Download Top ten most dangerous viruses in the world

Chapter 24 – 1 Answers
VOCABULARY REVIEW
1. Virus - an infective agent that typically consists of a nucleic acid molecule in a protein
coat, is too small to be seen by light microscopy, and is able to multiply only within the
living cells of a host.
2. Capsid - the coiled or polyhedral structure, composed of proteins, that encloses the
nucleic acid of a virus.
3. Retrovirus - any of a family of single-stranded RNA viruses having a helical envelope
and containing an enzyme that allows for a reversal of genetic transcription, from RNA to
DNA rather than the usual DNA
4. Lytic Cycle - The lytic cycle is the process in which a virus overtakes a. cell and uses the
cellular machinery of its host to reproduce.
5. Lysogenic Cycle - one of the two alternative life cycles of a virus inside a host cell,
whereby the virus that has infected a cell attaches itself to the host DNA and, acting like
an inert segment of the DNA, replicates when the host cell divides. This method of
replication is contrasted with the lytic cycle, whereby the virus that has entered a cell
takes over the cell's replication mechanism, makes viral DNA and viral proteins, and
then lyses (breaks open) the cell, allowing the newly produced viruses to leave the now
disintegrated host cell to infect other cells. While the lysogenic cycle causes no harm to
the host cell
MULTIPLE CHOICE
1.
2.
3.
4.
5.
D
C
D
C
C
SHORT ANSWER
1. The work of Wendell Stanley suggested that viruses are made of made of DNA or RNA
surrounded by a protein coat.
2. Many viruses become virulent due to opportunistic conditions. Radiation or certain
chemicals can cause a prophage to become virulent.
3. Infection of a host cell requires that the cell have a surface protein that can serve as a
receptor for the envelope protein of the retrovirus. The envelope protein of HIV-1 binds
to CD4 molecules.
4. Flu viruses are constantly changing, and different flu viruses circulate and cause illness
each season. Flu vaccines are made each year to protect against the flu viruses that
have changed. In addition, a person's immune protection from vaccination declines over
time.
5. This DNA then integrates into the DNA of the host cell. It then either undergoes the lytic
cycle, where it makes the cell produce copies of the phage and then explode, releasing
more; or it does the lysogenic cycle, where the DNA integrates, and then goes dormant,
not to be activated for phage replication until the cell is stressed a certain way.
This is great for genetic engineering because you can alter the phage to include what
DNA you want integrated into the host cell. The phage will then perform the
transformation of DNA for you. This process is called transduction.
STRUCTURES AND FUNCTIONS.
C.
A.
E.
D.
B.
Viruses of the lytic cycle are called virulent viruses. The lytic cycle is a five-stage cycle.
Attachment. The virus first attaches itself to a specific host cell. In the case of the T4
phage, a commonly studied bacteriophage that infects the bacterium Escherichia coli,
this attachment is done by the tail fibers of the virus having proteins that have an affinity
with the host cell wall. The virus attaches at places called receptor sites (Towle 1989). A
virus also may attach by simple mechanical forces.
Penetration. To infect a cell, a virus must first enter the cell through the plasma
membrane and (if present) the cell wall. It then releases its genetic material (either
single- or double-stranded RNA or DNA) into the cell. In the case of the T4 phage, after
attachment to the host cell, the virus first releases releases an enzyme that weakens a
spot in the cell wall of the host (Towle 1989). The virus then injects its genetic material
much like a hypodermic needle, pressing its sheath up against the cell and injecting its
DNA into the host cell through the weak spot in the cell wall. The empty capsid stays on
the outside of the host cell. Other viruses enter their host cell intact, and once inside the
capsid dissolves and the genetic material is released; this process is known as
uncoating (Towle 1989). Once the virus has infected the cell, it also can be targeted by
the immune system.
Replication. The virus' nucleic acid uses the host cell’s machinery to make large
amounts of viral components, both the viral genetic material (DNA or RNA) and the viral
proteins that comprise the structural parts of the virus. In the case of DNA viruses, the
DNA transcribes itself into messenger RNA (mRNA) molecules that are then used to
direct the cell's ribosomes. One of the first polypeptides to be translated is one that
destroys the hosts' 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. In the case of the T4 phage, the E. coli DNA is inactivated
and then the DNA of the viral genome takes over, with the viral DNA making RNA from
nucleotides in the host cell by using the enzymes of the host cell.
