2. Microorganisms What is a Pathogen? Microorganisms that causes disease There are five main groups of pathogens bacteria Viruses Fungi protista worms
3. 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.
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.
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 fever 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 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.
17. 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.
18. 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:
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 Cholera Tuberculosis Anthrax Bubonic plague
23. 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
24. 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.
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 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.
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;
35. 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
36. Tuberculosis Tubercle 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.
