Bacteria; structure and function

Bacteria; structure and function

1. Cytoplasmic membrane

   • Made of phospholipid bilayer- both have hydrophilic and hydrophobic molecules.
     • Functions as permeability barrier
       • Prevents loss of cell contents
         • Allows concentration of specific metabolites
           • Allows secretions of waste
       • Transport of molecules across membrane
         • Active process (water transport, both passive and active)
           • Accumulation against a concentration gradient
             • dependent on specific transport proteins (single molecule or chemical class)
               • Synthesis of proteins highly regulated
                 • Dependent upon concentration of specific molecule
   • Separates outside from inside
     • most molecules can't get through membrane layer, have to be transported via proteins

2. Types of transport events

   • Uniporter
     • Single transported molecule going from outside to inside
   • Symporter
     • Transported molecules and contransported molecules, outside to inside
   • Antiporter
     • Transported molecules outside --> in, contransported molecules in --> out.
   • All events require energy- (Proton-motive force, ATP)

3. Motility

   • Many prokaryotes are motile (can move independently)
     • Posses specialised structure; flagellum
   • Most spiral bacteria, about half bacilli are motile
     • Cocci generally non-motile
   • Some bacteria - "glide" - (secrete slime) aquatic microorganisms have gas vesicles

4. Structure of Flagellum;

   • about 20nm wide
     • attached at cell at one end, free at other
   • Composed of flagellum
   • Base (hook) connects flagellum to motor (basal body) arranged into rings and central rod
   • Mot proteins drive flagellum (requires energy)
   • Fli proteins = determine direction
   • Movement of flagella and cell motion
     • Flagella are semi rigid and rotate (like a propellor)
       • Driven by basal body- energy derived through PMF, proton movement across membrane to Mot complex
         • Polar and lophotricous flagella = rapid movement, soinning, dashing
           • Peritrichous flagella = mainly straight lines, slow, steady
     • Strength of PMF determines speed of rotation

5. Other surface structures

   • Fimbriae and pili
     • Look like flagella but not involved in motility
     • Pili
       • Similar to fimbriae, but fewer per cell
       • Involved in conjugation (sex pili)
         • Conjugation=crude form of bacterial sexual exchange
       • Used to attach to human tissues in some pathogens
   • Fimbriae
     • Shorter than flagella
       • More numerous
         • used too adhere to surfaces (animal tissues= pathogenicity)

6. Glycocalyx

   • Secretions of slimy materials
     • Composed of polysaccharide (and sometimes proteins)
   • Include capsules and slime layers
   • Capsules = rigid layers, tight matrix, excludes stains
   • Slime layer = easily deformed, does not exclude stains
   • Attachment of pathogens to host (glycocalyx binds to specific host tissues_
   • Resistance to phagocytosis and immune system
   • Bind water (resist desiccation?)

7. GRANULES

   • Inclusions observed in cells function to store energy or structural components
   • Carbon storage
   • Inorganic phosphate
   • Sulphur granules
   • Magnetosomes (crystals of magnetite {Fe3O4}, impart a magnetic field on cell)

8. ENDOSPORES

   • Form within a cell body (endo-)
   • Differentiated cells that are very resistant to heat, chemicals (acids, disinfectants), drying, radiation
     • Implications for sterilisation- food safety
       • Sterilisation- to eliminate all forms of microbial life
   • Seen under light microscope
   • Terminal, sub-terminal, central
   • FORMATION (Sporulation)
     • conversion of vegetative cell to non-growing heat resistant structure
       • occurs when cells stop growing, essential nutrients (C,N) exhausted
         • Takes ~ 8 hours (bacillus subtilis)
           • Over 200 genes involved
   • GERMINATION;
     • Endospores can remain dormant for years- convert to vegetative cell rapidly
       • activation by heating (sub=lethal temps, few minutes)
         • germination in presence of nutrients (minutes)
           • outgrowth (swelling due to synthesis of RNA, protein, DNA) call emerges and divides

9. "Rudimentary Bacteria"

   • Chlamydia
     • Very small, gram negative-type cells
       • Pleomorphic
     • Obligate, intracellular parasites
     • small genome, lack many metabolic functions
     • Cause psittacosis (pneumonia in birds,humans), trachoma (eye disease -- blindness in humans), STIs
     • Transmitted by direct contact, airborne (invade respiratory system)
     • two cell forms in life cycle
   • Mycoplasmas (Mycoplasma, Spiroplasma)
     • Smallest cellular organism 0.2--.3um
       • Highly pleomorphic
     • No cell walls (related to gram positive bacteria)
     • resistant to osmotic lysis (sterols in cell membrane)
     • free -living or parasitic
     • human pathogens cause pneumonia, secondary infections
     • resistant to antibiotics that inhibit cell wall synthesis