Chapter 15 The Evolution of Microbial Life Laura Coronado Bio 10 Chapter 15

Biology and Society: Can Life Be Created in the Lab? – A research group led by Craig Venter Synthesized the entire genome of Mycoplasma genitalium, a species of bacteria found naturally in the human urinary tract Transplanted the complete genome of one species of Mycoplasma bacteria into another – Hopes to c reate an artificial genome & transplant it into a genome-free host cell – An artificial organism that could be completely controlled might Clean up toxic wastes Generate biofuels Be unable to survive outside rigidly controlled conditions Laura Coronado Bio 10 Chapter 15

MAJOR EPISODES IN THE HISTORY OF LIFE – Earth was formed about 4.6 billion years ago. – Prokaryotes Evolved by 3.5 billion years ago Began oxygen production about 2.7 billion years ago Lived alone for almost 2 billion years Continue in great abundance today – Single-celled eukaryotes first evolved about 2.1 billion years ago. – Multicellular eukaryotes first evolved at least 1.2 billion years ago. Laura Coronado Bio 10 Chapter 15

Precambrian Common ancestor to all present-day life Origin of Earth Earth cool enough for crust to solidify Oldest prokaryotic fossils Atmospheric oxygen begins to appear due to photosynthetic prokaryotes Millions of years ago 4,5004,0003,5003,0002,500 Figure 15.1a Laura Coronado Bio 10 Chapter 15

PaleozoicMesozoicCenozoic Bacteria Archaea Plants Fungi Animals Prokaryotes Eukaryotes Protists Oldest eukaryotic fossils Origin of multicellular organisms Oldest animal fossils Plants and symbiotic fungi colonize land Extinction of dinosaurs First humans Millions of years ago Cambrian explosion 2,0001,5001, Figure 15.1b Laura Coronado Bio 10 Chapter 15

Major episodeMillions of years ago All major animal phyla established Plants and fungi colonize land Origin of Earth First multicellular organisms Oldest eukaryotic fossils Accumulation of O 2 in atmosphere Oldest prokaryotic fossils ,200 1,800 2,400 3,500 4,600 Figure 15.UN03 Laura Coronado Bio 10 Chapter 15

MAJOR EPISODES IN THE HISTORY OF LIFE – All the major phyla of animals evolved by the end of the Cambrian explosion, which began about 540 million years ago and lasted about 10 million years. – Plants and fungi First colonized land about 500 million years Were followed by amphibians that evolved from fish – What if we use a clock analogy to tick down all of the major events in the history of life on Earth? Laura Coronado Bio 10 Chapter 15

Humans Origin of solar system and Earth Pre sent Animals Coloniz of land ation Multi eukar cellular yotes Sing eukar cel yotes le- led Atmo oxy sphe ric gen Bil ars ons of ago ye li kary otes Pro Figure 15.2 Laura Coronado Bio 10 Chapter 15

Resolving the Biogenesis Paradox – 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 19 th century, it was commonly believed that life regularly arises from nonliving matter, an idea called spontaneous generation. – Today, most biologists think it is possible that life on early Earth produced simple cells by chemical and physical processes. Laura Coronado Bio 10 Chapter 15

Figure 15.3 Laura Coronado Bio 10 Chapter 15

A Four-Stage Hypothesis for the Origin of Life – According to one hypothesis, the first organisms were products of chemical evolution in four stages. – Stage 1: Abiotic Synthesis of Organic Monomers The first stage in the origin of life has been the most extensively studied by scientists in the laboratory. Laura Coronado Bio 10 Chapter 15

The Process of Science: Can Biological Monomers Form Spontaneously? – Observation: Modern biological macromolecules are all composed of elements that were present in abundance on the early Earth. – Question: Could biological molecules arise spontaneously under conditions like those on the early Earth? – Hypothesis: A closed system designed in the laboratory to simulate early Earth conditions could produce biologically important organic molecules from inorganic ingredients. – Prediction: Organic molecules would form and accumulate. Laura Coronado Bio 10 Chapter 15

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 were discharged into the chamber to mimic the prevalent lightning of the early Earth A condenser to cool the atmosphere, causing water and dissolved compounds to “rain ” into the miniature “sea” Laura Coronado Bio 10 Chapter 15

Stanley Miller re-creating his 1953 experiment Miller and Urey’s experiment “Sea” H2OH2O Sample for chemical analysis Cooled water containing organic molecules Cold water Condenser Electrode “Atmosphere” Water vapor CH 4 NH 3 H2H2 Figure 15.4 Laura Coronado Bio 10 Chapter 15

