biology in focus chapter 3
TRANSCRIPT
CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge
3Carbon and the Molecular Diversity of Life
Overview: Carbon Compounds and Life
Aside from water, living organisms consist mostly of carbon-based compounds
Carbon is unparalleled in its ability to form large, complex, and diverse molecules
A compound containing carbon is said to be an organic compound
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Critically important molecules of all living things fall into four main classes Carbohydrates Lipids Proteins Nucleic acids
The first three of these can form huge molecules called macromolecules
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Figure 3.1
Concept 3.1: Carbon atoms can form diverse molecules by bonding to four other atoms
An atom’s electron configuration determines the kinds and number of bonds the atom will form with other atoms
This is the source of carbon’s versatility
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The Formation of Bonds with Carbon
With four valence electrons, carbon can form four covalent bonds with a variety of atoms
This ability makes large, complex molecules possible
In molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape
However, when two carbon atoms are joined by a double bond, the atoms joined to the carbons are in the same plane as the carbons
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When a carbon atom forms four single covalent bonds, the bonds angle toward the corners of an imaginary tetrahedron
When two carbon atoms are joined by a double bond, the atoms joined to those carbons are in the same plane as the carbons
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Figure 3.2
Methane
StructuralFormula
MolecularFormula
Space-FillingModel
Ball-and-Stick ModelName
Ethane
Ethene(ethylene)
The electron configuration of carbon gives it covalent compatibility with many different elements
The valences of carbon and its most frequent partners (hydrogen, oxygen, and nitrogen) are the “building code” that governs the architecture of living molecules
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Figure 3.3
Hydrogen(valence 1)
Carbon(valence 4)
Nitrogen(valence 3)
Oxygen(valence 2)
Carbon atoms can partner with atoms other than hydrogen; for example: Carbon dioxide: CO2
Urea: CO(NH2)2
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Figure 3.UN01
Estradiol
Testosterone
Molecular Diversity Arising from Variation in Carbon Skeletons
Carbon chains form the skeletons of most organic molecules
Carbon chains vary in length and shape
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Animation: Carbon Skeletons
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Figure 3.4
(a) Length
(b) Branching
(c) Double bond position
(d) Presence of rings
Ethane Propane
Butane BenzeneCyclohexane
1-Butene 2-Butene
2-Methylpropane (isobutane)
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Figure 3.4a
(a) Length
Ethane Propane
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Figure 3.4b
(b) Branching
Butane 2-Methylpropane (isobutane)
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Figure 3.4c
(c) Double bond position
1-Butene 2-Butene
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Figure 3.4d
(d) Presence of rings
BenzeneCyclohexane
Hydrocarbons are organic molecules consisting of only carbon and hydrogen
Many organic molecules, such as fats, have hydrocarbon components
Hydrocarbons can undergo reactions that release a large amount of energy
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The Chemical Groups Most Important to Life
Functional groups are the components of organic molecules that are most commonly involved in chemical reactions
The number and arrangement of functional groups give each molecule its unique properties
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The seven functional groups that are most important in the chemistry of life: Hydroxyl group Carbonyl group Carboxyl group Amino group Sulfhydryl group Phosphate group Methyl group
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Figure 3.5Chemical Group
Hydroxyl group ( OH)
Compound Name Examples
Alcohol
Ketone
Aldehyde
Methylatedcompound
Organicphosphate
Thiol
Amine
Carboxylic acid,or organic acid
Ethanol
Acetone Propanal
Acetic acid
Glycine
Cysteine
Glycerolphosphate
5-Methyl cytosine
Amino group ( NH2)
Carboxyl group ( COOH)
Sulfhydryl group ( SH)
Phosphate group ( OPO32–)
Methyl group ( CH3)
Carbonyl group ( C O)
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Figure 3.5a
Chemical Group
Hydroxyl group ( OH)
Compound Name Examples
Alcohol
Ketone
Aldehyde
Amine
Carboxylic acid,or organic acid
Ethanol
Acetone Propanal
Acetic acid
Glycine
Amino group ( NH2)
Carboxyl group ( COOH)
Carbonyl group ( C O)
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Figure 3.5aa
Hydroxyl group ( OH)
Alcohol(The specific nameusually ends in -ol.)
