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Diversity in Microbial Cell Structures and Shapes

Explore the various sizes, shapes, and arrangements of bacterial cells, understanding the differences between eukaryotic and prokaryotic cells, and the unique structures found in prokaryotes. Dive into the world of microbial cell biology.

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Diversity in Microbial Cell Structures and Shapes

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  1. BIOL 3340 Chapter 3

  2. Chapter 3 Microbial Cell Structure

  3. Types of Cells • Two major classes: eukaryotes &prokaryotes. • Differences: the materials making up the nucleus of eukaryotic cells are separated from the rest of the cell by the nuclear membrane, whereas in prokaryotic cells these materials are not separated. • All animals and plant cells are eukaryotic including fungi. Bacteria, cyanobacteria and the mycoplasmas are prokaryotic.

  4. Size, Shape, andArrangement of Bacterial cells Cocci (s., coccus) – spheres • diplococci (s., diplococcus) – pairs • streptococci – chains • staphylococci – grape-like clusters • tetrads – 4 cocci in a square • sarcinae – cubic configuration of 8 cocci

  5. ……Size, Shape, andArrangement Bacilli (s., bacillus): – rods • coccobacilli – very short rods • vibrios – resemble rods, comma shaped • spirilla (s., spirillum) – rigid helices • spirochetes – flexible helices • mycelium – network of long, multinucleate filaments Check on line lab Manual for Bacterial shapes)

  6. ……Size, Shape, andArrangement • Sizes: • Typically ~ 0.1 - 20 m (with some exceptions) • Typical coccus: ~ 1 m (e.g. Staphylococcus) • Typical short rod: ~ 1 x 5 m (e.g. E. coli) • Barely within the best resolution of a good compound light microscope

  7. Bacterial Shapes

  8. Cell Structureof Procaryotes Prokaryotic cells The constituents of a typical bacterium are as follows: • Bacterial Cell Wall and Capsule– bacteria are surrounded by a cell wall, which not only contains polysaccharide but also contains protein and lipid. • In some bacteria, the cell wall is surrounded by the capsule. • The cell wall and capsule provide shape and form to the bacterium and also acts as a physical barrier between the bacterium and its environment. • Nucleoids – in bacteria the nuclear material is concentrated in a region called the nucleoid within the cytoplasm.

  9. A typical Bacterial Cell

  10. ….Cell Structure • There is no membrane-bound nucleus in prokaryotes. • Instead the DNA is located within a specialized region of the cytoplasm of the cell called the nucleoid region. • There is no nuclear membrane surrounding the nucleoid. • Bacterial flagella – many bacteria possess one or more flagella for locomotion.

  11. Gram-negative Cell Walls and Acid Fast Fast cell wall in Chapter 3

  12. Procaryotic Cell Membranes Cell Membranes: • membranes are an absolute requirement for all living organisms. • plasma membrane encompasses the cytoplasm • some procaryotes also have internal membrane systems

  13. Functions of the Plasma Membrane • separation of cell from its environment • selectively permeable barrier • some molecules are allowed to pass into or out of the cell • transport systems aid in movement of molecules • detection of and response to chemicals in surroundings with the aid of special receptor molecules in the membrane

  14. Fluid Mosaic Model of Membrane Structure

  15. …..Plasma membrane

  16. …..Plasma membrane

  17. …Phospholipid layer • polar ends • interact with water • hydrophillic • nonpolar ends • insoluble in water • hydrophobic

  18. Membrane Proteins Peripheral proteins: • loosely associated with the membrane and easily removed Integral proteins • embedded within the membrane and not easily removed

  19. Procaryotic Cytoplasm Cytoplamic Matrix: • Cytoplasm contains the nucleoid,ribosomes and inclusion bodies • lacks organelles bound by unit membranes • composed largely of water • is a major part of the protoplasm (the plasma membrane and everything within)

  20. ..Cytoplasmic Matrix • Viscous aqueous suspension of proteins, nucleic acid, dissolved organic compounds, mineral salts • Network of protein fibers similar to the eukaryotic cytoskeleton. Cytoplasmic Inclusion Bodies: • granules of organic or inorganic material that are stockpiled by the cell for future use. • some are enclosed by a single-layered membrane

  21. ….Cytoplasmic inclusions Cytoplasmic inclusions: • Glycogen Granules • Poly--hydroxybutyrate granules • Lipid droplets • Gas vacuoles • Metachromatic granules(Phosphate crystals or volutin granules) • Sulfur Granules

