Topic 5 - Viruses - Clickers Flashcards
How many capsomere proteins in an icosahedral capsid?
a) 20
b) 40
c) 60
d) 80
e) 100
c) 60
Explanation: An icosahedral capsid is composed of 60 identical capsomere proteins arranged symmetrically, minimizing genetic material use while maximizing stability.
Who coined the term “plaque”?
a) Antonie van Leeuwenhoek
b) Felix D’Heruelle
c) Donna Strickland
d) Carl Woese
e) Walter Reed
b) Felix D’Heruelle
Explanation: Felix D’Heruelle coined the term ‘plaque’ to describe clear zones formed by viral lysis of bacterial cultures.
What unique feature would you predict that viruses of Gram-positive bacteria would use for attachment?
a) D amino acids
b) Histones
c) Cellulose
d) Bactoprenol
e) Techoic acids
e) Techoic acids
Explanation: Teichoic acids are unique to Gram-positive bacteria and serve as specific attachment sites for certain bacteriophages.
Which is the best label to use for 😊?
a) nucleocapsid
b) prophage
c) bacteriophage
d) lysogen
e) integron
b) Prophage
Explanation: A prophage is the viral genome of a bacteriophage that has been integrated into the bacterial host’s DNA during the lysogenic cycle. In the diagram, 😊 represents the phase where the bacteriophage DNA has integrated into the bacterial chromosome and is replicating along with the host’s DNA, characteristic of a prophage.
The progressive hypothesis for the origin of viruses states that:
a) viruses evolved from mitochondria.
b) viruses evolved at the same time as their host cells.
c) viruses were once independent cells that became dependent on host cells.
d) genomic DNA gained the ability to replicate and transmit semi-autonomously.
d) genomic DNA gained the ability to replicate and transmit semi-autonomously.
Explanation: The progressive hypothesis suggests that viruses originated when genomic DNA or RNA gained the ability to replicate and transmit independently, evolving from mobile genetic elements within host cells.
Which statement is true? All…
a) viruses rely on host receptors for cell entry
b) viral genomes are linear
c) viruses can choose between lytic and lysogenic pathways
d) viruses must access the cell by membrane fusion or endocytosis
e) viruses are comprised of (at least) nucleic acid and protein
e) viruses are comprised of (at least) nucleic acid and protein
Explanation: All viruses contain genetic material (DNA or RNA) and a protein coat, making this a defining characteristic of viruses.
Which is the only method that offers an actual count of all viral particles?
a) Electron microscopy
b) Hemagglutination
c) Endpoint
d) Plaque assay
e) None - all generate titers
a) Electron microscopy
Explanation: Electron microscopy allows direct visualization and counting of all viral particles, both infectious and noninfectious, providing an actual count.
The plaque assay for determining viral titer measures:
a) the number of infected host cells.
b) all viruses including both infectious and noninfectious particles.
c) more than the number of virus particles present.
d) only infectious viral particles.
d) only infectious viral particles
Explanation: The plaque assay quantifies the number of infectious viral particles by counting plaques formed in a host cell monolayer.
The most reliable way to identify a virus is usually by:
a) host specificity
b) electron microscopy
c) nucleic acid analysis
d) the symptoms of the disease it causes
e) morphology of the virus
c) nucleic acid analysis
Explanation: Nucleic acid analysis is the most reliable method for identifying viruses as it provides specific genomic information unique to the virus.
Viroids and prions are not viruses.
a) True
b) False
a) True
Explanation: Viroids and prions lack key characteristics of viruses, such as a protein capsid or nucleic acid genome, and are considered distinct infectious agents.
Viroids can infect animals.
a) True
b) False
b) False
Explanation: Viroids are plant pathogens and do not infect animals. They consist of small, circular RNA molecules that interfere with plant gene expression.
Dimitri Ivanovski first discovered viruses.
a) True
b) False
a) True
Explanation: Dimitri Ivanovski is credited with the discovery of viruses in 1892 when he identified the tobacco mosaic virus as a non-bacterial infectious agent.
