Viruses Flashcards
How do viruses differ from life forms? (4)
-no functional organelles
-cannot produce their own energy/macromolecules
-metabolically inert outside of the host cell
-do NOT multiply by binary fission (can only replicate/survive within a host cell)
Obligate Intracellular Parasites
Ie. Viruses —> can only replicate/survive within a host cell
Are viruses alive? How do we know?
Yes: they can replicate within a cell, can be inactivated/denatured, and possess + replicate genes/simple genomes
- however, they require host symbiosis (are obligate parasites)
Death of cell is called
Lysis
Replication of the virus within a host cell results in:
Lysis (death of cell) which results in disease
What are the structural components of viruses?
-Nucleic Acid (RNA or DNA - not both)
-Surrounded by the Capsid (protein coat)
Some viruses may also contain:
-Lipid Envelope that contains Membrane Glycoprotein (recognition of host cell)
How big are viruses?
20-300nm (ie. VERY small
- requires an electron microscope to see)
Three types of “Giant Viruses” that have been discovered in amoeba:
- Mimivirus
- Pandoravirus
- Pithovirus
What structural component gives a virus its shape?
The Capsid
How many virus shapes are there?
Three
What are the three types of Virus shape? Describe them and give an example.
- Helical: capsid is cylindrical or “rod shaped”. May or may not have an envelope ex. Rhabdo Viruses (rabies) or Filoviruses (Ebola)
- Icosohedral: capsid is dimensional and somewhat round. May have an envelope ex. Retrovirus (feline leukemia) or NO envelope ex. Parvovirus
- Complex: capsid is a more complex arrangement, can be a combination of helical or icosohedral ex. Pox virus and bacteriophages
Virus nucleic acid contains either _____ or _____ and can be further classified as _____ or _____
DNA; RNA Linear; Circular
DNA / RNA in viruses can be _____ or _____ stranded
Single or double stranded
Example of DNA Linear Single Strand Virus
Parvovirus
Example of DNA Linear Double Stranded Virus
Herpesvirus
Example of DNA Circular Single Stranded Virus
M13
Example of DNA Circular Double Stranded Virus
Baculovirus
Example of RNA Linear Single Stranded Virus
TMV
Example of RNA Linear Double Stranded Virus
Reovirus
Example of RNA Circular Single Stranded Virus
Hepatitis D
Example of RNA Circular Double Stranded Virus
Trick: does not exist
Most viruses possess what type of genome
Single Stranded RNA
How do viruses recognise host cells?
Surface cell receptors
How do viruses infect their host (simplest terms)
Virus recognizes host cell through surface cell receptors; virus enters cell, sheds shell, and releases protein; virus takes cell’s energy (cell is often destroyed and bursts); virus moves on to a new cell
Viruses are classified into groups based on what criterion?
-type of nucleic acid (DNA or RNA?)
-shape of capsid (helical or icosahedral or complex?)
-envelope present or not?
-replication strategy
-genome sequence and organization
-other criteria (size, pH sensitivity, host range)
Virus species name is often just
The name of the disease. Example: Rabies Virus causes Rabies
How is the taxonomical naming of viruses different from other organisms
Viruses show only the species name, not the genus name
Viruses can be named after the place where they were first isolated. Give two examples.
-Hendra Virus
-Newcastle Disease Virus
Similar to other organisms, viruses are classified into:
-Family
-Genus
-Species
What are three virus evolution theories? What are some problems associated with each theory?
- Viruses are escaped pieces of host cell DNA (ie. escaped cell and evolved as its own entity)
-Does not work for full virus genomes (ie. viruses with more than one gene) - Viruses are degenerate unicellular life forms (ie. viruses were once cells but overtime lost certain genes that weren’t needed)
-Does not work as the viral genome sequence does not resemble the genome sequence of unicellular life - Viruses originated independently from host replication systems, with several separate viral origins occurring at different times (ie. Viruses evolved alongside cells)
Describe the best supported theory on how Viruses may have evolved
Viruses originated independently from complex molecules of protein and nucleic acid, evolving alongside their hosts. Several separate viral origins
Why are viruses so difficult to track from an evolutionary standpoint?
-Viruses leave no geological fossils
-Viruses have a huge range of diversity, indicating multiple ancestors
How are Henipaviruses transmitted? What species are affected?
-Fruit bats (flying foxes) are a reservoir host of Henipaviruses
-Transmitted to horses as Hendra Virus
-Transmitted to pigs as Nipah Virus
-ZOONOTIC
Why are viruses labelled as “important infectious diseases”
-quickly occurring mutation leading to increased virulence and expanded host range
-disrupts ecosystems
