Chapter 21

1. Chapter 21 Prokaryotes AP Biology Spring 2011

2. Objectives • Domains the two domains of prokaryotes • Describe the unique characteristics of prokaryotes and their metabolic diversity • Discuss how prokaryotes reproduce • Give examples of positive and negative impacts of bacteria on humans

3. Chapter 21.1-21.21.2 Viruses

4. Viruses • Read chapter 21.1-21.2 • Good refresher on viruses • Remember: • Structure • Viral replication • http://www1.teachertube.com/viewVideo.php?title=Viral_infection_and_replication&video_id=50887

6. Chapter 21.3 Viroids and Prions

7. Viroids and Prions • Since the 1970’s about 30 viroids have been identified • A viroid is a small circle of RNA that can affect organisms • Most affect plants; only one viroid known to affect humans • Prions are misfoldings of proteins • Accumulate in nervous system cells • Cause cell death and a spongiform pathology in the brain cell

8. Chapter 21.4 Prokaryotes- Enduring, Abundant, and Diverse

9. Evolutionary History and Classification • The earliest cells were prokaryotes, cells with no nucleus

10. Evolutionary History and Classification • Bacteria: • Classified based on shape, cell wall properties, metabolism, and other properties

11. Evolutionary History and Classification • Automated gene sequencing has elucidated prokaryote diversity • Shortly after life began there was a branching between bacteria and Archae • Which eventually led to Eukaryote lineage • Despite estimates of millions of species of bacteria, only about 5,000 named

12. Abundance and Metabolic Features • Bacteria are very successful and terms of reproduction • Metabolic diversity is key to reproductive success in bacteria

13. Abundance and Metabolic Features • Metabolic diversity: • Photoautotrophs are photosynthetic • Cyanobacteria • Chemoautotrophs use electrons that they strip from inorganic compounds and use that energy to build organic compounds from CO2 and water

14. Abundance and Metabolic Features • Photoheterotrophs use light energy and obtain carbon from organic compounds from their environment • Chemoautotrophs get both their carbon and their energy by breaking down organic compounds • This group includes many prokaryotes, some protists, and all animals and fungi • Usually parasites- get butrients from living host

15. Chapter 21.5 Prokaryotic Structure and Function

16. Cell Structure and Size • Modern prokaryotes include bacteria and archeans • They are unicellular and do not enclose their DNA in a nucleus • All prokaryotes have ribosomes • Some have infoldings of their membrane • Nearly all have a cell wall, some have an external slime coat that helps them adhere to surfaces

17. Cell Walls • Gram staining: can identify many bacteria species by their wall staining properties • Unknown species exposed to purple dye, then iodine, then alcohol wash, and finally a counterstain • Gram-positive: stays purple • Gram-negative: loses colour at first, then counterstain turns it pink

18. Gram Staining

19. Cell Structure and Size • Glycocalyx: sticky mesh, consists of polysaccharides, polypeptides, or both • Capsule: when highly organized and attached firmly • Slime layer: when less organized, and loosely attached

21. Cell Structure and Size • Three basic shapes: • Coccus: • Spherical • Bacillus: • Rod • Cylindrical • Spirillum: • Helical

22. Cell Structure and Size

23. Cell Structure and Size • Two kinds of filamentous structures may be attached to the cell wall • Bacterial flagellum: rotates like a propeller to pl the cell along • Pili: help bacteria attach to another in conjugation (exchange of DNA), or help them attach to surfaces

24. Reproduction and Gene Transfer • Reproductive rates in prokaryotes are high, some species can reproduce every 20 minutes • Some species reproduce using a budding mechanism • More commonly, reproduce with fission that is similar to mitosis

25. Reproduction and Gene Transfer • Some bacteria can also pass along genes without reproducing • During conjugation a plasmid, a small, self-replicating circle of DNA containing only a few genes, can be passed to another cell

26. Reproduction and Gene Transfer • Some F (fertilty) plasmids allow bacteria to engage in bacterial conjugation in which a pilus joins two prokaryotic cells to permit the transfer of plasmid DNA

27. Chapter 21.6 Prokaryotic Growth and Reroduction

28. Prokaryotic FIssion • When a bacterium divides, each daughter cell inherits a single chromosome • Circular double-stranded DNA molecule • Bacteria reproduce by prokaryotic fission • Results in two genetically identical daughter cells • Only bacteria and archaens reproduce by this type of cell division

29. Conjugation between cells • A plasmid is small, self-replicating circle of DNA containing only a few genes • Some F (fertility) plasmids allow bacteria to engage in bacterial conjugation in which a pilus joins two prokaryotic cells to permit transfer of plasmid DNA

30. Conjugation

31. Chapter 21.7 The Bacteria

32. The Heat Lovers • Thermophiles exist in extreme environments • Members of the genus Aquifex include bacteria that live in volcanic spring, thermal vents, and hot springs

33. The Cyanobacteria • Chloroplast-containing bacteria • Anabaena: by means of heterocysts, can fix nitrogen

34. Metabolically Diverse Proteobacteria • Make up largest, most diverse bacterial group (gram negative) • Theiomargarita namibiensis: • Chemeoautotroph that lives in marine environments and gets its energy from striping electrons from sulfur • Rhizobium: fixes nitrogen on roots of legumes

35. Metabolically Diverse Proteobacteria • E. Coli & H. Pylori: • Live in human digestive system • E. Coli 

36. Metabolically Diverse Proteobacteria • Some free living, chemoautotrophic proteobacteria exhibit complex behavior • Magnetoacteria: attracted by magnetic fields • Myxobacteria: move as a group and feed on soil bacteria

37. Gram Positive Heterotrophs • Gram Positive: • Not a monophyletic group • If all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group • Most are chemioheterotrophs with thick cell walls that retain gram stain

38. Gram Positive Heterotrophs • Lactobacillus: used in dairy product conversions such as yogurt • L.acidophilus: lowers the pH of skin and vaginal linings • Some form resistant endospores that can survive harsh environmental conditions • Ex. Clostridium tetani (tetnus) Tetnus

39. Spirochetes and Clamydias • Spirochetes: resemble a spring • Resposible for causing Lyme disease • Free living parasites or symbionts • Clamydias: intracellular parasites that affect animal cells • Cannot make DNA, pilfer it from cells

40. Chapter 21.8 Archaeans

41. The Third Domain • Archaeans: differ in their ribosomal DNA and cell walls • Resemble eukaryotic cells by making histones and sharing the same start codon for transcription • Some may resemble first cells on Earth • Recently this group has been subdivided into 3 major groups

42. Methanogens • Methane makers • Inhabit swamps, mud, sewage, and animal guts • Make ATP anaerobically by converting carbon dioxide and hydrogen to methane • Free oxygen kills them

43. Extreme Halophiles • Salt lovers • Can tolerate high salt environments such as brackish ponds, salt lakes, volcanic vents on seafloor, and the like • Most are heterotrophic aerobes, some can switch to a special photosynthesis, using bacteriorhodopsin to produce ATP • Light activating pigment embedded in plasma membrane, when it absorbs sunlight energy, changes shape and pumps H+ out from cell. H+ flows back into it, through ATP synthase and drives ATP formation

44. Extreme Thermophiles • Heat lovers • Live in hot springs and other very hot places such as thermal vents of the sea floor where temps exceed 250 degrees C • Use sulfur as source of electrons for ATP formation