41
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Polymers with glucose are helical
Polymers with glucose are straight
In straight structures, H atoms on one strand can bond with OH groups on other strands
Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants
Cell wall
Microfibril
Cellulosemicrofibrils in aplant cell wall
Cellulosemolecules
Glucosemonomer
10 m
0.5 m
Figure 5.8
8
Enzymes that digest starch by hydrolyzing linkages can’t hydrolyze linkages in 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
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Why do we care?
Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods.
Contains N-acetyl group which hydrogen bond. Is cross-linked with protein to form a strong exoskeleton for insects and crustaceans
Chitin also provides structural support for the cell walls of many fungi
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Structural Polysaccharides - Chitin
Figure 5.9
Chitin forms the exoskeletonof arthropods.
The structureof the chitinmonomer
Chitin is used to make a strong and flexiblesurgical thread that decomposes after thewound or incision heals.
Glycoproteins
Glycoproteins – carbohydrate + protein on outer surface of cell membranes – we will return to this when we study cell membranes
The form of carbohydrate stored in animals is?
1. Starch2. Glycogen3. Cellulose
Starch
Glyc
ogen
Cell
ulose
33% 33%33%
Which carbohydrate contains nitrogen?
1. Starch2. Cellulose3. Glycogen4. Chitin
Starch
Cell
ulose
Glyc
ogen
Chitin
25% 25%25%25%
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Starch is composed of glucose molecules joined by what kind of covalent bond?
1. β 1-4 Glycosidic linkage
2. α 1-4 Glycosidic linkage
50%50%
Lipids
Like carbohydrates, lipids are mainly made of carbon, hydrogen and oxygen
They are not soluble in water, they are soluble in nonpolar solvents
Types: 1. Triglycerides (Fats)2. Phospholipids3. Carotenoids4. Steroids5. Waxes
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
Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolarcovalent bonds
The most biologically important lipids are fats, phospholipids, and steroids
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I. Lipid - Triglycerides
Function Energy storage, insulation, protection
Triglycerides (triacylglycerol) are three fatty acids joined to glycerol
The fatty acids are covalently linked by an ester linkage through a condensation reaction
Figure 5.10a
(a) One of three dehydration reactions in the synthesis of a fat
Fatty acid(in this case, palmitic acid)
Glycerol
Figure 5.10b
(b) Fat molecule (triacylglycerol)
Ester linkage
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Ester vs Ether Triglycerides
Butter, lard (animal fat), and vegetable oils are all triglycerides
Differences are in the structure of the fatty acids
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
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Fatty Acids Fatty Acids
Saturated fatty acids – carbon chain has no double bonds CH3-(CH2-CH2)n-COOH
Unsaturated fatty acids – carbon chain has a double bond
Monounsaturated fatty acids have one double bond
Polyunsaturated fatty acids – more than one double bond
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Animation: Fats Right-click slide / select “Play”
Figure 5.11
(a) Saturated fat (b) Unsaturated fat
Structuralformula of asaturated fatmolecule
Space-fillingmodel of stearicacid, a saturatedfatty acid
Structuralformula of anunsaturated fatmolecule
Space-filling modelof oleic acid, anunsaturated fattyacid
Cis double bondcauses bending.
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(a) Saturated fat
Structuralformula of asaturated fatmolecule
Space-fillingmodel of stearicacid, a saturatedfatty acid
Figure 5.11a Figure 5.11b (b) Unsaturated fat
Structuralformula of anunsaturated fatmolecule
Space-filling modelof oleic acid, anunsaturated fattyacid
Cis double bondcauses bending.
Fats made from saturated fatty acids are called saturated fats, and are solid at room temperature
Most animal fats are saturated
Fats made from unsaturated fatty acids are called unsaturated fats or oils, and are liquid at room temperature
Plant fats and fish fats are usually unsaturated
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A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits
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
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Trans fat
Hydrogenated oils – unsaturated oils that have been chemically saturated so they will be solid at room temperature (Crisco)
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Trans Fats Hydrogenation is the process of adding
hydrogen to the unsaturated and polyunsaturated oils to saturate them.
