Bài giảng Biology - Chapter 27: Prokaryotes

Chapter 27ProkaryotesOverview: They’re (Almost) Everywhere!Most prokaryotes are microscopicBut what they lack in size they more than make up for in numbersThe number of prokaryotes in a single handful of fertile soilIs greater than the number of people who have ever livedProkaryotes thrive almost everywhereIncluding places too acidic, too salty, too cold, or too hot for most other organismsFigure 27.1Biologists are discoveringThat these organisms have an astonishing genetic diversityConcept 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic successMost prokaryotes are unicellularAlthough some species form coloniesProkaryotic cells have a variety of shapesThe three most common of which are spheres (cocci), rods (bacilli), and spirals1 m2 m5 m(a) Spherical (cocci)(b) Rod-shaped (bacilli)(c) SpiralFigure 27.2a–cCell-Surface StructuresOne of the most important features of nearly all prokaryotic cellsIs their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environmentUsing a technique called the Gram stainScientists can classify many bacterial species into two groups based on cell wall composition, Gram-positive and Gram-negative(a)Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye,which masks the added red dye.(b)Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between theplasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added.Figure 27.3a, bPeptidoglycanlayerCell wallPlasma membraneProteinGram-positivebacteria20 mOutermembranePeptidoglycanlayerPlasma membraneCell wallLipopolysaccharideProteinGram-negativebacteriaThe cell wall of many prokaryotesIs covered by a capsule, a sticky layer of polysaccharide or protein200 nmCapsuleFigure 27.4Some prokaryotes have fimbriae and piliWhich allow them to stick to their substrate or other individuals in a colony200 nmFimbriaeFigure 27.5MotilityMost motile bacteria propel themselves by flagellaWhich are structurally and functionally different from eukaryotic flagellaFlagellumFilamentHookCell wallPlasmamembraneBasal apparatus50 nmFigure 27.6In a heterogeneous environment, many bacteria exhibit taxisThe ability to move toward or away from certain stimuliInternal and Genomic OrganizationProkaryotic cellsUsually lack complex compartmentalizationSome prokaryotesDo have specialized membranes that perform metabolic functions(a) Aerobic prokaryote(b) Photosynthetic prokaryote0.2 m1 mRespiratorymembraneThylakoidmembranesFigure 27.7a, bThe typical prokaryotic genomeIs a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid regionFigure 27.81 mChromosomeSome species of bacteriaAlso have smaller rings of DNA called plasmidsReproduction and AdaptationProkaryotes reproduce quickly by binary fissionAnd can divide every 1–3 hoursMany prokaryotes form endosporesWhich can remain viable in harsh conditions for centuriesEndospore0.3 mFigure 27.9Rapid reproduction and horizontal gene transferFacilitate the evolution of prokaryotes to changing environmentsConcept 27.2: A great diversity of nutritional and metabolic adaptations have evolved in prokaryotesExamples of all four models of nutrition are found among prokaryotesPhotoautotrophyChemoautotrophyPhotoheterotrophyChemoheterotrophyMajor nutritional modes in prokaryotesTable 27.1Metabolic Relationships to OxygenProkaryotic metabolismAlso varies with respect to oxygenObligate aerobesRequire oxygenFacultative anaerobesCan survive with or without oxygenObligate anaerobesAre poisoned by oxygenNitrogen MetabolismProkaryotes can metabolize nitrogenIn a variety of waysIn a process called nitrogen fixationSome prokaryotes convert atmospheric nitrogen to ammoniaMetabolic CooperationCooperation between prokaryotesAllows them to use environmental resources they could not use as individual cellsIn the cyanobacterium AnabaenaPhotosynthetic cells and nitrogen-fixing cells exchange metabolic productsPhotosyntheticcellsHeterocyst20 mFigure 27.10In some prokaryotic speciesMetabolic cooperation occurs in surface-coating colonies called biofilmsFigure 27.111 mConcept 27.3: Molecular systematics is illuminating prokaryotic phylogenyUntil the late 20th centurySystematists based prokaryotic taxonomy on phenotypic criteriaApplying molecular systematics to the investigation of prokaryotic phylogenyHas produced dramatic resultsLessons from Molecular SystematicsMolecular systematicsIs leading to a phylogenetic classification of prokaryotesIs allowing systematists to identify major new cladesA tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematicsFigure 27.12Domain BacteriaDomainArchaeaDomainEukaryaAlphaBetaGammaEpsilonDeltaProteobacteriaChlamydiasSpirochetesCyanobacteriaGram-positivebacteriaKorarchaeotesEuryarchaeotesCrenarchaeotesNanoarchaeotesEukaryotesUniversal ancestorBacteriaDiverse nutritional typesAre scattered among the major groups of bacteriaThe two largest groups areThe proteobacteria and the Gram-positive bacteriaProteobacteriaChromatium; the smallglobules are sulfur wastes (LM)Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM)Bdellovibrio bacteriophorusAttacking a larger bacterium(colorized TEM)2.5 m1 m0.5 m10 m5 m2 mFigure 27.13 Rhizobium (arrows) inside a root cell of a legume (TEM) Nitrosomonas (colorized TEM)Chromatium; the smallglobules are sulfur wastes (LM)Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM)Bdellovibrio bacteriophorusAttacking a larger bacterium(colorized TEM)Helicobacter pylori (colorized TEM).Chlamydias, spirochetes, Gram-positive bacteria, and cyanobacteriaChlamydia (arrows) inside an animal cell (colorized TEM)Leptospira, a spirochete (colorized TEM)Streptomyces, the source of many antibiotics (colorized SEM)Two species of Oscillatoria, filamentous cyanobacteria (LM)Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM)2.5 m5 m5 m50 m1 mFigure 27.13ArchaeaArchaea share certaintraits with bacteriaAnd other traits with eukaryotesTable 27.2Some archaeaLive in extreme environmentsExtreme thermophilesThrive in very hot environmentsExtreme halophilesLive in high saline environmentsFigure 27.14MethanogensLive in swamps and marshesProduce methane as a waste productConcept 27.4: Prokaryotes play crucial roles in the biosphereProkaryotes are so important to the biosphere that if they were to disappearThe prospects for any other life surviving would be dimChemical RecyclingProkaryotes play a major roleIn the continual recycling of chemical elements between the living and nonliving components of the environment in ecosystemsChemoheterotrophic prokaryotes function as decomposersBreaking down corpses, dead vegetation, and waste productsNitrogen-fixing prokaryotesAdd usable nitrogen to the environmentSymbiotic RelationshipsMany prokaryotesLive with other organisms in symbiotic relationships such as mutualism and commensalismFigure 27.15Other types of prokaryotesLive inside hosts as parasitesConcept 27.5: Prokaryotes have both harmful and beneficial impacts on humansSome prokaryotes are human pathogensBut many others have positive interactions with humansPathogenic ProkaryotesProkaryotes cause about half of all human diseasesLyme disease is an example 5 µmFigure 27.16Pathogenic prokaryotes typically cause diseaseBy releasing exotoxins or endotoxinsMany pathogenic bacteriaAre potential weapons of bioterrorismProkaryotes in Research and TechnologyExperiments using prokaryotesHave led to important advances in DNA technologyProkaryotes are the principal agents in bioremediationThe use of organisms to remove pollutants from the environmentFigure 27.17Prokaryotes are also major tools inMiningThe synthesis of vitaminsProduction of antibiotics, hormones, and other products