What is a virus?
A submicroscopic, parasitic, filterable agent consisting of a nucleic acid surrounded by a protein coat.
Could a virus be defined as living?
Yes, when they multiply in the host cells they infect.
Define obligate intracellular parasite.
They require living host cells in order to multiply.
Name distinctive features of viruses (at least four).
1.Contain a single type of nucleic acid, either DNA or RNA.
2.Contain a protein coat that surrounds the nucleic acid.
3.Multiply inside living cells by using the synthesizing machinery of the cell.
4.Cause the synthesis of specialized structures that can
What are similarities and differences between typical bacteria, rickettsias/chlamydias, and viruses?
1.Viruses and rickettsias/chlamydias have intracellular parasite.
2. Typical bacteria and rickettsias/chlamydias have a plasma membrane.
3. Typical bacteria and rickettsias/chlamydias have binary fission.
4. rickettsias/chlamydias can and viruses pass thr
Why is host range important with viruses?
The spectrum of host cells the virus can infect.
What determines host range with viruses?
The viruses requirements for its specific attachment to the host cell and the availability within the potential host of cellular factors required for viral multiplication.
What is phage therapy and why might it become important?
Using bacteriophages to treat bacterial infections. Recent advances in our understanding of virus-host interactions.
What is the approximate size range of viruses?
20 to 1000 nm in length.
What is a virion?
Is a complete, fully developed, infectious viral particle composed of nucleic acid and surrounded by a protein coat outside of a host cell, and is a vehicle of transmission from one host cell to another.
What is a virion composed of?
Nucleic acid.
What do all viruses have?
Nucleic acid. (RNA or DNA)
What are the forms (nucleic acid) of viral genomes?
DNA or RNA. Single-stranded or double stranded. Linear or circular.
What is a capsid? a capsomere? an envelope? spikes?
Capsid: The nucleic acid of a virus is protected by this protein coat.
Capsomere: Each capsid is composed of these protein subunits.
Envelope: The capsid is covered by this, and consists of some combination of lipids, proteins, and carbohydrates.
Spikes:
What is the function of spikes?
Some viruses attach to host cells by means of this. These can be used as a means of identification for some viruses.
What can inactivate viral surface proteins?
The interaction between host antibodies and virus proteins.
What can happen when the gene for a viral surface protein is mutated?
Viruses can escape antibodies. Alter surface proteins, then the antibodies are not able to react with them.
How can the influenza A virus cross species barriers?
Undergoes changes in its spikes. (viruses escaping antibodies).
How can the influenza A virus cause a pandemic? What is the mechanism?
Although you may have produced antibodies to one influenza virus, the virus can mutate and infect you again. This is why you can get influenza more than once.
What is antigenic drift?
a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites.
What is antigenic shift?
s the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains.
What are the different morphologies of viruses?
Helical, Polyhedral, enveloped and complex
What is the function of the viral nucleic acid? the capsid? the spikes? the envelope?
Helical: Long rods that may be rigid or flexible. Viral nucleic acid is found within a hollow, cylindrical capsid that has a helical structure. Rabies and Ebola.
Polyhedral: Capsid is the shape of an icosahedron, a regular polyhedron with 20 triangular fa
What is the taxonomy of viruses? How are viruses grouped?
Help us organize and understand new viruses.
Grouped viruses that do not infect humans. Grouped into families based on genomics and structure. Virus is the genus name; family names end in viridae; and order names end in ales.
Adenoviridae
Respiratory infections in humans. Tumors in animals.
Papillomavirus
Warts and cervical and anal cancer.
Polyomavirus
Warts and cervical and anal cancer.
Orthopoxvirus
Smallpox, molluscum contagiosum (wartlike skin lesions) and cowpox.
Simplexvirus
Fever blisters, chickenpox, shingles, infectious mononucleosis, human cancer called Burkitt's lymphoma.
Varicellovirus
Fever blisters, chickenpox, shingles, infectious mononucleosis, human cancer called Burkitt's lymphoma.
Hepatitis B virus
Hepatitis B and liver tumors.
Poliovirus
Polio
Rhinovirus
Colds
Enterovirus
Colds
Hepatitis A, C, D & E
Colds.
Yellow fever, dengue and St. Louis and West Nile encephalitis.
Causes liver to swell.
Gastroenteritis.
Norovirus
Gastroenteritis.
Alphavirus
Eastern Equine encephalitis. Western Equine encephalitis, chikungunya, Rubella.
Flaviviridae
Yellow fever, dengue and St. Louis and West Nile encephalitis.
Coronavirus
Upper respiratory tract infections and the common cold. SARS virus.
Lyssavirus
Rabies and numerous animal diseases.
Filovirus
Ebola and Marburg viruses.
Influenza virus
Flu. Through red blood cells.
Hantavirus
Hemorrhagic fevers and Hantavirus pulmonary syndrome, associated with rodents.
Oncoviruses
RNA tumor viruses. Leukemia and tumors in animals.
