General1.To familiarize you v the structural materials of the virus, which canact together antigens during the epidemic process.2.To emphasize the distinctive nature of viral main point acid and its role in theinfection process.3.To familiarize you through the morphological types of virus in stimulate thatthis information deserve to be supplied in make a diagnosis.4.To construct an expertise of the virus replication cycle in bespeak toappreciate exactly how the physician have the right to interrupt this cycle.

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Specificeducational missions (terms and also concepts ~ above which you will certainly be tested)

GeneralProperties the Viruses


Modifications in viral nucleic acid1.Nucleicacid -contains 3-400 genesDeoxyribonucleicAcid (DNA) -unique featuresSingleand/or dual strandedGlycosylatedand/or methylatedCircularor linearBoundprotein moleculesUniquepurine and/or pyrimidine bases presentRibonucleotidespresentRibonucleicAcid (RNA) - unique featuresSingleor double strandedSegmentedor unsegmentedBoundprotein moleculesUniquepurine and/or pyrimidine bases presentFoldingpattern2.Capsid-The capsid accounts for many of the virion mass. It is the protein coatof the virus. The is a complicated and highlyorganized entity which gives form to the virus. Subunits calledprotomeresaggregate to kind capsomereswhich in turn aggregate to kind the capsid.3.Envelope-this is one amorphous structure composed of lipid, protein and also carbohydratewhich lies to the external of the capsid.It consists of a mosaic of antigens from the host and the virus. A naked virusis one without an envelope.4.Spikes.These are glycoprotein projections which have actually enzymatic and/or adsorptionand/or hemagglutinating activity. Theyarise native the envelope and are highly antigenic.Morphology(Symmetry)1.Icosahedral-The protomeres accumulation in groups of five or six to form thecapsomere.In electron micrographs,capsomeres are recognized as regularly spaced rings through a main hole.The shape and also dimensions of theicosahedron counts on features of its protomeres. All icosahedralcapsids have actually 12 corners each lived in by a pentoncapsomere and also 20 triangular faces, each containing the same number of hexoncapsomeres. Icosahedral symmetry isidentical tocubic symmetry.Icosahedral2.Helical-The protomeres are not group in capsomeres, however are bound to each otherso together to type a ribbon-like structure.This framework folds into a helix since the protomeres space thicker atone finish than at the other. The diameter the the helicalcapsid is determined by qualities of that is protomeres, when its lengthis identified by the size of the nucleic mountain itencloses.Helical3.Complex-e.g.,that displayed by poxvirus and rhabdovirus. This group comprisesall those viruses which do not fit into eitherof the above two groups.ComplexReplicationCycle1.Adsorption -Viruses can get in cells via phagocytosis, viropexis or adsorption.Adsorption is the many common process andthe many highly specific process. It calls for the interaction ofa unique protein on the surface ar of the virus through ahighly details receptor site on the surface of the cell.2.Penetration -This wake up by one or more processes.Envelopedviruses fuse your envelope v the membrane that the hold cell. This involveslocal digestion of the viral and also cellular membranes, combination of the membranesand concomitant release of the nucleocapsid right into the cytoplasm.Nakedviruses tie to receptor web page on the moving membrane, digest the membraneand get in into the cytoplasm intact.Both nakedand enveloped viruses can be ingested through phagocytic cells. However, inthis procedure they go into the cytoplasm attached in a cytoplasmic membranederived indigenous the phagocytic cell.3.Uncoating -During this phase cellular proteolytic enzyme digest the capsidaway from the nucleic acid. This constantly occurs inthe cytoplasm the the host cell. The period of the replication bike betweenthe end of the uncoating stage and maturation ofnew famous particles is termed theeclipse.Thus during the eclipse stage, no finish viral particles deserve to be viewedwithin thecell.4.Replication of nucleic acid. Replication of famous nucleic mountain is a complexand change process. The specific procedure dependson the nucleic mountain type.Replication of nucleic acidNOTE:Symmetrical warrior of DNA offers rise come double-stranded RNA.DNAvirus replication -with the exception of the poxviruses, every DNA virusesreplicate in the nucleus. In some instances one that the DNA strands is transcribed(in others both strands of a small part of the DNA may be transcribed)(step 4) into details mRNA, which subsequently is translated (step 5) come synthesizevirus-specific proteins such as tumor antigen and also enzymes essential forbiosynthesis of virus DNA. This duration encompasses the at an early stage virus functions.Host cabinet DNA synthesis is temporarily elevated and is then suppressedas the cabinet shifts end to the manufacture of viral DNA (step 6). Together theviral DNA proceeds to be transcribed, so late virus functions come to be apparent.Messenger RNA transcribed during the later on phase of epidemic (step 6)migrates to the cytoplasm and is analyzed (step 7). Proteins for viruscapsids room synthesized and also are transported come the nucleus to it is in incorporatedinto the complete virion (step 8).Assemblyof the protein subunits approximately the viral DNA results in the development ofcomplete virions (step 9), which room released after cabinet lysis.Thesingle-stranded DNA viruses an initial form a double stranded DNA, utilizinga host DNA-dependent DNA polymerase. They climate undergo a typical replicationcycle.

