Bacteria

Bacteria

1. GLYCOCALYX

   • extracellular polymeric substance (EPS) that surrounds cells composed of polysaccharide & polypeptid
     • If the substance is attached to the cell wall is called a capsule
       • Capsules protect pathogenic bacteria from phagocytosis
     • if the substance is loosely attached to the cell wall, is called slime layer
     • EPS protects cell & facilitates communication

2. FLAGELLA

   • long filamentous appendages that propel bacteria
     • Flagella is
       • peritrichous
       • polar
         • monotrichous
         • lophotrichous
         • amphitrichous
   • Is conformed by
     • Filaments
     • Flagelling
       • Chains around hollow core
     • Basal body
       • Central rod
         • Inserted in rings
   • prokaryotic flagellum
     • Rotate basal body
       • This causes diferente patterns of motility
         • When movement is in one direction is called run
         • When movement changes in direction to any way is called tumbles
         • Movement enables the bacteria move towards favorable environment
       • Motile bacteria pick up chemical stimuli with receptors
         • If signal is positive is called attractant
         • If signal is negative is called a repellent

3. AXIAL FILAMENTS

   • Spirochetes move by means of axial filaments or endoflagella
   • Bundles of fibrils arise at the end of the cell and spiral around the cell
     • This axial filaments produces movement of the outer sheat
       • This propels the spirochetes in a spiral motion

4. FIMBRIAE AND PILI

   • Used to attach and transfer DNA
   • Pili is the protein arranged around central core
     • Two types
       • Fimbriae
         • Occur at the poles of the bacterial cell
         • Is distributed over the entire surface of cell
         • They are involved in forming biofilms and substances
           • The substances are segregated in liquid, glass and rocks
       • Pili
         • Longer than fimbriae
         • Pili are involved in motility & DNA transfer
           • Twitching motility extends by the addition of subunits of pilis and makes contact with other cells and then retracts
             • This is called grappling hook model
         • Is used to bring bacteria together
           • This process is called conjugation
             • Conjugation or sex pili connects receptors to the surface to exchange DNA through this process

5. THE CELL WALL

   • Semirigid structure responsible for the shape of the cell that surrounds the plasma
   • The major function of cell wall is to prevent bacterial cells from rupturing when the water pressure inside
   • Contributes to the ability of some species to cause disease
   • Composition
     • Is composed of a macromolecular network called peptidoglycan
       • Consist in repeating disaccharide attached to polypeptides that surrounds & protect the cell
         • The disaccharide portion is made of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
           • Related to glucose
     • The cell wall contains components of peptidoglycan
       • NAM
       • NAG
       • The structure of the polypeptide link varies
         • Tetrapeptide side chains
           • four aminoacids attached to NAMs in the backbone
             • Amino acids are originated by alterating the pattern of D & L forms
             • Amino acids are found in other proteins that are L form
         • Parallel tetrapeptide side chains
           • These chains are bonded to each other or linked by pep- tide cross-bridge
             • Formed by a short chain of amino acids
           • When Penicillin interferes with the final linking of the peptidogly- can rows by peptide cross-bridges, the cell wall is weakened
             • This prodeces a lysis in the cell and the rupture of plasma membrane
   • Gram-Positive Cell Walls
     • thick, rigid structure of many layers of peptidoglycan,
     • Contains tei- choic acids, this is alcohol and phosphate.
       • li- poteichoic acid
         • Spans the peptidoglycan layer and is linked to the plasma membrane
       • wall teichoic acid,
         • It is linked to the peptidoglycan layer.
   • Gram-Negative Cell Walls
     • Consist of one or a very few layers of peptidoglycan and an outer membrane
       • The peptidoglycan is bonded to lipoproteins in the outer membrane and periplasm
         • The periplasm contains degradative enzymes and transport proteins
       • The outer membrane consist of lipopolysaccharides (LPS), lipoproteins, and phospholipids
         • Functions of the negative outer membrane
           • Factor of evading phagocytosis and the actions of complement
           • Provides a barrier to certain antibiotics
             • lysozymes
             • detergents
             • heavy metals
             • bile salts
             • certain dyes
         • Is a large complex molecule that contains lipids and carbohydrates
           • Three components
             • Lipid A
               • The lipid portion of the LPS and is embedded in the top layer of the outer membrane.
               • functions as an endotoxin
               • responsible for the symp- toms associated with infections by gram-negative bacteria
             • Core polysaccharide
               • attached to lipid A and contains unusual sugars
               • Provides stability
             • O polysaccharide.
               • Composed of sugar molecules
               • Antigen for distinguishing species of gram-negative bacteria.

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