Biochemistry
The Structure and Function of
Macromolecules
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 shape
Molecular
Formula
Methane
Ethane
Ethene (ethylene)
Structural
Formula
Ball-and-Stick
Model
Space-Filling
Model
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
Ethane
Propane
Butane
2-methylpropane
(commonly called isobutane)
Length
Branching
1-Butene
Double bonds
Cyclohexane
Rings
2-Butene
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
Isomers
• Isomers are compounds with
the same molecular formula
but different structures and
properties:
– Structural isomers have
different covalent
arrangements of their atoms
– Geometric isomers have the
same covalent arrangements
but differ in spatial
arrangements
– Enantiomers are isomers that
are mirror images of each other
Structural isomers differ in covalent partners, as shown
in this example of two isomers of pentane.
cis isomer: The two Xs
are on the same side.
trans isomer: The two Xs
are on opposite sides.
Geometric isomers differ in arrangement about a double
bond. In these diagrams, X represents an atom or group
of atoms attached to a double-bonded carbon.
L
isomer
D
isomer
Enantiomers differ in spatial arrangement around an
asymmetric carbon, resulting in molecules that are
mirror images, like left and right hands. The two
isomers are designated the L and D isomers from the
Latin for left and right (levo and dextro). Enantiomers
cannot be superimposed on each other.
Enantiomers
• Enantiomers are important in the pharmaceutical industry
• Two enantiomers of a drug may have different effects
• Differing effects of enantiomers demonstrate that organisms
are sensitive to even subtle variations in molecules
L-Dopa
(effective against
Parkinson’s disease)
D-Dopa
(biologically
Inactive)
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
STRUCTURE
(may be written HO—)
Ethanol, the alcohol present in
alcoholic beverages
NAME OF COMPOUNDS
Alcohols (their specific names
usually end in -ol)
FUNCTIONAL PROPERTIES
Is polar as a result of the
electronegative oxygen atom
drawing electrons toward itself.
Attracts water molecules, helping
dissolve organic compounds such
as sugars (see Figure 5.3).
Acetone, the simplest ketone
STRUCTURE
EXAMPLE
Acetone, the simplest ketone
NAME OF COMPOUNDS
Propanal, an aldehyde
Ketones if the carbonyl group is
within a carbon skeleton
FUNCTIONAL PROPERTIES
Aldehydes if the carbonyl group is
at the end of the carbon skeleton
A ketone and an aldehyde may
be structural isomers with
different properties, as is the case
for acetone and propanal.
STRUCTURE
EXAMPLE
Acetic acid, which gives vinegar
its sour taste
NAME OF COMPOUNDS
FUNCTIONAL PROPERTIES
Carboxylic acids, or organic acids
Has acidic properties because it is
a source of hydrogen ions.
The covalent bond between
oxygen and hydrogen is so polar
that hydrogen ions (H+) tend to
dissociate reversibly; for example,
Acetic acid
Acetate ion
In cells, found in the ionic form,
which is called a carboxylate group.
STRUCTURE
EXAMPLE
Glycine
Because it also has a carboxyl
group, glycine is both an amine and
a carboxylic acid; compounds with
both groups are called amino acids.
NAME OF COMPOUNDS
Amine
FUNCTIONAL PROPERTIES
Acts as a base; can pick up a
proton from the surrounding
solution:
(nonionized) (ionized)
Ionized, with a charge of 1+,
under cellular conditions
STRUCTURE
EXAMPLE
(may be written HS—)
Ethanethiol
NAME OF COMPOUNDS
Thiols
FUNCTIONAL PROPERTIES
Two sulfhydryl groups can
interact to help stabilize protein
structure (see Figure 5.20).
STRUCTURE
EXAMPLE
Glycerol phosphate
NAME OF COMPOUNDS
Organic phosphates
FUNCTIONAL PROPERTIES
Makes the molecule of which it
is a part an anion (negatively
charged ion).
Can transfer energy between
organic molecules.
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
Biochemistry
• Living organisms are composed of both inorganic
and organic molecules
• Inorganic molecules
– Relatively small, simple molecules that usually lack C
(a few have one C atom).
– Examples: CO2, NH3, H2O, O2, H2
• Organic molecules
– Larger, more complex, based on a backbone of C atoms
(always contain C as a major part of their structure).
– Examples: C6H12O6, C2H5COOH
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 water
molecule, forming a new bond
Longer polymer
Dehydration reaction in the synthesis of a polymer
Hydrolysis adds a water
molecule, 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
• 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:
Triose sugars
(C3H6O3)
Pentose sugars
(C5H10O5)
Hexose sugars
(C5H12O6)
Glyceraldehyde
Ribose
Galactose
Glucose
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 and
ring forms
Abbreviated ring
structure
Triose
(3-carbon sugar)
H
Pentoses
(5-carbon sugars)
O
1C
H 2 C OH
H C OH
3
H
Glyceraldehyde
5 CH2OH
5 CH2OH
O
4
H
H
3
OH
1
H H
2
OH OH
Ribose
O
OH
1
4
H
H
H
H
2
3
H
OH
Deoxyribose
29
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
