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Chapter 27

Chapter 27. Bacteria and Archaea. Fig. 27-2. 2 µm. 5 µm. 1 µm. (a) Spherical (cocci). (b) Rod-shaped (bacilli). (c) Spiral. Cell-Surface Structures.

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Chapter 27

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  1. Chapter 27 Bacteria and Archaea

  2. Fig. 27-2 2 µm 5 µm 1 µm (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral

  3. 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 • Eukaryote cell walls are made of cellulose or chitin • Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides

  4. Archaea contain polysaccharides and proteins but lack peptidoglycan • Using the Gram stain, scientists classify many bacterial species into Gram-positive and Gram-negative groups based on cell wall composition • Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant

  5. Fig. 27-3 Carbohydrate portion of lipopolysaccharide Outer membrane Peptidoglycan layer Cell wall Cell wall Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Gram- positive bacteria Gram- negative bacteria 20 µm (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. (a) Gram-positive: peptidoglycan traps crystal violet.

  6. Reproduction and Adaptation • Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours • Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries

  7. Fig. 27-9 Endospore 0.3 µm

  8. Prokaryotes can evolve rapidly because of their short generation times

  9. Fig. 27-10 EXPERIMENT Daily serial transfer 0.1 mL (population sample) New tube (9.9 mL growth medium) Old tube (discarded after transfer) RESULTS 1.8 1.6 Fitness relative to ancestor 1.4 1.2 1.0 10,000 0 5,000 15,000 20,000 Generation

  10. Concept 27.2: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes • Prokaryotes have considerable genetic variation • Three factors contribute to this genetic diversity: • Rapid reproduction • Mutation • Genetic recombination

  11. Transformation and Transduction • A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation • Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)

  12. Fig. 27-11-4 Phage DNA A+ B+ A+ B+ Donor cell A+ Recombination A+ A– B– Recipient cell A+ B– Recombinant cell

  13. Conjugation and Plasmids • Conjugation is the process where genetic material is transferred between bacterial cells • Sex pili allow cells to connect and pull together for DNA transfer • A piece of DNA called the F factor is required for the production of sex pili • The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome

  14. The F Factor as a Plasmid • Cells containing the F plasmid function as DNA donors during conjugation • Cells without the F factor function as DNA recipients during conjugation • The F factor is transferable during conjugation

  15. Fig. 27-13 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Recombinant F– bacterium A+ Hfr cell A+ A+ A+ F factor A– A+ A– A+ A– A– F– cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome

  16. R Plasmids and Antibiotic Resistance • R plasmids carry genes for antibiotic resistance • Antibiotics select for bacteria with genes that are resistant to the antibiotics • Antibiotic resistant strains of bacteria are becoming more common

  17. Table 27-1

  18. The Role of Oxygen in Metabolism • Prokaryotic metabolism varies with respect to O2: • Obligate aerobes require O2 for cellular respiration • Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration • Facultative anaerobes can survive with or without O2

  19. Nitrogen Metabolism • Prokaryotes can metabolize nitrogen in a variety of ways • In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3)

  20. 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 called heterocytes exchange metabolic products Video: Cyanobacteria (Oscillatoria)

  21. Fig. 27-14 Photosynthetic cells Heterocyte 20 µm

  22. Fig. 27-16 Domain Eukarya Eukaryotes Korarcheotes Euryarchaeotes Domain Archaea Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Proteobacteria Chlamydias Spirochetes Domain Bacteria Cyanobacteria Gram-positive bacteria

  23. The use of polymerase chain reaction (PCR) has allowed for more rapid sequencing of prokaryote genomes • A handful of soil many contain 10,000 prokaryotic species • Horizontal gene transfer between prokaryotes obscures the root of the tree of life

  24. Table 27-2

  25. Chapter 28 Protists

  26. Overview: Living Small • Even a low-power microscope can reveal a great variety of organisms in a drop of pond water • Protist is the informal name of the kingdom of mostly unicellular eukaryotes • Advances in eukaryotic systematics have caused the classification of protists to change significantly • Protists constitute a paraphyletic group, and Protista is no longer valid as a kingdom

  27. Fig. 28-01 1 µm

  28. Concept 28.1: Most eukaryotes are single-celled organisms • Protists are eukaryotes and thus have organelles and are more complex than prokaryotes • Most protists are unicellular, but there are some colonial and multicellular species

