4 carbon and the molecular diversity of life -...
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Carbon and the Molecular Diversity of Life
Organic Molecules and the Origin of Life on Earth
! Stanley Miller’s classic experiment 1953 demonstrated the abiotic synthesis of organic compounds
! He used CH4, NH3, CO2, H2S, and H2 as gases simulating the atmosphere on the early Earth
Water vapor
Cooled “rain” containing organic molecules
Sample for chemical analysis
Cold water
Condenser
Electrode
“Atmosphere” CH4
H2O “sea”
Carbon: The Framework of Biological Molecules
! Organic molecules are based on carbon • Each carbon atoms forms 4 covalent bonds • Allows for a great variety of molecular shapes
Molecule
(a) Methane
(b) Ethane
(c) Ethene (ethylene)
Molecular Formula
Structural Formula Ball-and-Stick Model Space-Filling
Model
CH4
C2H6
C2H4
Hydrogen (valence = 1)
Oxygen (valence = 2)
Nitrogen (valence = 3)
Carbon (valence = 4)
Lewis dot structures
Valences of the major elements of organic molecules Hydrocarbons: Carbon and Hydrogen
• Methane is the simplest hydrocarbon • CH4 = 1 carbon + 4 hydrogens
Hydrocarbons can form linear chains
• Ethane = C2H6 • Propane = C3H8 • Butane = C4H10
! Hydrocarbon branched chain
Hydrocarbons can form rings
• Cyclohexane = C6H12
Hydrocarbons can form a vast variety of structures
! Hydrocarbons can also have double or triple bonds between the carbons
Hydrocarbons
! Hydrocarbons are usually the wastes or decomposition products of living systems (e.g. fossil fuels)
! Other organic molecules in living organisms contain elements in addition to C and H • Carbohydrates • Lipids • Proteins • Nucleic Acids
Hydrocarbons: Mineral Oil, Natural Gas Isomers ! Isomers are compounds with the same molecular
formula but different structures and properties: • Structural isomers have different covalent
arrangements of their atoms
(a) Structural isomers
Pentane 2-methyl butane
Isomers
• Geometric isomers have the same covalent arrangements but differ in spatial arrangements
(b) Cis-trans isomers
cis isomer: The two Xs are on the same side.
trans isomer: The two Xs are on opposite sides.
Isomers
• Enantiomers are isomers that are mirror images of each other. They cannot be superimposed on each other
(c) Enantiomers
L isomer D isomer
CO2H
H
CH3
HNH2
CO2H
NH2
CH3
C C
L-Dopa (effective against Parkinson’s disease)!
D-Dopa (biologically Inactive)!
Enantiomers are important for the pharmaceutical industry Functional Groups have specific properties
Functional Groups, cont.