This process can also create unsaturated fats that now have a different configuration than the original oil
Labeled “partially hydrogenated oil”
Fats and Health
Heart disease is caused by plaque collecting in the blood vessels leading to the heart.
Cholesterol in the blood leads to more plaque building up in the vessels. LDL (bad cholesterol) – transports cholesterol to
the heart HDL (good cholesterol) – transports cholesterol
away from the heart
Fatty acids and Cholesterol Trans fats – worst type of fat, raise the bad
cholesterol (LDL) and lower the good cholesterol (HDL)
Saturated fats raise the bad cholesterol Sources = animal fats, dairy products, and some plant
oils (palm and coconut) Polyunsaturated fats – do not raise the bad
cholesterol but slightly lower good cholesterol Sources – many vegetable oils (corn and
safflower) Monounsaturated fats – do not increase either Sources – olive, canola and peanut oils;
avocado
Certain unsaturated fatty acids are not synthesized in the human body
These must be supplied in the diet
These essential fatty acids include the omega-3 fatty acids, required for normal growth, and thought to provide protection against cardiovascular disease
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Essential fatty acids
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Omega-3 Fats
Omega-3s are a type of unsaturated fat This fat has a carbon double bond located
three carbons from the end (end = omega) This is the healthiest type of fat Protect against heart disease by reducing bad
cholesterol Sources – fatty fish (salmon, tuna), walnuts
The major function of fats is energy storage
Humans and other mammals store their fat in adipose cells
Adipose tissue also cushions vital organs and insulates the body
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Function of Triglycerides
Which of these fats are the least healthy?
1. Polyunsaturated2. Omega 3 unsaturated3. Trans fat4. Saturated
Polyun
saturat
ed
Omeg
a 3 un
saturat
ed
Trans f
at Satu
rated
25% 25%25%25%
Which type of fatty acid does not contain a double bond?
1. Polyunsaturated2. Omega 3 unsaturated3. Trans fat4. Saturated
Polyun
saturat
ed
Omeg
a 3 un
saturat
ed
Trans f
at Satu
rated
25% 25%25%25%
II. Lipid - Phospholipids
Function Backbone of cell membranes
Similar structure as triglycerides but have: Glycerol 2 fatty acids Phosphate group (negatively charged) R group
II. Lipid - Phospholipids
Phospholipids are amphiphathic
Phosphate end of molecule soluble in water -hydrophilic.
Lipid (fatty acid) end is not soluble in water -hydrophobic.
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Figure 5.12
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilichead
Hydrophobictails
(c) Phospholipid symbol(b) Space-filling model(a) Structural formula
Hyd
roph
ilic
head
Hyd
roph
obic
tails
When phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior
The structure of phospholipids results in a bilayer arrangement found in cell membranes
Phospholipids are the major component of all cell membranes
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Phospholipid’s role in memebranes
Figure 5.13
Hydrophilichead
Hydrophobictail
WATER
WATER
III. Lipid - Carotenoids
Consist of isoprene units
Orange and yellow plant pigments Classified with lipids Some play a role in photosynthesis Animals convert to vitamin A
Isoprene-derived compounds
IV. Lipids - Steroids
Structure: Four fused rings
Examples: cholesterol, bile salts, reproductive hormones, cortisol
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Steroids - Functions
Functions include
Hormones - Signaling within and between cells (estrogen, testosterone, cortisol)
Cholesterol – Important part of cell membrane
Bile salts - Emulsify fat in small intestine
IV. Lipids - Steroids
Unlike triglycerides and phospholipids, steroids have no fatty acids
Structure is a four ring backbone, with side chains attached
Figure 5.14 Cholesterol V. Lipids - Waxes
Covers surface of leaves of plants.
Functions Minimizes water loss from leaves to air. Barrier against entrance of bacteria and
parasites into leaves of plants.
