Viruses “Scavenger Hunt”
Today, you will learn all about viruses by visiting various stations around the classroom while
using a worksheet to guide you. For each question, go to the assigned website/read the
article/watch the video and use the information to help you fill in the worksheet.
1. The Basics of a Virus – “What is a Virus? What is a Viral Infection?”
Article from:
a) What is the definition of a virus?
A virus is a microscopic organism consisting of genetic material surrounded by a protein,
lipid, or glycoprotein coat.
b) Where does this term come from?
Some microbiologists classify viruses as microorganisms, while others don't because they are
"nonliving" and describe viruses as microscopic infective agents.
c) The diagram on the below illustrates one type of virus (influenza). State the three general
components of a virus and describe it’s function. Label them on the diagram on the right.
Genetic Material
d) How can and do viruses spread (list four ways)?
Viruses may spread vertically (from mother to child) or horizontally (from person to person). Some
viruses can spread by simple contact, exchanges of saliva, coughing, or sneezing. Some require
sexual contact, while others go through the fecal-oral route via contaminated food or water. Still
other viruses require an insect like a mosquito to carry the virus from person to person.
2. Characteristics of a Virus – “What are the Essential Characteristics of Viruses?”
Article from:
a) List three non-living characteristics of a virus.
(1)They can be crystallized. (2)Outside the cell, they behave like inert chemicals. (3)They do not show
growth, development, nutrition, reproduction, etc.
b) List four living characteristics of a virus.
(1) They multiply within host cells. (2)They possess genetic material, either DNA or RNA. (3)There
are definite races or strains. (4) They exhibit mutations.
c) Based on the above characteristics, do you think viruses are living or non-living entities?
Explain. For me some viruses are non-living and living entities, because some viruses have
other characteristics and some have others. Some viruses have characteristics to be non-living
entities, other have others characteristics to be living entities.
3. Virus Morphology – “Four Shapes”
Article from:
Shape of Virus
Icosahedral virus
Diagram of Virus
Example of Virus
These viruses
possess a capsid that
is neither purely
helical, nor purely
icosahedral, and may
possess extra
structures such as
protein tails or a
complex outer
wall. Bacteriophages
have a complex
structure consisting of
an icosahedral head
bound to a helical tail
via a protein collar,
and a hexagonal base
plate with many
protein tail fibers
protruding from it.
Icosahedral capsid
symmetry results in a
spherical appearance
of viruses at low
magnification, but
consists of capsomers
arranged in a regular
geometrical pattern,
much like
a soccer ball, hence
they are not truly
Helical Ebola virus
Helical capsids are
composed of a single
type of protomer
stacked around a
central circumference
to form an enclosed
tube resembling a
spiral staircase. This
arrangement results in
rod-shaped virions
that can be short and
rigid, or long and
The Marburg virus
attracted widespread
press attention for an
outbreak in Angola.
Beginning in October
2004 and continuing
into 2005, the
outbreak was the
world's worst
epidemic of any kind
of hemorrhagic fever.
Marburg virus
4. Virus Reproduction: Basic reproduction (virus without envelope), The Lytic Cycle (for
bacteriophages) & The Lysogenic Cycle
4a. Virus Reproduction: BASIC REPRODUCTION
The diagram on the left shows the simplest viral reproductive
cycle of a virus. This occurs in viruses that do not have an
envelope. Use the following letters and descriptions to label the
A. Host enzymes transcribe the viral genome into viral mRNA,
which other hosts enzymes use to make more viral proteins.
B. Virus enters cell and is uncoated, releasing viral DNA and
capsid proteins.
C. Host ribosomes translate viral mRNA into capsid proteins.
D. Viral genomes and capsid proteins self-assemble into new virus
particles, which exit the cell.
E. Host enzymes replicate the viral genome.
4b. Virus Reproduction: LYTIC CYCLE
The Lytic Cycle is a viral reproductive cycle, during which a virus takes over all metabolic
activities of a cell and causes the host cell to die. Bacteriophages that ONLY reproduce using
the lytic cycle are called a virulent phages.