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Replication the poliovirusRNAvirus replication -with the exemption of the orthomyxoviruses and retroviruses,all RNA viruses replicate in the cytoplasm that the host cell. The exactprocess varies v the species of virus. The single-stranded RNA thatis released after uncoating will act together either: (a) the mRNA come synthesizeviral-coded proteins; or (b) a template to synthesize mRNA; or (c) a templateto synthesize double stranded RNA, which is then offered as a layout tosynthesize mRNA; or (d) a template to synthesize double-stranded DNA, whichis then made use of as a theme to synthesize mRNA. This last processoccurs only with the retroviruses (oncornaviruses).Thereplication the poliovirus, which contains a single-stranded RNA as itsgenome, provides a beneficial example. All of the steps are live independence ofhost DNA and occur in the cabinet cytoplasm. Polioviruses absorb to cellsat specific cell receptor web page (step 1), losing in the procedure one viruspolypeptide. The sites are particular for virus coat-cell interactions. Afterattachment, the virus particles room taken into the cabinet byviropexis(similarto pinocytosis) (step 2), and also the viral RNA is uncoated (step 3). The single-strandedRNA then serves as its own messenger RNA. This messenger RNA is translated(step 4), leading to the development of one RNA-dependent RNA polymerasethat catalyzes the manufacturing of areplicationintermediate (RI), a partly double-strandedmolecule consisting of a complete RNA strand and numerous partially completedstrands (step 5). In ~ the same time, inhibitors of cellular RNA and also proteinsynthesis space produced. Synthetic of (+) and (-) strands that RNA occursby similar mechanisms. The RI consists of one finish (-) strand and also manysmall piece of freshly synthesized (+) strand RNA (step 6). Thereplicativeform (RF) is composed of two finish RNA strands,one (+) and one (-).Thesingle (+) strand RNA is make in huge amounts and may perform any kind of oneof 3 functions: (a) serve as messenger RNA for synthesis of structuralproteins; b) offer as design template for ongoing RNA replication; or (c) becomeencapsulated, resulting in mature progeny virions. The synthesis of viralcapsid proteins (step 7) is initiated at around the same time together RNA synthesis.Theentire poliovirus genome acts as its own mRNA, developing a polysome of approximately350S, and is analyzed to form a single large polypeptide the is subsequentlycleaved to create the various viral capsid polypeptides. Thus, the poliovirusgenome serves as a polycistronic messenger molecule. Poliovirus containsfour polypeptides.5.Maturation and ReleaseEnvelopedviruses -In the mature of enveloped viruses, a capsid must first beassembled approximately the nucleic mountain to form the nucleocapsid, i m sorry is thensurrounded through the envelope. Throughout the assembly of the nucleocapsid, virus-codedenvelope protein are also synthesized. These migrate to the plasma membrane(if assembly wake up in the cytoplasm) or come the atom membrane (if assemblyoccurs in the nucleus) and become included into that membrane. Envelopesare formed approximately the nucleocapsids through budding of cellular membranes. NOTE:Enveloped viruses will have actually an antigenic mosaicism properties of thevirus and also the organize cell. Viruses space slowly and continuously exit bythe budding procedure with the results that: (a) the cabinet is not lysed; and(b) small intracellular accumulation of virus occurs; and also (c) inclusionbodies room not as apparent as through naked viruses.Complexviruses -These viruses, of i m sorry the poxvirus is a good example, beginthe maturation procedure by creating multilayered membranes about the DNA.These layers distinguish into 2 membranes: The inside one contains thecharacteristic nucleoid, when the external one repurchase the characteristicpattern the the surface of the virion.Theseform very characteristic cytoplasmic inclusion bodies. The viruses aregenerally released from the cabinet via cabinet lysis.Summary1.Viruses contain either DNA or RNA as their genetic material, however not both.This nucleic acid generally has unique chemicaland/or physical attributes which provides it distinguishable from person nucleicacid.2.Viral nucleic mountain is attached in a capsid comprised of protein subunitscalled protomeres.3.Some varieties of viruses have a membrane, the envelope, neighboring thecapsid; other types do not have an envelope, i.e.,they are naked. Enveloped viruses have glyco-protein spikes arisingfrom their envelope. These spikes have actually enzymatic,absorptive, hemagglutinating and/or antigenic activity.4.The morphology the a virus is identified by the setup of the protomeres.When protomeres aggregate into systems of 5 orsix (capsomeres) and also then condense to kind a geometric number having 20equal triangle faces and also 12 apices, the virus issaid to have actually icosahedral (cubic) morphology. Once protomeres aggregateto type a capped tube, castle are claimed to have actually helicalmorphology. Any type of other arrangement of the protomeres results in a complexmorphology.5.All viruses undergo a replication bicycle in your human hold cell consistingof adsorption, penetration, uncoating, nucleic acidreplication, maturation and release stages.6.During the famous replication cycle, an build-up of tires viruses,incomplete viruses and also viral components occurs in ~ the cell.This build-up is theinclusion body. The size, shape, locationand chemical properties of the inclusion body space usedby the pathology to diagnose viral transmittable disease.7.A virally-infected cell usually presents 3 signals that it is infected.The an initial is the production of double-stranded RNA,which cause interferon; the 2nd is the expression of famous proteinon the surface ar of the plasma membrane, hence causingactivation the cytotoxic T-cells, herbal killer cells and sometimes inductionof antibody synthesis. The 3rd is the formation of aninclusion body either within the cytoplasm or the cell core or an extremely rarelywithin both the cytoplasm and nucleus.8.In general, all DNA-containing viruses replicate in the organize cell nucleus.The exceptions to the dominance are the poxviruses.9.In general, every RNA-containing viruses replicate in the organize cell cytoplasm.The exceptions to the preeminence are the retroviruses andthe orthomyxoviruses.PreviousLecture
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