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Chapter 4: Functional Anatomy of Procaryotic and Eucaryotic Cells

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Distinguishing Features of Procaryotic Cells: Chapter 4: Functional 1. DNA is: u Not enclosed within a nuclear membrane. Anatomy of Procaryotic and u A single circular chromosome. Eucaryotic Cells u Not associated with histone proteins. 2. Lack membrane-enclosed organelles like mitochondria, chloroplasts, Golgi, etc. 3. Cell walls usually contain peptidoglycan, a complex polysaccharide. 4. Divide by binary fission. Distinguishing Features of Eucaryotic The Procaryotic Cell: Size, Shape, and Cells: Arrangement of Bacterial Cells 1. DNA is: Cell Size: u Enclosed within a nuclear membrane. u Dimensions of mostbacterial cells: u Several linear chromosomes. u Diameter: 0.2 to 2.0 mm. u Associated with histones and other proteins. u Human red blood cell is about 7.5-10 mm in diameter. u 2. Have membrane-enclosed organelles like Length : 2 to 8 mm. u Some cyanobacteria are up to 60 mm long. mitochondria, chloroplasts, Golgi, endoplasmic reticulum, etc. u Bacterial cells have large surface to volume ratios. Therefore all parts of the cell: 3. Divide by mitosis. u Are close to the surface. u Can be quickly reached by nutrients. Bacterial Cell Size Compared to The Procaryotic Cell: Size, Shape, Eucaryotic Cells and Viruses and Arrangement of Bacterial Cells Bacterial Cell Shapes & Arrangements: u Coccus (plural: cocci): Spherical. May have the following arrangements: u Diplococci : A pair of attached cocci. Remain attached after dividing. u Streptococci : Chainlike arrangement. u Tetrads : Groups of four. Divide in two planes. u Sarcinae : Groups of eight. Divide in three planes. uStaphylococci : Grapelike clusters. Divide in multiple planes. 1 Common Arrangements of Cocci The Procaryotic Cell: Size, Shape, and Arrangement of Bacterial Cells Bacterial Cell Shapes & Arrangements: u Bacillus (plural: bacilli): Rod-shaped. Most bacilli appear as single rods but may see: u Diplobacilli: A pair of attached bacilli. Remain attached after dividing. u Streptobacilli: Chainlike arrangement. u Coccobacillus : Intermediate shape between coccus and bacillus. Oval rods. Different Types of Bacilli The Procaryotic Cell: Size, Shape, and Arrangement of Bacterial Cells Bacterial Cell Shapes & Arrangements : u Spiral Bacteria: Have one or more twists: u Vibrio: A comma shaped cell. Look like curved rods. u Spirilla: Helical, corkscrew shaped bacteria with rigid bodies. u Use whiplike external flagella to move. u Spirochetes: Helical bacteria with flexible bodies. u Use axial filaments (internal flagella) to move. Spiral Shaped Bacteria The Procaryotic Cell: Size, Shape, and Arrangement of Bacterial Cells Bacterial Cell Shapes & Arrangements : u Other less common shapes: u Star u Flat and square u Triangular u Pleomorphic bacteria: Have several possible shapes. Found in a few groups: u Corynebacterium u Rhizobium Most bacteria are monomorphic: Maintain a single shape. However environmental factors may affect cell shape. 2 The Procaryotic Cell Structure Procaryotic Cell Structure I. Structures External to the Cell Wall 1. Glycocalyx: “Sugar coat”. u All polysaccharide containing substances found external to the cell wall, from the thickest capsules to the thinnest slime layers . u All bacteria have at least a thin slime layer. u Chemical composition varies widely with species. u A glycocalyx made of sugars is called an extracellular polysaccharide (EPS). u The glycocalyx may have several functions: u Attachment to host cells. u Source of nutrition. u Prevent dehydration. u Escape host immune system. Procaryotic Cell Structure Procaryotic Cell Structure I. Structures External to the Cell Wall I. Structures External to the Cell Wall 1. Glycocalyx: “Sugar coat”. 