Ethanol, the alcohol presentin alcoholic beverages
(may be written HO )
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Figure 3.5ab
Carbonyl group ( C O)Ketone if the carbonylgroup is within a carbonskeleton
Acetone, the simplest ketone
Aldehyde if the carbonylgroup is at the end of a carbon skeleton
Propanal, an aldehyde
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Figure 3.5ac
Carboxyl group ( COOH)
Acetic acid, which givesvinegar its sour taste
Carboxylic acid, or organic acid
Ionized form of COOH(carboxylate ion),found in cells
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Figure 3.5ad
Amino group ( NH2)
Glycine, an amino acid(note its carboxyl group)
Amine
Ionized form of NH2
found in cells
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Figure 3.5b
Methylatedcompound
Organicphosphate
Thiol Cysteine
Glycerolphosphate
5-Methyl cytosine
Sulfhydryl group ( SH)
Phosphate group ( OPO32–)
Methyl group ( CH3)
Chemical Group Compound Name Examples
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Figure 3.5ba
Sulfhydryl group ( SH)
Cysteine, a sulfur-containing amino acid
Thiol
(may be written HS )
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Figure 3.5bb
Phosphate group ( OPO32–)
Organic phosphate
Glycerol phosphate, whichtakes part in many importantchemical reactions in cells
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Figure 3.5bc
Methyl group ( CH3)
Methylated compound
5-Methyl cytosine, acomponent of DNA that hasbeen modified by addition ofa methyl group
ATP: An Important Source of Energy for Cellular Processes
One organic phosphate molecule, adenosine triphosphate (ATP), is the primary energy-transferring molecule in the cell
ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups
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Figure 3.UN02
Adenosine
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Figure 3.UN03
Adenosine Adenosine
ATP Inorganicphosphate
Energy
Reactswith H2O
ADP
Concept 3.2: 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
Some molecules that serve as monomers also have other functions of their own
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Cells make and break down polymers by the same process
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
These processes are facilitated by enzymes, which speed up chemical reactions
The Synthesis and Breakdown of Polymers
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Animation: Polymers
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Figure 3.6
Unlinked monomerShort polymer
Longer polymer
(a) Dehydration reaction: synthesizing a polymer
(b) Hydrolysis: breaking down a polymer
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Figure 3.6a
Unlinked monomerShort polymer
Longer polymer
(a) Dehydration reaction: synthesizing a polymer
Dehydration removesa water molecule,forming a new bond.
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Figure 3.6b
(b) Hydrolysis: breaking down a polymer
Hydrolysis addsa water molecule,breaking a bond.
The Diversity of Polymers
Each cell has thousands of different macromolecules Macromolecules vary among cells of an organism,
vary more within a species, and vary even more between species
An immense variety of polymers can be built from a small set of monomers
HO
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Concept 3.3: Carbohydrates serve as fuel and building material
Carbohydrates include sugars and the polymers of sugars
The simplest carbohydrates are monosaccharides, or simple sugars
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks
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Sugars
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Monosaccharides have molecular formulas that are usually multiples of CH2O
Glucose (C6H12O6) is the most common monosaccharide
Monosaccharides are classified by the number of carbons in the carbon skeleton and the placement of the carbonyl group
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Figure 3.7
GlyceraldehydeAn initial breakdown
product of glucose in cellsRibose
A component of RNA
Triose: 3-carbon sugar (C3H6O3) Pentose: 5-carbon sugar (C5H10O5)
Hexoses: 6-carbon sugars (C6H12O6)
Energy sources for organismsGlucose Fructose
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Figure 3.7a
GlyceraldehydeAn initial breakdown
product of glucose in cells
Triose: 3-carbon sugar (C3H6O3)
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Figure 3.7b
RiboseA component of RNA
Pentose: 5-carbon sugar (C5H10O5)
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Figure 3.7c
Hexoses: 6-carbon sugars (C6H12O6)
Energy sources for organismsGlucose 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 3.8
(a) Linear and ring forms
(b) Abbreviated ring structure
A disaccharide is formed when a dehydration reaction joins two monosaccharides
This covalent bond is called a glycosidic linkage
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Animation: Disaccharides
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Figure 3.9-1
Glucose Fructose
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Figure 3.9-2
1–2glycosidic
linkage
Glucose
Sucrose
Fructose
