1 Oxygen, Its Nature and Chemistry: What Is so Special About
This Element? ................................................ 1
1.1 A Brief Introduction to Oxygen .......................... 1
1.2 Atomic Structure of Oxygen: Chemical Bonding
Potential ............................................... 2
1.3 The Dioxygen Molecule ................................... 5
1.4 Reactive Oxygen Species ................................. 8
1.4.1 Superoxide 1O2-* .................................. 8
1.4.2 Hydrogen peroxide (H2O2) ......................... 9
1.4.3 Peroxyl radical (ROO*) ........................... 9
1.5 Ozone .................................................. 10
1.6 Water .................................................. 12
1.7 Water Vapor in the Atmosphere .......................... 15
1.8 Carbon Dioxide ......................................... 15
1.9 Solubility of Gases in Water ........................... 16
1.10 Hydrolysis and Dehydration: Central Water Reactions
in Biology ............................................. 16
1.11 Redox Reactions ........................................ 17
References .................................................. 18
2 A Brief History of Oxygen ................................... 21
2.1 Cosmic History of the Elements ......................... 21
2.1.1 The Sun and Solar System ......................... 24
2.2 Formation of Earth ..................................... 25
2.3 The Primordial Environment ............................. 27
2.3.1 Atmosphere of the Early Earth ................... 27
2.3.2 Water on the Earth' Surface: The Origin of
Oceans .......................................... 29
2.3.3 The First Greenhouse Effect ..................... 29
2.4 Life: Its Origins and Earliest Development ............. 30
2.5 A Billion Years of Life Without Dioxygen: Anaerobic
Metabolism ............................................. 32
2.5.1 Some Principles of Metabolism .................... 32
2.6 The Invention of Photosynthesis ........................ 35
2.7 How Oxygenic Photosynthesis Remodeled the Earth ........ 38
2.7.1 The First Rise of Dioxygen ...................... 38
2.7.2 Effects on Life: An Ecological Catastrophe? ..... 39
2.7.3 Effects on the Earth ............................ 40
References .................................................. 41
3 Coping with Oxygen .......................................... 43
3.1 The Impact of Oxygenation on an Anaerobic World ........ 43
3.2 Production of Reactive Oxygen Species .................. 44
3.3 Coping with Reactive Oxygen Species .................... 47
3.3.1 Scavenger Molecules ............................. 47
3.3.2 Enzymes for Detoxification of ROS ............... 49
3.3.3 Antioxidant Enzyme Systems ...................... 51
3.4 How to Avoid Reactive Oxygen Species? .................. 52
3.5 Evolving Defense Strategies ............................ 53
3.5.1 Aggregation for Defense ......................... 53
3.5.2 Melanin ......................................... 54
3.5.3 Oxygen Transport Proteins Prevent Creation
of Oxygen Radicals .............................. 55
3.6 Reactive Oxygen Species as Cellular Signals ............ 56
3.7 Dioxygen as a Signal: Oxygen Sensor .................... 56
3.8 Summary: Reactive Oxygen Species and Life .............. 57
References .................................................. 58
4 Aerobic Metabolism: Benefits from an Oxygenated World ....... 61
4.1 The Advantage to Being Aerobic ......................... 61
4.2 Evolution of an Aerobic Metabolism ..................... 62
4.2.1 Special Mechanisms Needed for Aerobic
Metabolism ...................................... 62
4.2.2 When and How Did Aerobes Arise? ................. 63
4.3 Eukaryotes: The Next Step in Evolution ................. 67
4.3.1 Distinction Between Prokaryotes and
Eukaryotes ...................................... 67
4.3.2 The Symbiotic Hypothesis ........................ 67
4.4 The Last Great Leap: Multicellular Organisms,
"Metazoans" ............................................ 69
4.4.1 When, Why, and How? ............................. 69
4.4.2 Collagen and Cholesterin ........................ 70
4.4.3 Half a Billion Years of Stasis? ................. 71
4.4.4 Emergence and Extinction of the Ediacaran
Fauna ........................................... 72
4.4.5 The Bilateral Body Plan ......................... 73
4.4.6 The "Cambrian Explosion": Fact or Artifact? ..... 74
References .................................................. 76
5 Facilitated Oxygen Transport ................................ 79
5.1 How to Deliver Dioxygen to Animal Tissues? ............. 79
5.2 Modes of Delivery ...................................... 80
5.2.1 Diffusion from the Surface ...................... 80
5.2.2 Transport via Blood as a Dissolved Gas .......... 81
5.2.3 Oxygen Transport Proteins: What They Must Do? ... 82
5.3 Modes of Dioxygen Binding to Oxygen Transport
Proteins ............................................... 84
5.3.1 Cooperative and Noncooperative Binding .......... 84
5.3.2 How Does Cooperativity Work?: Models for