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. – Since Miller and Urey’s experiments, laboratory analogues of the primeval Earth have produced All 20 amino acids Several sugars Laura Coronado Bio 10 Chapter 15

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 Rock Laura Coronado Bio 10 Chapter 15

Stage 3: Formation of Pre-Cells – 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 Swell or shrink when placed in solutions of different salt concentrations Laura Coronado Bio 10 Chapter 15

Inorganic compounds Abiotic synthesis of organic monomers Abiotic synthesis of polymers Formation of pre-cells Self-replicating molecules Membrane-enclosed compartment Complementary chain Polymer Organic monomers Figure 15.UN04 Laura Coronado Bio 10 Chapter 15

Stage 4: Origin of Self-Replicating Molecules – 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. Laura Coronado Bio 10 Chapter 15

Original “gene” Complementary RNA chain Figure 15.5 Laura Coronado Bio 10 Chapter 15

From Chemical Evolution to Darwinian Evolution – Over millions of years Natural selection favored the most efficient pre-cells The first prokaryotic cells evolved – Prokaryotes lived and evolved all alone on Earth for 2 billion years before eukaryotes evolved. Are found wherever there is life Far outnumber eukaryotes Can cause disease Can be beneficial – Prokaryotes live deep within the Earth and in habitats too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote to survive. Laura Coronado Bio 10 Chapter 15

Figure 15.6 Laura Coronado Bio 10 Chapter 15

Prokaryotes – Compared to eukaryotes, prokaryotes are Much more abundant Typically much smaller – Prokaryotes Are ecologically significant, recycling carbon and other vital chemical elements back and forth between organic matter, the soil, and atmosphere Cause about half of all human diseases Are more typically benign or beneficial Laura Coronado Bio 10 Chapter 15

Colorized SEM Figure 15.7 Laura Coronado Bio 10 Chapter 15

The Structure and Function of Prokaryotes – Prokaryotic cells Lack true nuclei Lack other membrane-enclosed organelles Have cell walls exterior to their plasma membranes – Prokaryotes come in several shapes: Spherical (cocci) Rod-shaped (bacilli) Spiral – Most prokaryotes are unicellular & very small Laura Coronado Bio 10 Chapter 15

Plasma membrane (encloses cytoplasm) Cell wall (provides Rigidity) Capsule (sticky coating) Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Pili (attachment structures) Colorized TEM Figure 4.4 Laura Coronado Bio 10 Chapter 15

Cytoskeleton RibosomesCentriole Lysosome Flagellum Nucleus Plasma membrane Mitochondrion Rough endoplasmic reticulum (ER) Golgi apparatus Smooth endoplasmic reticulum (ER) Idealized animal cell Idealized plant cell Cytoskeleton Mitochondrion Nucleus Rough endoplasmic reticulum (ER) Ribosomes Smooth endoplasmic reticulum (ER) Golgi apparatus Plasma membrane Channels between cells Not in most plant cells Central vacuole Cell wall Chloroplast Not in animal cells Figure 4.5 Laura Coronado Bio 10 Chapter 15

SHAPES OF PROKARYOTIC CELLS Spherical (cocci)Rod-shaped (bacilli)Spiral Colorized SEM Colorized TEM Figure 15.8 Laura Coronado Bio 10 Chapter 15

(a) Actinomycete(b) Cyanobacteria(c) Giant bacterium Colorized SEM LM Figure 15.9 Laura Coronado Bio 10 Chapter 15

The Structure and Function of Prokaryotes – Some prokaryotes Form true colonies Show specialization of cells Are very large – About half of all prokaryotes are mobile, using flagella. – Many have one or more flagella that propel the cells away from unfavorable places or toward more favorable places, such as nutrient-rich locales. Laura Coronado Bio 10 Chapter 15

Plasma membrane Cell wall Rotary movement of each flagellum Flagellum Colorized TEM Figure Laura Coronado Bio 10 Chapter 15

Procaryotic Reproduction – Most prokaryotes can reproduce by binary fission and at very high rates if conditions are favorable. – Some prokaryotes Form endospores, thick-coated, protective cells that are produced within the cells when they are exposed to unfavorable conditions Can survive very harsh conditions for extended periods, even centuries Laura Coronado Bio 10 Chapter 15

