Topic 6 infection, immunity and forensics revision

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  • 1. Topic 6Infection, Immunity and ForensicsRevision
  • 2. Microorganisms
    What is a Pathogen?
    Microorganisms that causes disease
    There are five main groups of pathogens
  • 3. Virus
    Smallest of all living organisms
    0.02 to 0.3 micrometer
    Viruses are not cells.
    Because they lack all cell organelles and cytoplasm.
    But they can invade other cells and take over their biochemistry to make more viruses.
    This is why they are still studied as living organisms.
  • 4. Obligate parasite
    Viruses are obligate parasites because they cannot reproduce and increase in number without a host.
    Facultative parasites
    Organisms that live as parasites only when a host is available or else they maintain a free living lifestyle
  • 5. Structure of virus
    Nucleic acid core (DNA or RNA) + protein coat (capsid)
    Capsid is made of protein subunits called capsomeres .
    Some viruses have lipid rich covering around capsid called the envelope.
    Envelope usually is formed from host cell membrane.
    Envelope may have spikes to help chemically recognize & attach to the host cell.
  • 6. TMV
    Tobacco Mosaic Virus
    Leaf infected with TMV
  • 7. Retroviruses
    Viruses with RNA as their genetic material.
  • 8. HIV - Replication
    HIV attaches to the surface of macrophage (host cell)
    gp120 protein (virus surface) + CD4 protein (host cell membrane)
    Reverse transcriptase makes a DNA copy of the viral RNA.
    DNA copy is replicated by the same enzyme.
    This new DNA moves into the nucleus and integrated into the host cell chromosome.
  • 9. HIV - Replication
    Using the host cell machinery, mRNA is synthesized from the new proviral DNA
    Viral mRNA is translated to make viral enzymes and structural proteins.
    Viral RNA genome is also made from the proviral DNA.
    The viral genome and structural proteins assemble to form the basic structure of the virus.
    These move out of the host cell by exocytosis, taking part of the cell membrane with it (lipid layer around the virus).
  • 10. HIV - Replication
    Eventually the gene that code for gp120 protein is mutated.
    The new protein attaches to a different CD4 protein present in T cells.
    The same cycle repeats in T cells.
    But as the virus leave the T cell, it destroys the cell membrane killing the host cell.
    This reduces the number of T cells in the body reducing immunity.
  • 11. HIV - Transmission
    Through sexual contact
    Through infected blood
    by intravenous drug users sharing needles
    repeated use of needles
    use of infected blood products
    from mother to foetus
    during early stages of pregnancy
    during birth
    through breastfeeding
  • 12. AIDS - Symptoms
    persistent diarrhoea
    weight loss
    secondary infections such as TB, pneumonia, Kaposi's sarcoma
  • 13. AIDS - Prevention
    Practicing monogamy
    Use of condoms
    Use of clean needles
    Awareness programmes
  • 14. Why is it difficult to create a vaccine for AIDS?
    The virus mutates rapidly
    Therefore the antigens on the viral surface continuously changes
    Working on animals to develop vaccines is not possible because HIV infects only humans
    The virus hides itself for years inside macrophages, therefore most vaccines may not work properly
  • 15. Bacteria
    Bacterial cells are about 10 times smaller than eukaryotic cells and are typically 0.5–5.0 micrometers in length.
    Bacteria are vital in recycling nutrients, and many important steps in nutrient cycles depend on bacteria, such as the fixation of nitrogen from the atmosphere.
    Large numbers of useful bacteria are found on the skin and in the digestive tract of humans and other animals.
  • 16. Structure of Bacteria
    Same function as eukaryotic cells (protein synthesis), but are smaller (70s rather than 80s).
    Always circular, and not in chromosome form.
    Naked (Histones are absent).
    Attached to cell membrane at least at one point.
  • 17. Structure of Bacteria
    Very small circles of DNA, containing non-essential genes.
    Can be exchanged between different bacterial cells.
    Cell membrane.
    made of phospholipids and proteins, like eukaryotic membranes.
