BIOL 251 PSA

• Pathogens


  Disease-causing microorganisms
• Pathogenicity


  Ability to cause disease
• Virulence


  Degree of pathogenicity
• Infection


  When body is invaded by a harmful microorganism
• Disease


  When the health of the human body is affected by an infection
• Portals of Entry


  • Mucous membranes
  • Skin
  • Parenteral route (direct deposition beneath the skin or membranes)
• Most pathogens have a preferred portal of entry
• Pathogens can cause disease without entering the body
• Pathogens entering through openings

  • Sweat gland ducts
  • Hair follicles
• Pathogens entering through punctures

  • Injection
  • Bite
  • Dry splits in skin
  • Injury/wounds
• If a pathogen doesn't enter through its preferred portal, disease may not occur
• ID50


  Infectious dose for 50% of a sample population, measures virulence of a microbe
• LD50


  Lethal dose for 50% of a sample population, measures potency of a toxin
• Numbers of invading microbes can upset the host's defense mechanism and cause disease
• Bacillus anthracis is an example of a pathogen where numbers of invading microbes are important
• Toxins


  Poisonous substances produced by microorganisms
• Adhesins or ligands


  • Surface molecules on pathogens that bind to complementary surface receptors of host cells

  
• Glycocalyx


  Capsule around the cell wall of some pathogens
• Functions of capsules


  • Impair phagocytosis
  • Examples: Streptococcus pneumoniae, Haemophilus influenzae, Bacillus anthracis

  
• Cell wall components


  • M protein resists phagocytosis (Streptococcus pyogenes)
  • Opa protein allows attachment to host cells (Neisseria gonorrhoeae)
  • Waxy lipid (mycolic acid) resists digestion (Mycobacterium tuberculosis)
• Enzymes


  • Coagulases: coagulate fibrinogen
  • Kinases: digest fibrin clots
  • Hyaluronidase: digests polysaccharides that hold cells together
  • Collagenase: breaks down collagen
  • IgA proteases: destroy IgA antibodies
• Antigenic variation allows pathogens to evade destruction by host antibodies
• Invasins


  • Surface proteins produced by bacteria that rearrange actin filaments of the cytoskeleton, causing membrane ruffling and allowing the pathogen to move from one cell to the next (e.g. Shigella and Listeria)

  
• Siderophores


  Proteins secreted by pathogens that bind iron more tightly than host cells
• Toxigenicity


  Ability of a microorganism to produce a toxin
• Toxemia


  Presence of toxin in the host's blood
• Types of toxins


  • Exotoxins
  • Endotoxins
• Exotoxins


  • Proteins produced and secreted by bacteria, soluble in bodily fluids, destroy host cells and inhibit metabolic functions (e.g. hemolysins, botulinum toxin, tetanus toxin)
• Enterotoxins


  • Exotoxins whose activity affects the small intestine, causing massive fluid secretion, vomiting and diarrhea (e.g. Vibrio enterotoxin, Shiga toxin)
• Endotoxins


  • Lipid A portion of lipopolysaccharides (LPS) of gram-negative bacteria, released when the bacteria die, cause fever, chills, body aches, weakness, severe septic shock and death
• Portals of Exit


  • Respiratory tract
  • Gastrointestinal tract
  • Genitourinary tract
  • Skin
  • Blood
• Pathogens exit the body through these portals in order to infect other healthy hosts
• DNA replication


  1. RNA primer initiates

  2. DNA gyrase relieves supercoiling

  3. DNA helicase separates strands

  4. DNA polymerase adds nucleotides 5' to 3'

  5. Removes RNA primers

  6. Replication fork where replication occurs

  7. Semiconservative name of whole process

  8. DNA ligase seals gaps between Okazaki fragments
• Important enzymes in DNA replication


  • DNA gyrase
  • DNA ligase
  • DNA polymerase
  • DNA helicase
  • RNA polymerase
• Constitutive genes


  Expressed at a fixed rate as needed
• Inducible genes


  Expressed only as needed
• Repressible genes


  Expressed only as needed
• Types of mutations


  • Point mutations
  • Silent mutations
  • Missense mutations
  • Nonsense mutations
  • Frameshift mutations
• DNA repair


  1. Proofreading

  2. Mismatch repair

  3. Repair of thymine dimers

  4. Direct repair
• Types of horizontal gene transfer in bacteria


  • Transformation
  • Conjugation
  • Transduction