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Viruses, Viroids, and Prions. Learning Objectives. Describe a protocell Define the main parts of a virus Describe major pathogenic viruses by: Enveloped or nonenveloped RNA or DNA Major diseases caused. Early Earth. Earth’s early properties essential for life

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Viruses, Viroids, and Prions


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    1. Viruses, Viroids, and Prions

    2. Learning Objectives • Describe a protocell • Define the main parts of a virus • Describe major pathogenic viruses by: • Enveloped or nonenveloped • RNA or DNA • Major diseases caused

    3. Early Earth • Earth’s early properties essential for life • Gravity high enough to retain atmosphere • Water in liquid form (distance from Sun) • Organic molecules from natural energy sources • Oparin-Haldane hypothesis • Early earth had reducing atmosphere • Allows complex organic molecules to form and persist (prebiotic soup of organics)

    4. 24.2 The Origin of Cells • Protocells formed with some properties of life • Living cells may have developed from protocells • Prokaryotic cells were the first living cells • Subsequent events increased the oxidizing nature of the atmosphere

    5. Miller-Urey Apparatus

    6. Early Macromolecules • Organic molecules are not alive by themselves • Macromolecules and aggregration needed • Macromolecule formation by subunits • Evaporation of water concentrates subunits • Dehydration synthesis connects subunits with H and OH removal

    7. Organic Molecule Aggregates • Clays facilitate organic molecule aggregates • Layered structure absorbs molecules and facilitates interactions, stores potential energy • No lipid bilayer assembly • Phospholipids assemble into bilayers in water • Formed spontaneously into vesicles • Can incorporate proteins and make new vesicles

    8. Prokaryotic First Cells • Approximately one billion years for development and evolution of first prokaryotic cells • Features required of first prokaryotes • Membrane bound • Nuclear region with DNA transcribed to RNA • Cytoplasmic region with RNA translated to amino acids/proteins • Cytoplasmic region for energy transformation • DNA replication and reproduction

    9. Virus • The minimum necessary to transmit nucleic acid molecules from one host cell to another • Viruses infect bacterial, animal, and plant cells by similar pathways • Viruses are NOT likely the first forms of life, but rather a degenerative type of evolution from early prokaryotes

    10. Viruses • Nonliving infective agents • No metabolic system of their own • Have minor to major effects on most organisms • Virus particle (virion) consists of a nucleic acid genome enclosed in a protein coat (capsid) • Bacteriophages commonly infect bacteria

    11. Viral Structure • Viral genome • DNA or RNA • Double-stranded or single-stranded • Few genes to 100 or more • Viral coat • Made of a single type of protein or up to 50 different proteins • Includes recognition proteins that bind host cell

    12. Major Humantropic Viruses • Most viruses can be classified as follows: • Envelope (lipid bilayer coat) or naked • Enveloped viruses must stay moist, easily disinfected • Naked viruses may last on surfaces for days • RNA or DNA, double or single, or retro • By the disease they cause (ex. Hepatitis viruses)

    13. Infection of Animals: Unenveloped Viruses • Virus binds to host using recognition proteins • Examples: adenovirus and poliovirus • Whole virus taken into host by endocytosis • Virus directs synthesis of new viruses like in bacteria, kills host when cell ruptured

    14. For RNA viruses • Single strand • Positive- Positive-sense (5' to 3') viral RNA signifies that a particular viral RNA sequence may be directly translated into the desired viral proteins • Negative-sense (3' to 5') viral RNA is complementary to the viral mRNA and thus must be converted to positive-sense RNA by an RNA polymerase prior to translation. • Ambisense- has both senses in one strand ex. Bunya

    15. Infection of Animals: Enveloped Viruses • Virus binds to host using recognition proteins • Examples: herpes, pox, HIV, influenza • Whole virus taken into host • Fusion of envelope with plasma membrane • Virus directs synthesis of new viruses • New viruses acquire envelope as they pass through plasma membrane (does not injure host)

    16. Viral Infection of Animals (1) • Pathogenic viruses cause diseases • Some cause cell death when cells rupture to release viral progeny • Some release cellular molecules that induce fever or inflammation • Some alter gene function of host cell, leading to cancer or other abnormalities

    17. Viral Infection of Animals (2) • Latent phase • Viruses remain in cell in an inactive form until triggered to become active • Similar to lysogenic cycle in bacteria • Most viral infections asymptomatic

    18. Virus Families: Adenovirus • Enveloped • DS DNA • Respiratory infections (colds) • Cause tumors in non-human cells • Part of the DNA integrates into the genome

    19. Virus Family: Bunyavirus • Enveloped • SS RNA • Cause arthropod-bourne hemorrhagic fevers

    20. Virus Family: Calicivirus • Unenveloped • SS RNA • Most common human one is Norovirus, or Norwalk virus • Gastrointestinal illness

    21. Virus Families: Flaviviruses • Enveloped • SS RNA • Yellow fever, Dengue (carried by mosquitos) • Hepatitis C- retrovirus, capable of causing liver cancer, chronic disease • Treated with peg interferon

    22. Typical Retrovirus

    23. Virus Family: Hepadnevirus • Enveloped • DS DNA • Hepatitis B • Acute disease- very common • Some patient develop chronic infections which may eventually lead to liver failure or cancer

    24. Virus Families: Herpesviruses • Enveloped • DS DNA- large genome! • 8 viruses • HSV I and II • Epstein Barr • Varicella-Zoster • Cytomegalovirus (CMV) • Roseola (HHV6 and 7) • Kaposi’s sarcoma

    25. Virus Families: Orthomyxovirus • Enveloped • SS RNA • Influenza • Viral coat has two major proteins- • Hemeaglutinin (H) • Neuraminidase (N) • Differences in subtypes

    26. Virus Family: Papovavirus • Unenveloped • DS DNA • Benign and malignant warts

    27. Virus Family: Paramyxoviruses • Enveloped • SS RNA • Parainfluenza • Measles • Mumps

    28. Virus Family: Picornaviruses • Enterovirus- polio, gastro illnesses • Rhinoviruses- common cold • Hepatitis A • Foot and mouth disease

    29. Virus Family: Poxvirus • Enveloped • DS DNA • Largest of viruses • Smallpox, cowpox

    30. Virus Family: Retroviruses • Enveloped • SS RNA • HTLV I and II • HIV

    31. Virus Family: Rhabdovirus • Enveloped • SS RNA • Rabies, VSV

    32. Viroids • Plant pathogens • Strands or circles of RNA • No protein coat • Viroid RNA may activate protein kinases (adds phosphate groups to proteins) • Leads to reduction in protein synthesis • Results in disease symptoms • Serious problem in some plant crops

    33. Prions • Infectious proteins with no associated nucleic acids • Misfolded versions of normal cellular proteins that can induce other normal proteins to misfold

    34. Prion Diseases Degenerate nervous system in mammals • Scrapie: Brain disease in sheep • Mad cow disease (Bovine spongiform encephalopathy): Spongy holes and protein deposits in brain tissue • Creutzfeldt-Jakob disease: Rapid mental deterioration, loss of vision and speech, paralysis • Kuru-cannibalistic tribe in New Guinea,

    35. Brain Tissue Damaged by BSE