Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 27 Prokaryotes

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

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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

LE 27-2 Spherical (cocci) Rod-shaped (bacilli) Spiral 5 µm2 µm1 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

LE 27-3 Pepridoglycan layer Cell wall Protein Gram- positive bacteria Gram-positive Gram-negative Gram- negative bacteria Pepridoglycan layer Cell wall Plasma membrane Lipopolysaccharide Plasma membrane Protein Outer membrane 20 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some prokaryotes have fimbriae and pili, which allow them to stick to their substrate or other individuals in a colony

LE 27-5 Fimbriae 200 nm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

LE 27-6 Flagellum Filament Cell wall Hook Basal apparatus Plasma membrane 50 nm Proton Driven Protein: Flaggelin Rotary

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Internal and Genomic Organization Prokaryotic cells usually lack complex compartmentalization Some prokaryotes do have specialized membranes that perform metabolic functions

LE 27-7 Thylakoid membranes Respiratory membrane Photosynthetic prokaryote Aerobic prokaryote 0.2 µm 1 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region

LE 27-8 Chromosome 1 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some species of bacteria also have smaller rings of DNA called plasmids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproduction Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rapid reproduction and horizontal gene transfer facilitate the evolution of prokaryotes in changing environments Bacteria can also share DNA though conjugation.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings E. coli conjugation

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

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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) Video: Cyanobacteria (Oscillatoria)

LE Heterocyte Photosynthetic cells 20 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms

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 A tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematics

LE Domain Bacteria Domain Archaea Domain Eukarya Universal ancestor Proteobacteria Alpha Beta Gamma Delta Epsilon Chlamydias Spirochetes CyanobacteriaGram-positive bacteria KorarchaeotesEuryarchaeotesCrenarcaeotesNanoarchaeotes Eukaryotes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Archaea Archaea share certain traits with bacteria and other traits with eukaryotes

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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 Methanogens live in swamps and marshes (&cows) 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 Cellulose Digesting Bacteria

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nitrogen Fixing Bacteria

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 Salmonella is another Video: Prokaryotic Flagella (Salmonella typhimurium) Video: Prokaryotic Flagella (Salmonella typhimurium)

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Antibiotics and bacteria Penicillin. Prevents Gram- positive bacteria from forming peptidoglycan, the major component of the cell wall. Without peptidoglycan, internal pressures cause the bacterium to swell and burst. Tetracycline antibiotics. Broadspectrum drugs that inhibit the growth of Gram- negative bacteria, rickettsiae, chlamydiae, and certain Gram-positive bacteria.

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, anthrax, plague, botulinum toxin

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

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Some other uses of prokaryotes: – Recovery of metals from ores – Synthesis of vitamins – Production of antibiotics, hormones, and other products