MICR20010D new.pptx

Where are the Viruses? Viruses • Acellular • Consist of DNA or RNA core • Core is surrounded by a protein coat • Coat may be enclosed in a lipid envelope • Viruses are replicated only when they are in a living host cell Figure 1.1e Phages • Bacteriophages are the most common biological entities...

Where are the Viruses? Viruses • Acellular • Consist of DNA or RNA core • Core is surrounded by a protein coat • Coat may be enclosed in a lipid envelope • Viruses are replicated only when they are in a living host cell Figure 1.1e Phages • Bacteriophages are the most common biological entities on earth. • Incredible specificity leading to emergence of phage therapy. • Key for us is the life cycle of phages as these again involve transfer of genetic material Lytic or life cycles A Borrowed Life • Viruses called bacteriophages can infect and set in motion a genetic takeover of bacteria, such as Escherichia coli • Viruses lead “a kind of borrowed life” between life-forms and chemicals • The origins of molecular biology lie in early studies of viruses that infect bacteria Figure 19.1 Structure of Viruses • Viruses are not cells • A virus is a very small infectious particle consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope Viruses replicate only in host cells • Viruses are obligate intracellular parasites, which means they can replicate only within a host cell • Each virus has a host range, a limited number of host cells that it can infect. Viruses • Can penetrate and grow inside host • Attach onto host cell and then enters – Effect host cell plasma membrane – Inhibit host DNA/RNA, protein synthesis – Can cause a Cytopathic effect (CPE) Cytoplasmic inclusion body in brain tissue-rabies on measles infection Giant cell formed Reported AIDS Cases in the United States Figure 14.4 Microbiology an introduction Figure 19.17 Fig 19.17 Microbiology an introduction “Our” Pandemic – Covid-19 • A Coronavirus – RNA Viruses • Cause diseases in Mammals and Birds • Predominantly cause mild infections • Some Exceptions – SARS – Severe acute respiratory syndrome 2003-4 – MERS – Middle East Respiratory Syndrome – 2012 – COVID-19 – SARS Cov-2 Why so problematic? • Large numbers of people asymptomatic • Very effective human to human spread • Severe disease in a subset of individuals The Solution? • Vaccines – Vaccine results show great promise – Protection evident but for how long? • Biotherapeutics – Large numbers of drugs entered pipeline including several monoclonal antibodies • Test and Trace – Faster and cheaper tests to allow control of pandemic. Where are the Fungi and Protists? Remember these are Eukaryotes Fungi • Eukaryotes • Chitin cell walls • Use organic chemicals for energy • Molds and mushrooms are multicellular, consisting of masses of mycelia, which are composed of filaments called hyphae Figure 31.6 introduction to Microbiology Figure 1.1b • Fungi are diverse and widespread • About 100,000 species of fungi have been described • It is estimated there are actually 1.5 million species of fungi • Fungi consist of mycelia, networks of branched hyphae adapted for absorption Figure 31.3 Campbell Biology Figure 31.6 Campbell Biology Fungal Diseases (Mycoses) • Systemic mycoses: Deep within body • Subcutaneous mycoses: Beneath the skin • Cutaneous mycoses: Affect hair, skin, and nails • Superficial mycoses: Localized, e.g., hair shafts Fungi as parasites • Toxic metabolic products from fungal growth in host • Allergic response- fungal growth in homes • Tichothecene toxins inhibit protein synthesis – Fusarium • Proteases – Candida albicans (skin) , Trichophyton • Capsule prevents phagocytosis – Cryptococcus neoformans- meningitis Pathogenic Properties of Fungi • Ergot toxin– Claviceps purpurea (grains)- hallucinations like LSD – Killed 40,000 in France in 944. – characterized by gangrene, nervous spasms, burning sensations, hallucinations, and temporary insanity • Aflatoxin– Aspergillus- can be carcinogenic • Mycotoxins – Neurotoxins: Phalloidin, amanitin • Amanita phalloides- also known as deathcap Ergots on rye Filamentous Fungi - Molds • Widespread • Found on bread and fruit • Aspergillus • Rhizopus • Sporulation and conidia Macropscopic Fungi Mushrooms • Produced for food Agaricus • Poisonous variants - Amanita • Normally mycelium but occasionally fruiting bodies Unicellular Fungi - The yeasts • Cell division by budding and occasionally mating • Can be pathogenic - Candida Albicans - filamentous phase • Facultative anaerobes and common where sugars are found • Saccharomyces cerevisiae • Bakers/Brewers yeast The Algae • Contain chlorophyll and carry out oxygenic photosynthesis • Most are microscopic but some can be macroscopic such as seaweeds • Large and diverse group Diversity in Algae • Generally unicellular or colony forming volvox and spirogyra • Contain chlorphyll and other pigments such as Xanthophyll or caratenoids Pathogenic Algae - Red Tide • Dinoflagellates • Gonyaulax neurotoxin kills fish and humans but harmless to shellfish • Pfeisteria -Again a neurotoxin this time causing lesions - has been known to kill billions of fish Lichens? • Symbiotic relationship between fungus and an algae or cyanobacterium. • Fungus provides anchor, algae provides the photosynthesis. Protozoa • Unicellular organisms without cell walls • Generally colourless and motile • Do not form spores or fruiting bodies Protozoa – The Amoebae • The Amoebae • Some shelled • Amoeboid movement • Entamoeba histolytica pathogenic in humans Protozoa – The Ciliates • Use cilia to achieve motility • Paramecium • Food engulfed into a food vacuole • Trichocysts to allow attachment • Methanogenic archaea • Parasitic? Protozoa - Flagellates • Motile • Euglenoids – Dunaliella • Some are pathogenic – Trypanosoma brucei • African sleeping sickness via Tsetse fly Protozoa – The Sporozoans • Obligate parasites • Many can be pathogenic • Plasmodium vivax • Toxoplasma gondii The Protozoa Anything left? Prions: The Simplest Infectious Agents • Prions are slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals • Prions propagate by converting normal proteins into the prion version • Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans are all caused by prions (Photo Credits: clockwise: Kunihiko Kobayashi; University of Iowa; Duke Medical School; University of California, Davis Prion disease agent  Agent insensitive to UV irradiation  distinct from conventional virus  devoid of DNA or RNA  The agent= composed primarily, even uniquely of a protein called Prion Figure 19.11 Prion Normal protein Original prion New prion Aggregates of prions CONVERSION PrPC PrPSc