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Viruses VIRUSES: General Information • Non Living • Contains a Caspid: Protein coat surrounding it. • Core is composed of either DNA or RNA. DNA VIRUSES • Contains either single strand or double strand of DNA • Virus inserts the viral DNA into host cell. • Occurs in the nucleus. VIRAL DNA REPLICATION • Cell Divides and viral DNA is replicated. • Viral DNA is produced every time the cell divides VIRAL DNA REPLICATION • Viral mRNA leaves the nucleus • Attaches to Ribosome's • Viral proteins are produced. RNA VIRUSES • Examples: Polio and Tobacco Mosaic Viruses. • Viral RNA enters the cell and travels directly to the ribosome. • Makes viral proteins. RETROVIRUS • • • • • Enters the cell as RNA Travels to the nucleus Converts viral RNA to viral DNA Uses Reverse Transcriptase Viral DNA inserts itself into the actual chromosomes of the host organism. (Provirus) RETROVIRUS (backwards virus / HIV) • The viral DNA is then replicated with the normal DNA • The cell now produces viral RNA to and makes viral proteins. RETROVIRUS • Example: HIV • HIV replicates very quickly • Takes over the cell • Mutates rapidly • Difficult to make a vaccine. 1. Attachment: Virus attaches to host cell Lytic Cycle 2. Entry: Nucleic Acid is injected into the cell 5. Lysis and Release: Host cell breaks open and new viruse are released. 3. Replication: Viral DNA is replicated 4. Assembly: New virus particles are assembled Lysogenic Cycle • Viral DNA becomes a part of the host cells chromosomes (provirus) • The virus is inactive but still replicates with the normal DNA. • Continues to replicated until it decides to enter the Lytic Cycle. • The virus will leave the host chromosomes and then undergoes Lytic Cycle. Comparison of Lytic and Lysogenic Cycles of Viruses