CHAPTER 11

• What is a virus?

  A microscopic infectious agent that replicates inside living cells
• What type of nucleic acid do viruses possess?

  Only one type: DNA or RNA
• How do viruses reproduce?

  From their nucleic acid alone
• What essential cellular systems do viruses lack genetic information for?

  Production of energy
• How do viruses synthesize their proteins?

  By hijacking the host cell's machinery
• What is absolute parasitism in viruses?

  Using host cell ribosomes for protein synthesis
• Can viruses replicate on inert media?

  No, they require viable host cells
• What does a virus's tropism refer to?

  The types of cells and tissues it can infect
• What is a virion?

  The mature infectious form of a virus
• What is the structure of a virion composed of?

  The viral genome and the capsid
• What are viroids?

  Small infectious RNA particles without a protein coat
• How long are viroids?

  About 250-350 nucleotides long
• What is an alternative perspective on viruses?

  They possess some properties of living organisms
• What is the first virus to be identified?

  Tobacco Mosaic Virus
• What is a key distinction among viruses?

  Whether or not they have envelopes
• What shape does the Ebola Virus have?

  A 6 or 8 figure shape
• What is the first step in the infection of a cell by a virus?

  Attachment to the cell surface
• What is required for viral attachment to occur?

  Specific receptors on the cell surface
• How do enveloped viruses penetrate host cells?

  By fusing with the plasma membrane
• What happens when enveloped viruses fuse with the plasma membrane?

  The internal components are delivered to the cytoplasm
• How do some enveloped viruses enter cells via endosomes?

  They require acid pH for fusion
• What occurs during the uncoating phase of viral infection?

  Nucleic acid is released for replication
• What is the eclipse phase in viral replication?

  The phase where the virus is undetectable
• How do DNA viruses replicate their genomes?

  Using DNA-dependent DNA polymerases
• What do RNA viruses use for genome replication?

  RNA-dependent RNA polymerases
• What is the role of viral mRNA in protein synthesis?

  It serves as a template on host ribosomes
• What are post-translational modifications (PTMs)?

  Changes that alter protein structure and function
• How is viral nucleic acid and protein synthesis regulated?

  By viral regulatory proteins interacting with host factors
• What happens during the release phase of viral infection?

  Viruses may be released by cell lysis or budding
• Can all released viral particles be infectious?

  No, not all are infectious
• What is the prion theory?

  It suggests agents devoid of nucleic acid
• What happens to PrPC after exposure to abnormal prion protein?

  It is altered post-translationally
• What do prions target in the body?

  Neurons
• What is the incubation period for prion diseases?

  Relatively long
• What diseases are caused by prions?

  Scrapie, BSE, and chronic wasting disease
• What is Bovine spongiform encephalopathy commonly known as?

  Mad-cow disease
• What is chronic wasting disease associated with?

  Mule deer