Standard SB3d: Compare and contrast viruses with living organisms. Headings Vocabulary Important Info Standard SB3d: Compare and contrast viruses with living organisms.

Viruses are NOT Alive!! They do not grow or develop: they only replicate They must replicate inside a host cell They are VERY small: need electron microscope

Naming Viruses Diseases they cause: “herpes virus” Numbers: “T4” If they only infect bacteria: “bacteriophage” or “phage”

Virus Structure Outer protein coat: “capsid”. May be many-sided; spiral; head w/tail Inner core of nucleic acid: DNA or RNA (HIV) Some have an envelope around the capsid

Virus Structure T4 HIV

Attachment to Host Cell Viruses attach to a specific receptor site on the host cell: “lock and key” Each virus can only attach to a few kinds of cells Ex: T4 only infects the bacteria E. coli, wart virus only infects skin cells

Viral Replication: Lytic Cycle Virus enters host cell: “injects” or is taken inside Virus takes over host cell’s DNA & tells host cell to make new viruses Virus parts are assembled by the host Host cell bursts and new viruses are released to infect other cells

Viral Replication: Lytic Cycle 1. Virus injects its nucleic acid 2. Virus DNA tells host cell to make more viruses 3. New viruses are assembled by host cell 4. New viruses are released when host cell bursts (“lysis”)

Viral Replication: Lysogenic Cycle Virus DNA enters host cell DNA: “provirus” Every time host cell divides; it copies the provirus too Provirus may leave the host DNA at any time and enter lytic cycle Ex: herpes, hepatitis B, chicken pox, HIV

Viral Replication: Lysogenic Cycle 1. Virus injects its nucleic acid 2. Virus DNA enters host cell as a “provirus” 3. Provirus copied with host cell’s DNA 4. New viruses are released when host cells bursts (“lysis”)

Treatment for Viruses Only treatment for a virus is a preventative vaccine before exposure to virus Vaccine contains heated viruses that can’t infect…but cause antibodies to be made