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MicroBiology Exam 3
Terms in this set (44)
What are the general features of viruses?
Simple, acellular, obligate parasites, 10-400 nM, nucleocapsid= genome of NA surrounded by protein, some enveloped (helical, icosahedral, complex)
How are viruses cultivated and assayed?
Living hosts, Cell culture, fertile eggs, plaque assay, particle count, disease symptoms, LD50
Discuss the structure of viruses; nucleocapsids and genomes
DNA or RNA ss/ds in capsid, protomers, capsomers (5 or6), envelope, (helical, icosahedral, complex)
Why is the taxonomy of viruses a difficult problem?
Unclear which characteristic should be used. Few components to evaluate and life cycles are highly diverse.
Discuss the ways that viruses might be grouped for classification
Nucleic acids, reproductive strategy, capsid symmetry, envelope, host, disease, size, etc.
In what ways do viruses resemble living organisms?
Use host components (processes) to reproduce, similar components to cell, proteins nucleic acids
Describe an RNA virus life cycle. What is the advantage of a viral genome made of RNA?
+ SS RNA to +/- RF RNA to + RNA = mRNA
-SSRNA to +/- RF RNA to + RNA = mRNA, but -RNA packaged
Ds RNA to both + and - RNA, use +RNA as mRNA, package ds RNA
Some bypass the nucleus
Discuss the difference between lytic and temperate phage.
Lytic phage is lysis only; temperate phage makes choice between lytic and prophage
Describe the life cycle of the retroviruses and compare them to the life cycle of DNA viruses
ssRNA reverse transcribe to DNA, compliment to ds DNA and integrate, make ssRNA for genome
DNA virus acts like normal host genome
What is the relationship of viruses to AIDS and Cancer? What are the similarities and differences found in cancer viruses and HIV?
Immune suppression by HIV also indirectly promotes cancer growth (suppressed immunity)
Tumor virus usually ds DNA with ability to integrate into host genome (mutation and/or altered gene expression)
Several leukemia virus htlv1 and 2 are retrovirus like HIV
Describe the one-step growth experiment. Why is it important and what did the experiment tell us about a viral life cycle?
Staged with defined times; latent period=no phage outside cell
Eclipse period=no phage inside cell
Rise period; burst size
Define the terms: virion, icosahedral, complex symmetry, protomer, capsomer, envelope, lytic, temperate, lysogenic, prophage, adsorption
What is the difference between a + strand virus and a - strand virus
+= mRNA (carries information for protein synthesis)
In many DNA genome bacteriophage, immediately after infection a family of early mRNA is synthesized. These mRNA are usually synthesized before viral DNA is made. What are some possible functions of the proteins encoded by early message?
Host cell take-over, degrade host DNA
When referring to viral genomes, what is meant by replicative form?
Double Host cell take-over, degrade host DNA -strand intermediate
What are the modes of entry used by eukaryotic viruses?
Endocytosis and plasma membrane fusion
What is the difference between persistent, chronic and latent viral infections?
Persistent=many years; chronic=virus always detected; latent=dormant virus
What types of human cancers are caused by viruses?
Burkitts lymphoma and nasophayngeal by EB
Liver hepB and C
Herpes virus 8 + HIV =Kaposis sarcoma
Human papilloma= cervical
HTLV = adult T cell and hairy cell leukemia
By what mechanisms do viruses cause cancer?
Carry oncogenes; mutation of tumor suppressor or normal to oncogene, alter gene regulation of host
What is a prion and how do prions cause Creutzfeld-Jakob disease
Proteinaceous infectious particle; abnormal version of protein in brain, C-J is genetic, vC-J is eating prion; PrPC to PrpSC
How does HIV shut down both cellular and humoral immunity?
Both Th1 and Th0 targeted. Th1 presents antigen to CTL, Th0 presents antigen to B cell to produce Plasma cell
Describe the classes of drugs used to treat HIV positive individuals?
NRTI; NNRTI, protease inhibitor; fusion inhibitor
Why is there no vaccine for AIDS?
Problems making virus for antigens; attenuated vaccine does not illicit immune response, antibodies against gp120/160 have low titer; viral passage between cells. Immune coated infected cells still active. Virus passes between cells; apes vs humans
A vaccine against HPV 16 and 18 now exists to prevent human cervical cancer. What are the mechanisms of action?
HPV can become integrated into cervical cells and acquire mutations that cause increased expression of two viral proteins (E6 and E7). These proteins block two host tumor suppressor proteins; one that down regulates cell proliferation (pRB) and one that promotes apoptosis (p53). The vaccine is a combination of four recombinant HPV protein. They are highly antigenic and represent the most oncogenic forms of HPV.
What is antigenic drift and antigenic shift? How are these phenomena related to influenza biology?
Drift= mutation Shift = combination of several viral genomes into new hybrid
The Baltimore classification of viral genomes has an unusual entry (Class VII).
Describe the life cycle of a typical virus in this class and note why this class is
Hepatitis B virus with ds DNA genome transcribed to mRNA placed in viral capsid then RT to DNA after packaging
Discuss the different types of vaccines (components used).
