Chapter 26 Viruses
Choose all the characteristics of acute viral infections.
-They involve rapid viral replication. -They result in the sudden symptom onset. -They often (although not always) establish at the site of infection.
What are the two main ways in which a virus can spread to infect secondary sites in the human body?
-Via neurological tissue -In blood or lymph
Place the steps of the HIV life cycle in order with the step following the introduction of the virus into the human bloodstream at the top.
1. The HIV gp120 glycoprotein attaches to the CD4 receptor of a CD4+ cell and one of two coreceptors. 2 Viral contents enter a CD4+ cell by endocytosis. 3 Reverse transcriptase synthesizes a double strand of DNA that is complimentary to the viral RNA.. 4 Genetic material from the virus enters the nucleus and is incorporated into the host genome by a viral enzyme. 5 Following a variable period of dormancy, the host cell machinery is directed to produce many copies of the virus. 6 Virus particles leave the host cell by budding.
During the acute phase of HIV infection, what is a typical load of viruses in the blood plasma?
5x10^6 virion ml
In the Baltimore classification there are how many groups of viruses and what are they separated based on
7 groups, separated based on how they replicate their genome
Viruses are unable to reproduce without which of the following?
A host cell
Which of the following is characteristic of the lytic cycle?
A large number of phages is released at a time.
Which of the following describes a virus?
A small biological particle comprised of nucleic acid enclosed in a protein coat
A(n) __ viral infection involves the rapid replication of the virus, often at the site of infection, which leads to sudden symptom onset.
Acute
When is the genome of HIV transcribed and translated to produce new RNA genomes, as well as proteins necessary for the assembly of new virions?
After the viral RNA has been copied into DNA and has integrated into a host chromosome
Which of the following statements are TRUE regarding archaeal viruses and bacteriophages?
Archaeal viruses are more diverse in their morphologies than bacteriophages. Both can have double-stranded DNA as their genome.
Which of the following best describes how a phage undergoes the lytic cycle?
Attachment, penetration, synthesis, assembly, release
Bacteria-infecting viruses are also known as which of the following?
Bacteriophage
Which of the following viruses uses the cellular machinery of a bacterium for its own replication?
Bacteriophage
The classification of viruses based on genome replication is known as the ---------classification after the scientist that first proposed it.
Baltimore
Why is it difficult to classify influenza viruses based on their host cell?
Because there are four types of influenza viruses that can infect many different hosts (humans, birds, pigs, dogs, cats)
Viruses that contain --- as their genetic material are often assigned to species group; the same is not true of viruses with --- as their genetic material
DNA, RNA
Viral genomes may be composed of __________ or __________ and may be _________ - stranded or _________- stranded.
DNA, RNA, Single, Double
Which of the following are symptoms associated with acute retroviral syndrome?
Diarrhea flu-like symptoms joint pain
virus sizes
Eukaryote - L;argest E. coli Influenza virus T2 virus protein
Choose all the conventional systematic groups that are also used to classify viruses
Family, Genus, Order
What is the effect of the initial acute disease episode after infection with an HSV-1 or HSV-2?
Formation of painful blisters at the site of infection
Most viruses have a capsid that is ------- or ----------- in terms of its basic structure and symmetry
Helical, icosahedral
How do viruses replicate
Host cells transcription and translation systems are used to replicate the genome and create capsid proteins
After the initial acute disease (painful blisters) subsides due to an immune response, where can HSV-1 and HSV-2 be found?
In the nuclei of sensory neurons that innervate the site of infection
How does HIV compromise the human immune system, allowing opportunistic infections to invade the body?
Infected CD4+ cells are killed until few are left.
Place the following steps in the reproductive cycle of a temperate bacteriophage in order, with the step following attachment at the top and the step preceding release at the bottom. Assume that the lysogenic cycle is initiated first.
Injection (penetration) integration propagation induction synthesis assembly
In order for HIV to replicate in a white blood cell, it must --------- its double-stranded DNA into a random host chromosome.
Integrate
How does HIV infect a CD4+ cell after binding to the CD4 receptor?
It binds to a coreceptor, and fuses with the cell membrane.
Choose the three types of persistent human viral infections based on the amount of virus present and when it is produced.
Latent Slow Chronic
A bacteriophage that integrates its own DNA into that of its host cell, allowing it to replicate with the host's genome is a(n) --------- phage
Lysogenic
A viral reproductive cycle that includes the production of a prophage is the ----- cycle
Lysogenic
Regarding bacteriophage, during which type of cycle does the phage enter a latent phase, allowing it to be replicated with the host cell?
Lysogenic
Bacteriophage exhibit two reproductive cycles: the --------- cycle, in which the latent phage is replicated with the host cell, and the ----- cycle, in which page undergo replication within the host cell, eventually causing it to rupture
Lysogenic Lytic
During which of the following reproductive cycles does a bacteriophage integrate its own DNA into the host cell's genome?
