The Viruses
In terms of being linear or circular, viral RNA is what? Viral DNA is what?
RNA: linear DNA: circular or linear
What is tropism?
The preference viruses have for partocular organs, tissues, or specialized cell types.
What are the 5 different modes of viral transmission? Give an example of a virus that is transmitted via each route.
Respiratory transmission: Influenza A virus Fecal-oral transmission: Enterovirus Blood-borne transmission: Hep B virus Sexual transmission: HIV Animal or Insect vectors: Rabies virus
How do the transcription and translation of a single-stranded negative sense RNA molecule and a double-stranded RNA molecule differ?
The negative sense molecule is transcribed by RNA polymerase into mRNA which then gets translated into a peptide. The positive sense molecule is used as mRNA and is translated into a peptide.
Describe the transcription and translation of a double-stranded RNA molecule.
The negative sense strand is transcribed by RNA polymerase into mRNA which then gets translated into a peptide.
Discuss the differences in translation of a virus with a genome that is a single nucleic acid (1) from those where the genome is distributed over a number of molecules (2).
(1): translation produces a large multifunctional protein that is cleaved to produce a number of distinct protein. (2): several mRNAs are produced and each is translated into separate proteins.
What are the 2 ways by which transformation of a cell occurs? (hint: think oncogenes)
1) when viral oncogenes are incorporated into the host genome. 2) When viral DNA is inserted near to a cellular oncogene.
Some viruses have an outer lipid bilayer membrane external to the coat or capsid called an ___________________.
Envelope
The ___________________ of the virus is acquired from the host cell during viral replication or release.
Envelope
What are the 2 different virus shapes?
Helical or Cylindrical (helical) Spherical (icosahedral)
Differentiate the proteins made in the early phase of viral infection from those made in the later phase.
In the early phase, the proteins produced will allow subsequent replication of viral nucleic acids. In the later phases, the proteins produced are those that are necessary for capsid formation.
Some viruses can transform the host cell. _____________ is the change of a differentiated host cell into a tumor or cancer cell.
Malignancy
Compare and contrast the ability of naked viruses and enveloped viruses to survive in the GI tract.
Naked viruses can survive and ifnect through the GI tract whereas enveloped viruses do not survive in the GI tract.
Compare and contrast how naked viruses spread vs how enveloped viruses spread.
Naked viruses lyse the cell to spread whereas enveloped viruses are released form the cell by budding.
What are the 6 steps in viral infection of a host cell?
1) Adsorption (attachment) 2) Penetration 3) Uncoating to release the genome 4) Virion component production 5) Assembly 6) Release from the cell
What are the 2 ways by which enveloped viruses can enter into a cell?
1) Direct fusion 2) Receptor mediated endocytosis (viropexis)
_________________________ involve interference with the normal regulation of division and response to external growth promoting and growth inhibiting factors.
Cancer-inducing viruses
Viruses that infect bacteria are referred to as ____________________
Bacteriophages
Describe the receptor-mediated endocytosis (viropexis) form in which enveloped viruses enter into cells.
The viral spikes of the viral envelope bind to the receptors on the host cell. The plasma membrane surrounds the virion and forms an endosomal vesicle. There is a low pH in the vesicle and this leads to a conformational change in the viral spike proteins. We then have fusion of the 2 membranes and release of the nucleocapsid into the cytoplasm.
In this type of viral infection, the virus goes through rounds of replication, the cell remains alive and viral particles are released slowly over time. The infected carrier can be symptomless and yet infect many others.
Persistent infeciton
What is positive sense RNA in a virus? What is negative sense RNA in a virus?
Positive sense RNA means it is viral mRNA. Negative sense RNA means it is complementary to or antisense of mRNA.
Describe the transcription and translation of a retrovirus.
The positive sense RNA is transcribed by viral reverse transcriptase into negative sense DNA. The negative sense DNA becomes double-stranded and its negative sense strand is transcribed by the host into mRNA. The mRNA is then translated into a peptide.
Describe the direct fusion way in which viruses can enter cells.
The virus envelope contains protein spikes which promote fusion of the viral membrane with the plasma membrane. The viral envelope becomes incorporated into the plasma membrane of the cell. The nucleocapsid is released directly into the cytoplasm.
How do naked viruses enter into a cell? How does this process differ between naked viruses and enveloped viruses?
They enter by receptor-mediated endocytosis (viropexis). In viropexis involving a naked virus, the low pH of the endosome exposes the hydrophobic domains resulting in binding of the virion to the membrane or the virion promoting lysis of the vesicle followed by release of the viral genome into the cytoplasm.
Most viruses contain how many copies of their genome?
They normally contain a single copy. *Retrovirus is the exception in that it carries 2 identical copies.
__________________ cells show changes in morphology, behavior, and biochemistry.
Transformed
How does viral mRNA make it so that viral products are synthesized preferentially?
Viral mRNA can displace host mRNA from ribosomes.
A set of genes, composed of either DNA or RNA, packages in a protein-containing coat called a capsid.
Virus
How does transcription of viruses containing DNA differ from those containing RNA in terms of the ability to use the host's own machinery?
RNA viruses must be transcribed using viral RNA polymerase. DNA viruses are able to use the host's own RNA polymerase.
The complete virus particle is called a ______________
Virion
What are the functions of the capsid or envelope of a virus?
1) Protect the nucleic acid genome from damage during extracellular passage. 2) Aid in entry into the cell 3) Package viral enzymes essential for the early steps of the infection process.
In virtually every case, the spikes or peplomers on viral surfaces are inportant for the 2 earliest steps of infection which are what?
Adsorption and penetration
Viral genomes can be made our of either _______ or _______.
DNA or RNA
What are some basic structures that all viruses have?
DNA or RNA on the inside of a capsid. Some are further packaged into an envelope. Glycoprotein structures called spikes on the surface. Enveloped DNA have a protein complex surrounding the genome called a nucleocapsid.
Discuss the differences between the direct and indirect mechanisms of virus-induced cancer.
Direct: the virus can express viral oncogenes that transform the cell. Indirect: Chronic viral infection of cells results in inflammation and mutation that results in tumor formation. Some virus infections may produce various proteins that start oncogenic transformation of cells.
Viruses have an obligate requirement for ________________ growth.
Intracellular
In enveloped viruses, what is the function of the nucleocapsid?
It condenses the viral nucleic acid genome
In this type of viral infection, the virus remains quiescent. The viral genome may be in the host cell cytoplasm or incorporated into the host genome. Replication takes place only when a signal triggers reactivation.
Latent infection
In this type of viral infection, the virus goes through rounds of replication, and many new viral particles are released via cell lysis.
Lytic infection
Compare and contrast how naked viruses and enveloped viruses survive in the outiside environment.
Naked viruses survive well in the outside world, they are environmentally stable whereas enveloped viruses are more susceptible to environmental factors such as drying, gastric acidity and bile.