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
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Storage Polysaccharides
Starch, a storage polysaccharide of plants, consists entirely of glucose monomers
Plants store surplus starch as granules The simplest form of starch is amylose
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Glycogen is a storage polysaccharide in animals Humans and other vertebrates store glycogen
mainly in liver and muscle cells
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Animation: Polysaccharides
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Figure 3.10
Starch granulesin a potato tuber cell
Cellulose microfibrilsin a plant cell wall
Glycogen granulesin muscletissue
Cellulosemolecules Hydrogen bonds
between —OH groups(not shown) attached tocarbons 3 and 6
Starch (amylose)
Glycogen
Cellulose
Glucosemonomer
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Figure 3.10a
Starch granulesin a potato tuber cell Starch (amylose)
Glucosemonomer
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Figure 3.10aa
Starch granulesin a potato tuber cell
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Figure 3.10b
Glycogen granulesin muscletissue
Glycogen
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Figure 3.10ba
Glycogen granulesin muscletissue
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Figure 3.10c
Cellulose microfibrilsin a plant cell wallCellulosemolecules
Hydrogen bondsbetween —OH groups oncarbons 3 and 6
Cellulose
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Figure 3.10ca
Cellulose microfibrilsin a plant cell wall
Structural Polysaccharides
The polysaccharide cellulose is a major component of the tough wall of plant cells
Like starch and glycogen, cellulose is a polymer of glucose, but the glycosidic linkages in cellulose differ
The difference is based on two ring forms for glucose
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Figure 3.11
(c) Cellulose: 1–4 linkage of glucose monomers
(b) Starch: 1–4 linkage of glucose monomers
(a) and glucose ring structures
Glucose Glucose
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Figure 3.11a
(a) and glucose ring structures
Glucose Glucose
In starch, the glucose monomers are arranged in the alpha () conformation
Starch (and glycogen) are largely helical In cellulose, the monomers are arranged in the beta
() conformation Cellulose molecules are relatively straight
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Figure 3.11b
(b) Starch: 1–4 linkage of glucose monomers
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Figure 3.11c
(c) Cellulose: 1–4 linkage of glucose monomers
In straight structures (cellulose), H atoms on one strand can form hydrogen bonds with OH groups on other strands
Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants
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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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Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods
Chitin also provides structural support for the cell walls of many fungi
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Concept 3.4: Lipids are a diverse group of hydrophobic molecules
Lipids do not form true 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 nonpolar covalent bonds The most biologically important lipids are fats,
phospholipids, and steroids
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Fats
Fats are constructed from two types of smaller molecules: glycerol and fatty acids
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 carbon skeleton
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Animation: Fats
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Figure 3.12
(b) Fat molecule (triacylglycerol)
Glycerol(a) One of three dehydration reactions in the synthesis of a fat
Ester linkage
Fatty acid(in this case, palmitic acid)
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Figure 3.12a
Glycerol(a) One of three dehydration reactions in the synthesis of a fat
Fatty acid(in this case, palmitic acid)
Fats separate from water because water molecules hydrogen-bond to each other and exclude the fats
In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride
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Figure 3.12b
(b) Fat molecule (triacylglycerol)
Ester linkage
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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Figure 3.13
(a) Saturated fat (b) Unsaturated fat
Structuralformula of asaturated fatmolecule
Structuralformula of anunsaturated fat molecule Space-filling
model ofstearic acid,a saturatedfatty acid Space-filling
model of oleicacid, an unsaturatedfatty acid Double bond
causes bending.
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Figure 3.13a
(a) Saturated fat
Structuralformula of asaturated fatmolecule
Space-fillingmodel ofstearic acid,a saturatedfatty acid
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Figure 3.13aa
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Figure 3.13b (b) Unsaturated fat
Structuralformula of anunsaturated fat molecule
Space-fillingmodel of oleic acid, an unsaturatedfatty acid Double bond
causes bending.
