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The Origin and Evolution of Microbial Life: Prokaryotes and Protists
Chapter 16 The Origin and Evolution of Microbial Life: Prokaryotes and Protists
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How Ancient Bacteria Changed the World
Photosynthetic prokaryotes dominated Earth from 3 billion years ago to 1 billion years ago Left the oldest known fossils, stromatolites Rocklike structures of layered bacterial mats and sediments Created Earth's aerobic atmosphere from the O2 they produced Today's cyanobacteria are descendents of the ancient photosynthetic prokaryotes
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EARLY EARTH AND THE ORIGIN OF LIFE
16.1 Life began on a young Earth The universe began with a "big bang" between 10 and 20 billion years ago Planet Earth formed from gathering interstellar matter some 4.6 billion years ago First atmosphere was mostly H2 gas Second atmosphere probably contained H2O, CO, CO2, N2, and some CH4 Volcanic activity, lightning, and UV radiation were intense
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Animation: The Geologic Record
Geologic and biological history have been closely intertwined since life began Primitive cellular organisms arose within a few hundred million years after Earth's crust solidified Most likely prokaryotes, as indicated by stromatolite fossils A clock analogy gives a perspective on developments over Earth's history Animation: The Geologic Record
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LE 16-01c Ceno- zoic Meso- zoic Humans Paleozoic Land plants Animals
Origin of solar system and Earth 1 4 Proterozoic eon Archaean eon Billions of years ago 2 3 Multicellular eukaryotes Prokaryotes Single-celled eukaryotes Atmospheric oxygen
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16.2 How did life originate? The first organisms came into being between 3.9 and 3.5 billion years ago A possible scenario Nonorganic molecules in oceans and atmosphere Organic monomers Polymers Membrane-surrounded aggregates capable of metabolism and self-replication
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TALKING ABOUT SCIENCE 16.3 Stanley Miller's experiments showed that organic molecules could have arisen on a lifeless earth In the 1920s, Oparin and Haldane proposed that organic chemistry could have evolved in early Earth's environment Contained no corrosive oxygen Was a reducing environment Would have led simple molecules to combine
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In 1953, Stanley Miller and Harold Urey tested the hypothesis
Used an artificial mixture of inorganic molecules (H2O, H2, CH4, and NH3) Created a laboratory environment that simulated conditions on early Earth Within days, some of the 20 amino acids that are found in organisms today were produced Many scientists now think deep-sea vents and submerged volcanoes provided the chemicals
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LE 16-03b CH4 “Atmosphere” Water vapor Electrode NH3 H2 Condenser Cold
Cooled water containing organic molecules H2O “Sea” Sample for chemical analysis
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16.4 The first polymers may have formed on hot rocks or clay
After small organic molecules, polymerization must have been the second major chemical step before life arose Polymerization occurs by dehydration synthesis Catalyzed by enzymes in living cell Can occur without enzymes when dilute solutions of monomers are dripped on hot mineral surfaces or on clays
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16.5 The first genetic material and enzymes may both have been RNA
The first biological polymers were most likely nucleic acids Replicate and store genetic information The first genes may have been RNA molecules that catalyzed their own replication RNA ribozymes can act like enzymes The "RNA world" is the hypothetical time when RNA was both genetic material and enzyme
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LE 16-05 C A A G G G C U A A C G U G G C A U G U G C A U U G C A U U U
Assembly of a complementary RNA chain, the first step in replication of the original “gene” Monomers Formation of short RNA polymers: simple “genes”
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16.6 Membrane-enclosed molecular cooperatives may have preceded the first cells
The earliest form of molecular cooperation might have involved primitive translation of simple RNA genes RNA acting as the template for the formation of polypeptides Polypeptide acting as an enzyme that aids RNA replication
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LE 16-06a RNA Self-replication of RNA Self-replicating RNA acts as
template on which poly- peptide forms. Polypeptide Polypeptide acts as primitive enzyme that aids RNA replication.