As you watch the video, write down the name of each stage, and describe what is happening in
each stage in point form.
Stage of Lytic Cycle
1. Penetration
2. Biosynthesis
3. Gene regulation
Description of Stage of Lytic Cycle – What is happening?
To infect a cell, a virus must first enter the cell through the plasma
membrane and (if present) the cell wall. Viruses do so by either attaching to
a receptor on the cell's surface or by simple mechanical force. The virus then
releases its genetic material (either single- or double-stranded RNA or DNA)
into the cell. In doing this, the cell is infected and can also be targeted by the
immune system.
The virus' nucleic acid uses the host cell’s machinery to make large amounts
of viral components. In the case of DNA viruses, the DNA transcribe itself
into messenger RNA (mRNA) molecules that are then used to direct the cell's
ribosomes. One of the first polypeptides to be translated destroys the host's
DNA. In retroviruses (which inject an RNA strand), a unique enzyme
called reverse transcriptase transcribes the viral RNA into DNA, which is then
transcribed again into RNA. Once the viral DNA has taken control it induces
the host cell's machinery to synthesize viral DNA, protein and starts
multiplying. About 25 minutes after initial infection, approximately 200 new
bacteriophages are formed and the bacterial cell bursts i.e. it has undergone
lysis. Newly formed phages are released to infect other bacteria and another
lytic cycle begins. The phage which causes lysis of the host is called a lytic or
virulent phage. The biosynthesis is (e.g. T4) regulated in three phases of
mRNA production followed by a phase of protein production.
There are three classes of genes in the phage genome that regulate whether
the lytic or lysogenic cycles will emerge. The first are the immediate early
genes, the second is the delayed early genes and the third is the late genes.
1. Immediate early genes: These genes code for two transcription
factors: N and cro. N is an anti-termination factor that is needed for
the transcription of the delayed early genes. cro has two functions.
The first function is to repress the activity of the repressor that is
needed to go into lysogeny. Note that a repressor coded by
the CI gene is needed to repress the lytic cycle from taking place.
The second function of cro is to initiate the transcription of the late
genes needed for the lytic cycle to go to completion.
2. Delayed early genes: The immediate early gene N is required to
express the delayed early genes. In lytic cells, the delayed early
gene which is most important is Q. These genes are also used to
express late genes.
3. The repressor: The repressor is needed to repress the lytic cycle for
lysogeny to proceed. It has 2 N domains that bind the DNA via a
helix turn helix motif and 2 C domains that dimerize to stabilize the
4. Maturation
5. Lysis
Lysis inhibition: T4-like phages contain a gene called rI which can
delay completed phage progeny from exiting an impregnated cell by
suppressing the expression of holin gene products usually up to four
hours in exponential phase growing cultures in rich media. Deletion
of rI cancels the inhibition effect. This is only observed when higher
concentrations of extracellular T4 phage particles are present.
After many copies of viral components are made, they are assembled into
complete viruses.
The phage then directs production of lysin, an enzyme that breaks down the
bacterial cell wall, which allows extracellular fluid to enter the cell. The cell
eventually becomes filled with viruses (typically 100-200) and liquid, and
bursts, or lyses; thus giving the lytic cycle its name. The new viruses are then
free to infect other cells.
4c. Virus Reproduction: LYSOGENIC CYCLE
Watch: and Textbook Printout
The Lysogenic Cycle is another type of viral reproductive cycle in which the genome of the
phage is replicated without destroying the host. Phages capable of using both modes of
reproduction (lytic and lysogenic) are referred to as temperate phages.
a) During the lysogenic cycle, the phage genome is mostly silent within the bacteria. Why?
b) What determines whether or not the lytic cycle or lysogenic cycle is entered?
It is determined by the receptor site on the cell and the success of the previous process.
5. The Immune System of Bacteria – Why haven’t phages exterminated all bacteria?
Article from:
a) What are restriction endonucleases (restriction enzymes) and what do they do?
