Biology 107 Carbon and Molecular Diversity September 3, 2003.
04 carbon and the molecular diversity of life
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LECTURE PRESENTATIONSFor CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
© 2011 Pearson Education, Inc.
Lectures byErin Barley
Kathleen Fitzpatrick
Carbon and the Molecular Diversity of Life
Chapter 4
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Overview: Carbon: The Backbone of Life
• Living organisms consist 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
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Figure 4.1
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Organic chemistry is the study of carbon compounds
• Organic chemistry is the study of compounds that contain carbon
• Organic compounds range from simple molecules to colossal ones
• 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 disproved when chemists synthesized these compounds
• Mechanism is the view that all natural phenomena are governed by physical and chemical laws
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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
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Figure 4.2EXPERIMENT
“Atmosphere”
Electrode
Condenser
CH4
H 2NH
3
Water vapor
Cooled “rain”containingorganicmolecules
Cold water
Sample for chemical analysis
H2O “sea”
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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
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The Formation of Bonds with Carbon
• With four valence electrons, carbon can form four covalent bonds with a variety of atoms
• This ability 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 atoms joined to the carbons are in the same plane as the carbons
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Figure 4.3
Name andComment
MolecularFormula
(a) Methane
(b) Ethane
CH4
Ball-and-Stick Model
Space-FillingModel
(c) Ethene (ethylene)
C2H6
C2H4
StructuralFormula
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• 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
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Figure 4.4
Hydrogen(valence 1)
Oxygen(valence 2)
Nitrogen(valence 3)
Carbon(valence 4)
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• Carbon atoms can partner with atoms other than hydrogen; for example:
– Carbon dioxide: CO2
– Urea: CO(NH2)2
O = C = O
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Figure 4.UN01
Urea
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Molecular Diversity Arising from Carbon Skeleton Variation
• Carbon chains form the skeletons of most organic molecules
• Carbon chains vary in length and shape
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Figure 4.5
(a) Length
Ethane 1-Butene
(c) Double bond position
2-ButenePropane
(b) Branching (d) Presence of rings
Butane 2-Methylpropane(isobutane)
Cyclohexane Benzene
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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
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Figure 4.6
Nucleus
Fat droplets
(b) A fat molecule(a) Part of a human adipose cell
10 m
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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
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Figure 4.7(a) Structural isomers
(b) Cis-trans isomers
(c) Enantiomers
cis isomer: The two Xsare on the same side.
trans isomer: The two Xsare on opposite sides.
CO2HCO2H
CH3
H NH2
L isomer
NH2
CH3
H
D isomer
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• 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
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Figure 4.8
Drug
Ibuprofen
Albuterol
ConditionEffective
EnantiomerIneffectiveEnantiomer
Pain;inflammation
Asthma
S-Ibuprofen R-Ibuprofen
R-Albuterol S-Albuterol
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A few chemical groups are key to the functioning of biological molecules
• Distinctive properties of organic molecules depend on the carbon skeleton and on the molecular components attached to it
• A number of characteristic groups called functional groups can replace the hydrogens attached to skeletons of organic molecules
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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
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Figure 4.UN02
Estradiol
Testosterone
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• The seven functional groups that are most important in the chemistry of life:
– Hydroxyl group– Carbonyl group– Carboxyl group– Amino group– Sulfhydryl group– Phosphate group– Methyl group
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Figure 4.9a
STRUCTURE
EXAMPLE
Alcohols(Their specificnames usuallyend in -ol.)
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
(may be written HO—)
Ethanol
• Is polar as a resultof the electronsspending moretime near theelectronegativeoxygen atom.
• Can form hydrogenbonds with watermolecules, helpingdissolve organiccompounds suchas sugars.
Hydroxyl
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Figure 4.9b
Carbonyl
STRUCTURE
EXAMPLE
Ketones if the carbonylgroup is within acarbon skeleton
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Aldehydes if the carbonylgroup is at the end of thecarbon skeleton
• A ketone and analdehyde may bestructural isomerswith different properties,as is the case foracetone and propanal.
Acetone
Propanal
• Ketone and aldehydegroups are also foundin sugars, giving riseto two major groupsof sugars: ketoses(containing ketonegroups) and aldoses(containing aldehydegroups).
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Carboxyl
STRUCTURE
EXAMPLE
Carboxylic acids, or organicacids
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Acetic acid
• Acts as an acid; candonate an H+ because thecovalent bond betweenoxygen and hydrogen is sopolar:
• Found in cells in the ionizedform with a charge of 1– andcalled a carboxylate ion.
Nonionized Ionized
Figure 4.9c
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Amino
Amines
Glycine
STRUCTURE
EXAMPLE • Acts as a base; canpick up an H+ from thesurrounding solution(water, in livingorganisms):
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
• Found in cells in theionized form with acharge of 1.
Nonionized Ionized
Figure 4.9d
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Sulfhydryl
Thiols
(may bewritten HS—)
STRUCTURE
EXAMPLE • Two sulfhydryl groups canreact, forming a covalentbond. This “cross-linking”helps stabilize proteinstructure.
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
• Cross-linking of cysteinesin hair proteins maintainsthe curliness or straightnessof hair. Straight hair can be“permanently” curled byshaping it around curlersand then breaking andre-forming the cross-linkingbonds.
Cysteine
Figure 4.9e
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Figure 4.9f
Phosphate
STRUCTURE
EXAMPLE
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Organic phosphates
Glycerol phosphate
• Contributes negativecharge to the moleculeof which it is a part(2– when at the end ofa molecule, as at left;1– when locatedinternally in a chain ofphosphates).
• Molecules containingphosphate groups havethe potential to reactwith water, releasingenergy.
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Figure 4.9g
Methyl
STRUCTURE
EXAMPLE
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Methylated compounds
5-Methyl cytidine
• Addition of a methyl groupto DNA, or to moleculesbound to DNA, affects theexpression of genes.
• Arrangement of methylgroups in male and femalesex hormones affects theirshape and function.
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ATP: An Important Source of Energy for Cellular Processes
• One phosphate molecule, adenosine triphosphate (ATP), is the primary energy-transferring molecule in the cell
• ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups
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Figure 4. UN04
Adenosine
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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
© 2011 Pearson Education, Inc.