Bacteria external structure.

Bacteria external structure.

1. Glycocalyx

   • "Sugar coat" slim layercapsule firmly attached to the cell wall.
     • Sticky polymer external to the cell wall. Composed of polysaccharide and polypeptide.
     • Protects pathogenic bacteria from phagocytosis by the cells of the host.
   • Any substance surrounding cells
   • A component present in biofilms. It helps cells inside to attach to their target.
     • Called "extracellular polymeric substance"
       • The EPS protects the cell from inside.
       • Facilitates communication among the cells
       • Enables cells to survive by attaching to various surfaces in different environments
         • surviving in teeth, water pipes, rocks, medical implants, and other bacterias.

2. Flagella.

   • Long filamentous appendages that propel bacteria.
     • Distributed around all the cell structure (peritrichous) or found at the poles of the cell (polar).
       • When polar, it can be found separately in one pole (monotrichous) or found in tufts coming from one or two poles (Lophotrichous)
   • Some bacteria don't have flagella, they are known as atrocious. (no protection)
     • Has motility when found on the cells
   • separated into 3 basic parts.
     • Long outer region
     • Basal body
       • Composed of a small central rod with rings
         • Gram-negative bacteria
           • 4 rings can be found
           • Fimbriae and pili
             • A shorter, straighter and thinner appendage used by the cells to attach and transfer DNA instead of motility.
             • This structure is conformed by a protein called pilin, found in the central core.
             • Different functions one with the other.
               • Fimbrae
                 • Occur at the poles of the bacterial cell and are distributed over the surface of it.
                 • Can be found in hundreds at a time.
                 • They stick to each other and to different surfaces around the cell and are involved in forming biofilms and some other aggregations in liquids and rocks, for example
               • Pili
                 • Longer than fimbriae
                 • found in couples per cell.
                 • Involved in motility, makes an addition of pilin and contact with the surface and other cells.
                 • It's reaction is called grappling hook model.
         • Gram-positive bacteria
           • 2 rings present.
     • Membrane

3. Cell wall

   • Is a semirigid structure responsible of the shape that every cell has.
   • Surrounds the underlying fragile plasma membrane
   • Protects the interior of the cell changes in the environment
   • Prevent bacterial cells from rupturing when the presion inside is bigger than in the outside
   • Composed of a macromolecular biological network called peptidoglycan
     • This consists of disaccharide attached by polypeptides, forming a lattice and protecting the cell
       • The disaccharide is formed by related compounds of glucose, structured as NAG and NAM.

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