The Evolution of Microbial Life

Transcription

1 1 Chapter 15 The Evolution of Microbial Life Chapter 15 Outline: The Evolution of Microbial Life Major Episodes in the History of Life The Origin of Life Prokaryotes Protists 2 PowerPoint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko Biology and Society: Has Life Been Created in the Lab? 3 Biology and Society: Has Life Been Created in the Lab? 4 How did life first arise on Earth? The newly installed genome To gain insight, scientists have took over the recipient cells, synthesized from scratch the entire genome of a small bacterium known as Mycoplasma mycoides and transplanted the artificial genome into the cells of a closely related species called Mycoplasma capricolum. began cranking out M. mycoides proteins, and reproduced to make more cells containing the synthetic M. mycoides genome.

2 Chapter 15 Outline: The Evolution of Microbial Life 5 MAJOR EPISODES IN THE HISTORY OF LIFE 6 Major Episodes in the History of Life Earth was formed about 4.6 billion years ago. The Origin of Life Prokaryotes Prokaryotes evolved by about 3.5 billion years ago, Protists began oxygen production about 2.7 billion years ago Many killed off because oxygen byproducts can be very toxic lived alone for more than a billion years, and continue in great abundance today. MAJOR EPISODES IN THE HISTORY OF LIFE 7 Figure 15.1a 8 Single-celled eukaryotes first evolved about 2.1 billion years ago. Ancestor to all present-day life Precambrian Multicellular eukaryotes first evolved at least 1.2 billion years ago. Origin of Earth Earth s crust solidifies Oldest prokaryotic fossils Atmospheric oxygen begins to appear 4,500 4,000 3,500 3,000 2,500 Millions of years ago

3 Figure 15.1b 9 Figure 15.1c 10 Precambrian Precambrian Paleozoic Mesozoic Cenozoic Bacteria Archaea Protists Plants Fungi Prokaryotes Eukaryotes Oldest eukaryotic fossils Origin of multicellular organisms 2,000 1,500 1,000 Millions of years ago Oldest animal fossils Cambrian explosion Oldest animal fossils Plants colonize land 1, Millions of years ago Animals Extinction of dinosaurs First humans MAJOR EPISODES IN THE HISTORY OF LIFE 11 MAJOR EPISODES IN THE HISTORY OF LIFE 12 All the major phyla of animals evolved by the end of the Cambrian explosion, which What if we use a clock analogy to tick down all of the major events in the history of life on Earth? began about 540 million years ago and lasted about 10 million years. Plants and fungi first colonized land about 500 million years ago and were followed by amphibians that evolved from fish.

4 Figure 15.2 Humans 13 Chapter 15 Outline: The Evolution of Microbial Life 14 Major Episodes in the History of Life 0 Origin of solar system and Earth The Origin of Life Resolving the Biogenesis Paradox A Four-Stage Hypothesis for the Origin of Life 1 4 From Chemical Evolution to Darwinian Evolution Prokaryotes 2 3 Protists THE ORIGIN OF LIFE 15 Resolving the Biogenesis Paradox 16 We may never know for sure how life on Earth began. All life today arises by the reproduction of preexisting life, or biogenesis. If this is true, how could the first organisms arise? From the time of the ancient Greeks until well into the 1800s, it was commonly believed that life regularly arises from nonliving matter, an idea called spontaneous generation.

5 Resolving the Biogenesis Paradox 17 A Four-Stage Hypothesis for the Origin of Life 18 Today, most biologists think it is possible that life on early Earth evolved from simple cells produced by According to one hypothesis, the first organisms were products of chemical evolution in four stages. chemical and 1. The abiotic synthesis of small organic molecules physical processes. 2. The joining of these molecules into macromolecules 3. The packaging of these molecules into pre-cells 4. The origin of self-replicating molecules that made inheritance possible Figure 15.UN04 Inorganic compounds 19 Stage 1: Abiotic Synthesis of Organic Monomers 20 1 Abiotic synthesis of organic monomers Organic monomers 2 Abiotic synthesis of polymers Polymer 3 Formation of pre-cells The first stage in the origin of life was the first to be extensively studied in the laboratory. Membrane-enclosed compartment 4 Self-replicating molecules Complementary chain

6 The Process of Science: Can Biological Monomers Form Spontaneously? Observation: Modern biological macromolecules are all composed of elements that were present in abundance on early Earth. Question: Could biological molecules arise spontaneously under conditions like those on early Earth? 21 The Process of Science: Can Biological Monomers Form Spontaneously? Hypothesis: A closed system designed to simulate early Earth conditions could produce biologically important organic molecules from inorganic ingredients. Prediction: Organic molecules would form and accumulate. 22 The Process of Science: Can Biological Monomers Form Spontaneously? Experiment: An apparatus was built to mimic the early Earth atmosphere and included hydrogen gas (H 2 ), methane (CH 4 ), ammonia (NH 3 ), and water vapor (H 2 O), sparks that were discharged into the chamber to mimic the prevalent lightning of early Earth, and 23 Figure 15.4 Water vapor CH 4 NH 3 H 2 Atmosphere Condenser Electrode Cold water 24 a condenser that cooled the atmosphere, causing water and dissolved compounds to rain into the miniature sea. H 2 O Sea Cooled water containing organic molecules Sample for chemical analysis Miller and Urey s experiment

7 The Process of Science: Can Biological Monomers Form Spontaneously? Results: After the apparatus had run for a week, an abundance of organic molecules essential for life had collected in the sea, including amino acids, the monomers of proteins. These laboratory experiments have been repeated and extended by other scientists and support the idea that organic molecules could have arisen abiotically on early Earth. 25 Stage 2: Abiotic Synthesis of Polymers Researchers have brought about the polymerization of monomers to form polymers, such as proteins and nucleic acids, by dripping solutions of organic monomers onto hot sand, clay, or rock. 26 Stage 3: Formation of Pre-Cells 27 Stage 3: Formation of Pre-Cells 28 A key step in the origin of life was the isolation of a collection of abiotically created molecules within a membrane. Laboratory experiments demonstrate that pre-cells could have formed spontaneously from abiotically produced organic compounds. Such pre-cells produced in the laboratory display some lifelike properties. They have a selectively permeable surface, can grow by absorbing molecules from their surroundings, and swell or shrink when placed in solutions of different salt concentrations.

