1. 1 Figure 3.5, page 75

2. Points to discuss  The functional anatomy of a prokaryotic cell  Morphological differences between Gram positive and Gram negative bacteria  Special characteristics of Rickettsia, Chlamydia and Mycoplasma  Types of bacteria- Morphological classification  Importance of bacterial morphology to their virulence

3. 3 4.1 Prokaryotic Diversity  The Domain Bacteria Contains Some of the Best Studied Prokaryotes The majority of the 18 phyla of Bacteria play a positive role in nature Proteobacteria contain the largest and most diverse group of species, including E. coli and many human pathogens Firmucutes consist of many gram-positive species, such as Bacillus, Clostridium, Staphylococcus, and Streptococcus Actinobacteria include Streptomyces, the genus that produces the antibiotic streptomycin Cyanobacteria carry out photosynthesis using chlorophyll, responsible for the appearance of oxygen in Earth’s early atmosphere Chlamydiae are extremely small, mostly pathogenic bacteria

4. 4  The Domain Archaea Contains Many Extremophiles Euryarchaeota contain: methanogens (live in anoxic environments) extreme halophiles (salt- lovers) thermoacidophiles (grow at high temperatures with low pH) Crenarchaeota tend to grow in hot, acidic environments such as hot springs and volcanic vents

5. 5 4.2 The Shapes and Arrangements of Prokaryotic Cells  Prokaryotes Vary in Cell Shape and Cell Arrangement A bacillus is a prokaryotic cell with a rod shape A spherical bacterial cell is a coccus Many cocci and some bacilli appear in groups or chains Figure 4.4a, page 111 Figure 4.4b, page 111

6. 6 Spiral shaped bacteria can appear as vibrios (comma-shaped), spirilla (helical), or spirochete Figure 3.5, page 112

7. 7 4.3 An Overview to Prokaryotic Cell Structure  Structure and organization are based on specific processes cells need to carry out: sensing/responding to stimuli compartmentation of metabolism growth reproduction Figure 4.6, page 113

8. Basic Morphology of a prokaryotic cell  Appendages- Flagella/ axial filaments Pili /Fimbriae  Cell envelope Glycocalyx (Capsule, Slime layer) Cell wall Cell membrane  Protoplasm Cytoplasm (cytosol) Ribosomes Mesosomes Granules Nucleoid/ Chromatin body Bacterial chromosomes & extrachromosomal genetic elements.

9. 9 4.4 External Prokaryotic Cell Structures  Pili Are Protein Fibers Extending from the Surface of Many Prokaryotes Pili help: attach cells to surfaces to form biofilms and microcolonies Some bacterial species have conjugation pili, used to transfer genetic material between cells Figure 4.7, page 114

10. 10  Prokaryotic Flagella Are Long Appendages Extending from the Cell Surface Flagella can be used for cell motility Prokaryotic flagella contain a helical filament, a hook, and a basal body Figure 4.9b, page 116

11. 11 Spirochetes contain endoflagella, which move the cell through torsion exerted on the cell by endoflagellar rotation Figure 4.11a, page 117

12. Cell Envelope  Layers external (outside) of cell protoplasm  3 basic layers Glycocalyx Cell wall Cell membrane

13. 13  The Glycocalyx Is an Outer Layer External to the Cell Wall The glycocalyx is an adhering layer of polysaccharides (and sometimes small proteins) A thick glycocalyx bound to the cell is a capsule A capsule is a thick, diffuse layer of polysaccharides is a slime layer It protects cells from the environment, and allows them to attach to surfaces Figure 4.12b, page 118

14. 14 4.5 The Cell Envelope  The Prokaryotic Cell Wall Is a Tough and Protective External Shell The cell wall protects the cell from injury, and to maintain cell shape and water balance Figure 4.13, page 120

15. 15 Cell walls in prokaryotes contain peptidoglycan Gram-positive bacteria have thick peptidoglycan cell walls containing teichoic acid Gram-negative bacteria have a two-dimensional peptidoglycan layer and no teichoic acid The gram-negative cell wall has an outer membrane, separated from the cell membrane by the periplasmic space The outer membrane contains proteins called porins that selectively allow small molecules into the periplasmic space

16. 16 Figure 4.14, page 123

17. Cell wall ( Contd.)  Specialized cell wall Mycolic acid- Mycobacteria and Nocardia  Bacteria lacking cell wall L forms - Gram + bacteria - protoplast Gram - bacteria - spheroplast Mycoplasma - Sterols in the cell wall offer some protection.

18. 18  The Archaeal Cell Wall Also Provides Mechanical Strength No archaea have peptidoglycan in the cell wall, but some have pseudopeptidoglycan Others have polysaccharides, proteins, or both The S-layer is the most common archaeal cell wall, consisting of protein or glycoprotein in a crystal lattice

19. Cell Membrane  Next layer just beneath the cell wall  Composition Phospholipids- 30-40 % Protein- 60-70% Lipid Bilayer Fluid mosaic model

20. Functions of cell membrane  Lipids Control transport Be selectively permeable Segregate reactions within the cell membrane  Membrane proteins Channels of transport Receive molecular signals binding molecules - receptor function

21. Functions of cell membranes (contd.)  membrane proteins acting as enzymes respiration toxin synthesis synthesis of structural molecules of outer layers of cell envelope.

