Transcript Chapter 27
Chapter 27 Prokaryotes PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: They’re (Almost) Everywhere! • Most prokaryotes are microscopic, but what they lack in size they make up for in numbers • There are more in a handful of fertile soil than the number of people who ever lived • Prokaryotes thrive almost everywhere, including places too acidic, too salty, too cold, or too hot for most other organisms • They have an astonishing genetic diversity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success • Most prokaryotes are unicellular, although some species form colonies • Prokaryotic cells have a variety of shapes • The three most common of which are spheres (cocci), rods (bacilli), and spirals Video: Tubeworms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-2 1 µm Spherical (cocci) 2 µm Rod-shaped (bacilli) 5 µm Spiral Cell-Surface Structures • An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment • Using the Gram stain, scientists classify many bacterial species into groups based on cell wall composition, Gram-positive and Gram-negative Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-3 Lipopolysaccharide Cell wall Pepridoglycan layer Cell wall Outer membrane Pepridoglycan layer Plasma membrane Plasma membrane Protein Protein Grampositive bacteria Gramnegative bacteria 20 µm Gram-positive Gram-negative • The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharide or protein Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-4 200 nm Capsule • Some prokaryotes have fimbriae and pili, which allow them to stick to their substrate or other individuals in a colony Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-5 Fimbriae 200 nm Motility • Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella • In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli Video: Prokaryotic Flagella (Salmonella typhimurium) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-6 Flagellum Filament 50 nm Cell wall Hook Basal apparatus Plasma membrane Internal and Genomic Organization • Prokaryotic cells usually lack complex compartmentalization • Some prokaryotes do have specialized membranes that perform metabolic functions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-7 1 µm 0.2 µm Respiratory membrane Thylakoid membranes Aerobic prokaryote Photosynthetic prokaryote • The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-8 Chromosome 1 µm • Some species of bacteria also have smaller rings of DNA called plasmids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproduction and Adaptation • Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours • Many prokaryotes form endospores, which can remain viable in harsh conditions for centuries Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-9 Endospore 0.3 µm • Rapid reproduction and horizontal gene transfer facilitate the evolution of prokaryotes in changing environments Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 27.2: A great diversity of nutritional and metabolic adaptations have evolved in prokaryotes • All four models of nutrition are found among prokaryotes: – Photoautotrophy – Chemoautotrophy – Photoheterotrophy – Chemoheterotrophy Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolic Relationships to Oxygen • Prokaryotic metabolism varies with respect to oxygen: – Obligate aerobes require oxygen – Facultative anaerobes can survive with or without oxygen – Obligate anaerobes are poisoned by oxygen Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nitrogen Metabolism • Prokaryotes can metabolize nitrogen in a variety of ways • In nitrogen fixation, some prokaryotes convert atmospheric nitrogen to ammonia Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metabolic Cooperation • Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells • In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells exchange metabolic products Video: Cyanobacteria (Oscillatoria) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-10 Photosynthetic cells Heterocyte 20 µm • In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 27.3: Molecular systematics is illuminating prokaryotic phylogeny • Until the late 20th century, systematists based prokaryotic taxonomy on phenotypic criteria • Applying molecular systematics to the investigation of prokaryotic phylogeny has produced dramatic results Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lessons from Molecular Systematics • Molecular systematics is leading to a phylogenetic classification of prokaryotes • It allows systematists to identify major new clades Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematics Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Proteobacteria Universal ancestor Domain Archaea Eukaryotes Nanoarchaeotes Crenarcaeotes Domain Bacteria Euryarchaeotes Korarchaeotes Gram-positive bacteria Cyanobacteria Spirochetes Chlamydias Epsilon Delta Gamma Beta Alpha LE 27-12 Domain Eukarya Bacteria • Diverse nutritional types are scattered among the major groups of bacteria • The two largest groups are the proteobacteria and the Gram-positive bacteria Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 27-13 PROTEOBACTERIA CHLAMYDIAS 2.5 µm 2.5 µm Subgroup: Alpha Proteobacteria Chlamydia (arrows) Rhizobium (arrows) SPIROCHETES 1 µm 5 µm Subgroup: Beta Proteobacteria Leptospira Nitrosomonas GRAM-POSITIVE BACTERIA Mycoplasmas covering a human fibroblast cell Streptomyces Chromatium 5 µm 10 µm Bdellovibrio bacteriophorus Chrondromyces crocatus 2 µm Subgroup: Epsilon Proteobacteria Heliocobacter pylori 50 µm CYANOBACTERIA Subgroup: Delta Proteobacteria Oscillatoria 1 µm 0.5 µm 5 µm Subgroup: Gamma Proteobacteria Archaea • Archaea share certain traits with bacteria and other traits with eukaryotes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some archaea live in extreme environments • Extreme thermophiles thrive in very hot environments • Extreme halophiles live in high saline environments Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Methanogens live in swamps and marshes and produce methane as a waste product Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 27.4: Prokaryotes play crucial roles in the biosphere • Prokaryotes are so important to the biosphere that if they were to disappear, the prospects for any other life surviving would be dim Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemical Recycling • Prokaryotes play a major role in the continual recycling of chemical elements between the living and nonliving components of ecosystems • Chemoheterotrophic prokaryotes function as decomposers, breaking down corpses, dead vegetation, and waste products • Nitrogen-fixing prokaryotes add usable nitrogen to the environment Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Symbiotic Relationships • Many prokaryotes live with other organisms in symbiotic relationships • In mutualism, both symbiotic organisms benefit • In commensalism, one organism benefits while neither harming nor helping the other in any significant way • In parasitism, one organism, called a parasite, benefits at the expense of the host Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 27.5: Prokaryotes have both harmful and beneficial impacts on humans • Some prokaryotes are human pathogens, but others have positive interactions with humans Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pathogenic Prokaryotes • Prokaryotes cause about half of all human diseases • Lyme disease is an example Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins • Exotoxins cause disease even if the prokaryotes that produce them are not present • Endotoxins are released only when bacteria die and their cell walls break down • Many pathogenic bacteria are potential weapons of bioterrorism Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotes in Research and Technology • Experiments using prokaryotes have led to important advances in DNA technology • Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some other uses of prokaryotes: – Recovery of metals from ores – Synthesis of vitamins – Production of antibiotics, hormones, and other products Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings