Chapter 4 Carbon and the molecular diversity of life OBJECTIVE: Understand the properties of carbon that make it so important to life Although cells are 70–95% water, the rest consists mostly of carbon-based compounds Carbon: unparalleled in ability to form large complex/diverse molecules Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds

Vitalism vs Mechanism Vitalism: Belief in life force Synthesis of complex compounds impossible Disproved in 1953 by Miller Mechanism: all natural phenomena governed by physical and chemical laws.

Sample for chemical analysis Fig. 4-2 EXPERIMENT “Atmosphere” CH4 Water vapor Electrode NH3 H2 Condenser Cooled water containing organic molecules Cold water Figure 4.2 Can organic molecules form under conditions believed to simulate those on the early Earth? H2O “sea” Sample for chemical analysis

CARBON Has 4 valence electrons Can form 4 covalent bonds Versatility in bonding Single Double Triple Can form molecules of almost infinite variability

Name and Comment Molecular Formula Structural Formula Ball-and- Figure 4.3 Name and Comment Molecular Formula Structural Formula Ball-and- Stick Model Space-Filling Model (a) Methane CH4 (b) Ethane C2H6 Figure 4.3 The shapes of three simple organic molecules. (c) Ethene (ethylene) C2H4

CARBON What determines the chemical properties of an element? Hydrogen (valence = 1) Oxygen (valence = 2) Nitrogen (valence = 3) Carbon (valence = 4)

2-Methylpropane (isobutane) Figure 4.5 (a) Length (c) Double bond position Ethane Propane 1-Butene 2-Butene (b) Branching (d) Presence of rings Figure 4.5 Four ways that carbon skeletons can vary. Butane 2-Methylpropane (isobutane) Cyclohexane Benzene

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

Isomers Isomers are compounds with the same molecular formula but different structures and properties Structural isomers have different covalent arrangements of their atoms Cis-trans isomers have the same covalent bonds but differ in spatial arrangements Enantiomers are isomers that are mirror images of each other

Figure 4.7 Three types of isomers Pentane 2-methyl butane (a) Structural isomers cis isomer: The two Xs are on the same side. trans isomer: The two Xs are on opposite sides. (b) Geometric isomers Figure 4.7 Three types of isomers L isomer D isomer (c) Enantiomers

Effective Enantiomer Ineffective Enantiomer Drug Condition Pain; Fig. 4-8 Effective Enantiomer Ineffective Enantiomer Drug Condition Pain; inflammation Ibuprofen S-Ibuprofen R-Ibuprofen Figure 4.8 The pharmacological importance of enantiomers Albuterol Asthma R-Albuterol S-Albuterol

Functional Groups Functional Groups: Attached to carbons skeleton and have diverse properties that dictate the behavior of organic molecules. The seven functional groups that are most important in the chemistry of life: Hydroxyl group Carbonyl group Carboxyl group Amino group Sulfhydryl group Phosphate group Methyl group

Estradiol Testosterone Fig. 4-9 Figure 4.9 A comparison of chemical groups of female (estradiol) and male (testosterone) sex hormones