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Microbiology Stephanie Lanoue
Prokaryote Cells Microbiology Stephanie Lanoue 4-1 Understand prokaryotic cells 4-2 Identify shapes of bacteria 4-3 Describe the structure and function of the glycocalyx. 4-4 Differentiate flagella, axial filaments, fimbriae and pili
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Prokaryotic Overview Prokaryote comes from the Greek word for “____nucleus”.
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Review Question Does a prokaryotic cell have a true membrane- bound nucleus?
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Structure of Bacterial Cells
External Structure Glycocalyx (sugar coat) Flagella Axial Filaments Fimbriae and Pili Cell Wall Internal Structure (to the cell wall) Cell membrane Cytoplasm Ribosome Inclusions Endospore Cause anthrax
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External Structure Glycocalyx (______ coat)
Many prokaryotes secret it on their surface Viscous (________) Gelatinous polymer Composed of polysaccharide, polypeptide, or both If it is organized and firmly attached to the cell wall is Capsule If it is unorganized and loosely attached to the cell wall is slime layer
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External Structure Glycocalyx Contribute to ______________
Capsules prevent phagocytosis Extracellular polymeric substance helps form biofilms
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External Structure (cont’d)
Flagella (singular, flagellum) Filamentous appendages external of the cell ________ bacteria Made of protein called flagellin Three basic parts of flagellum Filaments, long outermost region Protein flagellin, arranged in several chains Rotates for the movements Hook, Basal body, anchor the flagellum to the cell wall and plasma membrane
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Figure 4.7 Arrangements of bacterial flagella.
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External Structure (cont’d)
Mobility by Flagella Chemotaxis, movement of bacteria _______ or ______ from chemical Directed movement, in response to a chemical Movement to a chemical: chemical is a chemoattractant (e.g. sugar, amino acid) Movement away from chemical: chemical is a chemorepellent (toxic substance)
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External Structure (cont’d)
Fimbriae and Pili _____________ appendages that allow for attachment Mostly in gram-negative bacteria Shorter and thinner than flagella Composed of protein called pilin Two types with different functions Fimbriae a few – hundreds Main function is attachment, such as forming biofilm Neisseria gonorrhoeae, gonorrhea Help the microbe colonize mucous membranes
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Cell Wall Responsible for _______ of cells
__________ the cell membrane Prevent from rupturing, when water pressure inside is greater than outside Point of anchorage for flagella Contributes to pathogenicity Ability to cause disease, in some bacteria
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Figure 4.6 The Structure of a Prokaryotic Cell.
Capsule Cell wall Cytoplasm 70S Ribosomes Plasma membrane Cell wall Nucleoid containing DNA Capsule Inclusions
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Cell Wall Peptidoglycan, Rows are linked by polypeptides
Polymer of a repeating disaccharide in _______(Backbone ): Rows are linked by polypeptides
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Bacterial cell walls Gram Positive ______ peptidoglycan
Additional components, anchor the layers together and to plasma membrane
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Bacterial cell walls Gram Negative _______ peptidoglycan
Additional outer membrane made of polysaccharides, lipoproteins, and phospholipids
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Bacterial cell walls Gram-Negative Cell Walls
_________ from phagocytes and antibiotics Made of lipopolysaccharide (LPS)
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Cell Walls and the Gram Stain Mechanism
Crystal violet-iodine crystals form inside cell Gram-positive Alcohol dehydrates peptidoglycan Gram-negative Alcohol dissolves outer membrane and leaves holes in peptidoglycan CV-I washes out; cells are colorless Safranin added to stain cells
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Prokaryote Plasma (Cytoplasmic) Membrane
Phospholipid bilayer that _______ the cytoplasm Peripheral proteins on the membrane surface Integral and transmembrane proteins penetrate the membrane Lipid bilayer of plasma membrane Peptidoglycan Outer membrane Plasma membrane of cell
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Figure 4.14b Plasma membrane.
Outside Pore Lipid bilayer Peripheral protein Polar head Inside Integral proteins Nonpolar fatty acid tails Peripheral protein Polar head Lipid bilayer of plasma membrane
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Cell membrane function
Selective ____________ Selectively permeable Proteins, channel, large molecule pass through Disinfectants and Antiseptics many are aimed at disrupting the cell membrane Alcohol and detergents
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Internal Structure Cytoplasm The substance ______ the plasma membrane
Contains: 80% water Protien, enzymes Lipids Inorganic ions Cytoskeleton
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Internal Structure Bacterial chromosome: circular ______ of DNA that contains the cell's genetic information Plasmids: extrachromosomal genetic elements; carry non-crucial genes (e.g., antibiotic resistance, production of toxins)
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Internal Structure Ribosomes Sites of __________ synthesis
Made of protein and ribosomal RNA Some antibiotics are aimed at ribosomes of bacterial cells Streptomycin, Neomycin, Erythromycin and Tetracycline work by inhibiting protein synthesis by disrupting ribosomes
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Internal structure Endospores, Gram + bacteria
Resting cells; produced when nutrients are depleted ___________ to desiccation, heat, chemicals, and radiation Produced by Bacillus and Clostridium Sporulation: endospore formation Germination: endospore returns to vegetative state e.g. Clostridium sp. (clostridium tetani)
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Figure 4.21b Formation of endospores by sporulation.
An endospore of Bacillus subtilis
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Figure 4.21a Formation of endospores by sporulation.
Cell wall Cytoplasm Spore septum begins to isolate newly replicated DNA and a small portion of cytoplasm. Plasma membrane starts to surround DNA, cytoplasm, and membrane isolated in step 1. Plasma membrane Bacterial chromosome (DNA) Sporulation, the process of endospore formation Spore septum surrounds isolated portion, forming forespore. Two membranes Peptidoglycan layer forms between membranes. Spore coat forms. Endospore is freed from cell.
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