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Transcript of Essential Chemistry. Matter: Elements and Compounds Organisms are composed of matter Matter is...
Essential Chemistry
Matter: Elements and Compounds• Organisms are composed of matter• Matter is anything that takes up space and has
mass• Matter is found on the Earth in three physical states
– Solid – Liquid – Gas
• Matter is composed of chemical elements– Elements are substances that cannot be broken down into
other substances– There are 92 naturally occurring elements on Earth
Elements and Compounds• An atom is the smallest unit of matter that still retains the
properties of an element, it cannot be broken down to other substances by chemical reactions
• Each element consists of one kind of unique atom
• A compound is a substance consisting of two or more elements in a fixed ratio
Sodium Chlorine Sodium chloride
Atomic number
Element symbol
Mass number
Periodic Chart– Each element consists of one kind of atom– An atom is the smallest unit of matter that still
retains the properties of an element
Essential Elements of Life
• About 25 of the 92 elements are essential to life
• Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter
• Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur
• Trace elements are those required by an organism in minute quantities
– Four of these make up about 96% of the weight of the human body
– Trace elements occur in smaller amounts
Figure 2.3
Elements Essential to Life
Essential Elements of Life
S P O N C H
• Atoms are composed of subatomic particles– Nucleus - the atom’s central core
• A proton is positively charged
• A neutron is electrically neutral
• The number of protons (atomic number) determines the element
– Electrons orbit the nucleus and are negatively charged
The Structure of Atoms
Nucleus
Cloud of negativecharge (2 electrons)
(a)
(b)
2 Protons
2 Neutrons
2 Electrons
Orbitals• Electrons orbit the nucleus of an atom in specific electron shells• Each Orbital holds a maximum of 2 electrons each • Several orbitals may be the same distance from the nucleus and thus contain
electrons of the same energy. Such electrons are said to occupy the same energy level or shell.
• Rule of Eights for filling each shell:
Electron
Firstelectron shell(can hold2 electrons)
Outermostelectron shell(can hold8 electrons)
Carbon (C)Atomic number = 6
Nitrogen (N)Atomic number = 7
Oxygen (O)Atomic number = 8
Hydrogen (H)Atomic number = 1
Electron Shell Significance
• Electrons determine how an atom behaves when it encounters other atoms
• Outer orbital (valence shell) determines reactivity of atom - Electronegativity
• Atoms “desire” full outer orbitals– Give up electrons (Na)
– Take electrons (Cl)
– Share electrons (O2)
• Noble gases - full outer shells (inert)
• Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells– These interactions usually result in atoms staying
close together– The atoms are held together by chemical bonds
Chemical Bonding and Molecules
Chemical Products• Element: a substance composed of only one type of
atom (all the atoms have the same number of protons). • Molecule: a unit composed of two or more atoms
joined together by chemical bonds • Compound: a substance composed of 2 or more
elements that have been joined by chemical bonds• Mixture: a combination of 2 or more substances that do
NOT chemically bond e.g. sugar mixed with salt
• Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones
• Such changes in the chemical composition of matter are called chemical reactions
Chemical Reactions
Unnumbered Figure 2.1
Hydrogen gas Oxygen gas Water
Reactants Products
Chemical Reactions
• Types:– Synthesis reactions - atoms or molecules combine
to form a product– Decomposition reactions - molecules breakdown
into smaller molecules or atoms– Exchange reactions - molecules exchange
constituent components (swap partners)– Reversible reactions - the product of a previous
reaction can revert to the original reactants.
