1. Prokaryotes Chapter 20

2. Figure 5.1 The Scale of Life

3. Figure 5.2 Why Cells Are Small

4. Figure 5.3 (1) Looking at Cells

5. Figure 5.3 (2) Looking at Cells

6. The Prokaryotes: Domain Bacteria and Archaea Endospores –Dehydrate cell –Chromosome encased in heavy, protective coat –Allows bacteria to remain dormant during unfavorable environmental conditions

7. Figure 5.4 A Prokaryotic Cell

8. Figure 5.5 Prokaryotic Flagella

9. Bacterial Genome and Its Replication The bacterial chromosome is usually a circular DNA molecule with few associated proteins Many bacteria also have plasmids, smaller circular DNA molecules that can replicate independently of the chromosome Bacterial cells divide by binary fission Origin of replication Replication fork Termination of replication

10. Mutation and Genetic Recombination as Sources of Genetic Variation Rapid reproduction, mutation, and genetic recombination contribute to the genetic diversity of bacteria Since bacteria can reproduce rapidly, new mutations quickly increase genetic diversity More genetic diversity arises by recombination of DNA from two different bacterial cells Three processes bring bacterial DNA from different individuals together: –Transformation –Transduction –Conjugation

11. Mechanisms of Gene Transfer and Genetic Recombination in Bacteria Three processes bring bacterial DNA from different individuals together: –Transformation Transformation is the alteration of a bacterial cell’s genotype and phenotype by the uptake of naked, foreign DNA from the surrounding environment –Transduction phages carry bacterial genes from one host cell to another –Conjugation Conjugation is the direct transfer of genetic material between bacterial cells that are temporarily joined The transfer is one-way: One cell (“male”) donates DNA, and its “mate” (“female”) receives the genes

12. A+A+ Phage DNA A+A+ Donor cell B+B+ A+A+ B+B+ Crossing over A+A+ A–A– B–B– Recipient cell A+A+ B–B– Recombinant cell Sex pilus F plasmidBacterial chromosome F + cell Mating bridge F + cell Bacterial chromosome F – cell Conjunction and transfer of an F plasmid from and F + donor to an F – recipient Implication: Lateral Gene Transfer Complicates linear tree thinking!!

13. Figure 26.10 Lateral Gene Transfer Complicates Phylogenetic Relationships

14. Figure 26.1 The Three Domains of the Living World

15. Common Ancestor? Prokaryotic Genetic material was DNA DNA --> RNA --> Protein process in place –Genetic code established Circular chromosome Operons No introns Heterotroph (glycolysis/fermentation)

17. Prokaryotic Classification Domain Bacteria vs Archaea Cell Wall composition –Gram negative or gram positive Cell shape Mode of nutrition Molecular characteristics –rRNA sequence comparisons

18. Why 3 Domains? Prokaryotes include Domains Bacteria and Archaea –Archaea diverged from a prokaryotic lineage Archaea and Bacteria very distinct –No peptidoglycan –Branched hydrocarbons and ether linkages in cell membranes –Unique rRNA sequences –Archaea lineage lead to Domain Eukarya Archaea should share more ancestral traits with Eukarya than Bacteria –Translation machinery more similar –RNA polymerases more similar If left in single Kingdom, would result in Kingdom that was paraphyletic This Kingdom ‘Prokaryote’ would not include all decendents (the eukaryotes) of common ancestor

20. Domain Bacteria Typical prokaryotes –Include all gram positive and gram negative bacteria –Cyanobacteria

21. Figure 26.2 Bacterial Cell Shapes

22. Figure 26.5 The Gram Stain and the Bacterial Cell Wall

24. Prokaryotic Nutrition Dependence on oxygen –Obligate anaerobes: die in presence of oxygen –Facultative anaerobes: grow in either presence or absence of oxygen –Aerobic: require constant supply of oxygen Autotrophic –Do NOT give off O 2 PS I only Bacteriochlorophyll Green sulfur and purple bacteria –Anaerobic mud: CO 2 + 2 H 2 S --> sugar + 2 S –DO give off O 2 PS I and PS II Chlorophyll a (plants) Cyanobacteria –Some Cyanobacteria also able to fix N 2 ; probably first photoautotrophs of early Earth to release oxygen Heterotrophic –Decomposers (saprotrophs) –often capable of breaking down unusual materials –Symbiotic bacteria Mutualistic, commensalistic, or parasitic Nitrogen-fixing bacteria, Rhizobium

25. Figure 26.9 Bacteriochlorophyll Absorbs Long-Wavelength Light

26. Cyanobacteria Gram negative Photosynthesize similar to plants –First to introduce oxygen to atmosphere of early Earth Unicellular or colonial Many fix N 2 - only require water CO 2, N 2 to grow!!! Thylakoids Lichens - symbiotic relationship of cyanobacteria with fungi

27. Figure 26.15 Cyanobacteria

28. Figure 26.19 Modes of Nutrition in the Proteobacteria

29. Figure 36.11 The Nitrogen Cycle

30. Figure 36.9 A Nodule Forms

31. Figure 36.8 Nitrogenase Fixes Nitrogen

32. Domain Archaea rRNA sequence comparisons and cell wall/membrane composition distinguished them from Bacteria –Carl Woese Archaea more closely related to Eukarya –Share some ribosomal proteins not found in bacteria –Initiate transcription in same manner –Similar types of tRNA

33. Figure 26.22 Membrane Architecture in Archaea

34. Domain Archaea: Structure and Function Plasma membranes contain unusual lipids –Glycerol linked to branched-chain hydrocarbons rather than fatty acids No peptidoglycan in cell walls Unique habitats and metabolism