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Portage Learning BIOD 171 Module 6 (1)
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Portage Learning BIOD 171 Module 6 (1)
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Portage Learning BIOD 171 Module 6True or False: viruses can be classified as prokaryotic or eukaryotic - ANS-False. Viruses are
neither prokaryotic or eukaryotic
What is an obligate intracellular parasite? - ANS-viruses cannot replicate unless inside a living
host cell. As a parasite, a virus depends on its living host to provide the framework (proteins,
etc) to replicate—to make additional copies of itself.
What is a viral capsid? - ANS-a membrane-like protective structure that contains genetic
material similar to nucleus of eukaryotic cells.
What is the viral envelope, and what does the presence (or absence) of it tell you about the type
of virus? - ANS-The envelope surrounds the viral capsid, is derived from the host cell membrane
and serves as an additional barrier to the external environment. The overwhelming majority of
animal viruses are enveloped whereas the majority of plant or bacteria-infecting viruses are not.
What type of microscope would be used to study the shape of a viral capsid? - ANS-Due to its
size (~30-150 nm) most viral capsids must be visualized via electron microscopy.
How does the viral envelope both aid in cell entry as well as hide it from being detected by the
immune system? - ANS-The viral envelope contains the necessary proteins required for
interaction with host cells. As the envelope is derived from the host cell membrane, this
camouflages the virus and lowers the likelihood of immune detection by making it appear similar
to the normal biological host cell.
What must happen before viral replication of its genome can occur? - ANS-For all viruses, the
genome is replicated following attachment and entry, never before.
Describe the basic steps of the viral life cycle. - ANS-1. Attachment: Viral receptors bind to host
proteins on the surface of the cell.2. Entry: The virus fuses with the host membrane and enters
the cell3. Uncoating: (where applicable) the viral capsid disassembles4. Replication: The viral
genome provides the 'blueprint' to make copies of itself5. Exit: New viruses are produced and
leave the cell6. New infection: Newly produced viruses leave the host cell and go on to infect
new cells. The process outlined above now restarts.
What is a bacteriophage? - ANS-A virus that infects bacteria
What structural aspects make bacteriophages distinct from viruses that infect either animals or
plants? - ANS-Bacteriophages possess an icosahedral capsid head group and a helical tail.
Attached to the tail are fibrous extensions or 'legs' that aid in binding host cells. Notably, this
, particular structural arrangement has not been observed among viruses that infect either
animals or plants.
Which viral replicative process results in the destruction of the host cell? - ANS-The lytic
replication cycle occurs when a bacteriophage replicates within a host until it ruptures,
effectively destroying the host bacterial cell. The phrase lytic stems from 'lysis', meaning to
rupture or disintegrate (breakdown) a cell.
Describe the appearance of a bacterial culture infected with virus at the time of infection versus
later once viral replication is occurring at a high rate. - ANS-During the initial inoculation of virus
and bacteria, the media has a high degree of turbidity (cloudiness). However, as the lytic cycle
progresses and more and more bacterial cells are destroyed, the culture media turns from turbid
to clear, as turbidity is a function of the number of intact bacterial cells present in the media.
Thus, as bacterial cell numbers decrease due to lysis, the media becomes clearer.
To what family of viruses does rubella come from and how is it transmitted? - ANS-Rubella virus
belongs to a family of viruses called Togaviridae. Rubella is transmitted via air-borne particles
such as when a person coughs.
What is the common name for rubeola, and is it a DNA or RNA virus? - ANS-Rubeola is
commonly referred to as the measles and belongs to the family of viruses called Paramyxovirus.
Rubeola viruses are RNA viruses with a genome ~ 15,000 nucleotides long.
What disease state emerges as a viral reactivation of a prior infection with the varicella virus? -
ANS-Shingles, also known as Herpes zoster, is due to the reactivation of the varicella-zoster
virus (VZV). Because VZV lies dormant in inactive nerve cells, its reactivation typically results in
painful blisters. However, unlike the initial chickenpox rash, the blisters are localized and limited
to small areas.
What linear, double-stranded, enveloped DNA virus is the first virus (as of October 26, 1977) to
be declared eradicated? - ANS-Although once a major cause of death in the world, a smallpox
vaccine was developed in 1796 by Edward Jenner. Global vaccination efforts have prevented
smallpox from appearing in humans since October 26, 1977, making smallpox the first infectious
disease ever to be eradicated.
What are the two key glycoproteins found in the influenza virus? - ANS-The viral envelope
contains two key glycoproteins, hemagglutinins (HA) and neuraminidase (N). Hemagglutinins
are heavily involved in the entry of the viral particle into a host cell, while neuraminidase
proteins are involved in the budding and release of new viral particles from the host cell.
Describe the composition of HIV. - ANS-HIV contains two copies of single-stranded, linear RNA
that is enclosed by a capsid. The conical capsid surrounds the two RNA strands and is
comprised of ~2,000 copies of the viral protein p24. A viral envelope derived from the cell host
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