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Chapter 27

Chapter 27. Prokaryotes. Overview: They’re (Almost) Everywhere! Most prokaryotes are microscopic But what they lack in size they more than make up for in numbers The number of prokaryotes in a single handful of fertile soil Is greater than the number of people who have ever lived.

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Chapter 27

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  1. Chapter 27 Prokaryotes

  2. Overview: They’re (Almost) Everywhere! • Most prokaryotes are microscopic • But what they lack in size they more than make up for in numbers • The number of prokaryotes in a single handful of fertile soil • Is greater than the number of people who have ever lived

  3. Figure 27.1 • Prokaryotes thrive almost everywhere • Including places too acidic, too salty, too cold, or too hot for most other organisms

  4. Biologists are discovering • That these organisms have an astonishing genetic diversity • Even two strains of the species Escherichia coli can be very different from each other • Can live in symbiosis with humans or cause disease • Two domains: Archaea and Bacteria (Eubacteria)

  5. Concept 27.1:Structural, functional, and genetic adaptations contribute to prokaryotic success • Most prokaryotes are unicellular • Although some species form colonies or aggregate on occasion • Generally 1-10 μm in diameter • Genome (essential DNA) one large circle 1-10 x 106 bp

  6. 2 m 1 m 5 m (a) Spherical (cocci) (c) Spiral (b) Rod-shaped (bacilli) • Prokaryotic cells have a variety of shapes • The three most common of which are spheres (cocci), rods (bacilli), and spirals (spirilli) Figure 27.2a–c

  7. Cell-Surface Structures • One of the most important features 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 • Eukaryotes – made up of cellulose or chitin • Procaryotes – contains peptidoglycan

  8. Lipopolysaccharide Outer membrane Peptidoglycan layer Cell wall Cell wall Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Gram- positive bacteria Gram- negative bacteria 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. (a) 20 m Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between the plasma 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. (b) Figure 27.3a, b • Using a technique called the Gram stain • Scientists can classify many bacterial species into two groups based on cell wall composition, Gram-positive and Gram-negative

  9. Gram positive – thick peptidoglycan cell wall layer – holds on to violet dye • Gram negative – thinner peptidoglycan cell wall – does not hold onto violet dye, stains red • Generally more pathogenic to people • Double lipid bilayer protects against immune system and can secrete toxic lipopolysaccharides • antibiotics - many prevent cell wall formation

  10. 200 nm Capsule Figure 27.4 • The cell wall of many prokaryotes • Is covered by a capsule, a sticky layer of polysaccharide or protein

  11. Fimbriae 200 nm Figure 27.5 • Some prokaryotes have fimbriae and pili • Which allow them to stick to their substrate or other individuals in a colony

  12. Flagellum Filament 50 nm Hook Cell wall Basal apparatus Plasma membrane Figure 27.6 Motility • Most motile bacteria propel themselves by flagella • Which are structurally and functionally different from eukaryotic flagella

  13. In a heterogeneous environment, many bacteria exhibit taxis • The ability to move toward or away from certain stimuli • Can move toward oxygen and away from toxin • Colony formation stimulated by taxis toward each other (group formation)

  14. Internal and Genomic Organization • Prokaryotic cells usually lack complex compartmentalization • Do not have organelles (nucleus, Golgi apparatus, Rough ER, etc.)

  15. 0.2 m 1 m Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote Figure 27.7a, b • Some prokaryotes do have specialized membranes that perform metabolic functions

  16. Chromosome 1 m Figure 27.8 • The typical prokaryotic genome • Is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region

  17. Some species of bacteriam also have smaller rings of DNA called plasmids • Provide additional (though not essential) genes that impart certain characteristics such as antibiotic resistance • Can be transferred between bacteria through a process known as conjugation

  18. DNA replication and transcription/translation is very similar to eukaryotes except: • No introns/exons and gene splicing • Ribosomes are much smaller and different • Erythromycin and Tetracyline can interfere with procaryotic ribosomes without affecting eukaryotic ribosomes

  19. Reproduction and Adaptation • Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours • some divide every 20 minutes! • However, they face constant competition and need for substances to grow, thus population is limited

  20. Endospore 0.3 m Figure 27.9 • Many prokaryotes form endospores which can remain viable in harsh conditions for centuries

  21. Rapid reproduction and horizontal gene transfer facilitate the evolution of prokaryotes to changing environments • Can observe evoltuion and change in gene structure of a population over several years of growth

  22. Concept 27.2:A great diversity of nutritional and metabolic adaptations have evolved in prokaryotes • Examples of all four models of nutrition are found among prokaryotes • Photoautotrophy • Chemoautotrophy • Photoheterotrophy • Chemoheterotrophy