  • 18. Structure of Bacteria
    Tightly-folded region of the cell membrane containing all the proteins required for respiration and photosynthesis.
    Cell Wall.
    DIFFERENT from plant cell wall.
    Made of murein (a protein) {Peptidoglycan}
    There are two kinds of cell wall, which can be distinguished by a Gram stain:
  • 19. Structure of Bacteria
    Gram positive bacteria
    have a thick cell wall and stain purple
    Gram negative bacteria
    have a thin cell wall with an outer lipid layer and stain pink.
  • 20. Gram Stain
    Gram stain is used to colour the bacterial cell wall for identification.
    Teichoic acid present in the cell wall of gram positive bacteria bind to crystal violet in the gram stain to give the cell wall a purplecolour.
    Gram negative bacteria don't have teichoic acid, and the crystal violent is decolourised and are replaced by red safranine in the gram stain, so the wall appears pink.
  • 21. Structure of Bacteria
    Capsule (Slime Layer).
    Thick polysaccharide layer outside of the cell wall.
    Used for:
    Sticking cells together
    As a food reserve
    As protection against desiccation (drying out) and chemicals, and
    as protection against phagocytosis (being broken down by a white blood cell).
  • 22. Pathogenic bacteria
    Cause infectious diseases, including
    Bubonic plague
  • 23. Toxins produced by bacteria
    Lipopolysaccharides which are part of the outer layer of gram negative bacteria which cause symptoms of disease.
    cause fever, vomiting and diarrhoea
    examples: endotoxins from Salmonella, E. coli
  • 24. Toxins produced by bacteria
    Proteins produced and released into the body by bacteria which causes severe symptoms of disease.
    These soluble proteins cause damage to cell membranes, internal bleeding, affect neurotransmitters, and poison cells.
    Example: botulinum toxin produced from Clostridium botulinum.
  • 25. Bacterial reproduction
    Binary fission
    Replication of DNA
    Replication of plasmids
    Cytoplasm and cell wall splits into two
    Generation time
    The time between divisions of bacteria.
  • 26. Bacterial reproduction
    Many bacteria can acquire new genes by taking up DNA molecules from their surroundings.
    Transduction is the process by which bacterial DNA is moved from one bacterium to another by a virus.
    Some bacteria can transfer a portion of their chromosome to a recipient bacteria.
  • 27. Nuclear envelope
  • 28. Flagellum
  • 29. Glycogen
    • Made of {peptidoglycan / murein}
    • 30. does not contain cellulose
  • 31.
  • 32. Lungs
    They {are immune / are resistant / have been vaccinated / have had BCG};
    Have antibodies / have memory cells;
    3. Bacteria destroyed before they cause damage / eq.
  • 33. Prolonged drug treatment (3-9 months) / eq;
    Antibiotics / isoniazid / eq;
    At least 3 (antibiotics) are used / eq;
    Rest / healthy diet / direct observation therapy;
  • 34. Tuberculosis
    TB is caused by the bacterium
    Mycobacterium tuberculosis
  • 35. Tuberculosis
    Coughing up blood in sputum
    Damage to the lung tissue
    Suppression of immunity
    Loss of appetite
    Loss of weight
    Night sweats and fever
  • 36. Tuberculosis
    Mass of tissue formed in the lung as a result of inflammatory response to infection by the TB bacterium.
  • 37. Infection occurs through inhaling contaminated air or drinking infected milk.
    Primary infection - early stage of infection.
    Development of tubercle
    Bacteria are destroyed by WBC and the tissue heals.
    Some bacteria produce thick waxy layer around them and survive.
    When the person's immune system is weakened these bacteria become active and divide.
    This leads to active TB.
  • 38. Diagnosis of TB
    Sputum testing for bacteria
  • 39. Treatments
    Antibiotics are used for many months.
    A cocktail of different antibiotics are used.
  • 40. Prevention
    BCG (Bacillus Calmette Guerin)
    Improving living standards
    Treating diseases in cattle
    Protected clothing when contacting people with TB