The replication is often (for example, in T4) regulated in three phases of mRNA
production followed by a phase of protein production (Madigan and Martinko 2006). In
the early phase, the enzymes involved modify the hosts DNA replication by RNA
polymerase. Among other modifications, virus T4 changes the sigma factor of the host
by producing an anti-sigma factor so that the host promotors are not recognized any
more but now recognize T4 middle proteins. In the middle phase, the virus nucleic acid
is produced (DNA or RNA depending on virus type). In the late phase, the structural
proteins are produced, including those for the head and the tail.
Assembly. After many copies of viral components are made, they are assembled into
complete viruses. In the case of the T4 phage, proteins coded for by the phage DNA act
as enzymes for construction of the new phages (Towle 1989). The entire host
metabolism is directed toward this assembly, resulting in a cell filled with new viruses.
Lysis. After assembly of the new virus particles, an enzyme is produced that breaks
down the bacteria cell wall from within and allows fluid to enter. 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 and
start the process again.
24-2 VIRAL DISEASES
VOCABULARY REVIEW
1. Inactivated virus - Vaccines are made using several different processes. They may
contain live viruses that have been…
2. attenuated (weakened or altered so as not to cause illness); inactivated or killed
organisms or viruses; inactivated toxins (for bacterial diseases where toxins
generated by the bacteria, and not the bacteria themselves, cause illness); or merely
segments of the pathogen (this includes both subunit and conjugate vaccines).
3. oncogene - a gene that has the potential to cause cancer. In tumor cells, they are
often mutated or expressed at high levels.
MULTIPLE CHOICE
1. A
2. D
3. B
4. C
5. A
SHORT ANSWER
Top ten most dangerous viruses in the world
1. The most dangerous virus is the Marburg virus. It is named after a small and idyllic town
on the river Lahn - but that has nothing to do with the disease itself. The Marburg virus
is a hemorrhagic fever virus. As with Ebola, the Marburg virus causes convulsions and
bleeding of mucous membranes, skin and organs. It has a fatality rate of 90 percent.
2. There are five strains of the Ebola virus, each named after countries and regions in
Africa: Zaire, Sudan, Tai Forest, Bundibugyo and Reston. The Zaire Ebola virus is the
deadliest, with a mortality rate of 90 percent. It is the strain currently spreading through
Guinea, Sierra Leone and Liberia, and beyond. Scientists say flying foxes probably
brought the Zaire Ebola virus into cities.
3. The Hantavirus describes several types of viruses. It is named after a river where
American soldiers were first thought to have been infected with the Hantavirus, during
the Korean War in 1950. Symptoms include lung disease, fever and kidney failure.
4. The various strains of bird flu regularly cause panic - which is perhaps justified because
the mortality rate is 70 percent. But in fact the risk of contracting the H5N1 strain - one
of the best known - is quite low. You can only be infected through direct contact with
poultry. It is said this explains why most cases appear in Asia, where people often live
close to chickens.
5. A nurse in Nigeria was the first person to be infected with the Lassa virus. The virus is
transmitted by rodents. Cases can be endemic - which means the virus occurs in a
specific region, such as in western Africa, and can reoccur there at any time. Scientists
assume that 15 percent of rodents in western Africa carry the virus.
6. The Junin virus is associated with Argentine hemorrhagic fever. People infected with the
virus suffer from tissue inflammation, sepsis and skin bleeding. The problem is that the
symptoms can appear to be so common that the disease is rarely detected or identified
in the first instance.
7. The Crimea-Congo fever virus is transmitted by ticks. It is similar to the Ebola and
Marburg viruses in the way it progresses. During the first days of infection, sufferers
present with pin-sized bleedings in the face, mouth and the pharynx.
8. The Machupo virus is associated with Bolivian hemorrhagic fever, also known as black
typhus. The infection causes high fever, accompanied by heavy bleedings. It progresses
similar to the Junin virus. The virus can be transmitted from human to human, and
rodents often the carry it.