  29. Structural and Functional Diversity in Protists • Protists exhibit more structural and functional diversity than any other group of eukaryotes • Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell

  30. Protists, the most nutritionally diverse of all eukaryotes, include: • Photoautotrophs, which contain chloroplasts • Heterotrophs, which absorb organic molecules or ingest larger food particles • Mixotrophs, which combine photosynthesis and heterotrophic nutrition

  31. Protists can reproduce asexually or sexually, or by the sexual processes of meiosis and syngamy

  32. Endosymbiosis in Eukaryotic Evolution • There is now considerable evidence that much protist diversity has its origins in endosymbiosis • Mitochondria evolved by endosymbiosis of an aerobic prokaryote • Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium

  33. Fig. 28-02-1 Red alga Cyanobacterium Primary endosymbiosis Heterotrophic eukaryote Over the course of evolution, this membrane was lost. Green alga 1 µm

  34. Fig. 28-02-2 Plastid Dinoflagellates Secondary endosymbiosis Apicomplexans Red alga Cyanobacterium Primary endosymbiosis Stramenopiles Plastid Heterotrophic eukaryote Secondary endosymbiosis Over the course of evolution, this membrane was lost. Euglenids Secondary endosymbiosis Green alga Chlorarachniophytes

  35. The plastid-bearing lineage of protists evolved into red algae and green algae • On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote

  36. Five Supergroups of Eukaryotes • It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes • Our understanding of the relationships among protist groups continues to change rapidly • One hypothesis divides all eukaryotes (including protists) into five supergroups

  37. Fig. 28-03a Diplomonads Excavata Parabasalids Euglenozoans Dinoflagellates Apicomplexans Alveolates Ciliates Chromalveolata Diatoms Golden algae Brown algae Stramenopiles Oomycetes Chlorarachniophytes Rhizaria Forams Radiolarians Red algae Chlorophytes Archaeplastida Green algae Charophyceans Land plants Slime molds Gymnamoebas Amoebozoans Entamoebas Nucleariids Unikonta Fungi Opisthokonts Choanoflagellates Animals

  38. Fig. 28-03b Diplomonads Excavata Parabasalids Euglenozoans

  39. Fig. 28-03c Dinoflagellates Apicomplexans Alveolates Ciliates Chromalveolata Diatoms Golden algae Brown algae Stramenopiles Oomycetes

  40. Fig. 28-03d Chlorarachniophytes Rhizaria Forams Radiolarians

  41. Fig. 28-03e Red algae Chlorophytes Green algae Archaeplastida Charophyceans Land plants

  42. Fig. 28-03f Slime molds Amoebozoans Gymnamoebas Entamoebas Nucleariids Unikonta Fungi Opisthokonts Choanoflagellates Animals

  43. Ciliates • Ciliates, a large varied group of protists, are named for their use of cilia to move and feed • They have large macronuclei and small micronuclei • The micronuclei function during conjugation, a sexual process that produces genetic variation • Conjugation is separate from reproduction, which generally occurs by binary fission

  44. Fig. 28-11 Contractile vacuole Oral groove Cell mouth Cilia 50 µm Micronucleus Food vacuoles Macronucleus (a) Feeding, waste removal, and water balance MEIOSIS Haploid micronucleus Diploid micronucleus Compatible mates The original macronucleus disintegrates. Diploid micronucleus MICRONUCLEAR FUSION Key ConjugationReproduction (b) Conjugation and reproduction

  45. Diatoms • Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica • Diatoms usually reproduce asexually, and occasionally sexually

  46. Fig. 28-13 3 µm

  47. Video: Diatoms Moving • Diatoms are a major component of phytoplankton and are highly diverse • Fossilized diatom walls compose much of the sediments known as diatomaceous earth Video: Various Diatoms

  48. Alternation of Generations • A variety of life cycles have evolved among the multicellular algae • The most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms • Heteromorphic generations are structurally different, while isomorphic generations look similar

  49. Fig. 28-16-2 Sporangia 10 cm MEIOSIS Sporophyte (2n) Zoospore Female Developing sporophyte Gametophytes (n) Zygote (2n) Mature female gemetophyte (n) Male Egg FERTILIZATION Sperm Key Haploid (n) Diploid (2n)

  50. Some protists are parasitic • Plasmodium causes malaria • Pfesteria shumwayae is a dinoflagellate that causes fish kills • Phytophthora ramorum causes sudden oak death

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