1. - Describe the differencesin structure of a virion. Include in yourdescription thechemical composition of a virus and structures that make up a naked andanenvelopedviron.The simplest virions are made up of two fundamental components: nucleic acid (single-stranded or double-stranded RNA or DNA) and a capsid protein coat, which serves as a shell toprotect the viral genome from nucleases and binds the virion to particular receptors exposed tothe prospective host cell during infection.Structure and FunctionThe primary function of the virion is to deliver into the host cell its DNA or RNA genomeso that the host cell can express (transcribe and translate) the genome. Within a symmetricprotein capsid, the viral genome, often with related basic proteins, is packaged. Thenucleocapsid produces a nucleic acid-associated protein called the nucleoprotein, along withthe genome. In enveloped viruses, a lipid bilayer originating from the modified host cellmembrane surrounds the nucleocapsid and is studded with an outer layer of glycoproteinsenveloping the virus.Classification of VirusesMorphology:Viruses are classified according to size and shape, chemical composition andgenome structure, and replication mode.oHelical morphology is seen in many filamentous and pleomorphic virusnucleocapsids.oHelical nucleocapsids consist of a capsid protein helical array wrapped around anucleic acid helical filament.oThe nucleocapsids of several "spherical" viruses are distinguished byIcosahedral morphology. In identification and classification, the number andarrangement of the capsomeres (morphological subunits of the icosahedron) areuseful. Many viruses have anouter envelopeas well.oViruses' outer capsid and envelope proteins are glycosylated and essential fordetermining the virion's host range and antigenic composition.oBudding viruses often bear such host cell proteins as essential constituents ofthe viral envelope, in addition to virus-specified envelope proteins. It is possibleto accept virus envelopes as an extra protective coat.Chemical Composition and Mode of Replication: A virus genome may consist of DNA orRNA, which may be single, linear or circular stranded (ss) or double stranded (ds). Either onenucleic acid molecule (monopartite genome) or multiple nucleic acid segments (multipartitegenome) can occupy the whole genome.