Microbiology Chapter 4 Notes
Microbiology Chapter 4 Notes BIO 2600
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This 5 page Class Notes was uploaded by Katelyn Farris on Monday August 29, 2016. The Class Notes belongs to BIO 2600 at William Carey University taught by Dr. Cunningham in Fall 2015. Since its upload, it has received 5 views. For similar materials see Microbiology in Biology at William Carey University.
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Date Created: 08/29/16
Chapter 4 notes *4.3 Prokaryotic Profiles pg. 91 *Figure 4.1 Structure of a Bacterial Cell External Structures -Appendages -Two major groups 1. Motility – flagella and axial filaments 2. Attachment or channels – fimbrial and pili -Glycocalyx – surface coating Flagella -3 parts: 1. Filament – long, thin, helical structure composed of protein flagellin 2. Curved sheath 3. Basal Body – stack of rings firmly anchored in cell wall -Rotates 360 degrees -Number and arrangement of flagella varies -Monotrichous, lophotrichous, amphitrichous -Functions in motility through cell environment Flagellar Arrangements 1. Monotrichous – single flagellum at one end 2. Lophotrichous – small bunches emerging from the same site 3. Amphitrichous – flagella at both ends of cell 4. Peritrichous – flagella are dispersed randomly Flagellar Responses -Guide bacteria in a direction in response to external stimulus -Chemical stimuli – chemotaxis; positive and negative -Light stimuli -Signal sets flagella into rotary motion clockwise or counterclockwise Periplasmic Flagella -Internal flagella, enclosed in the space between the outer sheath and the cell wall peptidoglycan -Produce cellular motility by contracting and imparting twisting or flexing motion Fimbriae -Fine, proteinaceous, hair-like bristles emerging from the cell surface -Function in adhesion to other cells and surfaces Pili -Rigid tubular structure made of pilin protein -Found only in gram-negative cells -Function to join bacterial cells for partial DNA transfer called conjugation -Important in transfer of antibiotic resistance Glycocalyx -Coating of molecules external to the cell wall, made of sugars and/or proteins -Two types: 1. Slime layer – loosely organized and attached 2. Capsule – highly organized, tightly attached -Functions: - Protect cells from dehydration and nutrient loss - Inhibit killing by white blood cells by phagocytosis contributing to pathogenicity - Attachment – formation of biofilms - Related to quorum sensing *Pay attention to inside 4.1 in the book The Cell Envelope -External covering outside the cytoplasm -Composed of two basic layers: -Cell wall and cell membrane -Maintains cell integrity -Two different groups of bacteria demonstrated by Gram stain: -Gram-positive bacteria: thick cell wall composed primarily of peptidoglycan and cell membrane -Gram-negative bacteria: outer membrane, thin peptidoglycan layer, and cell membrane *Pay attention to pg. 73 inside 3.2 Structure of Cell Walls -Determines cell shape, prevents lysis (bursting) or collapsing due to changing osmotic pressure -Peptidoglycan is primary component: -Unique macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments Gram-Positive Cell Wall -Thick, homogeneous sheath of peptidoglycan -20-80 nm thick -Includes teihoic acid and lipoteichoic acid: function in cell wall maintenance and enlargement during cell division; move cations across the cell envelope; stimulate a specific immune response -Some cells have a periplasmic space, between the cell membrane and cell wall Gram-Negative Cell Wall -Composed of an outer membrane and a thin peptidoglycan layer -Outer membrane is similar to cell membrane bilayer structure -Outermost layer contains lipopolysaccharides and lipoproteins (LPS) -Lipid portion (endotoxin) may become toxic when released during infections -May function as receptors and blocking immune response -Contain porin proteins in upper layer – regulate molecules entering and leaving cell -Bottom layer is a thin layer of *Table 4.1 The Gram Stain -Differential stain that distinguishes cells with a gram-positive cell wall those with a gram-negative cell wall -Gram-positive – retain crystal violet and stain purple -Gram-negative – lose crystal violet and stain red from safranin counterstain -Important basis of bacterial classification and identification -Practical aid in diagnosing infection and guiding drug treatment Nontypical Cell Walls -Some bacterial groups lack typical cell wall structure, Ex. Mycobacterium and Nocardia -Gram-positive cell wall structure with lipid mycolic acid (cord factor) -Pathogenicity and high degree of resistance to certain chemicals and dyes -Basis for acid-fast stain used for diagnosis of infections caused by these microorganisms -Some have no cell wall, Ex. Mycoplasma -Cell wall is stabilized by sterols -Pleomorphic Cell Membrane Structure -Phospholipid bilayer with embedded proteins – fluid mosaic model -Functions in: -Providing site for energy reactions, nutrient processing, and synthesis -Passage of nutrients into the cell and the discharge of wastes -cell membrane is selectively permeable Bacterial Internal Structures -Cell cytoplasm: -Dense gelatinous solution of sugars, amino acids, and salts -70-80% water -serves as solvent for materials used in all cell functions Bacterial Internal Structures -Chromosomes -Single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell -Aggregated in a dense area called the nucleoid -DNA is tightly coiled -Plasmids -Small circular, double-stranded DNA -Free or integrated into the chromosome -Duplicated and passed on to offspring -Not essential to bacterial growth and metabolism -May encode antibiotic resistance, tolerance to toxic metals, enzymes, and toxins -Used in genetic engineering – readily manipulated and transferred from cell to cell -Ribosomes -Made of 60% ribosomal RNA and 40% protein -Consist of two subunits: large and small -Prokaryotic differ from eukaryotic ribosomes in size and number of proteins -Site of protein synthesis -Present in all cells -Inclusions and granules -Intracellular storage bodies -Vary in size, number, and content -Bacterial cell can use them when environmental sources are depleted -Examples: glycogen, particles of iron oxide, etc -Cytoskeleton -Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall Bacterial Internal Structures cont.. -Endospores -Inert, resting, cells produced by some G+ genera: Clostridium, Bacillus, and Sporosarcina -Have a 2-phase life cycle: -Vegatative cell – metabolically active and growing -Endospore – when exposed to adverse environmental conditions; capable of high resistance and very long-term survival -Sporulation – formation of endospores -Hardiest of all life forms -Withstands extremes in heat, drying, freezing, radiation, and chemicals -Not a means of reproduction -Germination – return to vegetative growth Endospores -Resistance linked to high levels of calcium and dipicolinic acid -Dehydrated, metabolically inactive -Thick coat -Longevity verges on immortality, 250 million years Bacterial Shapes, Arrangements, and Sizes -Vary in shape, size, and arrangement but typically described by one of three basic shapes: -Coccus – spherical -Bacillus – rod -Coccobacillus – very short and plump - Vibrio – gently curved Spirillum – helical, comma -Arrangement of cells is dependent on pattern of division and how cell remains attached after division Classification Systems in Prokaryotae 1. Microscopic morphology 2. Macroscopic morphology – colony appearance 3. Bacterial physiology 4. Serological analysis 5. Genetic and molecular analysis Bacterial Taxonomy Based on Bergey’s Manual -Bergey’s Manual of Determinative Bacteriology – Five-volume resource covering all known prokaryotes -Classification based on genetic information – phylogenetic -Two domains: Archaea and Bacteria -Five major subgroups with 25 different phyla
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