Cat has not sense of balance b c his cerebellum did not develop fully Lecture 6 Viruses the ultimate life form next to prions Classification Genome single stranded OR double stranded DNA OR RNA unipartite or multipartite segments Enveloped or non enveloped also Virus particle shape spherical cylindrical etc Size really really small Nuclear OR cytoplasmic Virus are very simple organism consist of a genome either DNA or RNA some are enveloped and some non All of them have a protein coat around the genome Some of them in addition have envelope around them the main way to classify is the structure of its genome and if it has a envelope or not The Lytic Cycle dsDNA virus dsDNA virus Herpesviridae Papilomaviridae Poxviridae etc 1 Adsorption tail fiber or spikes receptor 2 Entry a non enveloped endocytosis b enveloped fusion 3 uncoating release of nucleic acid from protein coat Focus on the steps of the lytic 1 adsorption very specific process 2 entry virus has to get into the cell if it is non enveloped it comes in by endocytosis tricks the cell if its enveloped it comes in by fusion Cell membrane fuses with the envelope after adsorption and that s how the virus gets in in either case the virus gets into the host cell 3 the genome has to be released by the protein coat The virus gets in the protein coat falls apart and that releases the genome into the cell The viral genome is then replicated and the genome is expressed to give you more protein coat 4 genome replication expression txn tla transcribed replicate viral genome nucleus host enzymes transcribe viral genome nucleus host enzymes translate viral proteins cytoplasm host enzymes 5 Maturation assembly of mature virus particles new genomes new coats cytoplasm 6 release of new virus particles lysis kills host or budding exocytosis may kill host cell eventually In the lytic cell the cell is taken over produces viruses with its own machinery and organelles and then dies releasing more viruses Expressed transcribed into RNA The host cell can copy DNA into DNA DNA into RNA RNA into protein kills the cell Summary Adsorption Entry Uncoating Genome replication expression viruses want to have the smallest genome as possible CANT go RNA to DNA or RNA to RNA 5 Maturation assemly you make thousands of new virus particles and then the virus particles get out of the cells but either budding or lysis A non enevelope virus lysis the cell breaks the cell open and that s how it gets out of the cell That immediately kills the cell An eneveloped virus which gets released by budding which is the reverse of endocytosis it gets bud off at the surface and releases the virus That enventually Adsorption a very specific interaction between the viral coat or envelope and the host cell s plasma membrane that largely determines host range receptor corruption Maturation Release Adsorption contact between the 2 Entry release of the cell Note i e T4 LPS rhinovirus ICAM 1 HIV CD4 etc Viruses w o Receptors go to Viruses w o receptors Cannot replicate It eventually dies out The Lysogenic Cycle dsDNA virus 1 Adsorption 2 Entry 3 Uncoating 4 Integration of viral genome into host chromosome nucleus lysogeny viral integrase 5 Virus remains quiescent in the host chromosome for some period of time Very much the same but instead of getting genome replicate expression you get integration of viral genome integrase EXCISSION Human cells don t know how to do integration b c it requires a gene of enzyme called 6 Excision virus genome excises itself from the host chromosome viral enzyme 9 release of new virus particles lysis kills host or budding exocytosis may kill host cell 7 Expression replicate viral genome host enzymes transcribe viral genome host enzymes translate viral proteins host enzymes 8 Maturation assembly of mature virus particles Summary lysogentic cyle eventually Adsorption Entry Uncoating Maturation Release Integration Quiescence Excision min to life Genome replication expression These are all double stranded DNA so far dsDNA virus Genome replication done by host enzymes dsDNA dsDNA RNA genome expression done by host enzymes new virus particles Coat Proteins What about other types of viruses dsDNA ssDNA dsRNA ssRNA retro viruses double RNA ssDNA Viruses Parvoviridae etc 1 Adsorption 2 Entry 3 Uncoating The most stable one is the double stranded DNA b c sinc there are 2 strand if one gets messed up wrong letter the other strand is there to tell you what letter really belongs there and it can be fixed even though it has the 2 strands RNA is less stable than Dna One reason they are less stable is b c of RNA polymerase is error prone pretty much RNA gets replicated into RNA and that enzyme is more likely to make mistakes and when you have two even more prone to mistakes and the same goes for single stranded RNA The least stable of all is retro viruses 4 Second strand synthesis ssDNA dsDNA Host Enzymes Single stranded DNA is not much different than double stranded other than that extra step to 5 Genome replication expression or lysogeny host enzymes 6 Maturation 7 Release make the double strand ssDNA Viruses http www mcb uct ac za tutorial dnagen htm SS DNA Virus host enzymes ssDNA dsDNA genome replication stage RNA new virus host enzymes genome expression stage particles Protein Single stranded RNA are more complicated If you have a RNA molecule that can be translated to protein its sense If don t have rna molecule that can be translated its antisense So antisense have to first be ssRNA Viruses ss RNA Viruses messenger sense Togaviridae Rubella Flaviviridae Hepatitis C West Nile Picornaviridae Polio Hepatitis A Rhino Filoviridae Ebola Marburg Paramyxoviridae Measles Mumps ss RNA Viruses anti sense Rhabdoviridae Rabies ss RNA Viral Replication 1 Adsorption 2 Entry 3 Uncoating 4 Replication Expression ss RNA many ss RNAs RNA dependent RNA Polymerase many ss RNA many ss mRNAs G RNA dependent RNA Polymerase many RNAs viral proteins host enzymes Coats many RNAs viral genomes genomes 5 Maturation 6 Release ss RNA Viral Replication http www mcb uct ac za tutorial iv html Ss rna Viruses viral enzymes 1st ss rna ss rna ss rna genome for new virus Host enzymes don t know how to do rna to rna so its carried out by the viral enzyme gene expression stage coat proteins by host enzymes Only the ss can transfer to coat proteins ss RNA Viral Replication 1 Adsorption 2 Entry 3 Uncoating 4 Replication Expression ss RNA many ss mRNAs RNA dependent RNAPolymerase many ss RNAs viral