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Prokaryotic Cells

Prokaryotic Cells. The Prokaryotic Cell. Members of the prokaryotic world make up a vast heterogeneous group of very small unicellular organisms. Include bacteria and archae , although the majority are bacteria The thousands species of bacteria are differentiated by many factors such as

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Prokaryotic Cells

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  1. Prokaryotic Cells

  2. The Prokaryotic Cell • Members of the prokaryotic world make up a vast heterogeneous group of very small unicellular organisms. • Include bacteria and archae, although the majority are bacteria • The thousands species of bacteria are differentiated by many factors such as • Morphology (shape), chemical composition (often detected by staining reactions), nutritional requirements, biochemical activities, and sources of energy (sunlight or chemicals)

  3. Size, Shape, and Arrangement • Bacteria come in many sizes, and several shapes. • Most range from 0.2 to 2.0 µm in diameter and 2-8 µm in length • Basic shapes include: spherical coccus(cocci in plural), rod-shaped bacillus (bacilli in plural), and spiral. • When cocci divide to reproduce, they can remain attached to each other • In pairs they are called diplococci • Chainlike structures are called streptococci

  4. Shape, and Arrangement • Spiral bacteria have one or more twists • Those that look like curved rods are called vibrio • Spirilla have a helical shape like a corkscrew, and have rigid bodies. Use flagella to move • Spirochetes are helical and flexible. These move by means of axial filaments. These filaments resemble flagella but are found within a flexible external sheath

  5. Shape and Arrangement • The shape of bacteria is determined by heredity. • Most bacteria are monomorphic: maintain a single shape • Environmental factors can alter that shape • Some bacteria like Rhizobium and Corynebacterium are pleomorphic: can have many shapes, not just one.

  6. Structures External to the Cell Wall • Possible structures external to the prokaryotic cell wall are: • Glycolax • Flagella • Axial filaments • Fimbrae • and Pili

  7. What is the Glycolax? • Means sugar coat & is the general term used for substances that surround cells • Bacterial glycolax is a viscous (sticky), gelatinous polymer that is external to the cell wall • Composed of a polysaccharide, polypeptide, or both • Two types • Capsule: substance is organized and is firmly attached to the cell wall • Slime layer: substance is unorganized and only loosely attached to the cell wall glycolax Fig. 1 Source for Fig. 1: http://emp.byui.edu/wellerg/The%20Cell%20Lab/Prokaryotic%20Cells/The%20Prokaryotic%20Cell.html

  8. Glycolax • Very important component of biofilms • Biofilms are densely packed communities of microbial cells that grow on living or inert surfaces • A glycolax that helps cells in a biofilm attach to their target environment and to each other is called an extracellular polymeric substance (EPS) • EPS protects the cells within it • Facilitates communication among them • and enables the cells to survive by attaching to various surfaces in their natural environment Fig. 2 Source for Fig. 2 http://www.microbiologybytes.com/blog/2010/09/08/the-biofilm-matrix/

  9. Flagella • Some prokaryotes have flagella which are long filamentous appendages that propel bacteria • Bacteria that lack flagella re referred to as atrichous (without projections) • Peritrichous: flagella distributed over the entire cell • Polar: at one or both poles or ends of the cell • Monotrichous: A single flagellum at one pole • Lopothrichous: a tuft of flagella coming from on pole • Amphitrichous: flagella at both poles of the cell

  10. Axial Filaments • Spirochetes have unique structure and motility • Move my means of axial filaments • Bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell • The rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion

  11. Fimbriae and Pili • Many gram-negative bacteria contain hair-like appendages that are shorter, straighter, and thinner than flagella • are used for attachment and transfer of DNA rather than for motility • Fimbrae can occur at the poles of the bacterial cell or entire surface of cell • Have a tendency to adhere to each other and to surfaces • Pili are usually longer than fimbrae and are found as one or two per cell • Involved in motility and DNA transfer

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