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Membranes may have separated aggregates of abiotically created molecules into protobionts
Contained self-replicating RNA and RNA-polypeptide co-ops Developed the ability to replicate and carry out primitive metabolism Would be acted on by natural selection and over millions of years would become more complex Early protobionts were gradually superseded by autotrophs and heterotrophs, the first prokaryotes
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LE 16-06c Membrane RNA Polypeptide
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16.7 Prokaryotes have inhabited Earth for billions of years
Are the oldest life-forms Remain the most numerous and widespread organisms today Survive in environments too extreme for eukaryotes
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Despite being small, prokaryotes have an immense impact on life
Cause serious illness Have beneficial relationships with other organisms Are essential in the decomposition of dead organisms
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16.8 Bacteria and archaea are the two main branches of prokaryotic evolution
Domains Bacteria and Archaea Probably evolved from a common ancestor Differ in nucleotide sequences and other molecular features Peptidoglycan present in bacteria but not archaea Archaea are more like eukaryotes than like bacteria
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16.9 Prokaryotes come in a variety of shapes
Prokaryotes may be shaped as Spheres (cocci) Rods (bacilli) Curves or spirals (vibrios, spirilla, spirochetes)
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16.10 Various structural features contribute to the success of prokaryotes
External structures Cell wall Maintains shape, protects, prevents lysis in hypotonic environment May be covered by a capsule that aids in protection, adhesion Distinguished as gram positive or gram negative
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LE 16-10a Colorized TEM 70,000 Capsule
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Pili Help in adhesion to other bacteria or surfaces Provide links during conjugation
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LE 16-10b Pili Colorized TEM 16,000
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Video: Prokaryotic Flagella (Salmonella typhimurium)
Motility Flagella Enable movement Have a propeller-like structure very different from eukaryotic flagella Video: Prokaryotic Flagella (Salmonella typhimurium)
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LE 16-10c Flagellum Colorized TEM 14,000 Plasma membrane Cell wall
Rotary movement of each flagellum
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Reproduction and adaptation
In favorable environments can reproduce exponentially very quickly Many have adaptations to withstand extreme environments Example: Bacterial endospore
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Internal organization
Simpler than eukaryotic cells in both structure and organization of genome About one-thousandth as much DNA as eukaryote Some have specialized membranes that perform metabolic functions
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Respiratory membrane Thylakoid membrane LE 16-10e TEM 45,000
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16.11 Prokaryotes obtain nourishment in a variety of ways
Types of Nutrition Autotrophs make their own organic compounds from inorganic sources Photoautotrophs harness sunlight for energy and use CO2 for carbon Chemoautotrophs obtain energy from inorganic chemicals instead of from sunlight
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Heterotrophs obtain their carbon atoms from organic compounds
Photoheterotrophs can obtain energy from sunlight Chemoheterotrophs are so diverse that almost any organic molecule can serve as food for some species Example: E. coli
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Metabolic Cooperation
Some cyanobacteria cooperate in photosynthesis and nitrogen fixation Metabolic cooperation occurs in surface-coating colonies called biofilms Example: dental plaque Between-species cooperation can occur
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16.12 Archaea thrive in extreme environments—and in other habitats
Extreme halophiles thrive in very salty places Extreme thermophiles thrive in very hot water Methanogens live in anaerobic environments Found in swamps and human intestine Give off methane as a waste product Archaea also inhabit moderate environments One of the most abundant cell types in the oceans
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Video: Hydrothermal Vent
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16.13 Bacteria include a diverse assemblage of prokaryotes
Bacteria are currently organized into nine groups based on molecular systematics Proteobacteria Five gram-negative groups on one clade Some important examples: Rhizobium, Salmonella, Vibrio cholerae, E. coli Chlamydias Some cause blindness, sexually transmitted disease
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Spirochetes Helical in shape Include those that cause syphilis and Lyme disease Gram-positive bacteria Very diverse Actinomyces subgroup decomposes organic matter in soil Streptomyces subgroup is the source of many antibiotics
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Video: Cyanobacteria (Oscillatoria)
