Structure, Classification & replication of Viruses Assistant Professor & Consultant Virologist College of Medicine & KKUH By: Dr.Malak El-Hazmi

Properties of Microorganisms Properties of Microorganisms characteristicParasiteFungiBacteriaVirus Cell Yes YesYesYesNo Type of nucleus nucleusEukaryoticEukaryoticProkaryotic----- Nucleic acid Both DNA DNA & RNA Both DNA & RNA Both DNA & RNA DNA or RNA RibosomePresentPresentPresentAbsent MitochondriaPresentPresentAbsentAbsent ReplicationMitosis Budding or mitosis Binary fission special

Characteristics of viruses  Acellular organisms  Tiny particles Internal coreInternal core Protein coatProtein coat Some Vs have lipoprotein mbSome Vs have lipoprotein mb  Obligate intracellular organisms  Replicate in a manner diff from cells ( 1V many Vs ) ( 1V many Vs )

Size ; nm

Viral Structure 1-Viral genome 1-Viral genome2-Capsid 3-Envelope

Viral Structure 1-Viral genome RNA RNA (Ribonucleic acid) (Ribonucleic acid)  All RNA Vs have ss except Reoviruses except Reoviruses  single / multiple  (+) polarity  (-) polarity DNA DNA (Deoxyribonucleic acid) (Deoxyribonucleic acid)  All DNA Vs have ds except Parvoviruses except Parvoviruses  Single molecule or All Vs are haploid,except retroviruses are diploid

2-Capsid  a protein coat  Subunit (capsomeres)  Genome (NA) + capsid = nucleocapsid = nucleocapsid  Function; Protects NA Protects NA Facilitates its entry into cell Facilitates its entry into cell Viral Structure

Symmetry based on arrangement of capsomeres  1-Cubic symmetry ( Icosahedral ) ( Icosahedral ) Adenovirus Herpesvirus

Symmetry based on arrangement of capsomeres  2- Helical symmetry  3- Complex symmetry poxviruses poxviruses Elongated (filoviruses) (filoviruses)Pleomorphic ( influenza v.) ( influenza v.)

Viral structure 3-Envelope Lipoprotein mb (host lipid,virus specific protein )  Budding  Envelope is derived from cell mb except herpesviruses from nuclear mb except herpesviruses from nuclear mb  Enveloped Vs are more sensitive to heat,dry & ether than nonenveloped Vs heat,dry & ether than nonenveloped Vs  Glycoprotein attaches to host cell receptor

Viral proteins  The outer viral ps  Mediate attachment to specific Rs  Induce neutralizing Abs  Target of Abs  The internal viral ps  Structural ps ( capsid ps of enveloped Vs )  Nonstructural ps ( enzymes) All ssRNA Vs (-) polarity have transcriptase All ssRNA Vs (-) polarity have transcriptase ( RNA dependent RNA polymerase) inside virions ( RNA dependent RNA polymerase) inside virions RetroVs & HBV contain reverse transcriptase RetroVs & HBV contain reverse transcriptase

Classification of viruses  Type of NA  The n. of strand  The polarity of viral genome of viral genome  Type of symmetry  The presence or absence of envelope absence of envelope

Medically Important Viruses ComplexPoxviridae IcosahedralHerpesviridaeHepadnaviridae IcosahedralAdenoviridaePapovaviridae Enveloped RNA DNA Nonenveloped Single-stranded double-stranded IcosahedralParvoviridae Nonenveloped

HelicalOrthomyxoviridaeParamyxoviridaeRhabdoviridaeFiloviridaeBunyaviridaeArenaviridae HelicalCoronaviridaeIcosahedralTogaviridaeFlaviviridaeRetroviridae IcosahedralReoviridae Enveloped RNADNA Nonenveloped Medically Important Viruses double-strandedSingle-stranded Nonenveloped IcosahedralPicornaviridaeHepeviridaeCaliciviridaeAstroviridae Pos- strand Neg - strand Enveloped

Replication  Adsorption (Attachment)  Penetration  Uncoating  Synthesis of viral components mRNAmRNA Viral proteinsViral proteins NANA  Assembly  Release Viral growth cycle

 Attachment site ; - glycoprotein - glycoprotein - folding in the capsid proteins. - folding in the capsid proteins.  The specificity of the attachment determines Host range of V.( narrow / broad)Host range of V.( narrow / broad) tissue specificity (tropism)tissue specificity (tropism) Attachment

Penetration 2-Endocytosis  Viral envelope fuses with endosome mb fuses with endosome mb  Nonenveloped V. lysis,pore 1-Fusion (enveloped Vs ) (enveloped Vs )

Replication  Adsorption (Attachment)  Penetration  Uncoating Release of viral genome - cytoplasm Release of viral genome - cytoplasm - nucleus - nucleus

Replication  Adsorption (Attachment)  Penetration  Uncoating  Synthesis of viral components  mRNA Viral genome transcription mRNA Viral genome transcription mRNA or act directly or act directly  Viral proteins mRNA translation viral proteins mRNA translation viral proteins  NA

Baltimore classification ( based on mRNA & NA synthesis )  ds DNA viruses  ds DNA viruses with reverse transcriptase (HBV)  ss DNA viruses  ss RNA viruses (+) strand or polarity  ss RNA viruses (-) strand or polarity  ss RNA viruses with reverse transcriptase (HIV)  ds RNA viruses

 All DNA Vs except poxVs replicate in nucleus (host cell DNA dependent RNA polymerase) (host cell DNA dependent RNA polymerase).  Most RNA Vs replicate in cytoplasm Except retroVs, influenza Vs, HDV. Except retroVs, influenza Vs, HDV. ss RNA viruses (+) strand or polarity ss RNA viruses (+) strand or polarity ssRNA(+) acts directly mRNA ssRNA(+) acts directly mRNA ss RNA viruses (-) strand or polarity ss RNA viruses (-) strand or polarity ssRNA (-) transcribed mRNA ssRNA (-) transcribed mRNA (V. RNA dependent RNA polymerase) (V. RNA dependent RNA polymerase) ds RNA viruses ds RNA viruses ds RNA transcribed mRNA ds RNA transcribed mRNA (V. RNA polymerase ) (V. RNA polymerase ) ss RNA viruses with reverse transcriptase ss RNA viruses with reverse transcriptase

 ss RNA viruses with reverse transcriptase (RT) (RNA dependent DNA polymerase) (RNA dependent DNA polymerase) V.ss RNA V.RT V.RT V.ds DNA V. integrase V. integrase Cell ds DNA V. Integrated ds DNA cell RNA polymerase cell RNA polymerase m RNA

Synthesis of viral components  mRNA Viral genome transcription mRNA Viral genome transcription mRNA or acts directly or acts directly  Viral proteins mRNA translation viral proteins mRNA translation viral proteins cell ribosome - early (enzymes) cell ribosome - early (enzymes) - late structural ps - late structural ps  replication of viral genome

Replication  Adsorption (Attachement)  Penetration  Uncoating  Synthesis of viral components mRNAmRNA Viral proteinsViral proteins NANA  Assembly NA + V. proteins = Virions NA + V. proteins = Virions  Release

Release Release  1-Budding (enveloped Vs) -cell mb* -nuclear mb (herpesVs) (herpesVs)  2- Cell lysis or rupture or rupture (nonenveloped) (nonenveloped)

Replication  Adsorption (Attachment)  Penetration  Uncoating  Synthesis of viral components mRNAmRNA Viral proteinsViral proteins NANA  Assembly  Release Viral growth cycle