1. Glycocalyx: u A. Capsules: Organized polysaccharide substance B.Slime Layer:Thin polysaccharide substance that is loosely attached to the cell wall. that is firmly attachedto the cell wall. u Not formed by all bacteria. u Not formed by all bacteria. u Important for virulence. u Important in virulence. u Oral bacteria stick to teeth due to slime layer and with time u Anthrax bacteria only cause anthrax if have protein capsule. produce dental plaque. u Only Streptococcus pneumoniae with capsule cause pneumonia. u Allow bacteria to adhere to objects in their environment so they can remain near sources of u Help bacteria escape the host immune system, by nutrients or oxygen. preventing destruction by phagocytosis. u Rock surfaces u When bacteria lose their capsules they become less likely u Plant roots to cause disease and more susceptible to destruction. u Help bacteria trap nutrients near cell and prevent dehydration. Procaryotic Cell Structure Procaryotic Cell Structure I. Structures External to the Cell Wall I. Structures External to the Cell Wall 2. Flagella (Sing. Flagellum): 2. Flagella (Sing. Flagellum): u About half of all known bacteria are motile, most u Flagella have three basic parts: use flagella. 1. Filament: Outermost region. u Long, thin, helical appendages. u Contains globular protein flagellin. u Not covered by a sheath like eucaryotic filaments. u A bacterium may have one or several flagella, 2. Hook: Wider segment that anchors filament to basal which can be in the following arrangements: body. u Monotrichous: Single polar flagellum at one end. 3. Basal Body: Complex structure with a central rod u Amphitrichous: Two polar flagella, one at each end. surrounded by a set of rings. u Lophotrichous: Two or more flagella at one or both u Gram negative bacteria have 2 pairs of rings. ends. u Gram positive bacteria only have one pair of rings. u Peritrichous: Many flagella over entire cell surface. 3 Flagellum of Gram-Negative Bacterium Procaryotic Cell Structure I. Structures External to the Cell Wall 2. Flagella (Sing. Flagellum): u Bacterial flagella move by rotation from basal body. u Flagellar movement may be either clockwise or counterclockwise. u Bacteria may be capable of several patterns of motility. u Runs or swims: Bacterium moves in one direction. u Tumbles: Bacterium changes direction. Caused by reversal of flagellar rotation. Patterns of Bacterial Motility Procaryotic Cell Structure I. Structures External to the Cell Wall 2. Flagella (Sing. Flagellum): u Taxis: Movement of a cell toward or away from a particular stimulus. u Chemotaxis: Movement in response to a chemical stimulus. u Phototaxis: Movement in response to a light stimulus. u Flagellar protein H antigens are used to identify important pathogens. u E. coli O157:H7: Causes bloody diarrhea associated with foodborne epidemics. Causes 200-500 deaths per year. Procaryotic Cell Structure Axial Filaments in Spirochetes I. Structures External to the Cell Wall 3. Axial Filaments (Endoflagella): u Bundles of fibers that are anchored at ends of the cell beneath the outer sheath. u Spiral around the cells. u Have similar structure to flagella. u Rotation of endoflagella produces a corkscrew motion. u May enable bacteria to penetrate body tissues. u Found in spirochetes: u Treponema pallidum: Cause of syphilis. u Borrelia burgdorferi: Cause of Lyme disease. 4 Procaryotic Cell Structure Procaryotic Cell Structure I. Structures External to the Cell Wall 4. Fimbriae and Pili: u Hairlike appendages that are shorter, straighter, and thinner than flagella. u Used for attachment rather than motility. u Found in Gram-negative bacteria. A. Fimbriae (Sing: fimbria) u May occur at poles or over entire cell surface. u Like glycocalyx, enable bacteria to adhere to surfaces. Important for colonization of host tissue. u Neisseria gonorrhoeae: Causes gonorrhea. Attach to sperm cells and mucous membranes through fimbriae. u Bacteria can attach to broth surface via fimbriae, forming a film-like layer called pellicle. Procaryotic Cell Structure Procaryotic Cell Structure I. Structures External to the Cell Wall II. The Cell Wall 4. Fimbriae and Pili: General Characteristics: B. Pili (Sing: pilus): Conjugation or sex pili u Semirigid structure that lies outside the cell u Only found in certain groups of bacteria. membrane in almost all bacteria. u Longer than fimbriae. u Two major functions: u Cells