Restriction endonucleases (often referred to as restriction
enzymes) act as a kind of immune system, protecting the cell from
the invasion of foreign DNA, as would occur when a virus
attempted to infect a bacterial cell. These restriction
endonucleases provided biologists with a tool to study and
manipulate DNA by enabling the generation of consistently sized
DNA fragments. They are now used for a wide range of
applications, including cloning, Southern hybridization analysis,
DNA sequencing and global gene expression analysis (SAGE).
b) List two reasons why phages haven’t exterminated all bacteria despite the fact that they
are capable of reproducing using the lytic cycle.
Bacteriophages were incubated with the different strains of E. coli
and the ability of the bacteriophage to kill the E. coli cells was
monitored. A bacteriophage will normally cause an infected bacterial
cell to break open, killing the cell, while releasing millions of
bacteriophage that had replicated within the cell. When bacteriophage
spilling out of E. coli strain B cells were isolated, they were found to
be very successful at re-infecting E. coli strain B cells. But when these
bacteriophages were incubated with E. coli strain K, it was found that
only a few of the bacteriophage could manage to replicate.
6. Viral Infections – “What is a Viral Infection?”
Article from:
Viruses are very specific. That is, they only infect a very limited range of species and target
certain organs and cells. These specific species/organs/cells are referred to the virus’ host
range. Using the information found on this website, fill in the following chart for the given
Name of Virus
Organism, Tissue, Organ, or
System Affected
Measles is an endemic disease;
meaning it is continually present in a
community and many people develop
resistance. If measles enters an area
where the people have never been
exposed the result can be devastating.
Nervous system
How it Affects the Organism,
Tissue, Organ or System
By infested with tapeworms.
The patient will generally feel a
tingling sensation in the affected area
at first. This will be followed by pain,
and then a rash.
Constricts the respiratory system.
Respiratory system
7. Case Study – HIV/AIDS (for homework – do your own research!)
Label the following parts of the HIV virus.
b) Why is HIV called a retrovirus?
Because of its syntoms their classification its there.
c) Fill in the following chart using point form notes.
History of HIV
Both HIV-1 and HIV-2 are believed to
have originated in non-human primates
in West-central Africa and to have
transferred to humans (a process
known a zoonosis) in the early 20th
century. HIV-1 appears to have
originated in southern Cameroon
through the evolution of SIV(cpz), a
simian immunodeficiency virus (SIV)
that infects wild chimpanzees (HIV-1
descends from the SIVcpz endemic in
the chimpanzee subspecies Pan
troglodytes troglodytes).The closest
relative of HIV-2 is SIV (smm), a virus
of the sooty mangabey (Cercocebus
atys atys), an old world monkey living
in litoral West Africa (from southern
Senegal to western Côte d'Ivoire). New
World monkeys such as the owl
Transmission of the HIV Virus and
Sexual transmission. It can happen
when there is contact with infected
sexual secretions (rectal, genital or oral
mucous membranes). This can happen
while having unprotected sex, including
vaginal, oral and anal sex or sharing sex
toys with someone infected with HIV.
Perinatal transmission. The mother
can pass the infection on to her child
during childbirth, pregnancy, and also
through breastfeeding. Blood
transmission. The risk of transmitting
HIV through blood transfusion is
nowadays extremely low in developed
countries, thanks to meticulous
screening and precautions
monkey are resistant to HIV-1 infection,
possibly because of a genomic fusion
of two viral resistance genes. HIV-1 is
thought to have jumped the species
barrier on at least three separate
occasions, giving rise to the three
groups of the virus, M, N, and O.
Treatment of HIV/AIDS
Emergency HIV pills. If an individual
believes they have been exposed to the
virus within the last 72 hours (three
days), anti-HIV medication, called PEP
(post-exposure prophylaxis) may stop
infection. Antiretroviral drugs. HIV is
treated with antiretrovirals (ARVs). The
treatment fights the HIV infection and
slows down the spread of the virus in
the body.
System/Cell Affected and How
This may affect the eyes,the lung and by
tumors, esophagitis, tubercolosis, retinitis.
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