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Figure 3.13ba
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, called
unsaturated fats or oils, are liquid at room temperature
Plant fats and fish fats are usually unsaturated
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The major function of fats is energy storage Fat is a compact way for animals to carry their
energy stores with them
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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
Phospholipids are major constituents of cell membranes
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Figure 3.14
(a) Structural formula (b) Space-filling model
Hydrophilichead
(d) Phospholipid bilayer
(c) Phospholipid symbol
Hydrophobictails
Choline
Phosphate
Glycerol
Fatty acids
Hyd
roph
ilic
head
Hyd
roph
obic
tails
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Figure 3.14ab
(a) Structural formula (b) Space-filling model
Choline
Phosphate
Glycerol
Fatty acids
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
This feature of phospholipids results in the bilayer arrangement found in cell membranes
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Figure 3.14cd
Hydrophilichead
(d) Phospholipid bilayer
(c) Phospholipid symbol
Hydrophobictails
Steroids
Steroids are lipids characterized by a carbon skeleton consisting of four fused rings
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
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Video: Cholesterol Stick Model
Video: Cholesterol Space Model
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Figure 3.15
Concept 3.5: 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 defense, storage, transport, cellular communication, movement, and structural support
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Animation: Contractile Proteins
Animation: Defensive Proteins
Animation: Enzymes
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Animation: Gene Regulatory Proteins
Animation: Hormonal Proteins
Animation: Receptor Proteins
Animation: Sensory Proteins
Animation: Storage Proteins
Animation: Structural Proteins
Animation: Transport Proteins
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Figure 3.16 Enzymatic proteins
Storage proteins
Hormonal proteins
Contractile and motor proteins
Defensive proteins
Transport proteins
Receptor proteins
Structural proteins
Enzyme
Function: Selective acceleration of chemical reactions
Function: Storage of amino acids
Example: Digestive enzymes catalyze the hydrolysis of bonds in foodmolecules.
Ovalbumin Amino acidsfor embryo
Examples: Casein, the protein of milk, is the major source of aminoacids for baby mammals. Plants have storage proteins in their seeds.Ovalbumin is the protein of egg white, used as an amino acid sourcefor the developing embryo.
Example: Insulin, a hormone secreted by the pancreas, causes othertissues to take up glucose, thus regulating blood sugarconcentration.
Function: Coordination of an organism’s activities
Normalblood sugar
Highblood sugar
Insulinsecreted
Examples: Motor proteins are responsible for the undulations of ciliaand flagella. Actin and myosin proteins are responsible for the contraction of muscles.
Function: Movement
Muscle tissue
Actin Myosin
30 m Connective tissue 60 m
Collagen
Examples: Keratin is the protein of hair, horns, feathers, and other skinappendages. Insects and spiders use silk fibers to make their cocoonsand webs, respectively. Collagen and elastin proteins provide a fibrousframework in animal connective tissues.
Function: Support
Signaling molecules
Receptorprotein
Example: Receptors built into the membrane of a nerve cell detectsignaling molecules released by other nerve cells.
Function: Response of cell to chemical stimuli
Examples: Hemoglobin, the iron-containing protein of vertebrateblood, transports oxygen from the lungs to other parts of the body.Other proteins transport molecules across cell membranes.
Function: Transport of substances
Transportprotein
Cell membrane
Antibodies
BacteriumVirus
Function: Protection against diseaseExample: Antibodies inactivate and help destroy viruses and bacteria.
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Figure 3.16a
Enzymatic proteins
Storage proteins
Defensive proteins
Transport proteins
Enzyme
Function: Selective acceleration of chemical reactions
Function: Storage of amino acids
Example: Digestive enzymes catalyze thehydrolysis of bonds in food molecules.
Ovalbumin Amino acidsfor embryo
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.
Function: Transport of substances
Transportprotein
Cell membrane
Antibodies
BacteriumVirus
Function: Protection against diseaseExample: Antibodies inactivate and help destroy viruses and bacteria.
