CHAPTER 4 CARBON AND THE MOLECULAR DIVERSITY …lhsteacher.lexingtonma.org/Pohlman/04A-ImportanceOfCarbon.pdf · CHAPTER 4 CARBON AND THE MOLECULAR DIVERSITY OF LIFE ... The Importance
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Section A: The Importance of Carbon1. Organic chemistry is the study of carbon compounds2. Carbon atoms are the most versatile building blocks of molecules3. Variation in carbon skeletons contributes the diversity of organic molecules
• Although cells are 70-95% water, the rest consistsmostly of carbon-based compounds.
• Proteins, DNA, carbohydrates, and other moleculesthat distinguish living matter from inorganicmaterial are all composed of carbon atoms bondedto each other and to atoms of other elements.• These other elements commonly include hydrogen (H),
oxygen (O), nitrogen (N), sulfur (S), and phosphorus(P).
• The study of carbon compounds, organicchemistry, focuses on any compound with carbon(organic compounds).• While the name, organic compounds, implies that these
compounds can only come from biological processes,they can be synthesized by non-living reactions.
• Organic compounds can range from the simple (CO2 orCH4) to complex molecules, like proteins, that may weighover 100,000 daltons.
1. Organic chemistry is the study of carboncompounds
• The overall percentages of the major elements oflife (C, H, O, N, S, and P) are quite uniform fromone organism to another.
• However, because of carbon’s versatility, these fewelements can be combined to build an inexhaustiblevariety of organic molecules.
• While the percentages of major elements do notdiffer within or among species, variations inorganic molecules can distinguish even betweenindividuals of a single species.
• The science of organic chemistry began in attemptsto purify and improve the yield of products fromother organisms.• Later chemists learned to synthesize simple compounds
in the laboratory, but they had no success with morecomplex compounds.
• The Swedish chemist Jons Jacob Berzelius was the firstto make a distinction between organic compounds thatseemed to arise only in living organisms and inorganiccompounds from the nonliving world.
• This lead early organic chemists to proposevitalism, the belief in a life outside the limits ofphysical and chemical laws.
• Support for vitalism began to wane as organicchemists learned to synthesize more complexorganic compounds in the laboratory.• In the early 1800’s the German chemist Friedrich
Wöhler and his students were able to synthesize ureafrom totally inorganic starting materials.
• In 1953, Stanley Miller at theUniversity of Chicago was ableto simulate chemical conditionson the primitive Earth todemonstrate the spontaneoussynthesis of organic compounds.
• With a total of 6 electrons, a carbon atom has 2 in thefirst shell and 4 in the second shell.• Carbon has little tendency to form ionic bonds by loosing
or gaining 4 electrons.
• Instead, carbon usually completes its valence shell bysharing electrons with other atoms in four covalent bonds.
• This tetravalence by carbon makes large, complexmolecules possible.
2. Carbon atoms are the most versatilebuilding blocks of molecules
• When carbon forms covalent bonds with four otheratoms, they are arranged at the corners of animaginary tetrahedron with bond angles near 109o.• While drawn flat, they are actually three-dimensional.
• When two carbon atoms are joined by a doublebond, all bonds around the carbons are in the sameplane.• They have a flat, three-dimensional structure.
• Hydrocarbons are organic molecules that consist ofonly carbon and hydrogen atoms.• Hydrocarbons are the major component of petroleum.
• Petroleum is a fossil fuel because it consists of thepartially decomposed remains of organisms that livedmillions of years ago.
• Fats are biologicalmolecules that havelong hydrocarbontails attached to anon-hydrocarboncomponent.
Fig. 4.5
• Isomers are compounds that have the samemolecular formula but different structures andtherefore different chemical properties.• For example, butane and isobutane have the same
molecular formula C4H10, but butane has a straightskeleton and isobutane has a branched skeleton.
• The two butanes are structural isomers, moleculeswith the same molecular formula but differ in thecovalent arrangement of atoms.
• Geometric isomers are compounds with the samecovalent partnerships that differ in their spatialarrangement around a carbon-carbon double bond.• The double bond does not allow atoms to rotate freely
around the bond axis.
• The biochemistry of vision involves a light-inducedchange in the structure of rhodopsin in the retina fromone geometric isomer to another.
• Even the subtle structural differences in twoenantiomers have important functional significancebecause of emergent properties from the specificarrangements of atoms.• One enantiomer of the drug thalidomide reduced
morning sickness, its desired effect, but the otherisomer caused severebirth defects.
• The L-Dopa isomeris an effective treatmentof Parkinson’s disease,but the D-Dopa isomeris inactive.