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The Molecules of Life
• Within cells, small organic molecules are joined together to form larger molecules
• Macromolecules are large molecules composed of thousands of covalently connected atoms
Most macromolecules are polymers, built from monomers
• A polymer is a long molecule consisting of many similar building blocks called monomers
• Three of the four classes of life’s organic molecules are polymers:
– Carbohydrates
– Proteins
– Nucleic acids
The Synthesis and Breakdown of Polymers
• Monomers form larger molecules by condensation reactions called dehydration reactions
• Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction
Short polymer Unlinked monomer
Dehydration removes a watermolecule, forming a new bond
Dehydration reaction in the synthesis of a polymer
Longer polymer
Hydrolysis adds a watermolecule, breaking a bond
Hydrolysis of a polymer
The Diversity of Polymers
• Each cell has thousands of different kinds of 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
1 2 3 HOH
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
Sugars
• Monosaccharides have molecular formulas that are usually multiples of CH2O
• Glucose is the most common monosaccharide
• Monosaccharides are classified by location of the carbonyl group and by number of carbons in the carbon skeleton
Triose sugars(C3H6O3)
GlyceraldehydeAld
ose
sK
eto
s es
Pentose sugars(C5H10O5)
Ribose
Hexose sugars(C6H12O6)
Glucose Galactose
Dihydroxyacetone
Ribulose
Fructose
• Monosaccharides serve as a major fuel for cells and as raw material for building molecules
• Though often drawn as a linear skeleton, in aqueous solutions they form rings
Linear andring forms
Abbreviated ringstructure
• A disaccharide is formed when a dehydration reaction joins two monosaccharides
• This covalent bond is called a glycosidic bond
• Lactose = Glu + Gal
• Maltose = Glu + Glu
• Sucrose = Glu + Fru
Glucose
Maltose
Fructose Sucrose
Glucose Glucose
Dehydrationreaction in thesynthesis of maltose
Dehydrationreaction in thesynthesis of sucrose
1–4glycosidic
linkage
1–2glycosidic
linkage
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
Starch granulesin a potato tuber cell
Cellulose microfibrilsin a plant cell wall
Glycogen granulesin muscletissue
Cellulosemolecules
Hydrogen bondsbetween —OH groups(not shown) attached tocarbons 3 and 6
Starch (amylose)
Glycogen
Cellulose
Glucosemonomer
Storage Polysaccharides
• Starch, a storage polysaccharide of plants, consists entirely of glucose monomers
• Plants store surplus starch as granules within chloroplasts and other plastids
Chloroplast Starch
1 µm
Amylose
Starch: a plant polysaccharide
Amylopectin
• Glycogen is a storage polysaccharide in animals
• Humans and other vertebrates store glycogen mainly in liver and muscle cells
Mitochondria Glycogen granules
0.5 µm
Glycogen
Glycogen: an animal polysaccharide
Structural Polysaccharides
• 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 ()
a Glucose
a and b glucose ring structures
b Glucose
Starch: 1–4 linkage of a glucose monomers.
Cellulose: 1–4 linkage of b glucose monomers.
• Polymers with alpha glucose are helical
• Polymers with beta 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
Cellulosemolecules
Cellulose microfibrilsin a plant cell wall
Cell walls Microfibril
Plant cells
0.5 µm
Glucosemonomer
• Enzymes that digest starch by hydrolyzing alpha linkages can’t hydrolyze beta 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
• Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods
• Chitin also provides structural support for the cell walls of many fungi
• Chitin can be used as surgical thread
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 becausethey consist mostly of hydrocarbons, which form nonpolar covalent bonds
• The most biologically important lipids are fats, phospholipids and steroids
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
Dehydration reaction in the synthesis of a fat
Glycerol
Fatty acid(palmitic acid)
• Fats separate from water because water molecules form hydrogen bonds with 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
Ester linkage
Fat molecule (triacylglycerol)
• 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
• The major function of fats is energy storage
(a) Saturated fat (b) Unsaturated fat
Structuralformula of asaturated fatmolecule
Structuralformula of anunsaturated fat molecule Space-filling
model ofstearic acid,a saturatedfatty acid
Space-fillingmodel of oleicacid, an unsaturatedfatty acid Double bond
causes bending.
