Transcript Chapter_04

Chapter 4: Carbon—The Backbone of Biological
Molecules
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Although cells are 70–95% water, the rest consists mostly of carbonbased compounds
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Carbon is unparalleled in its ability to form large, complex, and diverse
molecules
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Proteins, DNA, carbohydrates, and other molecules that distinguish
living matter are all composed of carbon compounds
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Organic chemistry is the study of carbon
compounds
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Organic compounds range from simple molecules to colossal ones
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Most organic compounds contain hydrogen atoms in addition to carbon
atoms
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Vitalism, the idea that organic compounds arise only in organisms,
was shown to be false when chemists synthesized many organic
compounds in the laboratory
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Mechanism is the view that all natural phenomena are governed by
physical and chemical laws
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Carbon atoms can form diverse molecules by
bonding to four other atoms
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An atom’s electron configuration is the key to its characteristics
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Electron configuration determines the kinds and number of bonds an
atom will form with other atoms
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With four valence electrons, carbon can form four covalent bonds with
a variety of atoms
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This tetravalence makes large, complex molecules possible
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In molecules with multiple carbons, each carbon bonded to four other
atoms has a tetrahedral shape
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However, when two carbon atoms are joined by a double bond, the
molecule has a flat shape
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Basic structures of Carbon containing molecules
Molecular
Formula
Methane
Ethane
Ethene (ethylene)
Structural
Formula
Ball-and-Stick
Model
Space-Filling
Model
Carbon can form bonds with atoms of many different elements
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The electron configuration of carbon gives it covalent compatibility with
many different elements
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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)
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Nitrogen
(valence = 3)
Carbon
(valence = 4)
Ethane
Propane
Butane
2-methylpropane
(commonly called isobutane)
Length
Molecular Diversity
Arises from Carbon
Skeleton Variation
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Branching
Carbon chains
form the
skeletons of most
organic molecules
1-Butene
Double bonds
2-Butene
Carbon chains
vary in length and
shape
Cyclohexane
Rings
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Benzene
Hydrocarbons
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Hydrocarbons are
organic molecules
consisting of ONLY
carbon and hydrogen
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Many organic
molecules, such as
fats, have
hydrocarbon
components
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Hydrocarbons can
undergo reactions
that release a large
amount of energy
Mammalian adipose
cells
A fat molecule
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Fat droplets (red) 100 µm
Isomers
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Isomers are compounds with the
same molecular formula but different
structures and properties:
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Structural isomers have
different covalent arrangements
of their atoms
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Geometric isomers have the
same covalent arrangements
but differ in spatial
arrangements
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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.
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Enantiomers and medicine
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Enantiomers are very
important in the
pharmaceutical industry
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Two enantiomers of a
drug may have different
effects
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Differing effects of
enantiomers demonstrate
that organisms are
sensitive to even subtle
variations in molecules
L-Dopa
(effective against
Parkinson’s disease)
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D-Dopa
(biologically
Inactive)
Functional groups are the parts of molecules
involved in chemical reactions
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Distinctive properties of organic molecules depend not only on the
carbon skeleton but also on the molecular components attached to it
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Certain groups of atoms are often attached to skeletons of organic
molecules
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The functional groups of compounds are the most Important
determinant in the chemistry of life
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Functional groups are the components of organic molecules that are
most commonly involved in chemical reactions
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The number and
arrangement of
functional groups
give each molecule
its unique
properties!
Female lion
Estradiol
Testosterone
Male lion
Functional Groups of organic molecules
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The six functional groups that are most important in the chemistry of
life:
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Hydroxyl group
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Carbonyl group
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Carboxyl group
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Amino group
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Sulfhydryl group
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Phosphate group
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Methyl group
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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.
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
Carboxylic acids, or organic acids
FUNCTIONAL PROPERTIES
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.
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.
Methyl
STRUCTURE
Methylated compounds
EXAMPLE
Addition of a methyl group
to DNA, or to molecules
bound to DNA, affects
expression of genes.
5-Methyl cytidine
5-Methyl cytidine is a
component of DNA that has
been modified by addition of
the methyl group.
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Arrangement of methyl
groups in male and female
sex hormones affects
their shape and function.
NAME OF
COMPOUND
FUNCTIONAL
PROPERTIES
ATP: An Important Source of Energy for Cellular
Processes
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One phosphate molecule, adenosine triphosphate (ATP), is the primary
energy-transferring molecule in the cell
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ATP consists of an organic molecule called adenosine attached to a
string of three phosphate groups
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