Viruses page 7 synthesis transcription of viral mrna

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Viruses Page 7 Synthesis (Transcription) of Viral mRNA Class I, Class II and Class VI • Host Cell RNA Pol II synthesizes Virus mRNA - Class III and Class V • Virus-Coded RNA Polymerase synthesizes Virus mRNA - Class IV • Virus Genome serves as mRNA Translation of Viral mRNA • Non-Structural Proteins (Early Proteins) - Non-Structural Proteins are Enzymes, Polymerases, Regulatory Proteins and Scaffolding Proteins that will not be a Structural Component in the Virus Capsid or Envelope Non-Structural Protein Synthesis usually occurs early in Viral Replication. Viruses need relatively small Amounts of Non-Structural Proteins. • Structural Proteins (Late Proteins) - Structural Proteins are Capsid and Envelope Proteins Structural Protein Synthesis usually occurs late in Viral Replication. Viruses need massive Amounts Structural Proteins. Synthesis of Viral Genome • Class I - Host Cell DNA Polymerase synthesizes Virus Genome • Class II - Host Cell DNA Polymerase synthesizes new Virus Genome • Class III, Class IV and Class V - Virus-Coded RNA Polymerase synthesizes new Virus Genome • Class VI 1- Virus-Coded Reverse Transcriptase synthesizes DNA Intermediate -- and then -- 2- Host Cell RNA Pol II synthesizes Virus Genome using this DNA Intermediate as a Template
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Viruses Page 8 Assembly • New Virus Particles are assembled within the Host Cell - Icosahedral Capsids are usually assembled as Empty Shells • Capsomers are assembled into “Faces” - Faces are used to assemble the Icosahedral Capsid • The Genome is packed into the completed Icosahedron The massive Amounts of Structural Proteins are frequently in and of themselves sufficient to change Conditions within the Host Cell such that these Structural Proteins Self-Assemble (“Crystallize”) into Nucleocapside. Release • Non-Enveloped Virus (Poliovirus) - The Host Cell is lysed • Virus Particles are released with Cell Contents • Enveloped Virus - The Host Cell is not Lysed • Budding (Influenza Virus, HIV) - Nucleocapsid Components bind to Cytoplasmic Domains of Envelope Proteins - The Host Cell Membrane is molded around the Nucleocapsid - The Virus acquires its Envelope as it extrudes through the Cell Membrane A Very Big Problem with Budding is that the Virus-Coded Envelope Proteins in the Host Cell Membrane act like a flashing Neon Sign advertising “Virus Infected Cell” to Natural Killer Cells and Cytotoxic T Cells. So some Viruses have learned to sneak-out the Back Door… • Exocytosis (Hepatitis B Virus) - The Virus “buds” through an Internal Cell Membrane, such as the Golgi or the Endoplasmic Reticulum • The Virus is transported via Vesicles to the Cell Membrane and released from the Cell The Virus-Coded Envelope Proteins are never visible on the Surface of the Cell so it ʼ s difficult for the Immune System to “see” that a Cell is infected with a Virus.
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