Endospore Colorized SEM Figure Laura Coronado Bio 10 Chapter 15

Procaryotic Nutrition – Prokaryotes exhibit four major modes of nutrition. Phototrophs obtain energy from light. Chemotrophs obtain energy from environmental chemicals. Species that obtain carbon from carbon dioxide (CO 2 ) are autotrophs. Species that obtain carbon from at least one organic nutrient—the sugar glucose, for instance—are called heterotrophs. – We can group all organisms according to the four major modes of nutrition if we combine the Energy source (phototroph versus chemotroph) and Carbon source (autotroph versus heterotroph) Laura Coronado Bio 10 Chapter 15

Nutritional ModeEnergy SourceCarbon Source Photoautotroph Chemoautotroph Photoheterotroph Chemoheterotroph Sunlight Inorganic chemicals Sunlight Organic compounds CO 2 Organic compounds Figure 15.UN06 Laura Coronado Bio 10 Chapter 15

MODES OF NUTRITION LightChemical Chemoautotrophs Photoautotrophs Photoheterotrophs Chemoheterotrophs Energy source Elodea, an aquatic plant Rhodopseudomonas Little Owl (Athene noctua) Bacteria from a hot spring Organic compounds Carbon source CO 2 Colorized TEM Figure Laura Coronado Bio 10 Chapter 15

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea – By comparing diverse prokaryotes at the molecular level, biologists have identified two major branches of prokaryotic evolution: Bacteria Archaea (more closely related to eukaryotes) – Some archaea are “extremophiles.” Halophiles thrive in salty environments. Thermophiles inhabit very hot water. Methanogens inhabit the bottoms of lakes and swamps and aid digestion in cattle and deer. Laura Coronado Bio 10 Chapter 15

(a) Salt-loving archaea(b) Heat-loving archaea Figure Laura Coronado Bio 10 Chapter 15

Bacteria and Humans – Bacteria interact with humans in many ways. – Bacteria and other organisms that cause disease are called pathogens. – Most pathogenic bacteria produce poisons. Exotoxins are poisonous proteins secreted by bacterial cells. Endotoxins are not cell secretions but instead chemical components of the outer membrane of certain bacteria. Laura Coronado Bio 10 Chapter 15

Haemophilus influenzae Cells of nasal lining Colorized SEM Figure Laura Coronado Bio 10 Chapter 15

– The best defenses against bacterial disease are Education Sanitation Antibiotics Laura Coronado Bio 10 Chapter 15

“Bull’s-eye” rash Tick that carries the Lyme disease bacterium Spirochete that causes Lyme disease SEM Figure Laura Coronado Bio 10 Chapter 15

Bioterrorism – Humans have a long and ugly history of using organisms as weapons. During the Middle Ages, armies hurled the bodies of plague victims into enemy ranks. Early conquerors, settlers, and warring armies in South and North America gave native peoples items purposely contaminated with infectious bacteria. In 1984, members of a cult in Oregon contaminated restaurant salad bars with Salmonella bacteria. In the fall of 2001, five Americans died from the disease anthrax in a presumed terrorist attack. Laura Coronado Bio 10 Chapter 15

Figure Laura Coronado Bio 10 Chapter 15

The Ecological Impact of Prokaryotes – Pathogenic bacteria are in the minority among prokaryotes. – Far more common are species that are essential to our well-being, either directly or indirectly. – Prokaryotes play essential roles in Chemical cycles in the environment The breakdown of organic wastes and dead organisms – Prokaryotes are used Bioremediation is the use of organisms to remove pollutants from Water Air Soil Decomposers in sewage treatment & petroleum spills. Laura Coronado Bio 10 Chapter 15

Liquid wastes Outflow Rotating spray arm Rock bed coated with aerobic prokaryotes and fungi Figure Laura Coronado Bio 10 Chapter 15

Figure Laura Coronado Bio 10 Chapter 15

PROTISTS Protists – Are eukaryotic – Evolved from prokaryotic ancestors – Are ancestral to all other eukaryotes Plants Fungi Animals Laura Coronado Bio 10 Chapter 15

The Origin of Eukaryotic Cells – Eukaryotic cells evolved by The infolding of the plasma membrane of a prokaryotic cell to form the endomembrane system and Endosymbiosis, one species living inside another host species, in which free-living bacteria came to reside inside a host cell, producing mitochondria and chloroplasts Laura Coronado Bio 10 Chapter 15

(a) Origin of the endomembrane system(b) Origin of mitochondria and chloroplasts Plasma membrane Ancestral prokaryote DNA Cytoplasm Endoplasmic reticulum Membrane infolding Nucleus Nuclear envelope Cell with nucleus and endomembrane system Photosynthetic eukaryotic cell Photosynthetic prokaryote Aerobic heterotrophic prokaryote Endosymbiosis (Some cells) Mitochondrion Chloroplast Figure Laura Coronado Bio 10 Chapter 15