Allostery ....................................... 86
5.3.3 Self-Assembly and Nesting ....................... 88
5.3.4 Why Complex Multisubunit Oxygen Transport
Proteins? ....................................... 89
5.4 Modulation of Dioxygen Delivery by Oxygen Transport
Proteins: Heteroallostery .............................. 89
5.4.1 Modulation by the Products of Anaerobic
Metabolism: the Bohr Effect ..................... 90
5.4.2 The Haldane Effect .............................. 90
5.4.3 The Root Effect ................................. 91
5.4.4 Temperature Dependence .......................... 92
5.4.5 Evolutionary Aspects of Regulation .............. 93
5.5 Diversity of Oxygen Transport Proteins ................. 93
5.5.1 Hemoglobins ..................................... 94
5.5.2 Hemerythrins .................................... 96
5.5.3 Hemocyanins ..................................... 96
5.6 Evolution of Oxygen Transport Proteins ................. 99
5.7 Was Snowball Earth a Possible Trigger for OPT
Evolution? ............................................ 101
5.8 From What Proteins Did Oxygen Transport Proteins
Evolve? ............................................... 102
5.9 Oxygen Transport Proteins and "Intelligent Design" .... 103
References ................................................. 103
6 Climate Over the Ages; Is the Environment Stable? .......... 107
6.1 Climate and Glaciations in Earth's History ............ 108
6.1.1 The First Massive Glaciations; the Huronion
Event: A Role for Methane? ..................... 108
6.1.2 Later Proterozoic Glaciations .................. 110
6.1.3 Phanerozoic Climate and Glaciations ............ 1ll
6.2 How Did Life Survive Glaciations? ..................... 116
6.3 Milestones of Life in the Phanerozoic ................. 118
6.4 Inorganic Cycling of Carbon Dioxide ................... 121
6.5 Is Our Environment Stable? ............................ 122
6.6 Recent Global Warming ................................. 124
References ................................................. 124
7 Global Warming: Human Intervention in World Climate ........ 127
7.1 Recent Climate Changes ................................ 127
7.2 Physical Consequences of Global Warming ............... 129
7.2.1 Shrinking Ice and Glaciers ..................... 129
7.2.2 Sea Level Changes .............................. 130
7.2.3 Changes in Ocean Currents ...................... 131
7.2.4 Local Climate and Weather ...................... 132
7.2.5 The Danger of Methane Releases ................. 133
7.2.6 Greenhouse to Icehouse and Vice Versa? ......... 133
7.3 Human Consequences of Global Warming .................. 134
7.3.1 Direct Consequences of C02 and Temperature
Increase ....................................... 134
7.3.2 Sea Level Rise ................................. 135
7.3.3 Extreme Weather ................................ 136
7.3.4 Effects on Agriculture ......................... 137
7.4 Control of Global Warming ............................. 138
7.4.1 Positive and Negative Natural Feedback
Mechanism ...................................... 138
7.4.2 Human Effects to Control Global Warming ........ 139
7.4.3 The Long View .................................. 139
References ................................................. 140
8 Oxygen in Medicine ......................................... 143
8.1 Hypoxia ............................................... 143
8.1.1 High-Altitude Hypoxia .......................... 144
8.1.2 Hypoxia Arising from Medical Conditions ........ 145
8.2 Oxidative Stress ...................................... 145
8.2.1 Nature of Oxidative Stress ..................... 145
8.2.2 Special Examples of Medical Consequences
of Oxidative Stress ............................ 146
8.3 Treatment of Oxidative Stress ......................... 149
8.4 Beneficial Roles of ROS ............................... 150
8.4.1 SCN and Primary Immune Response ................ 150
8.4.2 Nitric Oxide ................................... 151
References ................................................. 153
9 Oxygen and the Exploration of the Universe ................. 157
9.1 What Is Essential for the Development of Life as We
Know It? .............................................. 157
9.2 What Makes O2 Necessary for Complex Life on
Habitable Planets? .................................... 158
9.3 Seeking Evidence for Extraterrestrial Life ............ 158
9.4 Life in the Solar System? ............................. 161
9.4.1 Terrestrial Planets ............................ 161
9.4.2 Icy Moons ...................................... 163
9.5 Oxygen Supply Problems in Extraterrestrial Voyages .... 164
9.6 Problems Facing Extended Extraterrestrial Settlement
or Colonizaton ........................................ 166
9.6.1 Adjusting the Planetary Environment:
Terraforming ................................... 166
9.6.2 Adjusting the Organism: Bioforming ............. 167
References ................................................. 168
Index ......................................................... 169
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