Viral Classification, Structure, and Replication - PDF

Viral Classification, Structure, and Replication Chapter 44 Viruses First described as “filterable agents” ____________ obligate intracellular parasites – depend on biochemical machinery of host for replication –...

Viral Classification, Structure, and Replication Chapter 44 Viruses First described as “filterable agents” ____________ obligate intracellular parasites – depend on biochemical machinery of host for replication – reproduction occurs by assembly of the individual components A rather than by binary fission ("macromolecules that assemble) Nucleic acid, protein, and in some cases membrane (__________) envelopet Without envelope Naked = Physical structure and genetics of viruses have been optimized by mutation and selection to infect humans and other hosts 1  Classification Names may describe: – viral characteristics picornavirus – disease they are associated with poxviruses potential thing og – tissue or geographic local where they were first identified : preary · Norwalk virus Norwalk, Mbox - OHIO USDA Classification Viruses can be grouped by * characteristics such as: Transmission of Dengue Virus disease 1 – _________ hepatitis 2 – target tissue enteric (g) 2 – means of transmission respiratory a – _________ rector arboviruses Animal cycle transmission Arthropod to humans 2  Classification The most consistent and current means of classification is by physiological and biochemical characteristics such as: ⑮ – morphology bacterial – size Isome as big as presence or absence of envelope 7 – __________________ type of genome g DNA viruses associated with human disease are divided into 7 families S RNA viruses may be divided into at least 13 families S – means of replication Classification – Families of DNA Viruses Family'' Members*' Poxviridae' Smallpox(virus,"vaccinia"virus,"monkeypox," canarypox,"molluscum"contagiosum" Herpesviridae' Herpes(simplex(virus(types(1(and(2," = mono chine varicella5zoster"virus,"Epstein5Barr"virus,"" cytomegalovirus,"human"herpesviruses"6," 7,"and"8" Adenoviridae' ' Adenovirus( Hepadnaviridae' Hepatitis(B(virus( Papillomaviridae' Papilloma(virus( Polyomaviridae' JC(virus,"BK"virus,"SV40" Parvoviridae' Parvovirus(B19,"adeno5associated"virus" ! 3  Classification – Families of RNA Viruses Family'' Members*' Paramyxoviridae' ' Parainfluenza+virus,+Sendai+virus,+measles&virus,+ mumps+virus,+respiratory+syncytial+virus,+ metapneumovirus+ Orthomyxoviridae' Influenza&virus+types+A,+B,+and+C+ Coronaviridae' Coronavirus,+severe+acute+respiratory+syndrome+ Arenaviridae' ' Lassa&fever&virus,+Tacaribe+virus+complex+(Junin+and+ Machupo+viruses),+lymphocytic+choriomeningitis+ virus+ Rhabdoviridae' Rabies&virus,+vesicular+stomatitis+virus+ Filoviridae' Ebola&virus,+Marburg+virus+ Bunyaviridae' ' California&encephalitis&virus,+La+Crosse+virus,+sandfly+ fever+virus,+hemorrhagic+fever+virus,+Hanta+virus+ Retroviridae' ' Human+TEcell+leukemia+virus+types+I+and+II,+human& immunodeficiency&virus,+animal+oncoviruses+ Reoviridae' Rotavirus,+Colorado+tick+fever+virus+ Togaviridae' Rubella&virus;+western,+eastern,+and+Venezuelan+ equine+encephalitis+virus;+Ross+River+virus;+Sindbis+ virus;+Semliki+Forest+virus+ Flaviviridae' Yellow&fever&virus,+dengue+virus,+St.+Louis+ encephalitis+virus,+West+Nile+virus,+hepatitis+C+virus+ Zika Caliciviridae' Norwalk&virus,+calicivirus+ Picornaviridae' Rhinoviruses,+poliovirus,+echoviruses,+ coxsackievirus,+hepatitis+A+virus+ Delta' ' Delta+agent+ ! Virion Structure Units for measurement of virion size are nanometers (nm) – clinically important viruses range from 18 nm (parvoviruses) to 300 nm (poxviruses) – larger virions can hold a larger genome that can encode more proteins, and they are generally more complex 4  Virion Structure Virion Structure Parvovirus Smallpox virus CDC 5  Virion Structure Virion (virus particle) - – nucleic acid genome Nucleocapsid – capsid – protein coat - ____________ – envelope – membrane – certain essential or accessory enzymes to facilitate initial replication within the cell Virion Structure Viral genome – ____________ DNA single stranded double stranded linear circular RNA – _____________ positive sense (+) – like mRNA negative sense (-) double stranded (+/-) segmented 6 Virion Structure Baltimore Classification Virion Structure 7  Virion Structure The surface structures of the capsid and envelope mediate the interaction of the virus with the target cell through a viral attachment protein (______) VAP – removal or disruption of the outer packaging inactivates the virus – antibodies generated against the components of these structures Prevent infectious disease _______________ Virion Structure 8 Virion Structure Virion Structure 9  Virion Structure Capsid ______________ – rigid structure able to withstand harsh environmental conditions – generally resistant to drying, acid, and detergents including acid and bile of the enteric tract – many transmitted by the fecal-oral route and can endure transmission even in sewage Envelope ______________ – membranous structure can be maintained only in aqueous solutions – readily disrupted by drying, acidic conditions, detergents, and solvents – must remain wet and are generally Transmitted in flids _________________, respiratory droplet, blood, and tissue Virion Structure