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Transcript
Chapter 3 – Cell Structure and Function 9/10/14 MDufilho 1 Processes of Life What is the difference between a living thing and a non-living thing? 9/10/14 MDufilho 2 Figure 3.1 Examples of types of cells. 9/10/14 MDufilho 3 Processes of Life • Tell Me Why • The smallest free-living microbe—the bacterium Mycoplasma—is nonmotile. Why is it alive, even though it cannot move? 9/10/14 MDufilho 4 How are these cells similar? Prokaryote 9/10/14 Eukaryote MDufilho 5 Prokaryotic and Eukaryotic Cells: An Overview • Tell Me Why • In 1985, an Israeli scientist discovered a single-celled microbe, Epulopiscium fishelsoni. This organism is visible with the naked eye. Why did the scientist think Epulopiscium was eukaryotic? • What discovery revealed that the microbe is really a giant bacterium? 9/10/14 MDufilho 6 External Structures of Bacterial Cells • Two Types of Glycocalyces • Capsule • Composed of organized repeating units of organic chemicals • Firmly attached to cell surface • May prevent bacteria from being recognized by host • Slime layer • Loosely attached to cell surface • Water soluble • Sticky layer allows prokaryotes to attach to surfaces as biofilms 9/10/14 MDufilho 7 Figure 3.5 Glycocalyces. Glycocalyx (slime layer) Glycocalyx (capsule) 9/10/14 MDufilho 8 External Structures of Bacterial Cells • Flagella • Are responsible for movement • Have long structures that extend beyond cell surface • Are not present on all bacteria • Structure • Composed of filament, hook, and basal body • Basal body anchors the filament 9/10/14 MDufilho 9 Figure 3.6 Proximal structure of bacterial flagella. Filament Direction of rotation during run Rod Peptidoglycan layer (cell wall) Protein rings Cytoplasmic membrane Cytoplasm Filament Outer protein rings Outer membrane Rod Gram + Gram – Basal body Peptidoglycan layer Integral protein Inner protein rings Cell wall Cytoplasmic membrane Cytoplasm Integral protein 9/10/14 MDufilho 10 Figure 3.8 Axial filament. Endoflagella rotate Axial filament Axial filament rotates around cell Outer membrane Cytoplasmic membrane © 2015 Pearson Education, Inc. Spirochete corkscrews and moves forward Axial filament Figure 3.10 Fimbriae. 9/10/14 Flagellum Fimbria MDufilho 12 Figure 3.11 Pili. Pilus 9/10/14 MDufilho 13 Bacterial Cell Walls • Provide structure and shape and protect cell from osmotic forces • Assist some cells in attaching to other cells or in resisting antimicrobial drugs • Can target cell wall of bacteria with antibiotics • Give bacterial cells characteristic shapes • Composed of peptidoglycan • Scientists describe two basic types of bacterial cell walls • Gram-positive and Gram-negative 9/10/14 MDufilho 14 Bacterial Cell Walls • Gram-Positive Bacterial Cell Walls • Relatively thick layer of peptidoglycan • Contain unique polyalcohols called teichoic acids • Appear purple following Gram staining procedure • Presence of up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation 9/10/14 MDufilho 15 Prokaryotic Cell Walls • Gram-Negative Bacterial Cell Walls • Have only a thin layer of peptidoglycan • Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS) • Lipid A portion of LPS can cause fever, vasodilation, inflammation, shock, and blood clotting • May impede the treatment of disease • Appear pink following Gram staining procedure 9/10/14 MDufilho 16 Prokaryotic Cell Walls • Bacteria Without Cell Walls • A few bacteria lack cell walls • Often mistaken for viruses because of small size and lack of cell wall • Have other features of prokaryotic cells, such as ribosomes 9/10/14 MDufilho 17 Bacterial Cytoplasmic Membranes • Structure • Referred to as phospholipid bilayer • Composed of lipids and associated proteins • Integral proteins • Peripheral proteins • Fluid mosaic model describes current understanding of membrane structure 9/10/14 MDufilho 18 Bacterial Cytoplasmic Membranes • Functions??? 9/10/14 MDufilho 19 Cytoplasm of Bacteria • Cytosol • Liquid portion of cytoplasm • Mostly water • Contains cell's DNA in region called the nucleoid • Inclusions • May include reserve deposits of chemicals • Endospores • Unique structures produced by some bacteria • Defensive strategy against unfavorable conditions 9/10/14 MDufilho 20 Figure 3.23 Granules of PHB in the bacterium Azotobacter chroococcum. Polyhydroxybutyrate 9/10/14 MDufilho 21 Figure 3.24 The formation of an endospore. Steps in Endospore Formation Cell wall Cytoplasmic membrane 1 DNA is replicated. DNA 5 Spore coat forms around endospore. Spore coat 6 Endospore matures: Completion of spore coat. Increase in resistance to heat and chemicals by unknown process. Outer spore coat Vegetative cell 2 Cytoplasmic membrane invaginates to form forespore. 3 Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell's DNA disintegrates. Forespore First membrane Endospore 7 Endospore is released from original cell. Second membrane 8 4 A cortex of peptidoglycan is deposited between the membranes; meanwhile, dipicolinic acid and calcium ions accumulate within the center of the endospore. 9/10/14 Cortex MDufilho 22 Cytoplasm of Prokaryotes • Nonmembranous Organelles • Ribosomes • Sites of protein synthesis • Cytoskeleton • Can play different roles in the cell • Cell division • Cell shape • Segregation of DNA molecules • Movement through the environment 9/10/14 MDufilho 23 Endosymbiotic Theory Mitochondria and chloroplasts have 70S ribosomes, circular DNA, and two membranes. Why???? 9/10/14 MDufilho 24