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MICROBIOLOGY

What is a virus?. Obligate intracellular parasiteSmaller than bacteria: 20-450nm, unique mode of replicationComposition:Nucleic acid: DNA or RNA, linear or circular, monopartite or segmented, ds or ss, ve or ve polarityNucleocapsid: genome protein coat surrounding it: protects genome whilst in transitLipid envelope: help viruses enter host cells.

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MICROBIOLOGY

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    1. MICROBIOLOGY

    2. What is a virus? Obligate intracellular parasite Smaller than bacteria: 20-450nm, unique mode of replication Composition: Nucleic acid: DNA or RNA, linear or circular, monopartite or segmented, ds or ss, +ve or ve polarity Nucleocapsid: genome + protein coat surrounding it: protects genome whilst in transit Lipid envelope: help viruses enter host cells e.G HIV is segmentede.G HIV is segmented

    3. Classification ICTV classification: Order, family subfamily, genus species Baltimore classification: basically, how they make mRNA -ve sense RNA is complimentary to mRNA so needs to be converted to sense strand first so its then replicated-ve sense RNA is complimentary to mRNA so needs to be converted to sense strand first so its then replicated

    4. Measurement of viruses By observing disease in host Plaque assay: Infection of susceptible host cell, replication, release and infection of new cells. Area of killed cells large enough to be seen = plaque. Titres expressed as plaque forming units/ml Electron microscopy Polymerase chain reaction Immunological evidence of infection

    5. The Steps that cause disease Binding Virus surface proteins bind cell receptors Penetration enveloped ? fusion at cell surface non-enveloped ? genome/core passes through Eclipse phase Virus proteins expressed Nucleic acids replicated Assembly Release (cell lysis or budding) Latent period in HASV 10 hours, in eclipse phase no infectious particles presentLatent period in HASV 10 hours, in eclipse phase no infectious particles present

    6. Latency Herpes viruses, e.g. HSV or varicella zoster virus (VZV) After lytic infection viruses enter neurones and genomes are maintained as circular DNA (episomes) in nucleus May reactivate years later to cause recurrent infections E.g. cold sores, HSV; shingles, VZV

    7. INFLUENZA

    8. Influenza... Helical nucleocapsid 13.6kb RNA Ss ve 8 segments enveloped

    9. A bit about Haemagglutinin Trimer, binds to sialic acid Each monomer has HA1 and HA2 (contains fusogenic peptide)

    10. Method of Replication

    11. Relenza, Tamiflu http://www.pharmasquare.org/flash/Tamiflu.html#RNA This blocks the virus from disseminating.. Neurominidase removes sialic acid so the virus can be removed

    12. How do we get new epidemics Antigenic drift: radical change of surface proteins Antigenic drift: point mutations small change in surface proteins

    13. Bird Flu Very high mortality in man Spread from migrating birds to other birds and to man No spread from man to man discovered Dont get too happy ... Still a huge threat As can adapt better to humans: better binding, replication, transmission and escaping immune system

    14. How it can adapt.. Binding: Binds better to a2-3 than a2-6, a mutation can change a2-6 to a2-3 Replication efficiency: Avain flu polymerase has glutamic acid at 627 of PB2 (poor rep in humans), Human flu has lysine, efficient avian flu has lysine instead. Escape immunity: NS1 confers resistance to interferon mediated inhibition of influenza virus replication, avian NS1 becomes more resistant to human interferons

    15. Virus Immune evasion Antigenic variation: Hiding: establish a latent infection in which virus proteins are not expressed, so infected cell may not be recognised by immune system e.g herpes Express proteins that inhibit the immune response: Block antigen presentation via class I MHC Block recognition by NK cells Secrete proteins to capture cytokines, chemokines or interferons Block intracellular signalling pathways, or apoptosis

    16. Interferons Help us fight viruses Many viruses interfere with them Viruses evolve, then we evolve, then they evolve again etc Just gonna explain geoffs slides...

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