I. I.Biological Molecules Affected by natural selection Based on carbon skeletons Mostly polymers (made of monomers) A. A.Carbohydrates Sugars, starches, cellulose May be classified by number of sugar residues in molecule 1. 1.Monosaccharides Simple carbohydrates with one sugar residue Elements C, H and O in ratio CH 2 O Nutrients for cells; building blocks for complex carbohydrates Ex: Glucose, fructose, galactose 2. 2.Disaccharides Two linked monosaccharides Ex: Maltose (glucose + glucose), lactose (glucose + galactose), sucrose (glucose + fructose) 3. 3.Polysaccharides Polymers containing multiple monosaccharides Serve two important types of functions a. a.Energy storage (Ex: starch, glycogen) b. b.Structural support (Ex: cellulose, chitin)

I. I.Biological Molecules B. B.Lipids Fats and fat-like substances Chemically diverse; all insoluble in water but soluble in polar solvents 1. 1.Fats Used for energy storage, insulation, buoyancy 2. 2.Phospholipids Important components of cell membranes 3. 3.Steroids Common components of cell membranes Building blocks for hormones and other, complex biological molecules

I. I.Biological Molecules C. C.Proteins Polymers of amino acids Abundant: Account for > 50% of dry weight in most cells Functions 1. 1.Structural support 2. 2.Storage of amino acids 3. 3.Transport of other substances (Ex: hemoglobin) 4. 4.Signaling (Ex: chemical messengers) 5. 5.Cellular response to chemical stimuli (Ex: receptors) 6. 6.Movement (Ex: contractile proteins) 7. 7.Defense against foreign substances and pathogens (Ex: antibodies) 8. 8.Catalysis of biochemical reactions (Ex: enzymes)

I. I.Biological Molecules D. D.Nucleic Acids 1. 1.Deoxyribonucleic Acid (DNA) Can self-replicate (with help from enzymes) Passed from one generation to the next Primarily in nuclei of eukaryotic cells Comprises genes 2. 2.Ribonucleic Acid (RNA) Functions in protein synthesis

Fig. 17.3

II. II.Early Earth Earth ~4.6 billion years old First water ~3.9 bya First evidence of life ~3.8 bya (controversial) First fossils (bacteria-like) ~3.5 bya First eukaryotes ~2.2 bya First animal fossils ~700 mya A. A.Conditions High energy environment 1. 1.Violent thunderstorms 2. 2.Widespread volcanic activity 3. 3.Intense radiation (including uv) from early sun No ozone layer and sun more intense then vs. now 4. 4.Bombardment by meteors and other objects from space

III. III.Origin of Life on Earth A. A.Requirements for Origin of Life 1. 1.Little or no free oxygen (O 2 ) O 2 highly reactive; would have destroyed reduced compounds (chemical building blocks) 2. 2.Source of energy Intense radiation, volcanism, bombardment 3. 3.Availability of chemical building blocks Elements – C, H, N, O, P, S 4. 4.Time End of bombardment to first evidence of life >100 million years B. B.First Cells May Have Arisen through Four Stages 1. 1.Abiotic synthesis of small organic molecules (e.g. amino acids, nucleotides) 2. 2.Assembly of small organic molecules into polymers (e.g. proteins, nucleic acids) 3. 3.Packaging of macromolecules into protobionts Membranes Internal environment different from external environment 4. 4.Development of self-replicating molecules

III. III.Origin of Life on Earth C. C.Pre-Biotic Chemistry A.I. Oparin & J.B.S. Haldane (1920’s): Organic molecules necessary to life on earth might have arisen spontaneously from inorganic raw materials First empirical studies in 1950’s by Harold Urey & Stanley Miller (U. of Chicago)

III. III.Origin of Life on Earth C. C.Pre-Biotic Chemistry 1. 1.Urey-Miller Apparatus Formation of amino acids, complex hydrocarbons, sugars, lipids, nucleotides Questions: Enough NH 3 and CH 4 in earth’s early atmosphere? Reducing atmosphere? Alternative: Origin of life at hydrothermal vents Sources of hot water and minerals, including S & Fe compounds Alternative: Panspermia Amino acids found in meteorites

III. III.Origin of Life on Earth C. C.Pre-Biotic Chemistry 2. 2.Abiotic Synthesis of Polymers Clays may have helped Negatively charged (bind positively charged organic molecules) Contain minerals that might have catalyzed polymerization Amino acid solution + hot clay  AA polymers 3. 3.Protobionts Abiotically produced molecules surrounded by bilayered lipid membrane a. a.Highly organized b. b.Some forms reproduce when large enough c. c.Internal environment chemically distinct from outside d. d.Some forms carry out catalytic activity e. e.Some forms produce electrochemical gradients

Fig. 25.3

III. III.Origin of Life on Earth C. C.Characteristics of Early Life 1. 1.Self-Replication Proteins aren’t self-replicating RNA may carry out catalytic functions Ribozyme – Autocatalytic RNA RNA may have been first informational molecule DNA more stable; may have arisen from RNA 2. 2.Nutrition First cells likely heterotrophic No free oxygen in atmosphere of early earth First heterotrophs probably used anaerobic fermentation (less efficient than aerobic metabolism) First autotrophs may have used hydrogen sulfide (H 2 S) as hydrogen source (modern purple & green sulfur bacteria still get H from H 2 S) First autotrophs to split water for H probably ancestors of modern cyanobacteria (3.1 – 3.5 bya) Production of O 2 had profound effects