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Chapter 4: Carbon and the molecular diversity of life Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Living organisms are made up of chemicals based on carbon Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 4.2 Inquiry Could organic compounds have been synthesized abiotically on the early Earth? EXPERIMENT In 1953, Stanley Miller simulated what were thought to be environmental conditions on the lifeless, primordial Earth. As shown in this recreation, Miller used electrical discharges (simulated lightning) to trigger reactions in a primitive “atmosphere” of H2O, H2, NH3 (ammonia), and CH4 (methane)—some of the gases released by volcanoes . RESULTS A variety of organic compounds that play key roles in living cells were synthesized in Miller’s apparatus. CONCLUSION Organic compounds may have been synthesized abiotically on the early Earth, setting the stage for the origin of life. (We will explore this hypothesis in more detail in Chapter 26.) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Formation of Bonds with Carbon • Carbon has four valence electrons • forms four covalent bonds with a variety of atoms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Bonding versatility of carbon diverse molecules Name and Comments Molecular Structural Formula Formula H (a) Methane CH4 H C H H H H (b) Ethane C2H H C C H 6 (c) Ethene Figure 4.3 A-C (ethylene) H H H C2H4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H C C H H Ball-andStick Model SpaceFilling Model Carbon Skeleton Variation • Carbon chains (a) Length H H H C C H H H H Ethane H H H C C C H H H H Propane H H (b) Branching H H H H H C C C C H H H H H H H bonds H H H H H C C C C H H H (d) Rings Figure 4.5 A-D H C C C C C C H H H H Cyclohexane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H C C C H H H H H H H H H C C C C H 1-Butene H H H H H H 2-methylpropane (commonly called isobutane) Butane (c) Double C H 2-Butene H H C C C C C Benzene H H • Hydrocarbons – Found in many of a cell’s organic molecules Fat droplets (stained red) 100 µm Figure 4.6 A, B (a) A fat molecule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Mammalian adipose cells Isomers • Molecules with the same molecular formula but different structures and properties Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 3 types of isomers H (a) Structural isomers H H H H H H C C C C C H H H H H X (b) Geometric isomers H H Enantiomers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings C C H H H X H CO2H C H C X H C H NH2 NH2 CH3 Figure 4.7 A-C C C C CO2H (c) C H H H C H X C H H H H CH3 H • Enantiomers – important in the pharmaceutical industry Figure 4.8 L-Dopa D-Dopa (effective against Parkinson’s disease) (biologically inactive) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Functional Groups • Chemically reactive groups of atoms within an organic molecule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Give organic molecules distinctive chemical properties Estradiol OH CH3 HO Female lion OH CH3 CH3 O Figure 4.9 Male lion Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Testosterone • Functional groups FUNCTIONAL GROUP HYDROXYL CARBONYL CARBOXYL O OH (may be written HO STRUCTURE C C OH ) In a hydroxyl group (—OH), a hydrogen atom is bonded to an oxygen atom, which in turn is bonded to the carbon skeleton of the organic molecule. (Do not confuse this functional group with the hydroxide ion, OH–.) O The carbonyl group ( CO) consists of a carbon atom joined to an oxygen atom by a double bond. Figure 4.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When an oxygen atom is doublebonded to a carbon atom that is also bonded to a hydroxyl group, the entire assembly of atoms is called a carboxyl group (— COOH). • Functional groups NAME OF COMPOUNDS Alcohols (their Ketones if the carbonyl specific names usually end in -ol) group is within a carbon Carboxylic acids, or organic skeleton acids EXAMPLE H H H C C H H Aldehydes if the carbonyl group is at the end of the carbon skeleton H OH H C H C H H Ethanol, the alcohol present in alcoholic beverages C C H O C OH H H Acetone, the simplest ketone H Figure 4.10 H O H H C C H H O C Propanal, an aldehyde Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H Acetic acid, which gives vinegar its sour tatste • Functional groups AMINO SULFHYDRYL H (may be written HS H The amino group (—NH2) consists of a nitrogen atom bonded to two hydrogen atoms and to the carbon skeleton. O SH N PHOSPHATE ) O P OH OH The sulfhydryl group consists of a sulfur atom bonded to an atom of hydrogen; resembles a hydroxyl group in shape. Figure 4.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a phosphate group, a phosphorus atom is bonded to four oxygen atoms; one oxygen is bonded to the carbon skeleton; two oxygens carry negative charges; abbreviated P . The phosphate group (—OPO32–) is an ionized form of a phosphoric acid group (— OPO3H2; note the two hydrogens).