Dehydration
reaction in the
synthesis of maltose
1–4
glycosidic
linkage
Glucose
Glucose
Dehydration
reaction in the
synthesis of sucrose
Maltose
1–2
glycosidic
linkage
Glucose
Fructose
Sucrose
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
Chloroplast
• Starch, a storage
polysaccharide of plants,
consists entirely of
glucose monomers
• Plants store surplus
starch as granules within
chloroplasts and other
plastids
Starch
1 µm
Amylose
Amylopectin
Starch: a plant polysaccharide
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 ()
a Glucose
b Glucose
a and b glucose ring structures
Starch: 1–4 linkage of a glucose monomers.
– Polymers with alpha
glucose are helical
– Polymers with beta glucose
are straight
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
Cellulose microfibrils
in a plant cell wall
Cell walls
Microfibril
0.5 µm
Plant cells
Cellulose
molecules
 Glucose
monomer
Chitin
• 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
• 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 because they 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
Fatty acid
(palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat
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
Ester linkage
Fat molecule (triacylglycerol)
Glycerides
• Glycerol + 1 fatty acid = monoglyceride
• Glycerol + 2 fatty acids = diglyceride
• Glycerol + 3 fatty acids = triacylglycerol
(also called a triglyceride or fat.)
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
Stearic acid
Saturated fat and fatty 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
Oleic acid
Unsaturated fat and fatty acid.
cis double bond
causes 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).
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic
head
Hydrophobic
tails
Structural formula
Space-filling model
Phospholipid symbol
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
Water
Lipid head
(hydrophilic)
Lipid tail
(hydrophobic)
Micelle
Water
Phospholipid bilayer
Water
Phospholipids
• The structure of phospholipids results in a bilayer arrangement
found in cell membranes
• Phospholipids are the major component of all cell membranes
Hydrophilic
head
Hydrophobic
tails
WATER
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
• 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
 carbon
Amino
group
Carboxyl
group
Amino Acids
CH3
CH3
H
H3N+
C
CH3
O
H3N+
C
O–
H
Glycine (Gly)
C
H
H3N+
C
CH
CH3
CH3
O
C
H3N+
C
C
O–
Alanine (Ala)
CH2
CH2
O
O–
CH3
CH3
O
H3C
H3N+
C
H
Valine (Val)
Leucine (Leu)
C
O
C
O–
O–
H
CH
H
Isoleucine (Ile)
Nonpolar
CH3
CH2
S
NH
CH2
CH2
H3N+
C
H3N+
C
O–
H
Methionine (Met)
Figure 5.17
CH2
O
C
CH2
O
H3 N+
C
C
O–
H
Phenylalanine (Phe)
O
H2C
CH2
H2N
C
O
C
O–
H
C
O–
H
Tryptophan (Trp)
Proline (Pro)
Amino Acids
OH
NH2 O
C
NH2 O
OH
Polar
CH2
H3N+
C
CH
O
H3N+
C
O–
H
Serine (Ser)
C
C
SH
CH3
OH
CH2
O
H3N+
C
O–
H
C
CH2
O
C
H
O–
H3N+
CH2
O
H3N+
C
C
Electrically
charged
CH2
H3N+
C
O
O–
H
H3N+
NH3+
O
C
O
C
O–
H
C
CH2
CH2
CH2
CH2
CH2
C
O
CH2
C
O–
H3N+
C
H
NH2+
C
H3N+
H3N+
C
Lysine (Lys)
C
H
CH2
O–
NH
CH2
CH2
O
H
Glutamic acid
(Glu)
NH+
NH2
CH2
H
Aspartic acid
(Asp)
O–
H
C
CH2
C
H3N+
C
Basic
O–
O
CH2
O
Asparagine Glutamine
(Gln)
(Asn)
Tyrosine
(Tyr)
Acidic
–O
C
O–
H
Cysteine
(Cys)
Threonine (Thr)
C
CH2
O
C
O–
O
C
O–
Arginine (Arg)
Histidine (His)
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 threedimensional conformation
• A protein’s conformation
determines its function
• Ribbon models and spacefilling models can depict a
protein’s conformation
Groove
A ribbon model
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
 pleated sheet
Amino acid
subunits
 helix
Primary Structure
• 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
Amino end
Amino acid
subunits
Carboxyl end
Secondary Structure
• 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
 pleated sheet
Amino acid
subunits
 helix
Tertiary Structure
• 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
conformation
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Ionic bond
Quaternary Structure
• 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
Polypeptide
chain
 Chains
Iron
Heme
Polypeptide chain
Collagen
 Chains
Hemoglobin
Levels of Protein Structure
Interactions that Contribute to a Protein’s Shape
68
69
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
10 µm
Red blood Normal cells are
cell shape full of individual
hemoglobin
molecules, each
carrying oxygen.
10 µm
Red blood
cell shape
Fibers of abnormal
hemoglobin deform
cell into sickle
shape.
Sickle Cell Anemia
Sickle-cell hemoglobin
Normal hemoglobin
Primary
structure
Val
His
1
2
Leu
Thr
3
4
Pro
Glu
5
6
Secondary
and tertiary
structures
7
 subunit
Quaternary Normal
hemoglobin
structure
(top view)
Primary
structure
Secondary
and tertiary
structures
Molecules do
not associate
with one
another; each
carries oxygen.
His
1
2
Leu
Thr
3
4
Function
Val
Glu
5
6
7
 subunit
Sickle-cell
hemoglobin


