Introduction to viralogy.docx

Viruses Sub-microscopic Acellular obligate intracellular parasites They assemble and but do not grow as they lack machinery. Also lack apparatus for protein and energy generation. The origin is unknown for viruses. Can reproduce very fast, able to evolve. Structure of a virus Viruses can be divided...

Viruses Sub-microscopic Acellular obligate intracellular parasites They assemble and but do not grow as they lack machinery. Also lack apparatus for protein and energy generation. The origin is unknown for viruses. Can reproduce very fast, able to evolve. Structure of a virus Viruses can be divided into 2 groups. Enveloped- nucleic acid, capsid and phospholipid membrane. Unenveloped/ naked - nucleic acid, capsid. Viruses can be either icosahedral, helical, or complex shape/ structure. They are highly symmetric. Viruses can either contain RNA or DNA, cannot be both! Can be double stranded or single stranded. Can be linear or circular. RNA can be + strand or – strand. Only the + strand mRNA can be translated into viral protein. Baltimore classification- classified in terms of how they make their mRNA. 7 different groups. DsDNA /// // // Production of viral + mRNA. Some enzymes used come from the host cell. Or if the host cell doesn’t have them, then the virus will be coding for them to produce them. Life cycle of a virus Attachment (adsorption) Binding of attachment sites of the virus with receptor sites of the host cytoplasmic membrane It is the same for naked or enveloped virus. Both contain proteins on the outer surface of the virus which recognises specific proteins on the host cell. Penetration Naked virus Interaction of capsid and host cell membrane which causes rearrangement of the capsid proteins to allow nucleic acid entry. Naked virus can also enter via endocytosis. Enveloped virus The virus enters the host cell, and the viral envelope is removed. The capsid Is then enzymatically removed. It either fuses with the membrane or enters via endocytosis. Synthesis The viral genome directs the host cell replication and translation machinery to synthesis viral components. Assembly RNA viruses assemble in the cytosol and DNA viruses assembles in the nucleus. Release Naked virus The host cell deteriorates, and the virus is released. Enveloped virus Releases itself via budding, or releases by exocytosis. Transmission routes Air-droplet Faecal-oral Sexual Vector-borne. Blood