8 Stage 4: Origin of Self-Replicating Molecules 29 Figure Life is defined partly by the process of inheritance, which is based on self-replicating molecules. One hypothesis is that the first genes were short strands of RNA that replicated themselves without the assistance of proteins, perhaps using RNAs that can act as enzymes, called ribozymes. RNA monomers Figure Figure RNA monomers Formation of short RNA polymers: simple genes RNA monomers Formation of short RNA polymers: simple genes Assembly of a complementary RNA chain

9 Figure Figure 15.UN04 Inorganic compounds 34 1 Abiotic synthesis of organic monomers Original gene Organic monomers 2 Abiotic synthesis of polymers Polymer 3 Formation of pre-cells RNA monomers Formation of short RNA polymers: simple genes Assembly of a complementary RNA chain The complementary chain serves as a template of the original gene. Membrane-enclosed compartment 4 Self-replicating molecules Complementary chain From Chemical Evolution to Darwinian Evolution 35 Chapter 15 Outline: The Evolution of Microbial Life 36 Over millions of years Major Episodes in the History of Life natural selection favored the most efficient precells and The Origin of Life Prokaryotes yada yada yada They re Everywhere! the first prokaryotic cells evolved! The Structure and Function of Prokaryotes The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea Bacteria and Disease The Ecological Impact of Prokaryotes Protists

10 PROKARYOTES 37 They re Everywhere! 38 Prokaryotes lived and evolved all alone on Earth for about 2 billion years. Prokaryotes are found wherever there is life, have a collective biomass that is at least ten times that of all eukaryotes, thrive in habitats too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote, cause about half of all human diseases, and are more commonly benign or beneficial. They re Everywhere! Compared to eukaryotes, prokaryotes are 39 Figure 15.7 Colorized SEM 40 much more abundant and typically much smaller.

11 They re Everywhere! 41 The Structure and Function of Prokaryotes 42 Prokaryotes living in soil and at the bottom of lakes, rivers, and oceans help to decompose dead organisms and other organic waste material, returning vital chemical elements to the environment. Prokaryotic cells lack a membrane-enclosed nucleus, lack other membrane-enclosed organelles, typically have cell walls exterior to their plasma membranes, but display an enormous range of diversity. Figure Figure 4.5 Cytoskeleton Ribosomes Centriole Lysosome Not in most plant cells 44 Plasma membrane Plasma membrane Cell wall Mitochondrion Nucleus Colorized TEM Capsule Pili Ribosomes Nucleoid Prokaryotic flagellum Cytoskeleton Mitochondrion Nucleus Rough endoplasmic reticulum (ER) Ribosomes Smooth endoplasmic reticulum (ER) Rough endoplasmic reticulum (ER) Golgi apparatus Idealized animal cell Central vacuole Cell wall Chloroplast Plasma membrane Smooth endoplasmic reticulum (ER) Channels between cells Not in animal cells Idealized plant cell Golgi apparatus

12 PROTISTS 80 The Origin of Eukaryotic Cells 81 Protists are Eukaryotic cells evolved by eukaryotes that are not fungi, animals, or plants, mostly unicellular, and ancestral to all other eukaryotes. the infolding of the plasma membrane of a prokaryotic cell to form the endomembrane system and a process known as endosymbiosis. The Origin of Eukaryotic Cells Symbiosis is a more general association between organisms of two or more species. Endosymbiosis refers to one species living inside another host species and 82 Figure 15.19a Plasma membrane DNA Cytoplasm Ancestral prokaryote Membrane infolding Endoplasmic reticulum Nucleus 83 is the process by which eukaryotes gained mitochondria and chloroplasts. Nuclear envelope Cell with nucleus and endomembrane system (a) Origin of the endomembrane system

13 Figure 15.19b Aerobic heterotrophic prokaryote Endosymbiosis Photosynthetic prokaryote Chloroplast 84 The Diversity of Protists The group called protists consists of multiple clades but remains a convenient term to refer to eukaryotes that are not plants, animals, or fungi. 85 Mitochondrion Photosynthetic eukaryotic cell (b) Origin of mitochondria and chloroplasts The Diversity of Protists Protists obtain their nutrition in a variety of ways. Algae are autotrophs, producing their food by photosynthesis. 86 Evolution Connection: The Origin of Multicellular Life Multicellular organisms have specialized cells that are dependent on each other and perform different functions, such as feeding, waste disposal, gas exchange, and protection. 114

14 Evolution Connection: The Origin of Multicellular Life 115 Figure Colonial protists likely formed the evolutionary links between unicellular and multicellular organisms. The colonial green alga Volvox demonstrates one level of specialization and cooperation. Unicellular protist An ancestral colony may have formed when a cell divided and remained attached to its offspring. Figure Figure Unicellular protist An ancestral colony may have formed when a cell divided and remained attached to its offspring. Cells in the colony may have become specialized and interdependent. Unicellular protist An ancestral colony may have formed when a cell divided and remained attached to its offspring. Cells in the colony may have become specialized and interdependent. Additional specialization may have led to sex cells (gametes) and nonreproductive cells (somatic cells). Gamete Foodsynthesizing cells Foodsynthesizing cells Somatic cells Locomotor cells Locomotor cells