Periodic Chart
Ionic Bonds• When an atom loses or gains electrons, it
becomes electrically charged– Charged atoms are called ions
– Ionic bonds are formed between oppositely charged ions
Covalent bonds• A covalent bond forms when two atoms share one or
more pairs of outer-shell electrons
• Much stronger than ionic bonds – holds lots of Energy
Covalent Bonds
Figure 2.9
Hydrogen Bonds
• A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
• In living cells, the electronegative partners are usually oxygen or nitrogen atoms
(b)
()Hydrogen bond
()
()()
()
()
()()
Figure 2.11b
Carbon—Backbone of Biological Molecules
• Although cells are 70–95% water, the rest consists mostly of carbon-based compounds
• Carbon is unique in its ability to form large, complex, and diverse molecules
• Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds
Organic chemistry-the study of carbon compounds
• Organic compounds range from simple molecules to colossal ones
• Most organic compounds contain hydrogen atoms in addition to carbon atoms
• With four valence electrons, carbon can form four covalent bonds with a variety of atoms
• Needs 4 electrons - single, double or triple bonds
• This tetravalence makes large, complex molecules possible - can form long chains or rings
Carbon Molecules• 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 molecule has a flat shapeMolecularFormula
StructuralFormula
Ball-and-StickModel
Space-FillingModel
Methane
Ethane
Ethene (ethylene)
Carbon Molecules• 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
Hydrogen
(valence = 1)
Oxygen
(valence = 2)
Nitrogen
(valence = 3)
Carbon
(valence = 4)
Carbon Skeleton Diversity
• Carbon is a versatile atom
• Carbon can use its bonds to form an endless diversity of carbon skeletons
• Carbon chains form the skeletons of most organic molecules
LengthEthane Propane
Butane 2-methylpropane(commonly called isobutane)
Branching
Double bonds
Rings
1-Butene 2-Butene
Cyclohexane Benzene
Hydrocarbons
• 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
Functional Groups• Distinctive properties of organic molecules
depend not only on the carbon skeleton but also on the molecular components attached to it
• Certain groups of atoms called functional groups are often attached to skeletons of organic molecules
• Functional groups are the parts of molecules involved in chemical reactions
• The number and arrangement of functional groups give each molecule its unique properties
Functional Groups• The six functional groups that are most important in the
chemistry of life:– Hydroxyl group– Carbonyl group– Carboxyl group– Amino group– Sulfhydryl group– Phosphate group
Biochemistry: 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– Carbohydrates– Lipids– Proteins– Nucleic acids
Macromolecules - Polymers• A polymer is a long molecule consisting of many similar
building blocks called monomers• Most macromolecules are polymers, built from monomers• An immense variety of polymers can be built from a small set
of monomers• Three of the four classes of life’s organic molecules are
polymers:– Carbohydrates– Proteins– Nucleic acids
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
Carbohydrates• Carbohydrates serve as fuel and building material• They include sugars and the polymers of sugars• The simplest carbohydrates are monosaccharides,
or single (simple) sugars• Carbohydrate macromolecules are
polysaccharides, polymers composed of many sugar building blocks
Sugars
• Monosaccharides have molecular formulas that contain C, H, and O in an approximate ratio of 1:2:1
• Monosaccharides are used for short term energy storage, and serve as structural components of larger organic molecules
• Glucose is the most common monosaccharide
• Monosaccharides are classified by location of the carbonyl group and by number of carbons in the carbon skeleton
• 3 C = triose e.g. glyceraldehyde • 4 C = tetrose • 5 C = pentose e.g. ribose, deoxyribose • 6 C = hexose e.g. glucose, fructose, galactose • Monosaccharides in living organisms generally
have 3C, 5C, or 6C:
Monosaccharides
Triose sugars(C3H6O3)
GlyceraldehydeAld
ose
sK
eto
s es
Pentose sugars(C5H10O5)
Ribose
Hexose sugars(C5H12O6)
Glucose Galactose
Dihydroxyacetone
Ribulose
Fructose
Monosaccharides• Monosaccharides serve as a
major fuel for cells and as raw material for building molecules
• The monosaccharides glucose and fructose are isomers– They have the same chemical
formula– Their atoms are arranged
differently
• Though often drawn as a linear skeleton, in aqueous solutions they form rings Glucose Fructose
Monosaccharides
• In aqueous solutions, monosaccharides form rings
Linear andring forms
Abbreviated ringstructure
Monosaccharides: Hexoses
H H H H H
H
OH OH
OH O
OH H
OH O
CH2OH
Ribose
Pentoses (5-carbon sugars)
Deoxyribose
H H 4
5
1
3 2
4
5
1
3 2
CH2OH
Monosaccharides: Pentsoses
Disaccharides• A disaccharide is formed when a dehydration reaction joins two
monosaccharides• Disaccharides are joined by the process of dehydration synthesis• This covalent bond is called a glycosidic linkage
Glucose
Maltose
Fructose Sucrose
Glucose Glucose
Dehydrationreaction in thesynthesis of maltose
Dehydrationreaction in thesynthesis of sucrose
1–4glycosidic
linkage
1–2glycosidic
linkage
Disaccharides
• Lactose = Glucose + Galactose• Maltose = Glucose + Glucose• Sucrose = Glucose + Fructose• The most common disaccharide is
sucrose, common table sugar• Sucrose is extracted from sugar cane and
the roots of sugar beets
Polysaccharides• Complex carbohydrates are called polysaccharides
• They are polymers of monosaccharides - long chains of simple sugar units
• Polysaccharides have storage and structural roles
• The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages
(a) Starch
(b) Glycogen
(c) Cellulose
Storage Polysaccharides - Starch
• 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
Storage Polysaccharides - Glycogen
• 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 ()– Polymers with alpha
glucose are helical
– Polymers with beta glucose are straight
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.