• Fats made from saturated fatty acids are called saturated fats
• Most animal fats are saturated
• Saturated fats are solid at room temperature
• A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits
Saturated fat and fatty acid.
Stearic acid
• Fats made from unsaturated fatty acids are called unsaturated fats
• Plant fats and fish fats are usually unsaturated
• Plant fats and fish fats are liquid at room temperature and are called oils
Unsaturated fat and fatty acid.
Oleic acid
cis double bondcauses bending
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
(a) Structural formula (b) Space-filling model
Hydrophilichead
(d) Phospholipid bilayer
(c) Phospholipid symbol
Hydrophobictails
Choline
Phosphate
Glycerol
Fatty acids
Hyd
rop
hil
ic h
ead
Hyd
rop
ho
bic
tai
ls
• 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
WATERHydrophilichead
Hydrophobictails
WATER
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
Proteins have many structures, resulting in a wide range of functions
• Proteins account for more than 50% of the dry mass of most cells
• Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances
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 disease
Example: Antibodies inactivate and help destroy viruses and bacteria.
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
• Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions
• Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life
Substrate(sucrose)
Enzyme(sucrose)
Fructose
Glucose
Defensive proteins
Antibodies
BacteriumVirus
Function: Protection against disease
Example: Antibodies inactivate and help destroy viruses and bacteria.
Storage proteins
Function: 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.
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
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
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
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
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
Polypeptides
• Polypeptides are polymers of amino acids
• A protein consists of one or more polypeptides
Amino Acid Monomers
• Amino acids are organic molecules with carboxyl and amino groups
• Amino acids differ in their properties due to differing side chains, called R groups
• Cells use 20 amino acids to make thousands of proteins
Aminogroup
Carboxylgroup
carbon
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)
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)
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)
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 monomers to more than a thousand
• Each polypeptide has a unique linear sequence of amino acids
• Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus)
• NCC-NCC-NCC-NCC
New peptidebond forming
Peptide bond
Side chains
Back-bone
Amino end (N-terminus)
Carboxyl end(C-terminus)
Peptide bond
Protein Conformation and Function
• A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape
• The sequence of amino acids determines a protein’s three-dimensional conformation
• A protein’s conformation determines its function
• Ribbon models and space-filling models can depict a protein’s conformation
Antibody protein Protein from flu virus
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
Secondarystructure
Tertiarystructure
Quaternarystructure
Transthyretinpolypeptide
Transthyretinprotein
pleated sheet
helix
• 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
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
• 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 alpha helix and a folded structure called a beta pleated sheet
Secondary structure
Hydrogenbond
pleated sheet
helix
Hydrogen bond
strand
Tertiary structure
Transthyretinpolypeptide
Hydrophobicinteractions andvan der Waalsinteractions
Polypeptidebackbone
Disulfide bridge
Ionic bond
Hydrogenbond
Quaternary structure
Transthyretinprotein
• 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
Chains
ChainsHemoglobin
IronHeme
CollagenPolypeptide chain
Polypeptidechain
Sickle-Cell Disease: A Simple Change in Primary Structure
• A slight change in primary structure can affect a protein’s conformation and ability to function
• Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin
Red bloodcell shape
Normal cells arefull of individualhemoglobinmolecules, eachcarrying oxygen.
10 µm 10 µm
Red bloodcell shape
Fibers of abnormalhemoglobin deformcell into sickleshape.
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.
12
345
67
12
345
67
No
rmal
Sic
kle-
cell
5 m
5 m
What Determines Protein Conformation?
• In addition to primary structure, physical and chemical conditions can affect conformation
• Alternations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel
• This loss of a protein’s native conformation is called denaturation
• A denatured protein is biologically inactive
Denaturation
Renaturation
Denatured proteinNormal protein
The Protein-Folding Problem
• It is hard to predict a protein’s conformation from its primary structure
• Most proteins probably go through several states on their way to a stable conformation
• Chaperonins are protein molecules that assist the proper folding of other proteins
Chaperonin(fully assembled)
Hollowcylinder
Cap
Polypeptide
Correctlyfoldedprotein
An unfolded poly-peptide enters thecylinder from oneend.
Steps of ChaperoninAction:
The cap comesoff, and theproperly foldedprotein is released.
The cap attaches, causingthe cylinder to changeshape in such a way that it creates a hydrophilicenvironment for thefolding of the polypeptide.