This type of lipid is an important component of membranes
1. Triglycerides2. Phospholipids3. Waxes
Triglyc
erides
Phosph
olipids
Wax
es
33% 33%33%
Proteins include a diversity of 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
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Proteins
Functions – numerous and varied – Page 78 Facilitate chemical reactions (enzymes) Transport Movement of muscles Structure Cell signaling - Hormones (insulin) Nutrition Defense Components of cell membrane Immune response
Enzymes are a type of protein 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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Protein Functions - Enzymes
Enzymes
Enzymes are proteins that catalyze reactions = help reactions to happen – they speed up chemical reactions
They can only speed up reactions that would happen eventually (may take years)
They are usually specific for their substrates
They are not consumed (destroyed) in the process
Some enzymes need cofactors to function. Example = iron
Substrate = the thing that is being changed in the reaction
Active site = Place in the enzyme where the substrate binds.Product = The end result
Figure 5.15-a
Enzymatic proteins Defensive proteins
Storage proteins Transport proteins
Enzyme Virus
Antibodies
Bacterium
Ovalbumin Amino acidsfor embryo
Transportprotein
Cell membrane
Function: Selective acceleration of chemical reactionsExample: Digestive enzymes catalyze the hydrolysisof bonds in food molecules.
Function: Protection against diseaseExample: Antibodies inactivate and help destroyviruses and bacteria.
Function: Storage of amino acids Function: Transport of substancesExamples: Casein, the protein of milk, is the majorsource of amino acids for baby mammals. Plants havestorage proteins in their seeds. Ovalbumin is theprotein of egg white, used as an amino acid sourcefor the developing embryo.
Examples: Hemoglobin, the iron-containing protein ofvertebrate blood, transports oxygen from the lungs toother parts of the body. Other proteins transportmolecules across cell membranes.
Figure 5.15-b
Hormonal proteinsFunction: Coordination of an organism’s activitiesExample: Insulin, a hormone secreted by thepancreas, causes other tissues to take up glucose,thus regulating blood sugar concentration
Highblood sugar
Normalblood sugar
Insulinsecreted
Signalingmolecules
Receptorprotein
Muscle tissue
Actin Myosin
100 m 60 m
Collagen
Connectivetissue
Receptor proteinsFunction: Response of cell to chemical stimuliExample: Receptors built into the membrane of anerve cell detect signaling molecules released byother nerve cells.
Contractile and motor proteinsFunction: MovementExamples: Motor proteins are responsible for theundulations of cilia and f lagella. Actin and myosinproteins are responsible for the contraction ofmuscles.
Structural proteinsFunction: SupportExamples: Keratin is the protein of hair, horns,feathers, and other skin appendages. Insects andspiders use silk fibers to make their cocoons and webs,respectively. Collagen and elastin proteins provide afibrous framework in animal connective tissues.
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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, each folded and coiled into a three dimensional shape
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Amino Acids
Proteins are made up of amino acids
Amino acids are organic molecules with carboxyl and amino groups
There are 20 amino acids, each with a different substitution for R.
Figure 5.UN01
Side chain (R group)
Aminogroup
Carboxylgroup
carbon
Ionized amino acid
Ionized form
Figure 5.16Nonpolar 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)
Figure 5.16a
Nonpolar side chains; hydrophobicSide 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)
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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)
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)
Amino Acid Polymers
Amino acids are linked by peptide bonds
A polypeptide is a polymer of amino acids
Polypeptides range in length from a few to more than a thousand monomers
Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus)
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Figure 5.17
Peptide bond
New peptidebond forming
Sidechains
Back-bone
Amino end(N-terminus)
Peptidebond
Carboxyl end(C-terminus)
Protein Structure and Function
A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape
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Figure 5.18
(a) A ribbon model (b) A space-filling model
Groove
Groove
19
The sequence of amino acids determines a protein’s three-dimensional structure
A protein’s structure determines its function
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Protein Structure and Function 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