only have one or two sex pili. 1. Maintains characteristic shape of cell. u Attach two cells together, and allow the transfer 2. Prevents the cell from bursting when fluids flow into the cell by osmosis. of genetic material (DNA) between cells. u Contributes to bacterial ability to cause disease. u Medically important because allow for the transfer of antibiotic resistance genes from one u Site of action of some antibiotics . cell to another. u Very porous and does not regulate passage of materials into the cell. Procaryotic Cell Structure NAG-NAM Peptidoglycan Disaccharide II. The Cell Wall Composition: u Peptidoglycan (Murein): Made up of a repeating disaccharide attached by polypeptides to form a lattice. u Peptidoglycan is one immense covalently linked molecule, resembling multiple layers of chain link fence. u Disaccharide component: Made up of two monoscaccharides: u N-acetylglucosamine (NAG) u N-acetylmuramic acid (NAM) u Alternating disaccharides (NAG-NAM) are linked together in rows of 10 to 65 molecules. 5 A. Peptidoglycan Structure Procaryotic Cell Structure B. Gram-Positive Cell Wall Structure II. The Cell Wall Composition: u Peptidoglycan (Murein):. u Adjacent disaccharide rows are linked together by polypeptide chains which vary in composition, but always contain tetrapeptide side chains. u Parallel tetrapeptide side chains may be directly linked together or linked by a polypeptide cross-bridge. u Penicillininterferes with the final linking of peptidoglycan rows by peptide cross bridges. As a result, the cell wall is greatly weakened and cell undergoes lysis. Procaryotic Cell Structure Procaryotic Cell Structure II. The Cell Wall II. The Cell Wall Gram-Positive Cell Walls: Gram-Negative Cell Walls: u Consist of several layers of peptidoglycan, u Cell wall is thinner, more complexand more which form a thick , rigid structure (20-80 nm). susceptible to mechanical breakage than that of u Also contain teichoic acids, which are made up Gram-positive bacteria. of an alcohol and a phosphate group. Two types: u Consist of one or a few peptidoglycan layers and u Lipoteichoic acids: Span cell wall, linked to cell an outermembrane.
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  • The Puzzle of Coccoid Forms of Helicobacter Pylori: Beyond Basic Science

    The Puzzle of Coccoid Forms of Helicobacter Pylori: Beyond Basic Science

    antibiotics Review The Puzzle of Coccoid Forms of Helicobacter pylori: Beyond Basic Science 1, , 1,2, 1 1 3 Enzo Ierardi * y , Giuseppe Losurdo y , Alessia Mileti , Rosa Paolillo , Floriana Giorgio , Mariabeatrice Principi 1 and Alfredo Di Leo 1 1 Section of Gastroenterology, Department of Emergency and Organ Transplantation, University “Aldo Moro” of Bari, 70124 Bari, Italy; [email protected] (G.L.); [email protected] (A.M.); [email protected] (R.P.); [email protected] (M.P.); [email protected] (A.D.L.) 2 Ph.D. Course in Organs and Tissues Transplantation and Cellular Therapies, Department of Emergency and Organ Transplantation, University “Aldo Moro” of Bari, 70124 Bari, Italy 3 THD S.p.A., 42015 Correggio (RE), Italy; fl[email protected] * Correspondence: [email protected]; Tel.: +39-08-05-593-452; Fax: +39-08-0559-3088 G.L. and E.I. contributed equally and are co-first Authors. y Academic Editor: Nicholas Dixon Received: 20 April 2020; Accepted: 29 May 2020; Published: 31 May 2020 Abstract: Helicobacter pylori (H. pylori) may enter a non-replicative, non-culturable, low metabolically active state, the so-called coccoid form, to survive in extreme environmental conditions. Since coccoid forms are not susceptible to antibiotics, they could represent a cause of therapy failure even in the absence of antibiotic resistance, i.e., relapse within one year. Furthermore, coccoid forms may colonize and infect the gastric mucosa in animal models and induce specific antibodies in animals and humans. Their detection is hard, since they are not culturable. Techniques, such as electron microscopy, polymerase chain reaction, loop-mediated isothermal amplification, flow cytometry and metagenomics, are promising even if current evidence is limited.