Microbiology Chapter 2: Bacteria
Microbiology Chapter 2: Bacteria BIO 3304
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This 5 page Class Notes was uploaded by Suzy Reese on Thursday January 14, 2016. The Class Notes belongs to BIO 3304 at Mississippi State University taught by Dr. Janet Donaldson in Spring 2016. Since its upload, it has received 164 views.
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Date Created: 01/14/16
Microbiology Chapter 2: Bacteria Morphology of Bacteria Cells Bacteria can take many different shapes or morphologies -Spherical: s. coccus, pl. cocci -Rod-shaped: s. bacillus, pl. bacilli -Comma-shaped: s. vibrio, pl. vibrios -Spiral: s. spirillum, pl. spirilla -Pleiomorphic: varied shapes Bacteria can also assume multicellular organizations -Hyphae: branching filaments of cells -Mycelia: tufts of hphae -Trichomes: smooth, unbranched chains of cells The size of bacteria can vary greatly -Tend to be smaller than eukaryl cells -Bacteria are usually .5-5 micrometers in length -Small eukaryl cells are usually > 5 micrometers in diameter There are exceptions to the general size of bacterial cells -Thiomargarita namibiensis can get up to 700 micrometers in diameter -Epulopiscium fishelsoni can range from 200-700 micrometers X 80 micrometers -Some mycoplasma cells are only .2 micrometers in diameter The Cytoplasm What is in the cytoplasm of bacterial cells? -The largest area is the nucleoid region, housing the chromosomes and DNA replication machinery -Bacterial cells contain NO nucleus -The remainder of the cytoplasm is a stew of macromolecules (tRNA, rRNA, mRNA, proteins, etc) -Inclusion bodies may also be included o Polyhydroxybutyrate granules: carbon storage o Sulfur globules: sulfur storage o Gas vesicles: buoyancy control o Carboxysomes: location of carbon fixation reactions o Magnetosomes: organelle associated with direction finding *Prokaryotic can survive without inclusion bodies. This is because they only provide an advantage. Eukaryotic HAVE to have organelles to survive. The Bacterial Cytoplasm What kinds of internal structures help to organize bacterial cells? -The cytoskeleton is a series of internal proteins that assist in keeping everything in (or for moving it to) the right locations in the cell - Some cytoskeleton proteins are involved in cell wall synthesis during cell division or in moving internal components. The Cell Envelope What are the critical structural and functional properties of the bacterial cells envelope? -All cells have a plasma membrane o Seperates the interior of the cell from the external environment o Usually composed of a phospholipid bilayer with embedded proteins How do items cross the Plasma Membrane and get into a cell? o Oxygen and carbon dioxide are small and can diffuse across steadily o Water is helped across by aquaporin protein channels o Osmosis can cause a cell to swell with water or shrivel as water leaves, but a strong cell wall can help keep a bacterial cell alive during these hardships Nutrients cross the plasma membrans - Facilitated Diffusion: using a protein channel to move particles with a concentration gradient (no energy) - Active Transport: using energy to move particles AGAINST a concentration gradient o Co-transport mechanisms (symport/antisymport) o ATP binding cassette (ABC) transporters o Can use Active Transport to acquire nutrients and store o It is a survival mechanism The plasma membrane can also be used for capturing energy -Embedded electron transport chain can help create proton motive force (PMF) -Can be used to derive energy for motion (flagella) The plasma membrane can hold sensory systems -Proteins in the plasma membrane can be used to detect environment changes -The cell can use the detected changes to alter gene expression to respond Protein secretion and the plasma membrane: making proteins and shipping them outside the cell -The prteins made are chaperone proteins and proteins used to kill other bacteria Uses ATP Energy Toxins, siderophores, enzymes, etc Each peptidoglycan disaccharide subunit is o N-acetylmuramic acid (NAM) with a small peptide chain -The peptide varies by species o N-acetylglucosamine (NAG) While the amino acids in the peptide on NAM can vary from species to species, the way the peptides are crosslinked in the Cell Wall also vary Gram negative bacteria have a direct cross link The cell wall is critical, but are all cell wall structures the same? NO! -A stain method developed in 1884 by Hans Christian Gran can separate many microbes into one of two classes (Gram positive or Gram Negative) Gram positive cells have - A thick outer layer of peptidoglycan - A very narrow periplasmic space - Teichoic Acids in the peptidoglycan (negatively charged) Gram negative cells have - A varying width periplasmic space containing a very thin layer of peptidoglycan - An outer membrane composed of lipopolysaccharide (LSP) The LPS from Gram-negative cells can be HARMFUL - Lipid A portion induces a strong inflammatory response - Outer side chain of polysaccharides can vary dramatically and even be changed by the microbe to evade host immune responses. How can nutrients get through the cell walls? - The gram positive peptidoglycan layer has large pores throughout its matrix - The gram negative cell has porin and Ton B proteins in its outer membrane to transfer molecules into the periplasmic space o Once there, active transport mechanisms can move the molecule into the cytoplasm How can molecules get OUT of a Gram negative cell’s periplasmic space? - Some move from the periplasm to the outside directly. These are known as autotransporters - Some use single step (never entering the periplasm) transport systems The Bacterial Envelope How do structures on the surface of bacterial cells allow for complex interactions with the environment? -Motility from flagella: spiral, hollow, rigid, filaments extending from the cell surface o Locations and number vary from species to species Motility from flagella - By using chemoreceptor proteins to sense changes in concentrations of attractants or repellants cells can produce more funs to move in a particular direction The Bacterial Cell Surface So aside from motility, what other stuff is still left on the outside of bacterial cells? - Adherence molecules to stick to surfaces o Mediated by pili (s. pilus), fibers of pilin protein possess other proteins on their tips for sticking o A sex pilus is a different structure used for conjugation (sending a DNA plasmid from one cell to another) o Capsules can help bacteria form biofilms - Biofilms provide protection and enhanced survivability in harsh environments - Examples of biofilms include dental plaque and mold on bathroom surfaces Bacterial Taxonomy How are bacteria categorized? - Important! Most microbes still can’t be cultured - What we CAN grow, we name according to the standard binomial system o Species: group of strains sharing common features, while differing considerably from other strains o Genus: group of closely related species Classification depends on many features o Size/shape o Gram type o Colony morphology o Presence of structures such as capsules/endospores o Physiological/ metabolic traits o DNA Sequence data (in more recent years)
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