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Figure 3.16aa
Enzymatic proteins
Enzyme
Function: Selective acceleration of chemical reactionsExample: Digestive enzymes catalyze thehydrolysis of bonds in food molecules.
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Figure 3.16ab
Defensive proteins
Antibodies
BacteriumVirus
Function: Protection against diseaseExample: Antibodies inactivate and help destroy viruses and bacteria.
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Figure 3.16ac
Storage proteinsFunction: Storage of amino acids
Ovalbumin Amino acidsfor embryo
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.
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Figure 3.16aca
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Figure 3.16ad
Transport proteins
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.
Function: Transport of substances
Transportprotein
Cell membrane
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Figure 3.16b
Hormonal proteins
Contractile and motor proteins
Receptor proteins
Structural proteins
Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration.
Function: Coordination of an organism’s activities
Normalblood sugar
Highblood sugar
Insulinsecreted
Examples: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles.
Function: Movement
Muscle tissue
Actin Myosin
30 m Connective tissue 60 m
Collagen
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 afibrous framework in animal connective tissues.
Function: Support
Signaling molecules
Receptorprotein
Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells.
Function: Response of cell to chemical stimuli
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Figure 3.16ba
Hormonal proteins
Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration.
Function: Coordination of an organism’s activities
Normalblood sugar
Highblood sugar
Insulinsecreted
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Figure 3.16bb
Receptor proteins
Signaling molecules
Receptorprotein
Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells.
Function: Response of cell to chemical stimuli
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Figure 3.16bc
Contractile and motor proteins
Examples: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles.
Function: Movement
Muscle tissue
Actin Myosin
30 m
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Figure 3.16bca
Muscle tissue 30 m
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Figure 3.16bd
Structural proteins
Connective tissue 60 m
Collagen
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 afibrous framework in animal connective tissues.
Function: Support
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Figure 3.16bda
Connective tissue 60 m
Life would not be possible without enzymes Enzymatic proteins act as catalysts, to speed up
chemical reactions without being consumed by the reaction
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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
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Amino Acids
Amino acids are organic molecules with carboxyl and amino groups
Amino acids differ in their properties due to differing side chains, called R groups
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Figure 3.UN04
Side chain (R group)
Carboxylgroup
Aminogroup
carbon
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Figure 3.17 Nonpolar side chains; hydrophobic
Side chain (R group)
Glycine (Gly or G)
Alanine (Ala or A)
Methionine (Met or M)
Phenylalanine (Phe or F)
Polar side chains; hydrophilic
Leucine (Leu or L)
Isoleucine (le or )
Tryptophan (Trp or W)
Proline (Pro or P)
Valine (Val or V)
Serine (Ser or S)
Threonine (Thr or T)
Tyrosine (Tyr or Y)
Asparagine (Asn or N)
Cysteine (Cys or C)
Glutamine (Gln or Q)
Aspartic acid (Asp or D)
Glutamic acid (Glu or E)
Arginine (Arg or R)
Lysine (Lys or K)
Histidine (His or H)
Electrically charged side chains; hydrophilic
Acidic (negatively charged)
Basic (positively charged)
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Figure 3.17a
Nonpolar side chains; hydrophobicSide chain (R group)
Glycine (Gly or G)
Alanine (Ala or A)
Methionine (Met or M)
Phenylalanine (Phe or F)
Leucine (Leu or L)
Isoleucine (le or )
Tryptophan (Trp or W)
Proline (Pro or P)
Valine (Val or V)
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Figure 3.17b
Polar side chains; hydrophilic
Serine (Ser or S)
Threonine (Thr or T)
Tyrosine (Tyr or Y)
Asparagine (Asn or N)
Cysteine (Cys or C)
Glutamine (Gln or Q)
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Figure 3.17c
Aspartic acid (Asp or D)
Glutamic acid (Glu or E)
Arginine (Arg or R)
Lysine (Lys or K)
Histidine (His or H)
Electrically charged side chains; hydrophilic
Acidic (negatively charged)
Basic (positively charged)
Polypeptides
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 3.18
New peptidebond forming
Peptide bond
Side chains
Back-bone
Amino end (N-terminus)
Carboxyl end(C-terminus)
Peptide bond