Attenuated live virus, dead virus, virus components (subunits), mRNA encoding viral protein, viral vector expressing antigenic target components
Discuss the roles of neuraminidase (NA) and hemagglutinin (HA) in the influenza virus life cycle
HA binds to host receptor sialic acid containing surface protein. NA cleaves sialic acid-virus interaction to release virus from host surface.
How does SARS-CoV-2 interact with respiratory cells and how might this interaction produce a cytokine storm
Spike binds to ACE2 a surface protein in respiratory epithelia that down-regulates Angiotensin II levels. Blocked receptor= increased AngII leading to increased cell damage and increased cytokine release (inflammatory response). More infected cells = more cytokines
Lysogeny is the state in which a dsDNA virus genome
reproduces within the host cell genome after infection
he type of infection that produces virus over the course of a long time period is
A common geometric shape for viral capsids is the
proteins that are infectious without a viral genome
are likely to contain viral glycoproteins
Animal virus enters the host by
membrane fusion or endocytosis
is the term used to describe the interaction between cell surface receptors and the virus surface
Which of the following is a reason we take the flu vaccine every year
Enumeration of viral infection by plaque assay
requires lawns of cultured host cells
The one-step growth experiment performed by Delbruck and Ellis
was the first investigation of synchronous viral infection of cells
True or False
a. Virus are obligate parasites - T
b. Early bacteriophage mRNAs are likely to encode for capsid proteins- F
c. The gag gene of HIV encodes for envelope proteins - F
d. Integrase permits a virus to fuse with the host cytoplasm - F
e. AIDS is considered a direct contact disease - T
f. The replicative form (RF) of a viral genome is single-stranded -F
g. Tamiflu is a hemagglutinin inhibitor - F
h. Bacterial virus are usually enveloped - F
i. Virus is separated from cell debris primarily by centrifugation - T
j. NNRT drugs against AIDS block the HIV protease - F
k. The term virion refers to the intracellular form of a virus - F
l. Vaccines can be made from live or dead virus - T
m. CRISPR is an antiviral host defense mechanism - T
n. A nucleocapsid is the form of virus found in the host nucleus - F
o. During most successful viral reproduction, host cells are actively growing - T
p. Virus cannot survive outside the host - F
q. The CD4 receptor is found on both helper and cytotoxic T cells - F
r. Humans do not produce antibodies to HIV so no vaccine exists - F
s. Vaccination has eradicated smallpox disease from the planet - T
t. Gardasil prevents HPV infection in boys as well as girls - T
How is HIV able to shutdown of the entire immune system (cytotoxic immune cells as well as antibody production)? (10 points)
A correct answer requires that you state that the target cell for HIV is the T helper lymphocyte (CD4+). The reason that the loss of this cell causes both antibody and cellular immunity to fail is due its regulatory role. T helper cells receive information from macrophage that encounter foreign antigens and it is the responsibility of the T helper to pass on this information to B cells and T cells that are precursors of the antibody-producing plasma cells and the cytotoxic T cells, respectively. T helper cells also produce cytokines that activate both B and T cell differentiation. Loss of this activation means there will be no lymphocytes capable of eliciting an immune response.
Several variants of Bovine Spongiform Encephalopathy, a neurodegenerative disease, are known to exist in monkeys and humans. The rare Creutzfeld-Jakob disease (CJD) is found in 1 per every million people on the planet. However, a more common version of CDJ called new variant Creutzfeld-Jakob disease (vCJD) also exists. Describe the differences between these two diseases from the perspective of the biological agent responsible (10 points)
CJD is a genetic disease caused by inherited mutations in the PRNP gene on chromosome 20 in humans.
The mutant version produces a prion that alters neurological function by interacting with the normal PRNP and changing its conformation to the prion form.
vCJD is the version of the disease caused by eating prion-containing meat (BSE/Mad Cow) or being exposed to prions in other ways. This is the more common form because it is only necessary to eat contaminated beef (10 points)
Describe three ways an oncogenic virus might cause cancer in animals. Suppressing the immune system is excluded. (10 points)
1. The oncogenic virus might carry an oncogene (a mutant version of a normal growth regulatory gene that is now unable to receive the signals to stop growth). Src on RSV is an example.
2. A DNA virus or retrovirus that integrates into the genome can inactivate a tumor suppressor gene (a gene responsible for putting the breaks on cell growth)
3. Integration by a DNA virus or retrovirus might cause a viral promoter to be placed adjacent to a growth regulatory gene and cause over-expression of a growth-promoting gene product.
Describe (or draw) the key similarities and differences between the life cycle of a plus (+) strand RNA virus and a (-) strand RNA virus? (10 points).
The negative strand virus provides an opportunity for an extra step in regulation of the virus life cycle. If the virus has a + strand genome, it is the message and is directly used at the ribosome. If the virus has a negative strand to start with, the RNA-dependent RNA synthesis step that is required can make different amounts of mRNA due to this obligatory processing step. In addition, the - strand could also me modified in some ways that would not be allowed if it was the message (ie. processing for regulation).
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