Lysogenic cycle
Of the following list, which are the two most important types of cells killed by HIV?
Macrophages T-helper cells
------------ involves isolating DNA from an environmental sample, sequencing it, and comparing it to known sequences in DNA databases
Metagenomics
In order to study viruses in the environment, scientists isolate nucleic acids from an environmental sample, sequence them, and use computers to assemble genomes and compare them to known sequences in databases. This approach is known as _______.
Metagenomics
What disease agents are infectious proteins that can cause transmissible spongiform encephalopathies?
Prions
Viroids are infectious disease agents in plants that are composed solely of circular ---
RNA
What happens during antigenic drift in influenza viruses?
Small changes in the HA and NA genes accumulate due to mutation.
After the immune system can no longer control HIV, it starts killing cells expressing the CD4 antigen. Of those cells, the most important types are the T-__________ cells which coordinate the immune response and the __________, which engulf pathogenic bacteria.
T-helper macrophages
Which of the following are reasons why classifying viruses by disease they cause can be impractical?
The same disease can be caused by many different viruses. Some viruses do not appear to cause any disease Some viruses can cause different disease in different context.
Which of the following is the most effective form of AIDS treatment, even though it does not completely eliminate the virus from the patient's body?
The use of a combination of drugs that target different stages of the HIV life cycle
Which of the following may take place during bacteriophage reproduction after the phage genome is injected into the host cell?
The viral DNA is integrated into the genome of the host cell, allowing it to replicate when the host cell divides. Lysogenic phage becomes lytic when cell stress causes derepression of the prophage. New virus particles are synthesized by the cell and then released by lysis or budding.
Which of the following statements best describes viral genomes?
They may be circular or linear, single-stranded, or double-stranded, and composed of DNA or RNA
What are the two main ways in which a virus can spread to infect secondary sites in the human body?
Via neurological tissue In blood or lymph
How does the replication of HIV proceed after it enters a host cell?
Viral RNA is reverse-transcribed, incorporated into the host cell's DNA, and eventually used to produce many copies of the virus.
------- is a condition characterized by viruses freely circulating in the blood or lymph.
Viremia
_________ is a condition characterized by viruses freely circulating in the blood or lymph.
Viremia
Which infectious agents are composed solely of RNA?
Viroids
Which of the following statements most accurately describes the host specificity of viruses?
Viruses infect all types of organisms, but individual viruses are very limited in the species and cell types they can infect.
Small changes to the HA and NA genes of influenza viruses due to mutation are known as antigenic -----
drift
A(n) --------- disease is a disease that appears in the population for the first time, or that spreads to a new geographical area.
emerging
HIV enters a host T-helper cell by first binding to the CD4 receptor and a coreceptor such as CCR5, and then ------ with the cell membrane.
fusing
Attachment of HIV occurs when the ----- glycoprotein binds to the --- receptor on the surface of an immune system macrophage or T cell.
gp120, cd4
Which of the following are the two types of structure typical of most viral capsids
helical, Icosahedral
Most viruses have a capsid that is ------- or --------- in terms of its basic structure and symmetry.
helical, icosahedral
Viruses can infect all types of organisms that have been investigated for their presence, but each type of virus has a relatively narrow ---- ------
host, range
How does HIV compromise the human immune system, allowing opportunistic infections to invade the body?
it targets CH4+ cells
Compared to archaeal viruses, bacteriophages are
less diverse in their morphologies. Both can have double-stranded DNA as their genome.
HIV is transmitted when contaminated bodily fluids come into contact with a ------ --------, or directly enter tissues
mucous membrane
In ___________ viral infections, a virus or its genome can be found in the host for long periods of time: years, decades, and sometime for the rest of the host's life.
persistent
A disease that was prominent in the past, and whose incidence suddenly increases after a period of low incidence, is called a ----------- disease.
re-emerging
Once it enters the cytoplasm of a host cell and sheds its capsid, replication of HIV begins when ------- ----------- is used to synthesize a double strand of DNA from the viral RNA
reverse transcriptase
The genome of HIV consists of two identical ------ - stranded, ----- sense RNA molecules.
single, plus
Some studies suggest that there is more genetic variation in the viruses of an HIV-infected patient than in all influenza viruses worldwide. This, and difficulties in vaccine development may be attributed to
the inability of reverse transcriptase to proofread, which results in a high mutation rate.
The disease that causes the development of numerous small cavities in the brain of infected individuals due to death of neurons producing a spongy appearance is called
transmissible spongiform encephalopathy. (PRIONS)
Identify the disease agent that ranges from about 20-250 nm in diameter
virus