9. Scientists discovered the Kyasanur Forest Virus (KFD) virus in woodlands on the
southwestern coast of India in 1955. It is transmitted by ticks, but scientists say it is
difficult to determine any carriers. It is assumed that rats, birds and boars could be
hosts. People infected with the virus suffer from high fever, strong headaches and
muscle pain which can cause bleedings.
10. Dengue fever is a constant threat. If you're planning a holiday in the tropics, get
informed about dengue. Transmitted by mosquitoes, dengue affects between 50 and
100 million people a year in popular holiday destinations such as Thailand and India. But
it's more of a problem for the 2 billion people who live in areas that are threatened by
dengue fever.
2. Chickenpox and shingles are two diseases that are both caused by the varicella-zoster
virus. People who have been sick with chickenpox are also at risk for shingles. Initial
exposure to the varicella-zoster virus usually occurs during childhood and causes
chickenpox. The chickenpox symptoms resolve, but the virus remains resident and can
reactivate later in life, causing shingles. Vaccinations are available for both chickenpox
and shingles.
3. VIRAL CONTROL
a. Immunoprophylaxis against viral illnesses includes the use of vaccines or
antibody-containing preparations to provide immune protection against a specific
disease.
b. Active Prophylaxis (Vaccines) - Active immunization involves administering a
virus preparation that stimulates the body's immune system to produce its own
specific immunity. Viral vaccines now available for use include the following
types: (1) attenuated live viruses; (2) killed viruses; (3) recombinant produced
antigens. A vaccinee is a person who has been vaccinated.
c. Immune Response to Vaccines: Vaccination evokes an antibody response and
stimulates T lymphocytes. Vaccine effectiveness is assessed in terms of
percentage of recipients protected and the duration and degree of protection.
Most effective viral vaccines protect more than 90 percent of recipients and
produce fairly durable immunity.
d. Passive Prophylaxis - Passive immunity is conferred by administering antibodies
formed in another host. Human immunoglobulins remain a mainstay of passive
prophylaxis (and occasionally therapy) for viral illnesses; they are usually used to
protect individuals who have been exposed to a disease and cannot be protected
by vaccination.
e. Sanitation and Vector Control - Many viral diseases are controlled by reducing
exposure to the virus by (1) eliminating nonhuman reservoirs, (2) eliminating the
vector, and (3) improving sanitation.
f. Antiviral Chemotherapy - There are three types of antiviral agents: (1) virucidal
agents, which directly inactivate viruses, (2) antiviral agents, which inhibit viral
replication, and (3) immunomodulators, which boost the host immune response.
g. Interferons Virus-infected cells and cells induced with other agents, e.g., doublestranded polynucleotides, can secrete proteins called interferons, which protect
normal cells from viral infection. Therapeutic administration of interferon alpha
has proven effective for several human viral illnesses.
h. Cytokines - Cytokines are molecules produced by cells which modify the
biological responses of the same or other cells.
4. Cancers occur when the genetic material within cells, the cells' DNA, develops mutations
that cause the cell to divide uncontrollably. These mutations sometimes arise when the
DNA is damaged. However, viruses can have effects similar to these mutations when
they insert themselves into the DNA, and the end result is the same – uncontrolled cell
growth. Two types of human papillomaviruses (HPV) are thought to cause cervical
cancer this way.
5. If individuals from a community venture into a previously undeveloped forest, they may
encounter an animal that harbors a previously unknown virus. If these individuals
become infected, they can carry this infection to their community
6. Viruses (retroviruses) use have RNA that is reverse transcribed into DNA and ligated
into the host genome. Now if you develop a drug that attacks the transcriptional
machinery of the cell, you will most likely kill the host also because you are targeting the
enzyme RNA polymerase. As a result, you will be killing off both the virus and host cell
in the process. Which you do not want. You want to kill the viruse only. You can target
the reverse transcriptase enzyme, which will kill the virus, but not the host.
STRUCTURES AND FUNCTIONS
A. PROTEIN SPIKES
B. RNA
C. REVERSE TRANSCRIPTASE ENZYME
D. ENVELOPE
E. CAPSID