Capsid viruses – the viral capsid is assembled from individual proteins associated into progressively larger units subunits _________ protomers capsomeres Capsid procapsid/_________ – all of the components of the capsid have chemical features that assemblyinto a larger unit allow them to fit together and to __________ 10  Virion Structure Virion Structure Simple Icosahedron Icosadeltahedron 11  Virion Structure Virion Structure Symmetric Helical – ________________ appear as rods – icosahedral Nonsymmetric – complex forms associated with certain bacterial viruses (phages) 12  Virion Structure Tobacco Mosaic Virus Herpes Virus Bacteriophage Helical Icosadeltahedral Nonsymmetric Virion Structure Enveloped viruses Hemagglutinin – envelope composed of lipids, proteins, and glycoproteins membrane structurally similar to cellular membranes derived from cellular membranes – ___________________________ cellular proteins rarely found in viral envelope – most are round or pleomorphic ↓ exceptions: Most virus under microscope – poxviruses appear round – rhabdoviruses 13  human Virion Structure shaped" largest virus "bullet ↑ & Variola virus Rabies virus Virion Structure drawin tois are a * Be of Envelope Is very suceptible to drying detergents. Thus , degradation of this to be virulent away takes virus ability > - must be transmitted in Fluid 14  Memorize for Exam#2 [viral families] on Virion Structure criptase fectious own reverse quired trans IPB f & enzymes (HIV) measeles Viral Replication The major steps in viral replication are similar for all viruses – cell acts as a factory, providing substrates, energy, and ObligateIntracellular machinery necessary for synthesis of viral proteins and parasites replication of the genome – processes not provided by the cell must be encoded in the > - do not need genome of the virus (t) RNA Virus to bring in additional enzumes 15  Viral Replication A single round of the viral replication cycle can be separated into several phases: – ________________ Early phase virus must recognize an appropriate target cell attach to the cell penetrate the plasma membrane uncoat its genome t – __________________ Late phase begins with the __________________________ genome replication viral macromolecular synthesis proceeds through viral assembly and release & zand 3 can viruses Enveloped rosis endocy enter via membrane ( - orfusion winjecting into Viral Replication * Pink texts = antiviral drugs * I naked virus + receptor recognition 2 attachment [not phagocytosis] 1st PKR Phosphorylate transcription 3 penetration" endocytosis : = factors thereby decreasing , protein synthesis OAS : makes A-A-A-A , activate RNAsel and RNA (Chew up) cleaves Viral > - that Last MyGipase form aggregates resort stops assembly/function of ⑧ Naked : lysis + release I kills host) new virions release s'enveloped budding host cell treatment > does not kill ↳Div - : ↓ ↳ ISG of Tamfineuramdasa Examplea me) n Herpes/chicken pox releas Interferons Type I : Narelornm On interfering wi viral replication > - > - part of endogenous attack against Viral infections / IFN type XIB 16 -releases Cytokines -binds to receptor ( IRF  Viral Replication Uncoating of the genome from the capsid/envelope abolishes its infectivity and identifiable structure – eclipse period (when there is no identiable structure of a virus , no virion) ends with the appearance of new virions Latent ________________ period * – extracellular infections virus is not detected 11 – includes the eclipse period and ends with the release of new viruses latent period – only 1-10% of new viruses may be infectious mutations Ifidelity of Viral polymerases very low defective virions) = errors in manufacture and assembly of the virion ______________ Burst Size – the yield of infectious virus per cell Viral Replication > - Slow budding off cells, integrates into hosts O chromosomes > - Eclipse penod = Nothing detected as viwus > - Latent period = includes eclipse period nothing , to get detected ( ) ? detected but begin 17  Viral Replication we already have these virus DNA viruses , ↑ hijacks this machinery – replication of the DNA genome requires a DNA-dependent DNA polymerase, other enzymes, and dNTPs – transcription occurs in the nucleus, using host cell polymerases and other enzymes for viral mRNA synthesis viral promoter and enhancer elements are similar in sequence to those of the host cell and allow binding of the cell’s transcriptional activation factors and DNA-dependent RNA polymerase more complex viruses encode their own transcriptional activators, which enhance or regulate the expression of viral genes viral genes may have introns requiring posttrascriptional processing of the mRNA by the cell’s nuclear machinery (splicing) Viral Replication DNA viruses – replication of viral DNA follows the same biochemical rules as for cellular DNA replication is initiated at a unique DNA sequence of the genome called the origin (ori) – the site is recognized by cellular or viral nuclear factors and the DNA- dependent DNA polymerase of host or viral origin – semiconservative – viral and cellular DNA polymerases ____________________ » cellular primase » herpesviruses encode their own primase – viral polymerases are usually faster but less precise than host cell polymerases » _____________________ » drug target 18