Cellulose • 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
Cellulosemolecules
Cellulose microfibrilsin a plant cell wall
Cell walls Microfibril
Plant cells
0.5 µm
Glucosemonomer
Lipids• Lipids are the one class of large biological molecules
that do not form polymers• Utilized for energy storage, membranes, insulation,
protection• Greasy or oily substances• The unifying feature of lipids is having little or no
affinity for water - insoluble in water • Lipids are hydrophobic becausethey consist mostly
of hydrocarbons, which form nonpolar covalent bonds
Fats• The most biologically important lipids are fats,
phospholipids, and steroids• 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)
Fatty Acids• A fatty acid has a long hydrocarbon chain with a
carboxyl group at one end.
• 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, – Monounsaturated (one double bond)– Polyunsaturated (more than one double bond)
• H can be added to unsaturated fatty acids using a process called hydrogenation
• The major function of fats is energy storage
Stearate Oleate
Fats• 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
Glycerides
• Glycerol + 1 fatty acid = monoglyceride Glycerol + 1 fatty acid = monoglyceride
• Glycerol + 2 fatty acids = diglyceride Glycerol + 2 fatty acids = diglyceride
• Glycerol + 3 fatty acids = triglyceride (also Glycerol + 3 fatty acids = triglyceride (also called triacylglycerol or “fat”.)called triacylglycerol or “fat”.)
Ester linkage
Fat molecule (triacylglycerol)
Saturated Fats• 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
Unsaturated Fats• 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
Fat Sources
• Most animal fats contain saturated fatty acids and tend to be solid at room temperature
• Most plant fats contain unsaturated fatty acids. They tend to be liquid at room temperature, and are called oils.
Phospholipids• In phospholipids, two of the –OH groups on glycerol are joined to
fatty acids. The third –OH joins to a phosphate group which joins, in turn, to another polar group of atoms.
• The phosphate and polar groups are hydrophilic (polar head) while the hydrocarbon chains of the 2 fatty acids are hydrophobic (nonpolar tails).
Structural formula Space-filling model Phospholipid symbol
Hydrophilichead
Hydrophobictails
Fatty acids
Choline
Phosphate
Glycerol
Hyd
rop
ho
bic
tai
lsH
ydro
ph
i lic
hea
d
Phospholipids
Micelle
Phospholipid bilayer Water
Water
Water Lipid head (hydrophilic)
Lipid tail (hydrophobic)
Phospholipids• When phospholipids are added to water, they orient so that the
nonpolar tails are shielded from contact with the polar H2O may form micelles
• Phosopholipids also may 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
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• Testosterone and estrogen function as sex
hormones
Proteins• Proteins have many structures, resulting in a wide
range of functions• They account for more than 50% of the dry mass
of most cells• Protein functions
– Structural support / storage / movement - fibers – Catalysis - Enzymes– Defense against foreign substances– Immunoglobulins– Transport – globins, membrane transporters– Messengers for cellular communications - hormones
Proteins• A protein is composed of one or more polypeptides that
performs a function• A polypeptide is a polymer of amino acids joined by
peptide bonds to form a long chain• Polypeptides range in length from a few monomers to
more than a thousand• Each polypeptide has a unique linear sequence of amino
acids• A protein consists of one or more polypeptides which are
coiled and folded into a specific 3-D shape. • The shape of a protein determines its function.
Amino Acids• Amino acids are monomers of polypetides
• They composed of a carboxyl group, amino group, and an “R”Group
• 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
O
O–
H
H3N+ C C
O
O–
H
CH3
H3N+ C
H
C
O
O–
CH3 CH3
CH3
C C
O
O–
H
H3N+
CH
CH3
CH2
C
H
H3N+
CH3
CH3
CH2
CH
C
H
H3N+ C
CH3
CH2
CH2
CH3N+
H
C
O
O–
CH2
CH3N+
H
C
O
O–
CH2
NH
H
C
O
O–
H3N+ C
CH2
H2C
H2N C
CH2
H
C
Nonpolar
Glycine (Gly) Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile)
Methionine (Met) Phenylalanine (Phe)
C
O
O–
Tryptophan (Trp) Proline (Pro)
H3C
Figure 5.17
S
O
O–
Amino Acids
O–
OH
CH2
C C
H
H3N+
O
O–
H3N+
OH CH3
CH
C C
HO–
O
SH
CH2
C
H
H3N+ C
O
O–
H3N+ C C
CH2
OH
H H H
H3N+
NH2
CH2
O
C
C C
O
O–
NH2 O
C
CH2
CH2
C CH3N+
O
O–
O
Polar
Electricallycharged
–O O
C
CH2
C CH3N+
H
O
O–
O– O
C
CH2
C CH3N+
H
O
O–
CH2
CH2
CH2
CH2
NH3+
CH2
C CH3N+
H
O
O–
NH2
C NH2+
CH2
CH2
CH2
C CH3N+
H
O
O–
CH2
NH+
NH
CH2
C CH3N+
H
O
O–
Serine (Ser) Threonine (Thr)Cysteine
(Cys)Tyrosine
(Tyr)Asparagine
(Asn)Glutamine
(Gln)
Acidic Basic
Aspartic acid (Asp)
Glutamic acid (Glu)
Lysine (Lys) Arginine (Arg) Histidine (His)
Amino Acids
Amino Acids and Peptide Bonds
• Two amino acids can join by condensation to form a dipeptide plus H2O.