Bacillus anthracis, Staphylococcus, and Streptococcus are major pathogens Cyanobacteria Photosynthesize in a plantlike way Provide food for freshwater and marine ecosystems Video: Cyanobacteria (Oscillatoria)
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LE 16-13d Nitrogen-fixing cells Photosynthetic cells LM 650
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16.14 Some bacteria cause disease
CONNECTION 16.14 Some bacteria cause disease Pathogenic bacteria cause about half of human disease, mostly by producing poisons Exotoxins Secreted by cells Produce some of the most toxic poisons known Example: Staphylococcus aureus Harmless bacteria can also develop pathogenic strains
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Components of the outer membrane of gram-negative bacteria
Endotoxins Components of the outer membrane of gram-negative bacteria All induce fever, aches, sometimes shock Example: Salmonella Sanitation, antibiotics, and education have greatly reduced the incidence of bacterial disease Example: Lyme disease
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Tick that carries the Lyme disease bacterium Spirochete that cause
LE 16-14b Tick that carries the Lyme disease bacterium SEM 2,800 Spirochete that cause Lyme disease “Bull’s-eye” rash
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16.15 Bacteria can be used as biological weapons
CONNECTION 16.15 Bacteria can be used as biological weapons Bacteria have been used as biological weapons throughout history Examples: bubonic plague in the Middle Ages, anthrax in the United States in 2001 Biological weapons research began in the United States in 1943 and ended in 1969 The Biological Weapons Convention has been signed by 103 nations but is not always honored
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16.16 Prokaryotes help recycle chemicals and clean up the environment
CONNECTION 16.16 Prokaryotes help recycle chemicals and clean up the environment Prokaryotes are indispensable components of chemical cycles Contribute to aquatic food chains Release O2 to the atmosphere Fix nitrogen Decompose organic wastes and dead organisms to inorganic chemicals
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Prokaryotes function in bioremediation
Mainstays of sewage treatment facilities Used to clean up oil spills and toxic mine wastes
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LE 16-16a Rotating spray arm Rock bed coated with aerobic bacteria
and fungi Liquid wastes Outflow
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PROTISTS 16.17 The eukaryotic cell probably originated as a community of prokaryotes Eukaryotic cells evolved from prokaryotic cells more than 2 billion years ago Membrane infolding theory Endomembrane system probably evolved from infoldings of the plasma membrane
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Symbiosis: a close association between two or more species
Endosymbiotic theory Symbiosis: a close association between two or more species Endosymbiosis: one species living within another Mitochondria and chloroplasts probably evolved from prokaryotes that established residence within other, larger prokaryotes Supported by evidence from molecular systematics
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LE 16-17 Cytoplasm Plasma membrane Endoplasmic Nuclear reticulum
envelope Ancestral prokaryote Nucleus Membrane infolding Aerobic heterotrophic prokaryote Cell with nucleus and endomembrane system Some cells Photosynthetic prokaryote Ancestral host cell Endosymbiosis Mitochondrion Chloroplast Mitochondrion Photosynthetic eukaryotic cell
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Video: Vorticella Habitat
16.18 Protists are an extremely diverse assortment of eukaryotes Protists are mostly unicellular eukaryotes Algae: synthesize food by photosynthesis Protozoans: eat bacteria and other protists Protists are the simplest eukaryotes, but their cells are among the most elaborate in the world Protists are found almost anywhere there is water Video: Vorticella Habitat
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16.19 A tentative phylogeny of eukaryotes includes multiple clades of protists
The taxonomy of protists is a work in progress
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LE 16-19 Ciliates Fungi Plants Diplomonads Diatoms Amoebas Animals
Red algae Dinoflagellates Apicomplexans Water molds Euglenozoans Brown algae Green algae Cellular slime molds Choanoflagellates Plasmodial slime molds Closest algal relatives of plants Alveolates Stramenopila Amoebozoa Ancestral eukaryote
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16.20 Diplomonads and euglenozoans include some flagellated parasites
May be the most ancient surviving lineage of eukaryotes Are anaerobic Have two nuclei, multiple flagella, modified mitochondria Example: the intestinal parasite Giardia
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Include heterotrophs, photosynthetic autotrophs, pathogenic parasites
Euglenozoans Include heterotrophs, photosynthetic autotrophs, pathogenic parasites Examples: parasitic trypanosomes, pond-dwelling Euglena Video: Euglena Motion
