Class i double stranded dna mrna is synthesized using

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Class I • Double-stranded DNA • mRNA is synthesized using the Negative Sense DNA Strand as a Template - Most Class I Viruses use Host Cell RNA Polymerase II (Pol II) - Some Class I Viruses bring along their own RNA Polymerase • Examples: - Hepatitis B Virus [HBV] (Serum Hepatitis) - Herpes Simplex Virus [HSV] (Genital Herpes) - Epstein-Barr Virus [EBV] (Mononucleosis) - Varicella-Zoster Virus [VZV] (Chickenpox) Children are now nicknamed “Kids” even though they ʼ re obviously not Goats. Similarly, Children in the 1700s were nicknamed “Chicks”. Class II • Single-stranded, Positive Sense DNA or Negative Sense DNA • Double-stranded DNA intermediate generated by Host Cell DNA Polymerase • mRNA is synthesized using the Negative Sense DNA Strand as a Template - Class II Viruses use Host Cell RNA Pol II • Example: - Parvovirus Strain B19 (Fifth Disease) Class III • Double-stranded RNA(s) • mRNA is synthesized using the Negative Sense Strand as Template - Class III Viruses bring along their own RNA Polymerase • Example: - Rotavirus (L= wheel) (Infant Diarrhea)
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Viruses Page 5 Class IV • Single-stranded, Positive Sense RNA • Genome serves as mRNA • Examples: - Hepatitis A Virus [HAV] (Infectious Hepatitis) - Poliovirus (Polio) - Rhinovirus (G= nose) (Common Cold) - West Nile Virus (West Nile [Virus] Fever) - Hepatitis C Virus [HCV] (Post-Transfusion Hepatitis) - Yellow Fever Virus (Yellow Fever) - SARS Virus (Severe Acute Respiratory Syndrome) Class V • Single-stranded, Negative Sense RNA(s) • mRNA is synthesized using the Negative Sense RNA(s) as Template - Class V Viruses bring along their own RNA Polymerase • Examples: - Influenza Virus (Influenza) - Measles Virus (Rubeola) - Mumps Virus (Mumps) - Rabies Virus (L= to rave) (Rabies) Class VI • Positive Sense RNA • Expression and replication of the Genome requires the generation, integration, and transcription of a Double-stranded DNA intermediate • mRNA is synthesized using the Negative Sense DNA strand as Template - Class VI Viruses use Host Cell RNA Pol II • Example: - Human Immunodeficiency Virus (HIV) (AIDS)
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Viruses Page 6 Virus Replication Attachment • Cell Receptor Proteins exploited by Viruses - CD155 is the Poliovirus Receptor Protein (PVR) - Sialic Acid is the Influenza Virus Receptor - CD4 and CXCR4 (Fusin) are the HIV Co-Receptors on CD4 + T Cells - CD4 and CCR5 are the HIV Co-Receptors on Macrophage and Monocytes Receptor Proteins are not present for the Convenience of the Virus. They are present to perform a Cellular Function. The Virus is simply using them as a convenient, reliable way to enter an appropriate Host Cell. Uptake • Direct Entry (Poliovirus) - The Genome only is inserted into the Cytoplasm • Analogous to Bacteriophage Genome Entry The empty Capsid stays on the Surface and will eventually be taken- up by Endocytosis. • Receptor-Mediated Endocytosis (Influenza) - Attachment induces Endocytosis of intact Virus • Enveloped Viruses (Influenza) - Lowered pH in Endosome results in the Fusion of the Virus Envelope with the Endosome Membrane • The Nucleocapsid(s) enter the Cytoplasm • Non-Enveloped Viruses - Lowered pH in Endosome results in the Fusion of the Nucleocapsid(s) with the Endosome Membrane • The Genome enters the Cytoplasm • Membrane Fusion (HIV) - Attachment induces Fusion of the Virus Envelope and Host Cell Membrane • The Nucleocapsid enters the Cytoplasm
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