  22. Ribosomes Ribosomes: • complex structures consisting of protein and RNA • sites of protein synthesis • smaller than eucaryotic ribosomes • procaryotic ribosomes  70S • eucaryotic ribosomes  80S

  23. The Nucleoid Nucleoid: • irregularly shaped region • location of chromosome • usually 1/cell • not membrane-bound

  24. The Procaryotic Chromosome The Chromosomes: • usually a closed circular, double-stranded DNA molecule • looped and coiled extensively

  25. Plasmids Plasmids: • usually small, closed circular DNA molecules • exist and replicate independently of chromosome • have relatively few genes present

  26. Procaryotic Cell Walls Prokaryotic Cell Wall: • rigid structure that lies just outside the plasma membrane (detail to continue)

  27. Functions of Cell Wall • provides characteristic shape to cell • protects the cell from osmotic lysis • may also contribute to pathogenicity • very few procaryotes lack cell walls

  28. Cell Walls of Bacteria Gram Staining developed by Gram in 1888: • bacteria are divided into two major groups based on the response to gram-stain procedure • gram-positive bacteria stain purple • gram-negative bacteria stain pink • staining reaction due to cell wall structure

  29. Gram Positive and Gram negative

  30. Gram-Positive Cell Walls • Gram positive bacteria composed primarily of peptidoglycan • Peptidoglycan are polymers which contains N-acetylglucosamine and N-acetylmuramic acid and several different amino acids • Walls contain teichoic acid ( polymers of glycerol or ribitol joined by phosphate groups)

  31. ..Gram-Positive Cell Walls • The periplasmicspace lies between plasma membrane and cell wall and is smaller than that of gram-negative bacteria • periplasmhas relatively few proteins • enzymes secreted by gram-positive bacteria are called exoenzymes

  32. Gram-Negative Cell Walls • consist of a thin layer of peptidoglycan surrounded by an outer membrane • outer membrane composed of lipids, lipoproteins, and lipopolysaccharide (LPS) • no teichoic acids

  33. …..Gram Negative • more complex than gram-positive walls • periplasmic space differs from that in gram-positive cells • may constitute 20-40% of cell volume • many enzymes present in periplasm

  34. Gram Positive and Negative cell Wall

  35. Assignments • Features of a prokaryotic cell • List the differences between a gram positive and gram negative cell wall.

  36. Variations on Cell Wall Architecture Acid-fast Cell Walls: • Many genera in the “High GC gram-positive” bacterial group contain mycolic acids, embedded in the peptidoglycan . • Mycolic acids are a class of waxy, extremely hydrophobic lipids. • Certain genera contain very large amounts of this lipid, and are difficult to gram stain. • These genera may be identified by the “acid-fast” staining technique. • Includes Mycobacterium and Nocardia.

  37. ..Variations on Cell Wall Architecture Mycoplasmas: • Bacteria that are naturally have no cell walls • Includes Mycoplasma and Ureaplasma Archaea : • Have archaea cell walls with no peptidoglycan • Many have cell walls containing pseudomurein, a polysaccharide similar to peptidoglycan but containing N-acetylglucosamine and N-acetyltalosaminuronic acid .

  38. Capsules, Slime Layers, and S-Layers Layers of material lying outside the cell wall • capsules • usually composed of polysaccharides • well organized and not easily removed from cell • slime layers • similar to capsules except diffuse, unorganized and easily removed. • a capsule or slime layer composed of polysaccharides can also be referred to as a glycocalyx

  39. Glycocalyx

  40. S-layers: S-layers: • regularly structured layers of protein or glycoprotein. • in bacteria the S-layer is external to the cell wall. • Regular “floor tile” pattern. • Function not clear -- Stability?

  41. Functions of Capsules, Slime Layers, and S-layers • protection from host defenses (e.g., phagocytosis) • protection from harsh environmental conditions (e.g., desiccation) , chemicals or osmotic stress • attachment to surfaces • facilitate motility • nutrient Storage

  42. Pili and Fimbriae Fimbriae (s., fimbria) • short, thin, hairlike, proteinaceous appendages up to 1,000/cell • mediate attachment to surfaces sex pili (s., pilus): • similar to fimbriae except longer, thicker, and less numerous (1-10/cell) • required for mating

  43. Fimbriae

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