Part One - The Science and Building Blocks of Life 1

3. Macromolecules and the Origin of Life 38

3.1 What Kinds of Molecules Characterize Living Things? 39 Functional groups give specific properties to molecules 39 Isomers have different arrangements of the same atoms 40 The structures of macromolecules reflect their functions 40 Most macromolecules are formed by condensation and broken down by hydrolysis 41 3.2 What Are the Chemical Structures and Functions of Proteins? 42 Amino acids are the building blocks of proteins 42 Peptide bonds form the backbone of a protein 43 The primary structure of a protein is its amino acid sequence 44 The secondary structure of a protein requires hydrogen bonding 45 The tertiary structure of a protein is formed by bending and folding 46 The quaternary structure of a protein consists of subunits 46 Both shape and surface chemistry contribute to protein specificity 46 Environmental conditions affect protein structure 48 Chaperonins help shape proteins 48 3.3 What Are the Chemical Structures and Functions of Carbohydrates? 49 Monosaccharides are simple sugars 49 Glycosidic linkages bond monosac¬charides 50 Polysaccharides store energy and provide structural materials 51 Chemically modified carbohydrates contain additional functional groups 53 3.4 What Are the Chemical Structures and Functions of Lipids? 54 Fats and oils store energy 55 Phospholipids form biological membranes 55 Not all lipids are triglycerides 56 3.5 What Are the Chemical Structures and Functions of Nucleic Acids? 57 Nucleotides are the building blocks of nucleic acids 57 The uniqueness of a nucleic acid resides in its nucleotide sequence 59 DNA reveals evolutionary relationships 60 Nucleotides have other important roles 60 3.6 How Did Life on Earth Begin? 61 Could life have come from outside Earth? 61 Did life originate on Earth? 61 Chemical evolution may have led to polymerization 62 RNA may have been the first biological catalyst 62 Experiments disproved spontaneous generation of life 63