Cell Structure

Cell Structure

1. Prokaryotic

   • divide by binary fission
   • no nucleus
   • small; 0.2-1.0 micrometers
   • 1 circular chromosome, NOT in a membrane
   • NO membrane-bound organelles
   • Archaea
     • pseudomurein cell walls
   • Bacteria
     • peptidoglycan in cell walls
       • cell walls maintain cell shape, help with attachment to other cells, prevent osmotic lysis
     • External structures
       • Glycocalyces
         • Capsule
           • neatly organized
           • firmly attached to cell
           • No capsule = non disease causing
         • Slime layer
           • unorganized, loose, water soluble
           • biofilm
         • Functions
           • attachment
           • prevents phagocytosis
           • lower cell's susceptibility to antimicrobial compounds
       • Flagella
         • NOT IN ALL bacteria
         • Structure
           • filament, hook, basal body
           • responsible for movement
           • IMP. for bacteral pathoogenicity
           • outside wall
         • Arrangement
           • monotrichous (1 at 1 end)
           • amphitrichous (1 at both ends)
           • lophotrichous (multiple at 1 end)
           • petritrichous (all over cell wall)
         • motility
           • rotate flagells to run or tumble
           • move toward/away from stimuli (taxis)
         • Axial filaments (spirochetes)
           • anchored at 1 end of cell
           • rotation causes corkscrew motion
           • AKA endoflagella
       • Fimbriae
         • Imp. for biofilms, adherence
         • sticky, bristle-like, shorter than flagella
         • rod-like, proteinaceaous extensions
         • lacks hook or basal body, if cell lack fimbriae, it's not disease-causing
       • Pili
         • Type of fimbriae (longer than fimbriae, shorter than flagella)
         • 1 or 2 per cell
         • mediate transfer of DNA from cell to cell (CONJUGATION PILI)
     • Plasma membrane
       • phospholipid bilayer
       • Integral proteins (transmembrane)
       • peripheral proteins
       • functions
         • energy storage
         • harvest light energy in photosynthetic bacteria
         • selectively permeable
         • allow substances to cross membranes via protein channels
         • maintain concentration & electrical grdnts.
       • damage
         • cell leakage

2. Eukaryotic