Micro Lecture Exam 2

• What is a virus?

  an acellular entity containing genetic information and a protein coat surrounding
• How do viruses infect cells?

  Bacteriophage and plaque
• What is a Virion?

  an entire virus particle with a capsid (protein shell) and a core of nucleic acid (RNA/DNA)
• What is the intracellular replication complex?

  a process in which a virus forces a host cell to work for it instead of for the host (pirate)
• What is integration?

  when the virus becomes part of the cell genome and the cell replicates the virus genome along with its own
• What is a Viral Shunt?

  prevents microbial particulate organic matter from traveling up trophic levels (recycles and sets the boundaries)
• What is a Host Range?

  the range of hosts that are subject to infection by virus (Narrow: HIV)(Broad: West Nile)
• Are viruses the same throughout all domains?

  NO, they are different across domains
• Why is chronic viral disease hard to treat?

  The viruses use our own cell components so we cannot remove them without harming ourselves.
• What two goals does the virus structure allow it to achieve?

  Virus Genome remains intact and is able to infect a host cell
• What is the function of a capsid?

  protects the nucleic acids from degradation and acts as a transport mechanism
• What is the meaning of Icosahedral/an example?

  a 20-sided virus/ herpes
• What does Filamentous mean?

  helical (ebola/TMV)
• What is the advantage of having symmetry as a virus?

  allows for use of repeating subunits that allow for genome space to be saved (each subunit is encoded by the same genes)
• Where can one sometimes find a capsid?

  inside an envelope composed of host cell membrane
• What do Spike proteins do?

  attach envelope to capsid and facilitate attachment of virus to host cell
• What is a Tegument?

  area between the capsid and envelope (may contain proteins)
• What is the structure of a Filamentous virus?

  • simple capsid of protein monomers that form helical tube around genetic material
  • genetic material = RNA or DNA
  • vary in size to accommodate different lengths of nucleic acids
• What are the parts on a virus?

  -genome

  -collar/neck

  -tail sheath

  -baseplate

  -tail fibers
• What is an example of an asymmetrical viral particle?

  Vaccina poxvirus
• What contains a complex structure and nucleic acid delivery service?

  Tailed Viruses
• What is a viroid?

  -nucleic acid genome is the infectious particle

  -NO protein coat

  -most are RNA and infect plants

  -potato spindle tuber (circular, single stranded RNA)
• What is a prion?

  an infectious agent consisting of proteins ONLY (no nucleic acids)
• What virus type is unaffected by treatments meant to destory nucleic acids? (i.e. UV radiation/Nucleases)

  Prions
• What is the function of a protein in a prion in an abnormal confirmation?

  it binds to a normally folding protein of the same class and alters the conformation of those proteins (misfolding)
• Why is protein misfolding, caused by prion proteins, detrimental to the host cell?

  -leads to formation of harmful aggregates that disrupt the cell function, causing death.

  -host can become infected with an aberrant protein

  -misfolding can then occur in host cell
• Characteristics of Viral Genomes?

  -Range greatly in size

  -fewer necessary genes (capsid, enzyme, envelope proteins)
• How is a larger viral genome organized? Example?

  -more like a bacterial genome

  -Mimi virus: believed to have evolved from intracellular parasitic bacterium
• What are the five classifications of Viruses?

  -Genome composition

  -Capsid Symmetry

  -Envelope

  -Size of virus particle

  -Host Range
• What are the steps in which a virus must take to infect a host?

  -host recognition and attachment

  -genome entry

  -assembly of virions

  -exit and transmission
• How does a virus recognize the host and attach?

  -through the use of cell surface receptors

  -viruses adapted to bind to the protein and use it to access the cell (Phage Lambda and maltose)
• What is the function of phage reproduction?

  insert nucleic acids through the cell envelope while the capsid remains on the outside of the cell (ghost capsid)
• What are the steps of the Lytic cycle?

  Attachment, injection, replication, expression, lysis
• In lytic cycle: what happens to the phage genome?

  it is injected into the host cell
• In lytic cycle: how is the virus genome replicated after injection?

  -it uses the host cell machinery to reproduce phage particles

  -replicating phage genomes

  -expressing phage mRNA to make enzymes and capsids
• In lytic cycle: what happens when the host cell lyses?

  -New phage particles are released
• In lytic cycle: what steps are taken before host cell lyses?

  -viral genomes expressed by host cell RNA polymerase and ribosomes are used to make proteins

  -phage genome is replicated

  -capsid proteins are produced

  -capsid proteins assemble into the capsid and package the newly replicated phage genomes
• What is burst size?

  number of virus particles released following cell lysis
• What can happen with temperate phages in Lysogeny?

  they can be integrated into the host cell genome
• What are the steps of Lysogeny?

  1. upon entry, the linear DNA circularizes
  2. genome recombines into host cell @ site specific recombination of DNA
  3. when host replicates its own DNA, it will replicate the integrated viral DNA as well
  4. prophage directs its own excision from the host genome
  5. DNA will circularize and enter into the lytic cycle (triggered by environmental conditions