22. 22  The Cell Membrane Represents the Interface between the Cell Environment and the Cell Cytoplasm The cell membrane is a fluid layer of phospholipid and protein (the fluid mosaic model) The phospholipid molecules are arranged in a bilayer Hydrophobic fatty acid chains in the phospholipids form a permeability barrier Figure 4.15, page 124

23. 23  The Cell Membrane Represents the Interface between the Cell Environment and the Cell Cytoplasm (cont.) Antimicrobial substances may disrupt or dissolve the bilayer Membrane proteins perform or aid in many functions, such as: cell wall synthesis energy metabolism DNA replication sensation of stimuli molecule transport Figure 4.15, page 124

24. 24 Transport of molecules can be passive (facilitated diffusion) or active (active transport)

25. 25  The Archaeal Cell Membrane Differs from Bacterial and Eukaryal Membranes Hydrophobic lipid tails are attached to glycerol differently in archaea Fatty acids are usually absent Adjacent lipid tails are bound together forming a lipid monolayer, instead of a bilayer

26. Mesosomes  Folds of cell membrane into the cytoplasm  They increase the internal surface area for the cell wall associated activities  Other role proposed for the mesosomes is that they act as guides for the duplicated nucleic acids during the cell division.

27. Cytoplasm  Cell pool  Bacterial chromosome  Plasmids  Ribosomes  Granules or inclusions

28. Cell Pool  Mostly water  Solvent for all nutrients Sugars Amino acids Salts  Metabolic enzymes

29. 29 4.6 The Cell Cytoplasm and Internal Structures  The Nucleoid Represents a Subcompartment Containing the Chromosome The nucleoid is a central subcompartment in the cytoplasm where DNA aggregates Figure 4.17, page 126

30. 30 The chromosome is usually a closed loop of DNA and protein The DNA contains the genes (hereditary information) The complete set of genes is called the genome Most cells have only one copy of each gene (are haploid), so cannot undergo mitosis like eukaryotes

31. 31  Plasmids Are Found in Many Prokaryotic Cells Plasmids are molecules of DNA smaller than the chromosome Each plasmid is a closed loop, containing 5-10 genes Plasmids can be transferred between cells and can be used as vectors in genetic engineering R plasmids carry genes for resistance to antibiotics

32. 32  Other Subcompartments Exist in the Prokaryotic Cytoplasm There are hundreds of thousands of ribosomes, used for protein synthesis Inclusion bodies store nutrients or building blocks for cellular structures Some aquatic bacteria use gas vesicles to float on the water’s surface Magnetosomes contain crystals of magnetite or greigite, allowing cells to respond to magnetic fields Microfocus 4.4, page 128

33. 33  Prokaryotic Cells Have a “Cytoskeleton” Prokaryotes contain a homolog of eukaryotic tubulin It forms filaments similar to those found in microtubules Proteins homologous to eukaryotic actin can help determine cell shape Crescentin, a homolog to eukaryotic intermediate filaments, also assists in cell shape Figure 4.18a, page 128

34. Granules and Inclusions  Inclusions- Membrane bound packets of energy rich organic nutrients.- food stores e.g.Glycogen, Polyhydroxy-buterate  Granules Not bound by membrane Inorganic in nature e.g. polyphosphate (metachromatic), Sulfur.

35. Bacterial endospore (Spore)  One of the toughest forms of microorganisms  Formed in adverse conditions.  Can withstand extremes of heat  Can withstand dessication as well as a large variety of chemicals.  contain calcium dipicolinate  Not a method of reproduction  Bacillus and Clostridium

36. The Formation of Bacterial Spore

39. Characteristics of Rickettsia, Chlamydia and Mycoplasma  Rickettsia and Chlamydia are obligate intracellular “parasites”-unable to survive outside a host cell  Rickettsia- Gram negative coccobacilli- arthropod vectors  Chlamydia- spherical gram negative but no peptidoglycan, unique growth cycle, no ATP generating mechanism  Mycoplasma- Lack cell wall- variable shape, cannot be stained by Gram stain

40. Naturally Wall-less Genus  Mycoplasma Cannot be gram stained

41. Characteristics of Rickettsia and Chlamydia  Rickettsia and Chlamydia are obligate intracellular “parasites”- unable to survive outside a host cell  Rickettsia- Gram negative coccobacilli- arthropod vectors  Chlamydia- spherical gram negative but no peptidoglycan, unique growth cycle, no ATP generating mechanism

42. Rickettsia

43. 43 4.7 The Prokaryotic/Eukaryotic Cell— Revisited  Prokaryotes can carry out the “complex” metabolic and biochemical processes typically associated with eukaryotic cells  Spatial separation of transcription and translation occurs in prokaryotes as well as eukaryotes Figure 4.19, page 131