Lentivirus
AIDS.
Reovirus
Mild respiratory infections transmitted by arthropods. Colorado tick fever.
What is a bacteriophage?
Viruses that infect bacteria.
What is a plaque? What are PFUs? Why are they helpful?
Plaque: A number of clearings, visible against a lawn of bacterial growth on the surface of the agar.
PFUs: (plague forming unit) The concentrations of viral suspensions measured by the number of plaques.
Each plaque corresponds to a single virus in the i
What three methods are used to cultivate animal viruses?
Involve using living animals: used as a diagnostic procedure for identifying and isolating a virus from a clinical speciman. After the animal is inoculated with the speciman, the animal is observed for signs of disease of is killed so that infected tissue
What are the advantages & disadvantages of using living animals to grow viruses?
Disadvantages: Some human viruses cannot be grown in animals or can be grown but do not cause disease.
Advantages: Some animal viruses can be cultured only in living animals.
What are the advantages & disadvantages of using embryonated eggs to grown viruses?
Advantages: Convenient and inexpensive form of host for many animal viruses.
Disadvantages: Allergic reactions to eggs.
How can viruses be grown in embryonated eggs?
Viral growth is signaled by the death of the embryo. by embryo cells damage or by the formation of typical pocks or lesions on the egg membranes.
What are the advantages & disadvantages of using cell culture for growing viruses?
Advantages: Preferred type of growth medium for viruses.
Disadvantages: There are still some viruses that have never been successfully cultivated in the cell culture. The cell lines must be kept free of microbial contamination.
What is the cytopathic effect and why is it important in cell culture?
Normal cells tend to adhere to the glass or plastic container and reproduce to form a monolayer. Viruses infecting such a monolayer sometimes cause the cells of the monolayer to deteriorate as they multiply. The cell deterioration is called this.
What are primary cell lines? diploid cell lines? continuous cell lines?
Primary: Derived from tissue slices, tend to die out after only a few generations.
Diploid: developed from human embryos can be be maintained for about 100 generations and are widely used for culturing viruses that require a human host.
Continuous cell li
Describe the polymerase chain reaction (PCR) method. Why is it so useful?
based on using the ability of DNA polymerase to synthesize new strand of DNA complementary to the offered template strand. Virologists can identify and characterize viruses by using this.
Why is PCR used in identification of viruses?
To characterize viruses.
What is the purpose of the one-step growth curve? How is it set up? What is it measuring?
For multiplication of viruses. The data are obtained by infecting every cell in culture medium and cells for virions and viral proteins and nucleic acids.
Describe the lytic cycle for T-even bacteriophages.
lytic cycle: ends with lysis and death of the host cell
Occurs in five stages, attachment, penetration, biosynthesis, maturation and and release.
Describe the lysogenic cycle for Bacteriophage Lambda.
Lysogenic cycle: Host cell remains alive.
PG 383
What are three important results of lysogeny?
Lysogenic cells are immune to re-infection by the same phage
Phage Conversion (acquire new properties),
Specialized Transduction (phage packages some bacterial DNA with its own viral DNA)
What is phage conversion? Why is it important? Which specific disease-causing microorganisms have undergone phage conversion (know those stated in chapter 13 in the book).
The host cell may exhibit new properties.
Corynebacterium diphtheriae, Clostridium Botulinum and E. Coli.
What is specialized transduction?
Only certain bacterial genes can be transferred. Uses a bacteriophage.
What happens when a cell leaves lysogeny? When might it happen (what conditions are needed)?
Certain animal viruses can undergo processes very similar to lysogeny. Animal viruses that can remain latent in cells for long periods without multiplying or causing disease may become inserted into a host chromosome or remain separate from host DNA in a
What are the similarities and differences in viral multiplication between bacteriophage and animal viruses?
Attachment:
Bacteriophages: Tail fibers attach to cell wall proteins.
Animal Viruses: Attachment sites are plasma membrane proteins and glycoproteins.
Entry:
Bacteriophages: Viral DNA is injected into host cell.
Animal Viruses: Capsid enters by receptor-m
What are the stages of viral multiplication in animal viruses?
Attachment, entry, uncoating, biosynthesis, chronic infection and release.
Why can attachment of a virus occur in some people but not in others?
Receptor sits are inherited characteristics of the host, the receptor for a particular virus can vary from person to person.
If an antibody binds to the viral protein needed for attachment, can the virus infect the cell?
Yes, used to treat some viral infections.
What happens in attachment for animal viruses?
Attach to complementary receptor sites on the host cells surface. Distributed over the surface of the virus. The sites themselves vary from group of viruses to another.
What is pinocytosis and why is it important for viral entry?
the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
What are the methods of entry used by enveloped viruses?
Fusion: the viral envelope fuses with the plasma membrane and releases the capsid into the cells cytoplasm. .
What happens in uncoating? Where does this occur?
The separation of the viral nucleic acid from its protein coat once the virion is enclosed within the vesicle.
