The Viruses Viruses Definitions Composition Protein Nucleic Acid Obligate intracellular parasites pathogens Infectious particles Non living Culture Need host cells first must culture host cells then infect with virus Small particles Main Types of Viruses Based on general structure Complex Enveloped Naked or Non enveloped Naked vs Enveloped Structural Organization Basic Structures Covering Capsid all viruses protein Envelope some but not all viruses lipid Central core nucleic acid core Hollow space area that contains nucleic acid Capsids Two basic types based on shape Helical Capsids Icosahedral Capsids Envelopes Lipid bilayer Flexible outer layer Obtained from host Often has viral proteins on surface Called spikes Envelopes Irregular Complex Coverings Medical Importance of Viral Coverings Covering Protects virus Relates to how easy disinfectants can destroy viruses Covering used by virus to attach to host cell Covering is recognized by immune system of host Nucleic Acid Core Area that contains viruses nucleic acid DNA or RNA never both May be single stranded ss or double stranded ds Linear circular or segmented ssRNA may be either sense or sense sense functions as mRNA can be translated immediately sense complimentary strand strand must be transcribed then strand acts as mRNA Nucleic Acid Core Nucleic acid contains genes to instruct host cell how to make more viruses Small genome 4 to several hundred genes Other core substances Enzymes polymerases nucleases others Basic Viral Taxonomy Viral Families DNA Viruses 6 important families of human pathogens Poxviridae smallpox virus Papillomaviradae benign tumors warts Parvoviridae gasteronteritis Hepadnaviridae hepatitis B Herpesviridae chicken pox herpes simplex Adenoviridae respiratory infections Viral Families RNA Viruses 12 important families of human pathogens Orthomyxoviridae influenza Paramyxoviridae mumps measles respiratory infections Rhabdoviridae rabies Togaviridae yellow fever rubella encephalitis Retroviridae AIDS T cell leukemia Reoviridae rotavirus diarrheal disease encephalitis Picornaviridae polio hepatitis A Coronaviridae respiratory infections Caliciviridae Norwalk virus gasteroenteritis Filoviridae Ebola virus hemorrhagic fever Arenaviridae Lassa virus hemorrhagic fever Bunyaviridae encephalitis Viral Replication Viral Replication Basic Stages Adsorption Penetration Synthesis Maturation assembly Release Bacteriophages Viruses which infect bacteria Easy to study T Even Coliphages Two types of replication Lytic Cycle Lysogenic Cycle Typical Bacteriophage Lytic Cycle Adsorption Penetration Synthesis Assembly Maturation Release Lysogenic Cycle Cycle carried out by temperate phages Viral nucleic acid incorporated into bacterial chromosome Viral nucleic acid now called a prophage No immediate synthesis maturation or release Prophage duplicated along with bacterial chromosome as bacteria divide Lysogeny Medical significance Corynebacterium diphtheriae Bacterial chromosome only weakly pathogenic Bacterial chromosome prophage very pathogenic Prophage codes for toxin Animal Viruses More varied replication cycles than bacteriophages Still have same basic stages Adsorption Very similar capsid or envelope proteins Penetration and Uncoating Several methods endocytosis membrane fusion translocation direct penetration Absorption Penetration and Uncoating Animal Viruses Replication Stages cont Synthesis and Maturation Quite varied depending on type of viral nucleic acid Release Several methods lysis exocytosis budding Budding or Exocytosis Special Types of Animal Viruses The persistant viruses and oncogenic viruses Persistent Animal Viruses Persistent virus causes long lasting infection Chronic infection long lasting but virus always detectable Hepatitis B HIV Latent infection latency long lasting but virus dormant undetectable no symptoms no antibody production Herpesviruses simplex zoster Epstein Barr viruses remain inside host cells relatively inactive little or no immediate host cell damage can become reactivated virus begins to replicate host cell damage disease Herpes zoster Oncogenic viruses persistent animal viruses viral nucleic acid incorporated into host genome redirect normal growth patterns of host cells leads to neoplasia cancer examples Burkitt s lymphoma Epstein Barr virus some leukemias retroviruses Human papillomavirus cervical cancer Other Infectious Particles Prions infectious protein particles PrP pathogens of animals cause chronic persistent infections Examples scrapie sheep BSE cattle Creutzfelt Jacob disease humans Kuru humans Viroids infectious RNA particles pathogens of plant cells End Go to Taxonomy and Diversity
View Full Document
Unlocking...