• The bond between 2 amino acids is called a 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
A ribbon model
Groove
Groove
A space-filling model
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
Amino acidsubunits
pleated sheet
helix
Levels of Protein Structure
70
Interactions that Contribute to a Interactions that Contribute to a Protein’s ShapeProtein’s Shape
70 70 70
71
Enzymes as Catalysts• To increase reaction rates:
– Add Energy (Heat) - molecules move faster so they collide more frequently and with greater force.
– Add a catalyst – a catalyst reduces the energy needed to reach the activation state, without being changed itself. Proteins that function as catalysts are called enzymes.
Reactant
Product
CatalyzedUncatalyzed
Product
Reactant
Activationenergy
Activationenergy
En
erg
y su
pp
lied
En
erg
y re
leas
ed
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Activation Energy and Catalysis
Enzymes Are Biological Catalysts• Enzymes are proteins that carry out most catalysis in living
organisms.• Unlike heat, enzymes are highly specific. Each enzyme
typically speeds up only one or a few chemical reactions.• Unique three-dimensional shape enables an enzyme to
stabilize a temporary association between substrates.• Because the enzyme itself is not changed or consumed in
the reaction, only a small amount is needed, and can then be reused.
• Therefore, by controlling which enzymes are made, a cell can control which reactions take place in the cell.
Substrate Specificity of Enzymes• Almost all enzymes are globular proteins with one or more active sites on their surface.• The substrate is the reactant an enzyme acts on• Reactants bind to the active site to form an enzyme-substrate complex.• The 3-D shape of the active site and the substrates must match, like a lock and key• Binding of the substrates causes the enzyme to adjust its shape slightly, leading to a
better induced fit.• When this happens, the substrates are brought close together and existing bonds are
stressed. This reduces the amount of energy needed to reach the transition state.
Substate
Active site
Enzyme
Enzyme- substratecomplex
1 The substrate, sucrose, consistsof glucose and fructose bonded together.
Bond
Enzyme
Active site
The substrate binds to the enzyme, forming an enzyme-substrate complex.
2
H2O
The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks.
3
Glucose Fructose
Products are released, and the enzyme is free to bind other substrates.
4
The Catalytic Cycle Of An Enzyme
Conformational Change and Enzyme Activity• 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
Effects of Temperature and pH• Each enzyme has an optimal temperature in
which it can function
Optimal temperature for enzyme of thermophilic
Rat
e o
f re
actio
n
0 20 40 80 100Temperature (Cº)
(a) Optimal temperature for two enzymes
Optimal temperature fortypical human enzyme
(heat-tolerant) bacteria
Effects of Temperature and pH– Each enzyme has an optimal pH in which it can function
Figure 8.18
Rat
e o
f re
actio
n
(b) Optimal pH for two enzymes
Optimal pH for pepsin (stomach enzyme)
Optimal pHfor trypsin(intestinalenzyme)
10 2 3 4 5 6 7 8 9
Nucleic Acids
• 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
5 end
3 end
Nucleoside
Nitrogenousbase
Phosphategroup
Nucleotide
Polynucleotide, ornucleic acid
Pentosesugar
Phosphate group
Sugar
Nitrogenous base
N
N
O
4’
5’
1’
3’ 2’
2 8
7 6
3 9 4
5
P CH2
O
– O
O –
OH R OH in RNA
H in DNA
O
N
NH2
N 1
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)
Nitrogenous bases
• Purines have a double ring structure and include adenine (A) and guanine (G).
• Pyrimidines have a single ring structure and include cytosine (C), thymine (T), and uracil (U) – found only in RNA
Adenine
Guanine
C C
N N
N
C
H
N
C
C H
O
H
Cytosine (both DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
H C C
N C
H
N
C
NH2
N
N
C H O C C
N C
H
N
C H
H
O C C
N C
H
N
C
O
H H3C
H
O C C
N C
H
N
C
O
H H
H
P U R I N E S
P Y R I M I D I N E S
NH2
NH2
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
ATP• Adenosine triphosphate (ATP), is the primary energy-
transferring molecule in the cell • ATP is the “energy currency” of the cell• ATP consists of an organic molecule called adenosine
attached to a string of three phosphate groups• The energy stored in the bond that connects the third
phosphate to the rest of the molecule supplies the energy needed for most cell activities