Chapter 13: Viruses, Viroids, Prions

• what is a virus?

  a miniscule, acellular, infectious agent having either DNA or RNA
• State what a virus requires to function:

  - nucleic acid (RNA or DNA)

  - host to grow

  - capsid

  - envelope (some)
• What is the capsid composed of?

  protein subunits called capsomeres
• What is a capsid?

  protein coat surrounding a virus that provides protection for viral nucleic acid and means of attachment to host's cells
• what is the structure of a bacteriophage?

  Capsid, tail sheath, tail fibers, and base plate

  
• why are viruses host-specific?

  due to the affinity of viral surface proteins for complementary proteins on host cell surface
• what is a generalist virus?


  these infect many kinds of cells in many different hosts.
• where is the envelope acquired?

  from the host cell during viral replication or release
• what is an example of a virally coded glycoprotein?

  spike proteins
• what is the role of envelope proteins?

  host recognition
• what are virus reliant on from host cells?

  organelles and enzymes to produce new virions (replication)
• state the stages of the lytic replication cycle:

  - attachment

  - entry

  - synthesis

  - assembly

  - release
• do both eukaryotic and prokaryotic cells have a latent phase?

  no, only eukaryotic
• what stage of the lytic cycle determines the severity of the virus?

  attachment
• what are the different methods of the release stage of the lytic cycle?

  - lysis

  - budding
• what is lysogeny?


  nucleic acid gets incorporated into the host genome
• Why is lysogeny advantageous to a bacteriophage?

  the genetic material of the bacteriophage can be passed on to future generations of cells to change the phenotype of the bacteria
• what triggers the lytic cycle?

  stress
• what is the restriction/modification system?

  When host cells alter their own DNA(palindromic sites) by methylating it.

  Then when unmethylated DNA is introduced it can be degraded and the host cells aren't.
• What are palindromic sequences?


  Complementary strands, read the same back and fourth.
• What is CRISPR-Cas9?


  A system that allows precise genome editing by cutting out DNA and inserting new DNA in its place.
• what is the suicide system?

  occurs when the promoter up regulates lethal genes to misdirect the bacteriophage by accumulating phages and then killing the cell
• what is the function of the CAS protein?

  cuts viral DNA from phage and places it by repeated sequences of DNA
• what do cells with CAS-9 direct?

  a knockout of a specific gene
• State how China used the CRISPR system.

  - knocked out the gene for CCR5(a co-receptor) that HIV binds to in embryonic cells
• state differences of animal viruses:

  - some envelopes

  - eukaryotic cells

  - lack of cell wall
• state the different methods of entry of animal viruses?

  -bacteriophage

  - endocytosis

  - fusion with host membrane
• what is (+)ssRNA virus?

  positive single strand RNA virus that is "ready to go"
• what is (-) ssRNA?

  negative single stranded RNA that must be converted into a (+) ssRNA
• What is dsRNA?


  double stranded RNA
• where do most DNA virus assemble?

  nucleus
• where do most RNA viruses assemble?


  cytoplasm
• what does the formation of an envelope require?

  budding to "steal" host membrane
• what is the latency phase?


  virus remains dormant in host cells
• what are viroids?


  extremely small, circular pieces of RNA that are infectious and pathogenic in plants
• what do viroids lack?

  capsid
• what do viroids trigger?

  continuous rolling circle replication
• what are prions?


  Proteinaceous infectious particles
• what is cellular PrP protein?

  normal structure of alpha helices
• What is prion PrP?

  Prion PrP is disease causing and has beta sheets. It is anchored in lipid rafts which play a role in normal brain activity(mad cow disease).