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Figure 3.18a
Peptide bond
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Figure 3.18b
Side chains
Back-bone
Amino end(N-terminus)
Carboxyl end(C-terminus)
Peptide bond
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 3.19
(a) A ribbon model (b) A space-filling model
GrooveGroove
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Figure 3.19a
(a) A ribbon model
Groove
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Figure 3.19b
(b) A space-filling model
Groove
The sequence of amino acids, determined genetically, leads to a protein’s three-dimensional structure
A protein’s structure determines its function
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Figure 3.20
Antibody protein Protein from flu virus
Four Levels of Protein Structure
Proteins are very diverse, but share three superimposed levels of structure called primary, secondary, and tertiary structure
A fourth level, quaternary structure, arises when a protein consists of more than one polypeptide chain
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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 from interactions between multiple polypeptide chains
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Video: Alpha Helix with No Side Chain
Video: Alpha Helix with Side Chain
Video: Beta Pleated Sheet
Video: Beta Pleated Stick
Animation: Introduction to Protein Structure
Animation: Primary Structure
Animation: Secondary Structure
Animation: Tertiary Structure
Animation: Quaternary Structure
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Figure 3.21a Primary structure
Amino end
Carboxyl end
Primary structure of transthyretin
125
95
90
100105110
120
115
80
70 60
85
75
6555
504540
2530
35
20 15
1051
Amino acids
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Figure 3.21aa
Primary structure
Amino end
2530 20 15
1051
Amino acids
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Figure 3.21b
Secondarystructure
Tertiarystructure
Quaternarystructure
Transthyretinpolypeptide
Transthyretinprotein
pleated sheet
helix
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Figure 3.21ba
Secondary structure
Hydrogenbond
pleated sheet
helix
Hydrogen bond
strand
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Figure 3.21bb
Tertiary structure
Transthyretinpolypeptide
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Figure 3.21bc
Quaternary structure
Transthyretinprotein
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Figure 3.21c
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Figure 3.21d
Hydrogenbond
Disulfidebridge
Polypeptidebackbone
Hydrophobicinteractions andvan der Waalsinteractions
Ionic bond
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Figure 3.21e
Collagen
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Figure 3.21f
HemeIron
subunit
subunit
subunit
subunitHemoglobin
Sickle-Cell Disease: A Change in Primary Structure
Primary structure is the sequence of amino acids on the polypeptide chain
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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© 2014 Pearson Education, Inc.
Figure 3.22
subunit
subunit
Function Red Blood CellShape
QuaternaryStructure
Secondaryand TertiaryStructures
PrimaryStructure
Normal hemoglobin
Sickle-cell hemoglobin
Exposed hydro-phobic region
Molecules crystallizedinto a fiber; capacity tocarry oxygen is reduced.
Molecules do notassociate with oneanother; each carriesoxygen.
1234567
1234567
Nor
mal
Sick
le-c
ell
5 m
5 m
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Figure 3.22a
subunit
FunctionQuaternaryStructure
Secondaryand TertiaryStructures
PrimaryStructure
Normal hemoglobin
Molecules do notassociate with oneanother; each carriesoxygen.
1234567
Nor
mal
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Figure 3.22aa
5 m
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Figure 3.22b
subunit
FunctionQuaternaryStructure
Secondaryand TertiaryStructures
PrimaryStructure
Sickle-cell hemoglobin
Exposed hydro-phobic region
Molecules crystallizedinto a fiber; capacity tocarry oxygen is reduced.
1234567
Sick
le-c
ell
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Figure 3.22ba
5 m
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
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© 2014 Pearson Education, Inc.
Figure 3.23-1
Normal protein
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Figure 3.23-2
Normal protein Denatured protein
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Figure 3.23-3
Denatured proteinNormal protein
Protein Folding in the Cell
It is hard to predict a protein’s structure from its primary structure
Most proteins probably go through several intermediate structures on their way to their final, stable shape
Scientists use X-ray crystallography to determine 3-D protein structure based on diffractions of an X-ray beam by atoms of the crystalized molecule
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© 2014 Pearson Education, Inc.