Compare biosynthesis of DNA & RNA viruses. What type of viral nucleic acid is associated with special features of biosynthesis? (for example, how do RNA, + strand viruses compared to RNA, double-stranded viruses?)
PG 388
What is the sense strand and antisense strand for RNA?
Sense: The RNA within the virion, it can act as mRNA.
Antisense: The new strand, serves as a template to produce additional + strands.
Why are RNA-dependent RNA Polymerase sometimes needed?
Catalyzes the synthesis of another strand of RNA, which is complementary in base sequence to the original infecting strand.
What is reverse transcriptase and why it needed for some viruses?
Viruses carry these, which uses the viral RNA as a template to produce complementary double-stranded DNA. It also degrades the original viral RNA.
What is a provirus?
When the viral DNA is then integrated into a host cell chromosome. The provirus never comes out of the chromosome.
What are the pathways of multiplication used for the ssRNA (+ strand), ssRNA (- strand), and dsRNA viruses?
a) After uncoating, single-stranded RNA (ssRNA) viruses with a + strand genome are able to synthesize proteins directly from their + strand. Using the
+ strand as a template, they transcribe - strands to produce additional + strands to serve as mRNA and b
What is the pathway of multiplication and inheritance for Retroviridae?
1) Retrovirus enters by fusion between attachment spikes and the host cell receptors.
2) Uncoating releases the two viral RNA genomes and the viral enymes reverse transcriptase, integrate, and protease.
3) Reverse transcriptase copies viral RNA to produce
What are the possible methods of maturation and release of animal viruses? Do they always result in death?
The first step in viral maturation is the assembly of the protein capsid; this assembly is usually a spontaneous process. The cap- sids of many animal viruses are enclosed by an envelope consist- ing of protein, lipid, and carbohydrate, as noted earlier.
How were viruses connected to cancer?
Name three reasons why it is so difficult to connect viruses to cancer?
The viral cause of cancer can often go unrecognized for sev- eral reasons. First, most of the particles of some viruses infect cells but do not induce cancer. Second, cancer might not de- velop until long after viral infection. Third, cancers do not seem
What are oncogenes?
Cancer-causing alterations to cellar DNA affects part of the genome.
What are oncoviruses?
Viruses capable of inducing tumors in animals.
What is transformation?
Tumor cells undergo transformation; that is, they acquire properties that are distinct from the properties of uninfected cells or from infected cells that do not form tumors.
What is T antigen? Where can it be found? From where does it come?
After being transformed by viruses, many tumor cells contain a virus- specific antigen on their cell surface, called tumor-specific transplantation antigen (TSTA), or an antigen in their nu- cleus, called the T antigen. Transformed cells tend to be less r
Give three examples of DNA oncoviruses.
Adenoviridae, Herpes- viridae, Poxviridae, Papovaviridae, and Hepadnaviridae.
-HPV, cervical cancer, HBV
What cancer does HPV cause?
Virtually all cervical and anal cancers.
What cancer does EBV cause?
Bone marrow cancer/ bone
What cancer does HBV cause?
Liver cancer.
Name a human RNA virus that causes cancer.
The human T-cell leukemia viruses (HTLV-1 and HTLV-2) are retroviruses that cause adult T-cell leukemia and lymphoma in humans. (T cells are a type of white blood cell involved in the immune response.)
How could retroviruses cause cancer?
The ability of retroviruses to induce tumors is related to their production of a reverse transcriptase by the mechanism described earlier (see Figure 13.19). The provirus, which is the double-stranded DNA molecule synthesized from the viral RNA, becomes i
What is a latent infection? Compare it to an acute infection or a persistent infection.
Is the ability of a pathogenic virus to lie dormant (latent) within a cell, denoted as the lysogenic part of the viral life cycle. A persistent or chronic viral infection occurs gradually over a long period. Typically, persistent viral infections are fata
What are some examples of latent infections.
All of the human herpesviruses can remain in host cells through- out the life of an individual. When herpesviruses are reactivated by immunosuppression (for example, AIDS), the resulting infec- tion may be fatal.
What is a persistent infection? Why are they important?
A persistent or chronic viral infection occurs gradually over a long period. Typically, persistent viral infections are fatal.
A number of persistent viral infections have in fact been shown to be caused by conventional viruses. For example, several years
What are some examples of persistent infections?
For example, several years after causing measles, the measles virus can be responsible for a rare form of encephalitis called subacute scle- rosing panencephalitis (SSPE).
What are prions?
is a small infectious particle composed of abnormally folded protein that causes progressive neurodegenerative conditions. These mis-folded proteins do not multiply in the host organism that they infect.
What can and cannot destroy prions?
Prions cannot be destroyed by boiling, alcohol, acid, standard autoclaving methods, or radiation.
Can be destroyed by incineration.
What are examples of diseases caused by prions?
Mad cow disease and Creutzfeldt-jakob disease.
Can prion diseases be inherited? transmitted?
Yes and Yes