  23. Major nutritional modes in prokaryotes

  24. Metabolic Relationships to Oxygen • Prokaryotic metabolism • Also varies with respect to oxygen

  25. 1. Obligate aerobes • Require oxygen 2. Facultative anaerobes • Can survive with or without oxygen 3. Obligate anaerobes • Are poisoned by oxygen

  26. Nitrogen Metabolism • Prokaryotes can metabolize nitrogen • In a variety of ways • In a process called nitrogen fixation, some prokaryotes convert atmospheric nitrogen to ammonia • Process is absolutely essential for the growth of most plants that require N in the form of nitrates, nitrites, or ammonia

  27. Metabolic Cooperation • Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells • One cell does X while other cells do Y • Anabaena – filament cells do photosynthesis while heterocysts carry out N-fixation

  28. In the cyanobacterium Anabaena • Photosynthetic cells and nitrogen-fixing cells exchange metabolic products Photosynthetic cells Heterocyst 20 m Figure 27.10

  29. 1 m Figure 27.11 • In some prokaryotic species • Metabolic cooperation occurs in surface-coating colonies called biofilms (recruit others to form colonies)

  30. 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

  31. Lessons from Molecular Systematics • Molecular systematics • Is leading to a phylogenetic classification of prokaryotes • Is allowing systematists to identify major new clades

  32. Domain Archaea Domain Eukarya Domain Bacteria Proteobacteria Gram-positive bacteria Nanoarchaeotes Crenarchaeotes Euryarchaeotes Korarchaeotes Cyanobacteria Spirochetes Chlamydias Eukaryotes Gamma Epsilon Alpha Beta Delta Universal ancestor • A tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematics

  33. Bacteria • Diverse nutritional types • Are scattered among the major groups of bacteria • The two largest groups are • The proteobacteria and the Gram-positive bacteria

  34. Rhizobium (arrows) inside a root cell of a legume (TEM) Nitrosomonas (colorized TEM) Chromatium; the small globules are sulfur wastes (LM) Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Bdellovibrio bacteriophorus Attacking a larger bacterium (colorized TEM) Helicobacter pylori (colorized TEM). • Proteobacteria 2.5 m 1 m 0.5 m Chromatium; the small globules are sulfur wastes (LM) 5 m 10 m Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Bdellovibrio bacteriophorus Attacking a larger bacterium (colorized TEM) 2 m Figure 27.13

  35. Chlamydias, spirochetes, Gram-positive bacteria, and cyanobacteria 2.5 m Chlamydia (arrows) inside an animal cell (colorized TEM) 5 m Leptospira, a spirochete (colorized TEM) 1 m 5 m Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM) Streptomyces, the source of many antibiotics (colorized SEM) Figure 27.13 50 m Two species of Oscillatoria, filamentous cyanobacteria (LM)

  36. Table 27.2 Archaea • Archaea share certaintraits with bacteria • And other traits with eukaryotes

  37. Figure 27.14 • Some archaea live in extreme environments (extremophiles) • Extreme thermophiles - thrive in very hot environments • Extreme halophiles – thrive in salty places

  38. Methanogens - live in swamps and marshes and produce methane as a waste product

  39. 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

  40. Chemical Recycling • Prokaryotes play a major role • In the continual recycling of chemical elements between the living and nonliving components of the environment in ecosystems

  41. Chemoheterotrophic prokaryotes function as decomposers • Breaking down corpses, dead vegetation, and waste products • Nitrogen-fixing prokaryotes • Add usable nitrogen to the environment

  42. Figure 27.15 Symbiotic Relationships • Many prokaryotes • Live with other organisms in symbiotic relationships such as mutualism and commensalism

  43. Other types of prokaryotes • Live inside hosts as parasites

  44. Concept 27.5:Prokaryotes have both harmful and beneficial impacts on humans • Some prokaryotes are human pathogens • But many others have positive interactions with humans, serving as tools in agriculture and industry

  45. 5 µm Figure 27.16 Pathogenic Prokaryotes • Prokaryotes cause about half of all human diseases • Lyme disease is an example

  46. Pathogenic prokaryotes typically cause disease • By releasing exotoxins or endotoxins • Many pathogenic bacteria are potential weapons of bioterrorism (e.g. Bacillus anthracis, C. botulinum, etc.)

  47. Prokaryotes in Research and Technology • Experiments using prokaryotes • Have led to important advances in DNA technology

  48. Figure 27.17 • Prokaryotes are the principal agents in bioremediation • The use of organisms to remove pollutants from the environment

  49. Prokaryotes are also major tools in • Mining • The synthesis of vitamins • Genetic engineering - production of antibiotics, hormones, and other products

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