Figure 3.24
Digital detectorCrystal
Experiment
Results
X-raysource X-ray
beam
X-ray diffractionpattern
DiffractedX-rays
DNARNA
RNApolymerase
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Figure 3.24a
Digital detectorCrystal
Experiment
X-raysource X-ray
beam
X-ray diffractionpattern
DiffractedX-rays
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Figure 3.24b
Results
DNARNA
RNApolymerase
Concept 3.6: 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
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© 2014 Pearson Education, Inc.
Figure 3.25-1
CYTOPLASMNUCLEUS
Synthesisof mRNA mRNA
DNA
1
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Figure 3.25-2
CYTOPLASM
mRNAMovement ofmRNA intocytoplasm
NUCLEUS
Synthesisof mRNA mRNA
DNA
2
1
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Figure 3.25-3
CYTOPLASM
Ribosome
Aminoacids
mRNA
Polypeptide
Synthesisof protein
Movement ofmRNA intocytoplasm
NUCLEUS
Synthesisof mRNA mRNA
DNA
3
2
1
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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Animation: DNA and RNA Structure
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Figure 3.26
Sugar-phosphate backbone(on blue background)
(a) Polynucleotide, or nucleic acid
(b) Nucleotide
(c) Nucleoside components
5 end
3 end
5C
5C
3C
3C
Phosphategroup Sugar
(pentose)
Nitrogenousbase
Nucleoside
Nitrogenous basesPyrimidines
Cytosine (C) Thymine(T, in DNA)
Uracil(U, in RNA)
Purines
Adenine (A) Guanine (G)
Sugars
Deoxyribose (in DNA) Ribose (in RNA)
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Figure 3.26aSugar-phosphate backbone(on blue background)
(a) Polynucleotide, or nucleic acid
(b) Nucleotide
5 end
3 end
5C
5C
3C
3C
Phosphategroup Sugar
(pentose)
Nitrogenousbase
Nucleoside
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Figure 3.26b
(b) Nucleotide
Phosphategroup Sugar
(pentose)
Nitrogenousbase
Nucleoside
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Figure 3.26c
Nitrogenous basesPyrimidines
Cytosine (C) Thymine(T, in DNA)
Uracil(U, in RNA)
Purines
Adenine (A) Guanine (G)
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Figure 3.26d
Sugars
Deoxyribose (in DNA) Ribose (in RNA)
Each nitrogenous base has one or two rings that include nitrogen atoms
The nitrogenous bases in nucleic acids are called cytosine (C), thymine (T), uracil (U), adenine (A), and guanine (G)
Thymine is found only in DNA, and uracil only in RNA; the rest are found in both DNA and RNA
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The sugar in DNA is deoxyribose; in RNA it is ribose
A prime () is used to identify the carbon atoms in the ribose, such as the 2 carbon or 5 carbon
A nucleoside with at least one phosphate attached is a nucleotide
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Nucleotide Polymers
Adjacent nucleotides are joined by covalent bonds that form between the —OH group on the 3 carbon of one nucleotide and the phosphate on the 5 carbon of 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
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The Structures of DNA and RNA Molecules
RNA molecules usually exist as single polypeptide chains
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
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The nitrogenous bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C)
This is 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
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© 2014 Pearson Education, Inc.
Animation: DNA Double Helix
Video: DNA Stick Model
Video: DNA Surface Model
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Figure 3.27
(a) DNA
Sugar-phosphatebackbones
5
5
3
3
(b) Transfer RNA
Base pair joinedby hydrogen bonding
Hydrogen bonds
Base pair joinedby hydrogen bonding
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Figure 3.27a
(a) DNA
Sugar-phosphatebackbones
5
5
3
3 Base pair joinedby hydrogen bonding
Hydrogen bonds
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Figure 3.27b
Sugar-phosphatebackbones
(b) Transfer RNA
Hydrogen bonds
Base pair joinedby hydrogen bonding
DNA and Proteins as Tape 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
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© 2014 Pearson Education, Inc.
Figure 3.UN05
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Figure 3.UN06
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Figure 3.UN06a
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Figure 3.UN06b
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Figure 3.UN07