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CAMPBELL
BIOLOGY
TENTH
EDITION
Reece • Urry • Cain • Wasserman • Minorsky • Jackson
4
Carbon and
the Molecular
Diversity of
Life
Lecture Presentation by
Nicole Tunbridge and
Kathleen Fitzpatrick
© 2014 Pearson Education, Inc.
Overview: Carbon: The
Backbone of Life
• Although cells are 70–95% water, the rest
consists mostly of carbon-based compounds
• Carbon is unparalleled 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
© 2014 Pearson Education, Inc.
Figure 4.1 What properties make carbon the basis of all life?
Organic chemistry is the study of
carbon compounds
• Organic chemistry is the study of
compounds that contain carbon
• Organic compounds can range from simple
molecules, such as CH4, to complex
molecules such as proteins, which may
have molecular masses greater than
hundred thousand daltons.
• Most organic compounds contain hydrogen
atoms in addition to carbon atoms.
Carbon
• The overall percentages of the major
elements of life (C, H, O, N, S, and P) are
quite uniform from one organism to
another.
• Because of carbon’s versatility, these few
elements can be combined to build an
inexhaustible variety of organic molecules.
Vitalism and Mechanism
• Early organic chemists proposed vitalism, the
belief that physical and chemical laws do not
apply to living things and that organic
compounds arise only in organisms.
• Vitalism was disproved when chemists
synthesized organic compounds.
• Mechanism is the view that all natural
phenomena are governed by physical and
chemical laws and Organic chemistry was
redefined as the study of organic compounds,
regardless of origin.
Organic Molecules and the Origin of
Life on Earth
• Stanley Miller’s classic experiment
demonstrated the abiotic synthesis of
organic compounds
• Experiments support the idea that abiotic
synthesis of organic compounds, perhaps
near volcanoes, could have been a stage in
the origin of life
© 2014 Pearson Education, Inc.
Figure 4.2
EXPERIMENT
“Atmosphere”
CH4
Water vapor
Electrode
Condenser
Some of Stanley
Miller’s original
vials from his
1958 hydrogen
sulfide (H2S)
experiment
Cooled “rain”
containing
organic
molecules
H2O
“sea”
Cold
water
Inquiry: Can organic molecules
form under conditions believed to
simulate those on the early
Earth?
Sample for chemical analysis
Carbon atoms can form diverse
molecules by bonding to four other
atoms
• Electron configuration is the key to an atom’s
characteristics
• Electron configuration determines the kinds and
number of bonds an atom will form with other
atoms
© 2011 Pearson Education, Inc.
The Formation of Bonds with
Carbon
• With four valence electrons,
carbon can form four
covalent bonds with a
variety of atoms
• This tetravalence 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 molecule has a flat
shape
Fig. 4-3
Name
The shapes of three simple organic molecules
Molecular Structural
Formula
Formula
Ball-and-Stick Space-Filling
Model
Model
Methane
Ethane
Ethene
(ethylene)
In molecules with multiple carbon atoms, every carbon atom bonded to four
other atoms has a tetrahedral shape.
When two carbon atoms are joined by a double bond, all bonds around those
carbons are in the same plane and have a flat, three-dimensional structure.
Valences of common organic
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.
© 2011 Pearson Education, Inc.
CO2
O=C=O
• In carbon dioxide, one carbon atom forms two double bonds
with two different oxygen atoms.
• In the structural formula, O=C=O, each line represents a pair of
shared electrons. This arrangement completes the valence
shells of all atoms in the molecule.
• Although CO2 can be classified as either organic or inorganic,
its importance to the living world is clear: CO2 is the source of
carbon for all organic molecules found in organisms.
Urea
Each atom forms covalent bonds to complete its valence shell.
© 2011 Pearson Education, Inc.
Molecular Diversity Arising from
Carbon Skeleton Variation
• Carbon chains form
the skeletons of most
organic molecules
• Carbon chains vary in
length and shape
© 2011 Pearson Education, Inc.
Carbon Skeleton Variations
Hydrocarbons-only H and C
Many organic molecules, such as fats, have hydrocarbon components
Hydrocarbons can undergo reactions that release a large amount of energy
© 2014 Pearson Education, Inc.
Figure 4.6
Nucleus
Fat droplets
10 µm
(a) Part of a human adipose cell
(b) A fat molecule
Isomers
• Isomers are compounds with the same
molecular formula but different structures and
properties:
– Structural isomers have different covalent
arrangements of their atoms
– Cis-trans isomers have the same covalent
bonds but differ in spatial arrangements
– Enantiomers are isomers that are mirror
images of each other
© 2014 Pearson Education, Inc.
Animation: Isomers
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Isomers- Compounds with the same
molecular formula but different structures
and properties
Structural Isomers:
Differ in covalent arrangements of
their atoms.
Cis-trans isomers:
Same covalent arrangements but
differ spatially because of the
inflexibility of double bonds.
Figure 4.7
© 2014 Pearson Education, Inc.
Isomers
•
•
•
•
•
Enantiomers are possible when
four different atoms or groups
of atoms are bonded to an
asymmetric carbon.
The four groups can be
arranged in space in two
different ways that are mirror
images of each other.
Usually one is biologically
active, while the other is
inactive.
Even subtle structural
differences in two enantiomers
may have important functional
significance because of
emergent properties from
specific arrangements of atoms.
For example, one enantiomer of
the drug thalidomide reduces
morning sickness, the desired
effect, but its isomer causes
severe birth defects.
© 2014 Pearson Education, Inc.
Figure 4.7
Isomers
• Enantiomers are important in the
pharmaceutical industry
• Two enantiomers of a drug may have
different effects
• Usually only one isomer is biologically
active
• Differing effects of enantiomers
demonstrate that organisms are
sensitive to even subtle variations in
molecules
© 2014 Pearson Education, Inc.
