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Functional Anatomy of Prokaryotic and Eukaryotic Cells
Ch 4: Functional Anatomy of Prokaryotic and Eukaryotic Cells
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Student Learning Outcomes (SLOs)
Compare and contrast the overall cell structure of prokaryotes and eukaryotes. Identify the three basic shapes of bacteria. Describe structure and function of the glycocalyx, flagella, fimbriae, and pili. Compare and contrast the cell walls of gram-positive bacteria, gram-negative bacteria, acid-fast bacteria, and mycoplasmas. Differentiate between protoplasts and spheroplasts. Describe the structure, chemistry, and functions of the prokaryotic plasma membrane. Identify the functions of the nucleoid and ribosomes. Describe the functions of endospores, sporulation, and endospore germination. What you should remember from Bio 31: Define organelle. Describe the functions of the nucleus, endoplasmic reticulum, ribosomes, Golgi complex, lysosomes, vacuoles, mitochondria, chloroplasts, peroxisomes. Explain endosymbiotic theory of eukaryotic evolution.
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SLOs cont.: Check Your Understanding
What is the main feature that distinguishes prokaryotes from eukaryotes? How would you be able to identify streptococci through a microscope? Why are bacterial capsules medically important? How do bacteria move? Why are drugs that target cell wall synthesis useful? What happens to protoplasts and spheroplasts when put into hyper- or hyptonic solutions? Where is the DNA located in a prokaryotic cell? Under what conditions do endospores form?
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Comparing Prokaryotic and Eukaryotic Cells
Common features? Distinctive features: ?
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Prokaryotes: Size, Shape, Arrangement
Average size: µm µm Three basic shapes Bacillus, -i Coccus, -i Spirals (Vibrio, Spirillum, Spirochete) Most monomorphic, some pleomorphic Variations in cell arrangements (esp. for cocci) Review Figs. 4.1, 4.2, and 4.4
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Spiral Bacteria Figure 4.4
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Pleomorphic Corynebacteria
Monomorphic E. coli
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Cell Arrangement Figs. 4.1 and 4.2
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External Structures located outside of cell wall Glycocalyx
Flagellum /-a Axial filaments Fimbria /-ae Pilus /-i Foundation Fig. 4.6
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Glycocalyx Many bacteria secrete external surface layer composed of sticky polysaccharides, polypeptides, or both (= extracellular polymeric substance) Capsule: organized and firmly attached to cell wall Slime layer: unorganized and loosely attached Allows cells to attach key to biofilms Prevents phagocytosis virulence factor E.g.: B. anthracis, S. pneumoniae, S. mutans
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Flagellum – Flagella Anchored to wall and membrane
Number and placement determines if atrichous, monotrichous, lophotrichous, amphitrichous, or peritrichous Compare to Fig 4.7
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Flagellar Arrangement
_______ ___________
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Motility Due to rotation of flagella
Mechanism of rotation: “Run and tumble” Move toward or away from stimuli (taxis) Chemotaxis (also phototaxis and magnetotaxis) Flagella proteins are called H antigens (e.g., E. coli O157:H7)
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“Run and Tumble” Fig 4.9
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Fimbriae and Pili Pili: transfer DNA from one cell to another; also some role in motility Fimbriae adhere attachment
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__________ __________ __________ ?
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Cell Wall Rigid for shape & protection prevents osmotic lysis
Consists of Peptidoglycan (murein) polymer of 2 monosaccharide subunits N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) Linked by polypeptides (forming peptide cross bridges) with tetrapeptide side chain attached to NAM Fully permeable to ions, aa, and sugars (Gram positive cell wall may regulate movement of cations) Fig 4.12
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Fig 4.13
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Gram + Cell Wall Gram – Cell Wall
Thick layer of peptidoglycan Negatively charged teichoic acid on surface Thin peptidoglycan Outer membrane Periplasmic space
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Gram-Positive Cell Walls
Teichoic acids Lipoteichoic acid links to plasma membrane Wall teichoic acid links to peptidoglycan May regulate movement of cations Polysaccharides provide antigenic variation Fig.4.13b
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Gram-negative Cell Wall
Lipid A of LPS acts as endotoxin; O polysaccharides are antigens for typing, e.g., E. coli O157:H7 Gram neg. bacteria are less sensitive to medications because outer membrane acts as additional barrier. LPS layer = outer layer of outer membrane Fig 4.13 c (protein rich gel-like fluid)
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Gram Stain Mechanism Crystal violet-iodine crystals form in cell.
Gram-positive Alcohol dehydrates peptidoglycan CV-I crystals do not leave Gram-negative Alcohol dissolves outer membrane and leaves holes in peptidoglycan. CV-I washes out For further details and practical application see lab
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Bacteria with No Cell Wall: Mycoplasmas
Instead, have cell membrane which incorporates cholesterol compounds (sterols), similar to eukaryotic cells Cannot be detected by typical light microscopy This EM of M. hyorhinis Shape ?
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Bacteria with Acid-fast Cell Walls
Genus Mycobacterium and Nocardia mycolic acid (waxy lipid) covers thin peptidoglycan layer Do not stain well with Gram stain use acid-fast stain
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Damage to Cell Wall Lysozyme digests disaccharide in peptidoglycan.
Penicillin inhibits peptide bridges in peptidoglycan. Protoplasts and Spheroplasts
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Internal Structures: Cell Membrane
Analogous to eukaryotic cell membrane: Phospholipid bilayer with proteins (Fluid mosaic model) Permeability barrier (selectively permeable) Diffusion, osmosis and transport systems Different from eukaryotic cell membrane: Role in Energy transformation (electron transport chain for ATP production) Damage to the membrane by alcohols, quaternary ammonium (detergents), and polymyxin antibiotics causes leakage of cell contents.
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Fig 4.14
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Movement of Materials across Membranes
See Bio 31! Review on your own if necessary (pages 92 – 94)
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Cytoplasm and Internal Structures
Location of most biochemical activities Nucleoid: nuclear region containing DNA (up to 3500 genes). Difference between human and bacterial chromosome? Ribosomes (smaller than in eukaryotes) Inclusion bodies: granules containing nutrients, monomers, Fe compounds (magnetosomes)
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Plasmids: small, nonessential, circular DMA (5 – 100 genes)
Compare to Fig. 4.6 Plasmids: small, nonessential, circular DMA (5 – 100 genes) Replicate independently
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Endospores For special staining technique: see lab! Dormant, tough, non-reproductive structure; germination vegetative cells Spore forming genera: __________ Resistance to UV and radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants Relationship to disease Sporulation: Endospore formation Germination: Return to vegetative state
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Sporulation Fig. 4.21
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The Eukaryotic Cell See BIO 30!
Review on your own if necessary (pages 94 – 102)
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Clinical Case: Infection Detection
In the Clinic Gram Stain of Urine the end Clinical Case: Infection Detection
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