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Topic 6 infection, immunity and forensics revision
 

Topic 6 infection, immunity and forensics revision

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    Topic 6 infection, immunity and forensics revision Topic 6 infection, immunity and forensics revision Presentation Transcript

    • Topic 6Infection, Immunity and ForensicsRevision
    • Microorganisms
      What is a Pathogen?
      Microorganisms that causes disease
      There are five main groups of pathogens
      bacteria
      Viruses
      Fungi
      protista
      worms
    • Virus
      Smallest of all living organisms
      Size
      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.
    • 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
    • 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.
    • TMV
      Tobacco Mosaic Virus
      Leaf infected with TMV
    • Retroviruses
      Viruses with RNA as their genetic material.
    • 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.
    • 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).
    • 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.
    • 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
    • AIDS - Symptoms
      fever
      persistent diarrhoea
      weight loss
      secondary infections such as TB, pneumonia, Kaposi's sarcoma
    • AIDS - Prevention
      Practicing monogamy
      Use of condoms
      Use of clean needles
      Awareness programmes
    • 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
    • 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.
    • Structure of Bacteria
      Ribosomes.
      Same function as eukaryotic cells (protein synthesis), but are smaller (70s rather than 80s).
      DNA.
      Always circular, and not in chromosome form.
      Naked (Histones are absent).
      Attached to cell membrane at least at one point.
    • Structure of Bacteria
      Plasmid.
      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.
    • Structure of Bacteria
      Mesosome.
      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:
    • 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.
    • 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.
    • 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).
    • Pathogenic bacteria
      Cause infectious diseases, including
      Cholera
      Tuberculosis
      Anthrax
      Bubonic plague
    • Toxins produced by bacteria
      Endotoxins
      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
    • Toxins produced by bacteria
      Exotoxins
      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.
    • 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.
    • Bacterial reproduction
      Transformation
      Many bacteria can acquire new genes by taking up DNA molecules from their surroundings.
      Transduction
      Transduction is the process by which bacterial DNA is moved from one bacterium to another by a virus.
      Conjugation
      Some bacteria can transfer a portion of their chromosome to a recipient bacteria.
    • Nuclear envelope
      Glycogen
      Lipids
      Plasmids
      Flagellum
    • Flagellum
      DNA
    • Glycogen
      • Made of {peptidoglycan / murein}
      • does not contain cellulose
    • 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.
    • Prolonged drug treatment (3-9 months) / eq;
      Antibiotics / isoniazid / eq;
      At least 3 (antibiotics) are used / eq;
      Rest / healthy diet / direct observation therapy;
    • Tuberculosis
      TB is caused by the bacterium
      Mycobacterium tuberculosis
    • Tuberculosis
      Symptoms
      Coughing up blood in sputum
      Weakness
      Damage to the lung tissue
      Suppression of immunity
      Loss of appetite
      Loss of weight
      Night sweats and fever
    • Tuberculosis
      Tubercle
      Mass of tissue formed in the lung as a result of inflammatory response to infection by the TB bacterium.
    • 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.
    • Diagnosis of TB
      X-rays
      Sputum testing for bacteria
    • Treatments
      Antibiotics are used for many months.
      A cocktail of different antibiotics are used.
    • Prevention
      BCG (Bacillus Calmette Guerin)
      Improving living standards
      Treating diseases in cattle
      Protected clothing when contacting people with TB