• Scientists use X-ray crystallography to determine a protein’s conformation
• Another method is nuclear magnetic resonance (NMR) spectroscopy, which does not require protein crystallization
Photographic film
Diffracted X-rays
X-raysource X-ray
beam
X-raydiffraction pattern
Crystal
Nucleic acid
3D computer modelX-ray diffraction pattern
Protein
Digital detectorCrystal
Experiment
Results
X-raysource X-ray
beam
X-ray diffractionpattern
DiffractedX-rays
DNARNA
RNApolymerase
Nucleic acids store and transmit hereditary information
• The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene
• Genes are made of DNA, a nucleic acid
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 in ribosomes
NUCLEUS
DNA
CYTOPLASM
mRNA
mRNA
Ribosome
Aminoacids
Synthesis ofmRNA in the nucleus
Movement ofmRNA into cytoplasmvia nuclear pore
Synthesis of protein
Polypeptide
The Structure of Nucleic Acids
• Nucleic acids are polymers called polynucleotides
• Each polynucleotide is made of monomers called nucleotides
• Each nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group
• The portion of a nucleotide without the phosphate group is called a nucleoside
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 bases
Pyrimidines
Cytosine (C) Thymine(T, in DNA)
Uracil(U, in RNA)
Purines
Adenine (A) Guanine (G)
Sugars
Deoxyribose (in DNA) Ribose (in RNA)
5 end
3 end
Nucleoside
Nitrogenousbase
Phosphategroup
Nucleotide
Polynucleotide, ornucleic acid
Pentosesugar
Sugar-phosphatebackbones
5
5
3
3 Base pair joinedby hydrogen bonding
Hydrogen bonds
Nucleotide Monomers
• Nucleotide monomers are made up of nucleosides and phosphate groups
• Nucleoside = nitrogenous base + sugar
• There are two families of nitrogenous bases:
– Pyrimidines have a single six-membered ring
– Purines have a six-membered ring fused to a five-membered ring
• In DNA, the sugar is deoxyribose
• In RNA, the sugar is ribose
Nitrogenous bases
Pyrimidines
Purines
Pentose sugars
CytosineC
Thymine (in DNA)T
Uracil (in RNA)U
AdenineA
GuanineG
Deoxyribose (in DNA)
Nucleoside components
Ribose (in RNA)
Nucleotide Polymers
• Nucleotide polymers are linked together, building a polynucleotide
• 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 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
The DNA Double Helix
• A DNA molecule has two polynucleotides spiraling around an imaginary axis, forming a double helix
• In the DNA double helix, the two backbones run in opposite 5´ to 3´ directions from each other, an arrangement referred to as antiparallel
• One DNA molecule includes many genes
• The nitrogenous bases in DNA form hydrogen bonds in a complementary fashion: A always with T, and G always with C
Sugar-phosphatebackbone
3 end5 end
Base pair (joined byhydrogen bonding)
Old strands
Nucleotideabout to beadded to anew strand
5 end
New strands
3 end
5 end3 end
5 end
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
Animations and Videos
• Macromolecules – 1
• Macromolecules – 2
• Polymers
• Biomolecules – Carbohydrates
• Carbohydrates
• Glucose in Water
• Dehydration and Hydrolysis
Animations and Videos
• Disaccharides
• Polysaccharides
• Bozeman – Carbohydrates
• Fats
• Lipids
• Biomolecules – Lipids
• Bozeman - Lipids
Animations and Videos
• Proteins
• Protein Structure – 1
• Protein Structure – 2
• Life Cycle of a Protein
• Peptide Bond Formation
• Dehydration Synthesis of Amino Acids
• Protein Folding - 1
Animations and Videos
• Protein Folding – 2
• Protein Organization
• Protein Denaturation
• Bozeman – Proteins
• How Enzymes Work
• Enzyme Action and the Hydrolysis of Sucrose
• Enzyme Catalysis - 1
Animations and Videos
• Enzyme Catalysis – 2
• Allosteric Regulation of Enzymes
• Allosteric Enzyme
• Enzyme Changing Shape
• Bozeman – Enzymes
• Bozeman - Nucleic Acids
• Testing Organic Substances
• Chapter Quiz Questions – 1
Animations and Videos
• Chapter Quiz Questions – 2