Morphology and taxonomy

• Virions are the actual viral particles consisting of a single molecule of nucleic acid (DNA or RNA) surrounded by a protein coat called the capsid
• The genome of a virus codes for its infectivity and can be double or single stranded, linear or circular, have a plus or minus sense, and be haploid or diploid
• Capsids cover the nucleic material of viruses and are composed of structural units called capsomeres, giving shape to the virus
• Capsids can be helical/filamentous, rod-shaped with the genome at the center of the helix, and most animals with helical nucleocapsids are enveloped
• Capsids can be cubical/icosahedral, with the nucleic acid condensed at the core and surrounded by a protein coat
• Some viruses have complex capsids that are a combination of the prior types, not symmetrical in appearance
• Functions of the capsid include protecting the viral genome, introducing the viral genome to the host cell, acting as a stimuli for antibody production, and being used in diagnostic tests
• Some viruses have an envelope composed of lipoproteins surrounding the capsid, acquired when the capsid passes through a cellular membrane
• Proteins associated with the envelope include glycoproteins that create spikes or peplomers, fusion proteins aiding in entering and leaving cells, and matrix proteins providing added rigidity to the virion
• Enveloped viruses are more easily killed as their envelope can react against chemicals and physical agents, removing the envelope stops the replication process
• Temperature is crucial for viral stability, with surface proteins denatured at 55-60°C, affecting cellular attachment, penetration capabilities, and uncoating
• Viral preservation methods include short-term refrigeration at 4°C, long-term use of dry ice (-79°C), liquid nitrogen (-196°C), and the use of dimethyl sulphoxide (DMSO)
• The half-life of viruses varies with temperature, with viruses surviving for seconds at high temperatures and years at very low temperatures
• Viruses are well preserved in an isotonic environment, with most stable at pH 5 to 9, while enveloped viruses are inactivated at pH 5 to 6 except for some exceptions
• Antibiotics have no effect against viruses as they target bacteria, and chemical inactivants like ether, chloroform, aldehydes, and others can kill viruses
• Viruses can be named after diseases, places, hosts, Latin/Greek words, virus discoverers, or how they were originally thought to be contracted
• Viruses are classified based on the International Committee on Taxonomy of Viruses (ICTV) into orders, families, subfamilies, genera, species, and isolates/strains/serotypes/genotypes/variants
• The Baltimore classification groups viruses based on their genome and method of viral mRNA synthesis into 7 groups
• Viruses can be further classified based on their shape and presence of an envelope, categorized into naked icosahedral RNA, enveloped icosahedral RNA, and complex viruses with various shapes and envelope presence
• Viruses can also be grouped based on their shape and presence of an envelope, including helical enveloped RNA viruses
• Maintaining viral stability is crucial for preserving the infectivity and structure of viruses, impacting their ability to infect host cells and cause diseases