Transcript Chap. 4 Lecture

Chapter 4
Carbon and the Molecular
Diversity of Life
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1
• Overview: Carbon—The Backbone of Biological
Molecules
• All living organisms
– Are made up of chemicals based mostly on the
element carbon
2
Figure 4.1
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• Concept 4.1: Organic chemistry is the study of
carbon compounds
• Organic compounds
– Range from simple molecules to colossal ones
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•
The concept of vitalism
–
Is the idea that organic compounds arise only within living
organisms
–
Was disproved when chemists synthesized the compounds in the
laboratory
In 1953, Stanley Miller simulated what were thought to be environmental
EXPERIMENT conditions on the lifeless, primordial Earth. As shown in this recreation,
Miller used electrical discharges (simulated lightning) to trigger reactions
in a primitive “atmosphere” of H2O, H2, NH3 (ammonia), and CH4
(methane)—some of the gases released by volcanoes.
RESULTS
A variety of organic compounds that play key roles in living cells were
synthesized in Miller’s apparatus.
Organic compounds may have been synthesized abiotically on the
CONCLUSION early Earth, setting the stage for the origin of life. (We will explore
Figure 4.2
this hypothesis in more detail in Chapter 26.)
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4
• Concept 4.2: Carbon atoms can form diverse
molecules by bonding to four other atoms
5
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The Formation of Bonds with Carbon
• Carbon has four valence electrons
• This allows it to form four covalent bonds with a
variety of atoms
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• The bonding versatility of carbon
– Allows it to form many diverse molecules,
including carbon skeletons
Name and
Comments
Molecular Structural
Formula
Formula
Ball-andStick Model
SpaceFilling
Model
H
(a) Methane
CH4
H C
H
H
(b) Ethane
H H
C2H
H C C H
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(c) Ethene
Figure 4.3 A-C (ethylene)
H H
H
C2H4
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H
C C
H
H
7
• The electron configuration of carbon
– Gives it covalent compatibility with many
different elements
Hydrogen
Oxygen
Nitrogen
Carbon
(valence = 1)
(valence = 2)
(valence = 3)
(valence = 4)
H
O
N
C
Figure 4.4
8
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Molecular Diversity Arising from Carbon Skeleton
Variation
• Carbon chains
– Form the skeletons of most organic molecules
– Vary in length and shape
H H H
H C C C H
H H H
Propane
H
H C H
H
H
H H H H
(b) Branching
H C C C C H
H C C C H
H H H
H H H H
2-methylpropane
Butane
(commonly called isobutane)
H H H H
H H H H
(c) Double bonds H
H C C C C H
C C C C H
H
H
H H
1-Butene
2-Butene
H
H
H
H
C
H
H
C C H
C H
(d) Rings
H C
C
H
H C
C
H
H
C
C
C
(a) Length
Figure 4.5 A-D
H H
H C C H
H H
Ethane
Cyclohexane
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Benzene
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Hydrocarbons
• Hydrocarbons
– Are molecules consisting of only carbon and
hydrogen
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• Hydrocarbons
– Are found in many of a cell’s organic
molecules
Fat droplets (stained red)
Figure 4.6 A, B
(a) A fat molecule
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100 µm
(b) Mammalian adipose cells
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Isomers
• Isomers
– Are molecules with the same molecular
formula but different structures and properties
12
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• Three types of isomers are
– Structural
– Geometric
– Enantiomers
(a) Structural isomers
(b) Geometric isomers
H H H H H
H C C C C C H
H H H H H
X
C C
H
(c) Enantiomers
H
H C H
H C H
H
H
H C C C H
H H H
H
X
X
H
CO2H
C
H
CH3
C C
X
H
CO2H
NH2NH2
C
H
CH3
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Figure 4.7 A-C
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• Enantiomers
– Are important in the pharmaceutical industry
Figure 4.8
L-Dopa
D-Dopa
(effective against
Parkinson’s disease)
(biologically
inactive)
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14
• Concept 4.3: Functional groups are the parts of
molecules involved in chemical reactions
15
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The Functional Groups Most Important in the
Chemistry of Life
• Functional groups
– Are the chemically reactive groups of atoms
within an organic molecule
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– Give organic molecules distinctive chemical
properties
Estradiol
OH
CH3
HO
Female lion
OH
CH3
CH3
O
Testosterone
17
Figure 4.9
Male lion
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• Six functional groups are important in the
chemistry of life
– Hydroxyl
– Carbonyl
– Carboxyl
– Amino
– Sulfhydryl
– Phosphate
18
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• Some important functional groups of organic
compounds
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
CARBOXYL
O
OH
(may be written HO
C
C
OH
)
STRUCTURE In a hydroxyl group (—OH),
a hydrogen atom is bonded
to an oxygen atom, which in
turn is bonded to the carbon
skeleton of the organic
molecule. (Do not confuse
this functional group with the
hydroxide ion, OH–.)