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16.21 Alveolates have sacs beneath the plasma membrane and include dinoflagellates, apicomplexans, and ciliates Alveolates are characterized by membrane-enclosed sacs beneath the plasma membrane Dinoflagellates Unicellular algae reinforced by cellulose plates Characteristic spinning movement caused by two flagella in grooves Cause red tides
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Apicomplexans are parasites of animals
One end (apex) contains a complex of organelles specialized for penetrating host cells Example: Plasmodium, which causes malaria
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LE 16-21b Apex TEM 26,000 Red blood cell
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Ciliates use cilia to move and feed
Nearly all are free living Have two types of nuclei
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LE 16-21c Cilia Macronucleus LM 60
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Video: Dinoflagellate
Video: Paramecium Cilia Video: Paramecium Vacuole Video: Stentor Video: Vorticella Cilia Video: Vorticella Detail
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16.22 Stramenopiles are named for their "hairy" flagella and include the water molds, diatoms, and brown algae Stramenopiles include several groups of heterotrophs and algae Water molds Fungus-like Generally decompose dead organisms in freshwater habitats
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Diatoms Photosynthetic, unicellular algae Have a unique, glassy cell wall Contain silica Two halves fit together like a box and lid Key source of food in all aquatic environments Diatomaceous earth made of thick sediments of fossilized diatoms
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Brown algae Large, complex, multicellular marine algae Color from pigments in chloroplasts Include many seaweeds Example: kelp
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Video: Water Mold Oogonium
Video: Water Mold Zoospores Video: Diatoms Moving Video: Various Diatoms
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16.23 Amoebozoans have pseudopodia and include amoebas and slime molds
Amoebozoan amoebas Move and feed by means of lobe-shaped pseudopodia Mostly free living, some parasitic
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A plasmodial slime mold is a multinucleate plasmodium
Large and branching but not multicellular Engulfs food by phagocytosis as it grows Cytoplasmic streaming distributes nutrients Forms reproductive structures under adverse conditions Common where there is moist, decaying organic matter
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Cellular slime molds have a three-stage life cycle
Mostly exist as solitary amoeboid cells When food is short, amoeboid cells form a slug-like mobile aggregate Some cells dry up and form a stalk supporting an asexual reproductive structure in which other cells develop into spores Decompose rotting organic matter
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LE 16-23c Slug-like aggregate Amoeboid cells Reproductive structure
45 Slug-like aggregate LM 1,000 Amoeboid cells Reproductive structure 15
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Video: Amoeba Pseudopodia
Video: Plasmodial Slime Mold Streaming Video: Plasmodial Slime Mold
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16.24 Red algae and green algae are the closest relatives of land plants
Molecular evidence suggests that descendants of an ancient protist evolved into red and green algae Red algae Red color comes from pigment that masks chlorophyll Live in warm tropical waters Contribute to coral reefs
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Green algae Named for pigment in chloroplasts May be unicellular, colonial, or multicellular Some are large and complex enough to qualify as seaweeds
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Most green algae have complex life cycles involving alternation of generations
Diploid gametophyte generation Haploid sporophyte generation
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LE 16-24c Mitosis Male gametophyte Spores Mitosis Gametes Female gametophyte Meiosis Fusion of gametes Sporophyte Zygote Key Mitosis Haploid (n) Diploid (2n)
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Video: Volvox Daughter
Video: Chlamydomonas Video: Volvox Colony Video: Volvox Daughter Video: Volvox Female Spheroid Video: Volvox Flagella Video: Volvox Inversion 1 Video: Volvox Inversion 2 Video: Volvox Sperm and Female
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16.25 Multicellularity evolved several times in eukaryotes
Multicellular organisms are fundamentally different from unicellular ones Specialized cells perform different functions, are dependent on each other Ancestors of multicellular organisms were probably unicellular protists that lived in colonies Specialization may have led to distinctions between sex cells and somatic cells
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LE 16-25 Gamete Locomotor cells Somatic cells Food- synthesizing cells
Unicellular protist Colony Early multicellular organism with specialized, interdepen- dent cells Later organism that produces gametes
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At least three different lineages from the ancestral eukaryote led to multicellular forms
Brown algae Fungi and animals Red algae, green algae, and plants The oldest known fossils of multicellular eukaryotes date from 1.2 billion years ago
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