Pro
Exposed
hydrophobic
region

Quaternary
structure

Val


Function
Glu
Molecules
interact with
one another to
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.


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
Normal protein
Denatured protein
Renaturation
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
DNA
Synthesis of
mRNA in the nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
Movement of
mRNA into cytoplasm
via nuclear pore
Ribosome
Synthesis
of protein
Polypeptide
Amino
acids
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
Nucleoside
Nitrogenous
base
Phosphate
group
Nucleotide
3 end
Polynucleotide, or
nucleic acid
Pentose
sugar
Nitrogenous base
NH2
6
7N 5
N1
8
2
9 N 4 N3
Phosphate group
O
–O
P
O CH2
5’
O–
O
4’
1’
3’
2’
OH
OH in RNA
R
Sugar
H in DNA
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 sixmembered 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
Cytosine
C
Thymine (in DNA) Uracil (in RNA)
U
T
Purines
Adenine
A
Guanine
G
Pentose sugars
Deoxyribose (in DNA)
Nucleoside components
Ribose (in RNA)
Nitrogenous bases
NH2
• 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
N
P
U
R
I
N
E
S
H
C
C
N
C
N
C
C
H
N
H
O
N
H
C
C
Guanine
N
H
C
N
C
C
N
NH2
Cytosine
(both DNA
and RNA)
NH2
Adenine
P
Y
R
I
M
I
D
I
N
E
S
H
C
H
C
C
N
N
C
O
H
O
H3C
C
H
C
C
N
Thymine
(DNA only)
N
H
C
O
H
H
Uracil
(RNA only)
O
H
C
H
C
C
N
H
N
H
C
O
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
5 end
3 end
Sugar-phosphate
backbone
Base pair (joined by
hydrogen bonding)
Old strands
Nucleotide
about to be
added to a
new strand
5 end
New
strands
5 end
3 end
5 end
3 end
ATP
• Adenosine triphosphate (ATP), is the primary energytransferring 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