Bài giảng Biology - Chapter 4: Carbon and the Molecular Diversity of Life

Chapter 4Carbon and the Molecular Diversity of LifeOverview: Carbon—The Backbone of Biological MoleculesAll living organismsAre made up of chemicals based mostly on the element carbonFigure 4.1Concept 4.1: Organic chemistry is the study of carbon compoundsOrganic compoundsRange from simple molecules to colossal onesThe concept of vitalismIs the idea that organic compounds arise only within living organismsWas disproved when chemists synthesized the compounds in the laboratoryIn 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.A variety of organic compounds that play key roles in living cells were synthesized in Miller’s apparatus.EXPERIMENTRESULTSCONCLUSIONOrganic 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.)Figure 4.2Concept 4.2: Carbon atoms can form diverse molecules by bonding to four other atomsThe Formation of Bonds with CarbonCarbon has four valence electronsThis allows it to form four covalent bonds with a variety of atomsThe bonding versatility of carbonAllows it to form many diverse molecules, including carbon skeletons(a) Methane(b) Ethane(c) Ethene (ethylene)Molecular FormulaStructural FormulaBall-and-Stick ModelSpace-Filling ModelHHHHHHHHHHHHHHCCCCCCH4C2H6C2H4Name and CommentsFigure 4.3 A-CThe electron configuration of carbonGives it covalent compatibility with many different elementsHONCHydrogen(valence = 1)Oxygen(valence = 2)Nitrogen(valence = 3)Carbon(valence = 4)Figure 4.4Molecular Diversity Arising from Carbon Skeleton VariationCarbon chainsForm the skeletons of most organic moleculesVary in length and shapeHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCHHHHHHH(a) Length(b) Branching(c) Double bonds(d) RingsEthanePropaneButane2-methylpropane(commonly called isobutane)1-Butene2-ButeneCyclohexaneBenzeneHHHHHFigure 4.5 A-DHydrocarbonsHydrocarbonsAre molecules consisting of only carbon and hydrogenHydrocarbonsAre found in many of a cell’s organic molecules(a) A fat molecule(b) Mammalian adipose cells100 µmFat droplets (stained red)Figure 4.6 A, BIsomersIsomersAre molecules with the same molecular formula but different structures and propertiesThree types of isomers areStructuralGeometricEnantiomersHHHHHHHHHHHHHHHHHHHHHHHHHHHHCO2HCH3NH2CCO2HHCH3NH2XXXXCCCCCCCCCCCCCCC(a) Structural isomers(b) Geometric isomers(c) EnantiomersHFigure 4.7 A-CEnantiomersAre important in the pharmaceutical industryL-Dopa(effective against Parkinson’s disease)D-Dopa(biologically inactive)Figure 4.8Concept 4.3: Functional groups are the parts of molecules involved in chemical reactionsThe Functional Groups Most Important in the Chemistry of LifeFunctional groupsAre the chemically reactive groups of atoms within an organic moleculeGive organic molecules distinctive chemical propertiesCH3OHHOOCH3CH3OHEstradiolTestosteroneFemale lionMale lionFigure 4.9Six functional groups are important in the chemistry of lifeHydroxylCarbonylCarboxylAminoSulfhydrylPhosphateSome important functional groups of organic compoundsFUNCTIONALGROUPSTRUCTURE(may be written HO ) HYDROXYL CARBONYL CARBOXYLOHIn 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–.)When an oxygen atom is double-bonded to a carbon atom that is also bonded to a hydroxyl group, the entire assembly of atoms is called a carboxyl group (—COOH).COOCOHFigure 4.10The carbonyl group ( CO) consists of a carbon atom joined to an oxygen atom by a double bond.Some important functional groups of organic compoundsAcetic acid, which gives vinegar its sour tatsteNAME OF COMPOUNDSAlcohols (their specific names usually end in -ol)Ketones if the carbonyl group is within a carbon skeleton Aldehydes if the carbonyl group is at the end of the carbon skeletonCarboxylic acids, or organic acidsEXAMPLEPropanal, an aldehydeAcetone, the simplest ketoneEthanol, the alcohol present in alcoholic beveragesHHHHHCCOHHHHHHHHCCHCCCCCCOHOHOHHHHHOHFigure 4.10Some important functional groups of organic compoundsFUNCTIONALPROPERTIES Is polar as a result of the electronegative oxygen atom drawing electrons toward itself. Attracts water molecules, helping dissolve organic compounds such as sugars (see Figure 5.3). A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal. Has acidic properties because it is a source of hydrogen ions.The covalent bond between oxygen and hydrogen is so polar that hydrogen ions (H+) tend to dissociate reversibly; for example, In cells, found in the ionic form, which is called a carboxylate group.HHCHHCOOHHHCOCO+ H+Figure 4.10Some important functional groups of organic compoundsThe amino group (—NH2) consists of a nitrogen atom bonded to two hydrogen atoms and to the carbon skeleton. AMINO SULFHYDRYL PHOSPHATE(may be written HS )The sulfhydryl group consists of a sulfur atom bonded to an atom of hydrogen; resembles a hydroxyl group in shape.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).NHHSHOPOOHOHFigure 4.10Some important functional groups of organic compoundsBecause it also has a carboxyl group, glycine is both an amine and a carboxylic acid; compounds with both groups are called amino acids.GlycineEthanethiolGlycerol phosphateOCHOCHHNHHHCCSHHHHHHOHCCCOPOOHHHOHOHFigure 4.10Some important functional groups of organic compounds Acts as a base; can pick up a proton from the surrounding solution: Ionized, with a charge of 1+, under cellular conditions.(nonionized)(ionized)NHHH+NHH Two sulfhydryl groups can interact to help stabilize protein structure (see Figure 5.20). Makes the molecule of which it is a part an anion (negatively charged ion).Can transfer energy between organic molecules.Figure 4.10The Chemical Elements of Life: A ReviewThe versatility of carbonMakes possible the great diversity of organic molecules