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Animation: Protein Structure IntroductionRight-click slide / select “Play”
Figure 5.20a Primary structure
Aminoacids
Amino end
Carboxyl end
Primary structure of transthyretin
Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word
Primary structure is determined by inherited genetic information
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Primary Structure of Proteins
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Animation: Primary Protein StructureRight-click slide / select “Play”
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Animation: Secondary Protein Structure Right-click slide / select “Play”
The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone
Typical secondary structures are a coil called an helix and a folded structure called a pleated sheet
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Secondary Structure of Proteins
Secondary structure
Hydrogen bond
helix
pleated sheet
strand, shown as a flatarrow pointing towardthe carboxyl end
Hydrogen bond
Figure 5.20c
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 structure
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Tertiary Structure of Proteins
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Animation: Tertiary Protein StructureRight-click slide / select “Play”
Figure 5.20e
Tertiary structure
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Figure 5.20f
Hydrogenbond
Disulfidebridge
Polypeptidebackbone
Ionic bond
Hydrophobicinteractions andvan der Waalsinteractions
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
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Quaternary Structure of Proteins
Figure 5.20g
Quaternary structure
four identicalpolypeptides
Hemoglobin
HemeIron
subunit
subunit
subunit
subunit
Figure 5.20i
Figure 5.20j
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Animation: Quaternary Protein Structure Right-click slide / select “Play”
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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
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Figure 5.21
PrimaryStructure
Secondaryand TertiaryStructures
QuaternaryStructure Function Red Blood
Cell Shape
subunit
subunit
Exposedhydrophobicregion
Molecules do notassociate with oneanother; each carriesoxygen.
Molecules crystallizeinto a fiber; capacityto carry oxygen isreduced.
Sickle-cellhemoglobin
Normalhemoglobin
10 m
10 m
Sick
le-c
ell h
emog
lobi
nN
orm
al h
emog
lobi
n
1234567
1234567
What Determines Protein Structure?
In addition to primary structure, physical and chemical conditions can affect structure
Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel
This loss of a protein’s native structure is called denaturation
A denatured protein is biologically inactive© 2011 Pearson Education, Inc.
Figure 5.22
Normal protein Denatured protein
tu
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 or chaperones 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 misfoldedproteins
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Figure 5.23
The cap attaches, causingthe cylinder to changeshape in such a way thatit creates a hydrophilicenvironment for thefolding of the polypeptide.
CapPolypeptide
Correctlyfoldedprotein
Chaperonin(fully assembled)
Steps of ChaperoninAction:
An unfolded poly-peptide enters thecylinder fromone end.
Hollowcylinder
The cap comesoff, and theproperly foldedprotein isreleased.
1
2 3
23
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
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Determining the Structure of Proteins Figure 5.24
DiffractedX-rays
X-raysource X-ray
beam
Crystal Digital detector X-ray diffractionpattern
RNA DNA
RNApolymerase II
EXPERIMENT
RESULTS
Nucleic acids store, transmit, and help express 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 made of monomers called nucleotides
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The Roles of Nucleic Acids
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 on ribosomes
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Figure 5.25-1
Synthesis ofmRNA
mRNA
DNA
NUCLEUSCYTOPLASM
1
Figure 5.25-2
Synthesis ofmRNA
mRNA
DNA
NUCLEUSCYTOPLASM
mRNAMovement ofmRNA intocytoplasm
1
2
24
Figure 5.25-3
Synthesis ofmRNA
mRNA
DNA
NUCLEUSCYTOPLASM
mRNA
Ribosome
AminoacidsPolypeptide
Movement ofmRNA intocytoplasm
Synthesisof protein
1
2
3
The Components 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 one or more phosphate groups
The portion of a nucleotide without the phosphate group is called a nucleoside
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Nucleotides
Their functions include: Energy (ATP) Coenzymes that aid enzyme function (NAD+) Messengers within cells (GTP)
Nucleotides consists of a sugar, phosphate groups, and a base.