Figure 4.8 The pharmacological importance of enantiomers
Drug
Effects
Ibuprofen
Reduces
inflammation
and pain
Albuterol
Relaxes bronchial
(airway) muscles,
improving airflow
in asthma
patients
Effective
Enantiomer
Ineffective
Enantiomer
S-Ibuprofen
R-Ibuprofen
R-AIbuterol
S-AIbuterol
Fig. 4-UN9
L-dopa
Effective for Parkinson’s disease
D-dopa
Not effective
A few number of chemical groups are key
to the functioning of biological molecules
• The distinctive properties of an organic molecule depend
not only on the arrangement of its carbon skeleton but
also on the chemical groups attached to that skeleton.
• If we start with hydrocarbons as the simplest organic
molecules, characteristic chemical groups can replace
one or more of the hydrogen atoms bonded to the
carbon skeleton of a hydrocarbon.
• These chemical groups may be involved in chemical
reactions or may contribute to the shape and function of
the organic molecule in a characteristic way, giving it
unique properties.
© 2014 Pearson Education, Inc.
Chemical Groups
• The basic structure of
testosterone and estradiol
is the same.
• Both are steroids with
four fused carbon rings,
but the hormones differ in
the chemical groups
attached to the rings.
• As a result, testosterone
and estradiol have
different shapes, causing
them to interact differently
with many targets
throughout the body.
The Chemical Groups Most Important in
the Processes of 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
• Seven chemical groups are most important to the chemistry of life:
1. hydroxyl,
2.carbonyl,
3.carboxyl,
4.amino,
5. sulfhydryl,
6. phosphate, and
7. methyl groups.
• The first six chemical groups are functional groups. They are
hydrophilic and increase the solubility of organic compounds in
water.
• Adding functional group change property of organic compound
from hydrophobic to hydrophilic.
• Methyl groups are not reactive but add 3-D shape in organic
molecules.
© 2014 Pearson Education, Inc.
Chemical Group
Hydroxyl group (—OH)
Compound Name
Examples
Alcohol
Ethanol
Carbonyl group (
C＝O)
Ketone
Aldehyde
Acetone
Carboxyl group (—COOH)
Propanal
Carboxylic acid, or
organic acid
Acetic acid
Amino group (—NH2)
Amine
Glycine
Sulfhydryl group (—SH)
Thiol
Cysteine
Phosphate group (—OPO32−)
Organic
phosphate
Glycerol phosphate
Methyl group (—CH3)
Methylated
compound
5-Methyl cytosine
Figure 4.9 Some biologically important chemical groups
1
In a hydroxyl group (—OH) a hydrogen atom forms a polar covalent bond with
an oxygen atom, which forms a polar covalent bond to the carbon skeleton.
Because of these polar covalent bonds, hydroxyl groups increase the solubility
of organic molecules.
Organic compounds with hydroxyl groups are alcohols, and their names
typically end in -ol.
2
• A carbonyl group (C=O) consists of an oxygen atom joined to
the carbon skeleton by a double bond.
• If the carbonyl group is on the end of the skeleton, the
compound is an aldehyde.
• If the carbonyl group is within the carbon skeleton, the
compound is a ketone.
• Isomers of aldehydes and ketones have different properties.
3
A carboxyl group (O=C-OH) consists of a carbon atom with a double bond to
an oxygen atom and a single bond to the oxygen atom of a hydroxyl group.
Compounds with carboxyl groups are carboxylic acids.
A carboxyl group acts as an acid because the combined electronegativities of
the two adjacent oxygen atoms increase the chance of dissociation of
hydrogen as an ion (H+).
4
An amino group (—NH2) consists of a nitrogen atom bonded to two hydrogen atoms
and the carbon skeleton.
Organic compounds with amino groups are amines.
The amino group acts as a base because it can pick up a hydrogen ion (H+) from the
solution.
Amino acids, the building blocks of proteins, have amino and carboxyl groups (O=COH) .
5
A sulfhydryl group (—SH) consists of a sulfur atom bonded to a hydrogen
atom and to the backbone.
This group resembles a hydroxyl group in shape.
Organic molecules with sulfhydryl groups are thiols.
Two sulfhydryl groups can interact to help stabilize the structure of proteins.
6
A phosphate group (O=PO32−) consists of a phosphorus atom bound to four
oxygen atoms (three with single bonds and one with a double bond).
A phosphate group connects to the carbon backbone via one of its oxygen atoms.
Phosphate groups are anions with two negative charges because 2 protons
dissociate from the oxygen atoms.
One function of phosphate groups is to transfer energy between organic
molecules.
7
Methyl Groups
Addition of a methyl group
to DNA, or to molecules
bound to DNA, affects the
expression of genes.
Arrangement of methyl
groups in male and female
sex hormones affects their
shape and function.
Methyl
A ethyl group is a chemical group, but it is not a functional group
because it is not reactive.
© 2011 Pearson Education, Inc.
ATP: An Important Source of Energy
for Cellular Processes
• Adenosine triphosphate, or
ATP, is the primary energy
transferring molecule in
living cells.
• ATP consists of an organic
molecule called adenosine
attached to a string of three
phosphate groups.
• When one inorganic
phosphate ion is split off as
a result of a reaction with
water, ATP becomes
adenosine diphosphate, or
ADP.
• In a sense, ATP “stores” the
potential to react with water,
releasing energy that can be
used by the cell.
The Chemical Elements of Life:
A Review
• The versatility of carbon makes possible
the great diversity of organic molecules
• Variation at the molecular level lies at the
foundation of all biological diversity