Ch. 4 Carbon and the Molecular Diversity of Life

A. Overview cells 72% water, 25% carbon-based compounds, 2% salts Carbon can form large, complex, and diverse molecules because each carbon atom makes 4 stable covalent bonds. Proteins Nucleic acids (DNA and RNA) Carbohydrates Lipids C H HH H C H O N P S

B. Carbon Bonding Study of carbon-based molecules called organic chemistry Most organic compounds contain hydrogen as well C H HH H

First organic molecules synthesized on planet proved by Urey-Miller experiment Why carbon as the building block? 4 valence electrons Water vapor H2H2 NH 3 “Atmosphere” Electrode Condenser Cold water Cooled water containing organic molecules Sample for chemical analysis H 2 O “sea” CH 4

With 4 valence electrons, carbon can form four covalent bonds with a variety of atoms. tetravalence makes large, complex molecules possible. each carbon bonded to four other atoms has a tetrahedral shape. However, when two carbon atoms are joined by a double bond, the molecule has a flat shape. tetrahedral

Name Molecular Formula Structural Formula Ball-and-Stick Model Space-Filling Model (a) Methane (b) Ethane (c) Ethene (ethylene)

EthanePropane 1-Butene2-Butene (c) Double bonds (d) Rings CyclohexaneBenzene Butane2-Methylpropane (commonly called isobutane) (b) Branching (a) Length

a.Diamond b.Graphite c.Lonsdaleite d.Fullerene e.Fullerene f.Fullerene g.Amorphous carbon h.Carbon Nanotube

Hydrocarbons are organic molecules consisting of only carbon and hydrogen. Many organic molecules, such as fats, have hydrocarbon components in long hydrocarbon chains. Hydrocarbons can undergo reactions that release a large amount of energy (i.e. gasoline).

Hydrocarbons are non-polar, not soluble in H 2 O, hydrophobic stable very little attraction between molecules gas at room temperature

C. Polymers Long molecules built by linking repeating building blocks or monomers in a chain covalent bonds Put together by dehydration synthesis (remove H 2 O) H2OH2O HO H HH Dehydration synthesis

joins monomers by “taking” H 2 O out one monomer donates OH –,other monomer donates H + requires energy & enzymes Condensation reaction H2OH2O HO H HH enzyme Dehydration synthesis

H2OH2O HOH H H enzyme Digestion uses H 2 O to breakdown polymers reverse of dehydration synthesis cleave off one monomer at a time H 2 O is split into H + and OH – H + & OH – attach to ends requires enzymes releases energy Hydrolysis Digestion

D. Functional Groups Isomers are compounds with the same molecular formula but different structures and properties: Structural isomers have different covalent arrangements of their atoms. Geometric isomers have the same covalent arrangements but differ in spatial arrangements. Enantiomers are isomers that are mirror images of each other.

(b) Geometric isomers cis isomer: The two Xs are on the same side. trans isomer: The two Xs are on opposite sides. Pentane (c ) Enantiomers L isomer D isomer Pentane (a) Structural isomers 2-methyl butane

Enantiomers, mirror image isomers, important in the pharmaceutical industry. Two enantiomers of a drug may have different effects. Differing effects of enantiomers demonstrate that organisms are sensitive to even subtle variations in molecules.

Drug Ibuprofen Albuterol Condition Pain; inflammation Asthma Effective Enantiomer S-Ibuprofen R-Albuterol R-Ibuprofen S-Albuterol Ineffective Enantiomer

Distinctive properties of organic molecules depend not only on the carbon skeleton but also on the molecular components attached to it. A number of characteristic groups are often attached to skeletons of organic molecules. These are called functional groups.

FUNCTIONAL GROUPS MOST IMPORTANT IN LIFE Hydroxyl group-OH Carbonyl group-C=O Carboxyl group-COOH Amino group-NH 2 Sulfhydryl group-SH Phosphate group-OPO 3 2- Methyl group-CH 3