There are 5 nucleotide bases: Adenine, Thymine, Uracil, Guanine, Cytosine
Nucleic Acids
Nucleic Acids are a chain or chains of nucleotides
The nucleotides are covalently bonded by phosphodiester linkage between the phosphates and sugars
Figure 5.26
Sugar-phosphate backbone5 end
5C
3C
5C
3C
3 end
(a) Polynucleotide, or nucleic acid
(b) Nucleotide
Phosphategroup Sugar
(pentose)
Nucleoside
Nitrogenousbase
5C
3C
1C
Nitrogenous bases
Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA)
Adenine (A) Guanine (G)
Sugars
Deoxyribose (in DNA) Ribose (in RNA)
(c) Nucleoside components
Pyrimidines
Purines
25
Figure 5.26abSugar-phosphate backbone5 end
5C
3C
5C
3C
3 end(a) Polynucleotide, or nucleic acid
(b) Nucleotide
Phosphategroup Sugar
(pentose)
Nucleoside
Nitrogenousbase
5C
3C
1C
Figure 5.26c
Nitrogenous bases
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Adenine (A) Guanine (G)
Sugars
Deoxyribose (in DNA)
Ribose (in RNA)
(c) Nucleoside components
Pyrimidines
Purines
Nucleoside = nitrogenous base + sugar There are two families of nitrogenous bases
Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring
Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring
In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose
Nucleotide = nucleoside + phosphate group
© 2011 Pearson Education, Inc.
The Components of Nucleotides Nucleotide Polymers
Nucleotides are linked together to build a polynucleotide polymer
Adjacent nucleotides are joined by covalent bonds that form between the —OH group on the 3carbon of one nucleotide and the phosphate on the 5 carbon on the next
These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages
The sequence of bases along a DNA or mRNA polymer is unique for each gene
© 2011 Pearson Education, Inc.
The Structures of DNA and RNA Molecules
RNA molecules usually exist as single polynucleotideschains
DNA molecules have two polynucleotides spiraling around an imaginary axis, forming a double helix
In the DNA double helix, the two backbones run in opposite 5→ 3 directions from each other, an arrangement referred to as antiparallel
One DNA molecule includes many genes
© 2011 Pearson Education, Inc.
The nitrogenous bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C)
Called complementary base pairing
Complementary pairing can also occur between two RNA molecules or between parts of the same molecule
In RNA, thymine is replaced by uracil (U) so A and U pair
© 2011 Pearson Education, Inc.
The Structures of DNA and RNA Molecules
26
Figure 5.27
Sugar-phosphatebackbonesHydrogen bonds
Base pair joinedby hydrogen bonding
Base pair joinedby hydrogen
bonding
(b) Transfer RNA(a) DNA
5 3
53
DNA and Proteins as Measures of Evolution
The linear sequences of nucleotides in DNA molecules are passed from parents to offspring
Two closely related species are more similar in DNA than are more distantly related species
Molecular biology can be used to assess evolutionary kinship
© 2011 Pearson Education, Inc.
Figure 5.UN02 Figure 5.UN02a
Figure 5.UN02b Fatty acids are joined to glycerol by what kind of linkage?
1. Peptide2. Gycosidic3. Phosphodiester4. Ester
Peptid
e
Gyc
osidi
c Phos
phodie
ster
Ester
25% 25%25%25%
27
Important Concepts
Know the vocabulary of the lecture and reading
What are the different types of biological molecules, their functions and be able to identify their structures
What are the types of carbohydrates and what types of organisms they are found in, what are their functions, identify their structures
Be able to describe the differences in the carbohydrates’ structures and the implications these difference have on our ability to digest them
Important Concepts
What are the types of starches and what structure stores starch?
What are the different types of lipids and their biological functions
What are the types of dietary triglycerides and which are healthy – know the order from healthiest to least healthy
What is the structure of amino acids, what bond links amino acids together, how they link together. Be able to draw and amino acid structure.
Important Concepts
Be able to describe protein structure including primary, secondary etc. Know what forces hold alpha helixes and beta sheets together, know the forces that help shape tertiary structure.
Know examples of steroids and functions of each type of steroids.
What are enzymes, what is their function, what are their properties, what are the active site, the substrates, and the products.
Important Concepts
What is the structure of nucleotides, you should be able to identify the bases but you don’t need to draw their structure. What are nucleic acids what are their functions. Know the examples of nucleic acids and nucleotides
Which molecules join together to form what molecules (monomer and polymers) what are the linkages called
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