Figure 4.10
O
The carbonyl group
( CO) consists of a
carbon atom joined to
an oxygen atom by a
double bond.

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When an oxygen atom is doublebonded to a carbon atom that is
also bonded to a hydroxyl group,
the entire assembly of atoms is
called a carboxyl group (—
COOH).
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• Some important functional groups of organic
compounds
NAME OF
COMPOUNDS
Alcohols (their specific
names usually end in -ol)
EXAMPLE
H
H
H
C
C
H
H
Ketones if the carbonyl group is Carboxylic acids, or organic
within a carbon skeleton
acids
Aldehydes if the carbonyl group
is at the end of the carbon
skeleton
H
OH
H
C
H
C
H
H
Ethanol, the alcohol
present in alcoholic
beverages
H
O
C
H
C
OH
H
H
Acetone, the simplest ketone
H
Figure 4.10
C
O
H
H
C
C
H
H
O
C
Propanal, an aldehyde
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Acetic acid, which gives vinegar
its sour tatste
H
20
• Some important functional groups of organic
compounds
FUNCTIONAL  Is polar as a result of the
PROPERTIES electronegative oxygen atom
drawing electrons toward
itself.
 Attracts water molecules,
helping dissolve organic
 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,
 A ketone and an
aldehyde may be
structural isomers with
different properties, as
is the case for acetone
and propanal.
compounds such as sugars
(see Figure 5.3).
H
H
C
H
Figure 4.10
H
O
C
OH
H
C
H
O
+ H+
C
O
 In cells, found in the ionic
form, which is called a
carboxylate group.
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• Some important functional groups of organic
compounds
AMINO
SULFHYDRYL
H
O
SH
N
(may be written HS
H
The amino group (—NH2)
consists of a nitrogen atom
bonded to two hydrogen
atoms and to the carbon
skeleton.
PHOSPHATE
)
O P OH
OH
The sulfhydryl group
consists of a sulfur atom
bonded to an atom of
hydrogen; resembles a
hydroxyl group in shape.
Figure 4.10
In a phosphate group, a
phosphorus atom is bonded to four
oxygen atoms; one oxygen is
bonded to the carbon skeleton; two
oxygens carry negative charges;
abbreviated P . The phosphate
group (—OPO32–) is an ionized
form of a phosphoric acid group (—
OPO3H2; note the two hydrogens).
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• Some important functional groups of organic
compounds
H
O
C
HO
C
H
H
N
H
H
Glycine
Figure 4.10
H
H
C
C
H
H
OH OH H
SH
H
C
C
C
H
H
H
O
O
P
O
O
Ethanethiol
Glycerol phosphate
Because it also has a carboxyl
group, glycine is both an amine
and a carboxylic acid;
compounds with both groups
are called amino acids.
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• Some important functional groups of organic
compounds
 Acts as a base; can pick
up a proton from the
surrounding solution:
H
N
(nonionized)
 Makes the molecule of which
interact to help stabilize
protein structure (see
Figure 5.20).
it is a part an anion (negatively
charged ion).
Can transfer energy between
organic molecules.
H
+N
H
 Two sulfhydryl groups can
H
H
(ionized)
 Ionized, with a charge
Figure 4.10
of 1+, under cellular
conditions.
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The Chemical Elements of Life: A Review
• The versatility of carbon
– Makes possible the great diversity of organic
molecules
25
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