The Diversity of Protists – Protists are not one distinct group but instead represent all the eukaryotes that are not plants, animals, or fungi. – Protists can be Unicellular Multicellular – More than any other group, protists vary in Structure Function Laura Coronado Bio 10 Chapter 15

Protists Classification – The classification of protists remains a work in progress. – The four major categories of protists, grouped by lifestyle, are Protozoans Slime molds Unicellular algae Seaweeds Laura Coronado Bio 10 Chapter 15

Protozoans – Protists that live primarily by ingesting food are called protozoans. – Protozoans with flagella are called flagellates and are typically free-living, but sometimes are nasty parasites. Amoebas are characterized by – Great flexibility in their body shape – The absence of permanent organelles for locomotion Most species move and feed by means of pseudopodia (singular, pseudopodium), temporary extensions of the cell. Amoebas may have a shell, as seen in forams, or no shell at all. Laura Coronado Bio 10 Chapter 15

Protozoans – Apicomplexans are Named for a structure at their apex (tip) that is specialized for penetrating host cells and tissues All parasitic, such as Plasmodium, which causes malaria – Ciliates Are mostly free-living (nonparasitic), such as the freshwater ciliate Paramecium Use structures called cilia to move and feed Laura Coronado Bio 10 Chapter 15

A flagellate: Giardia A foram An apicomplexan A ciliate An amoeba Another flagellate: trypanosomes Food being ingested Pseudopodium of amoeba Red blood cell LM TEM LM Colorized SEM Apical complex Cilia Oral groove Figure Laura Coronado Bio 10 Chapter 15

Slime Molds – Slime molds resemble fungi in appearance and lifestyle, but the similarities are due to convergence, and slime molds are not at all closely related to fungi. – The two main groups of these protists are Plasmodial slime molds Cellular slime molds Laura Coronado Bio 10 Chapter 15

Slime Molds – Plasmodial slime molds Can be large Are decomposers on forest floors Are named for the feeding stage in their life cycle, an amoeboid mass called a plasmodium – Cellular slime molds have an interesting and complex life cycle that changes between a Feeding stage of solitary amoeboid cells Sluglike colony that moves and functions as a single unit Stalklike reproductive structure Laura Coronado Bio 10 Chapter 15

Figure Laura Coronado Bio 10 Chapter 15

LM Amoeboid cells Slug-like colony Reproductive structure Figure Laura Coronado Bio 10 Chapter 15

Unicellular and Colonial Algae – Algae are Photosynthetic protists Found in plankton, the communities of mostly microscopic organisms that drift or swim weakly in aquatic environments – Unicellular algae include Diatoms, which have glassy cell walls containing silica Dinoflagellates, with two beating flagella and external plates made of cellulose Laura Coronado Bio 10 Chapter 15

Green Algae – Green algae are Unicellular Sometimes flagellated, such as Chlamydomonas Colonial, sometimes forming a hollow ball of flagellated cells, as seen in Volvox Laura Coronado Bio 10 Chapter 15

(a) A dinoflagellate, with its wall of protective plates (c) Chlamydomonas, a unicellular green alga with a pair of flagella (b) A sample of diverse diatoms, which have glossy walls (d) Volvox, a colonial green alga Colorized SEM SEM LM Figure Laura Coronado Bio 10 Chapter 15

Seaweeds – Seaweeds Are only similar to plants because of convergent evolution Are large, multicellular marine algae Grow on or near rocky shores Are often edible – Seaweeds are classified into three different groups, based partly on the types of pigments present in their chloroplasts: Green algae Red algae Brown algae (including kelp) Laura Coronado Bio 10 Chapter 15

Green algaeRed algaeBrown algae Figure Laura Coronado Bio 10 Chapter 15

Evolution Connection: The Origin of Multicellular Life – Multicellular organisms have interdependent, specialized cells that perform different functions, such as feeding, waste disposal, gas exchange, and protection—and are dependent on each other. – Colonial protists likely formed the evolutionary links between unicellular and multicellular organisms. Laura Coronado Bio 10 Chapter 15

Unicellular protist Colony Locomotor cells Food-synthesizing cells Early multicellular organism with specialized, interdependent cells Later organism with gametes and somatic cells Somatic cells Gamete Figure Laura Coronado Bio 10 Chapter 15