Download Carbon and Molecular Diversity of Life

Objectives
Carbon and Molecular Diversity of Life
• Explain how carbon’s electron configuration accounts for its ability to
form large, complex, and diverse organic molecules.
• Describe how carbon skeletons may vary, and explain
how this variation contributes to the diversity and complexity of organic
molecules.
• Describe the basic structure of a hydrocarbon and explain why these
molecules are hydrophobic.
• Distinguish among the three types of isomers: structural, geometric,
and enantiomer.
• Name the major functional groups found in organic molecules. Describe
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Organic chemistry is the study of carbon compounds
Organic compounds range from simple molecules to colossal
ones
• The concept of vitalism is the idea that organic compounds
arise
only within living organisms
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It was disproved when Friedrich Wohler accidently synthesized
urea from ammonium cyanate in1828
Vitalism crumbled completely after several decades of
laboratory synthesis of increasingly complex organic
compounds
The formation of bonds with carbon
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The key to an atom's chemical characteristics is its
electron configuration
The electron configuration of carbon gives it covalent
compatibility with many different elements
Carbon has 6 electrons, with 2 in the first electron shell
and 4 in the second shell; thus, it has 4 valence electrons
in a shell that holds 8 electrons
Carbon can form four covalent bonds with other carbon
atoms
- linked carbon atoms form the backbone of organic
molecules
Molecular Diversity arising from carbon skeleton variation
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Carbon chains form the skeletons of most organic
molecules
– chains vary in length and shape
• The carbon backbone may be straight, branched or
arranged in closed rings
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Some carbon skeletons have double bonds, which
vary in number and location
Such variation in carbon skeletons is one important
source of the molecular complexity and diversity that
characterize living matter
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The versatility of carbon’s bond forming is the basis for isomers
Isomers molecules with the same molecular formula but different
structures and properties
– three types of isomers
• structural-differ in the covalent arrangements of their atoms
• cis-trans- carbons have covalent bonds to the same atoms, but these
atoms differ in their spatial arrangements due to the inflexibility of
double bonds
• enantiomers- mirror images of each other and that differ in shape due
to the presence of an asymmetric carbon
Hydrocarbons
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Hydrocarbons are molecules consisting of only carbon and
hydrogen
– hydrocarbons are found in many of a cell’s organic molecules
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Atoms of hydrogen are attached to the carbon skeleton
wherever electrons are available for covalent bonding
Although hydrocarbons are not prevalent in most living
organisms, many of a cell's organic molecules have regions
consisting of only carbon and hydrogen
The Pharmacological importance of enantiomers
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Important to pharmaceutical industry as molecules used as
drugs often have enantiomers which have no or undesired
effects
• thalidomide
– one enantiomer acts as sedative, other causes severe birth
defects
• L-dopamine and D-dopamine
– one useful in treating Parkinson’s disease, other has no effect
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Methamphetamine also occurs in two enantiomers that have
very different effects
One enantiomer is highly addictive stimulant, other has much
weaker effect (found in OTC for nasal congestion
Functional Groups
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Functional groups covalently linked to the carbon backbone of
hydrocarbons give the molecule distinctive chemical properties
Functional groups important in the chemistry of life:
– hydroxyl (-OH): polar, dissolves in water
– carbonyl (=CO): polar, dissolves in water
– carboxyl (-COOH): hydrogen dissociates; weak acid
– amino (-NH2): accepts hydrogen; basic
– sulfhydryl (-SH): can form disulfide bonds
– phosphate (-PO4): acidic and polar, dissolves in water
– methyl (-CH3): non-polar
• Addition of different side groups to the same backbone
significantly changes a molecule’s action
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Consider the differences estradiol (female sex hormone)
with testosterone (male sex hormone)
Both are steroids, organic molecules with a common
carbon skeleton in the form of four fused rings
These sex hormones differ only in the chemical groups
attached to the rings
• Living matter consists mainly of carbon, oxygen, hydrogen, and
nitrogen, with smaller amounts of sulfur and phosphorus
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The versatility of carbon makes possible the great diversity of
organic molecules
At the foundation of all biological diversity lies this variation at
the molecular level