Micro Exam 3

What is a virion?

A complete, fully developed viral particle

What is a capsid in a virus?

It is a coat made of protein subunits called capsomeres that protects the viral genome

What genome makes up a virus?

Viruses can have DNA or RNA, which can be single- or double-stranded, and linear or circular

What is an envelope in the context of viruses?

A lipid, protein, and carbohydrate coating derived from the host cell

Why are viruses considered obligatory intracellular parasites?

They require living host cells to multiply and cannot reproduce independently

What is the typical size range of viruses?

Viruses range from approximately 20 nm to 1000 nm in length.

What's the consequence of a virus lacking ribosomes?

Cannot synthesize proteins; no ATP-generating mechanism, no "metabolism"

What is the function of viral proteins that protrude through the capsid?

They mediate attachment of the virus to host cells and determine the tissues and organisms the virus can infect = "antigens" to which antibodies bind

Where do proteins in viruses come from if no ribosomes are present?

The host cell

Does either bacteria or viruses have intracellular parasites?

Viruses

Does either bacteria or viruses have a plasma membrane?

Bacteria

Does either bacteria or viruses undergo binary fission?

Bacteria

Does either bacteria or viruses pass through bacteriological filters?

Viruses

Does either bacteria or viruses posses both DNA or RNA?

Bacteria

Does either bacteria or viruses have ATP-generating metabolism?

Bacteria

Does either bacteria or viruses have ribosomes?

Bacteria

Are either bacteria or viruses sensitive to antibiotics?

Bacteria

Are either bacteria or viruses sensitive to interferon?

Viruses

What is the host range of a virus?

The spectrum of host cells that a virus can infect, often specific to certain types of cells

What is pathogenicity vs. virulence

Pathogenicity is whether something can cause disease while virulence is the measure of damage caused

What are the factors that affect the host range?

Whether the virus can get into the host cell, if the cell has the right machinery for the virus to replicate, and if the infectious virus can get out of the cell and spread the infection

What are bacteriophages?

Viruses that infect bacteria

What are the general morphologies of viruses?

Helical, polyhedral, enveloped, or complex

Helical viruses

Hollow, cylindrical capsid

Polyhedral viruses

Many-sided

Enveloped viruses

Contain proteins in envelope

Complex viruses

Complicated structures

How are viruses classified?

Nucleic acid type, replication strategy, capsid symmetry, and presence of an envelope

How are bacteriophages grown in the laboratory?

Viruses must be grown in living cells and bacteriophages are grown in bacteria which form plaques on the surface of agar

What are plaque-forming units (PFU)?

Plaque corresponding to a single virus

How are animal viruses grown in embryonated eggs?

Virus is injected into the egg and the viral growth is signaled by changes or death of the embryo

How are animal viruses grown in cell cultures?

Tissues are treated with enzymes to separate cells and virally infected cells are detected by their deterioration, known as the cytopathic effect (CPE)

What are cytopathic effects (CPE)?

Visible effects of viral infection on a cell

What are serological tests?

Western blotting—reaction of the virus with antibodies

What are the methods of viral identification for nucleic acids?

RFLPs (restriction fragment length polymorphism) and PCR

What does a western blot do?

Uses antibodies to detect specific proteins in a mixture

What are the steps of a western blot?

1. Proteins (in a mixture) are separated by size using gel electrophoresis

2. Separated proteins are transferred from the gel to a "membrane,"

maintaining their pattern of separation (this is the "blotting" part)

3. Proteins of interest in the mixture are bound to a "primary" antibody that recognizes them

4. The primary antibody is visualized using a "secondary" antibody coupled to an enzyme

5. The enzyme is exposed to its substrate, and catalyzes a reaction that produces detectable light

How does viral multiplication occur?

It must invade a host cell and take over the host's metabolic machinery using the one-step growth curve

What is the significance of the lytic cycle in bacteriophages?

It leads to the lysis and death of the host cell, resulting in the release of new virions

What occurs during the lysogenic cycle of a bacteriophage?

The phage DNA integrates into the host cell DNA, becoming a prophage and remaining latent

What is phage conversion?

When a host cell exhibits new properties due to the presence of a lysogenic phage

What are the steps of viral multiplication in animal cells?

Attachment, entry, uncoating, biosynthesis, maturation, and release.

What is the primary method for growing bacteriophages in the laboratory?

Bacteriophages are grown in bacteria, forming plaques on agar surfaces.

What is the cytopathic effect (CPE)?

The deterioration of virally infected cells, which can be detected in cell cultures.

What is a Western blot used for?

To detect specific proteins in a mixture, often used diagnostically for viral infections.

What is the role of PCR in viral identification?

It is used to amplify and detect viral nucleic acids for identification purposes.

How do enveloped viruses typically release from host cells?

By budding from the host cell membrane.

What is the difference between the lytic and lysogenic cycles?

The lytic cycle results in cell death and release of virions, while the lysogenic cycle integrates viral DNA into the host genome without immediate cell death.

What is the function of tail fibers in T-even bacteriophages?

They attach the phage to the host cell during the attachment phase of the lytic cycle.

What is the significance of the primary antibody in a Western blot?

It binds to specific proteins of interest in the sample being tested.

What happens during the maturation phase of viral multiplication?

Nucleic acid and capsid proteins assemble to form new virions.

What is the role of enzymes during the uncoating phase of viral multiplication?

They facilitate the removal of the viral capsid to release the viral genome into the host cell.

What is the purpose of plaque-forming units (PFU) in virology?

To quantify the number of infectious viral particles in a sample.

Where do DNA viruses replicate their DNA?

In the nucleus of the host using viral enzymes.

How do DNA viruses synthesize their capsid?

In the cytoplasm using host cell enzymes.

Name an example of a DNA virus.

Adenoviridae, Poxviridae, Herpesviridae, Papovaviridae, Hepadnaviridae.

How do RNA viruses multiply in host cells?

In the cytoplasm using RNA-dependent RNA polymerase.

What is the function of + (sense) strand ssRNA in viruses?

It serves as mRNA for protein synthesis.

What happens to - (antisense) strand ssRNA in viruses?

It is transcribed to a + strand to serve as mRNA for protein synthesis.

What is an example of an RNA virus?

Coronaviridae, Orthomyxoviridae, Rhabdoviridae, Reoviridae.

What is the role of reverse transcriptase in retroviruses?

It produces DNA from the viral RNA genome.

What is a provirus?

Viral DNA integrated into the host chromosome.

What is the main risk factor for cervical cancer?

Infection with high-risk human papillomaviruses (HPVs).

How does the E6 protein from HPV contribute to cancer?

It binds to p53, leading to its degradation and loss of function.

What is the function of the p53 protein in cells?

It regulates the cell cycle and prevents DNA damage propagation.

What type of cancer is associated with oncogenic viruses?

Sarcoma and adenocarcinomas.

What is latency in viral infections?

A state where the virus remains dormant in the host cell.

What is antigenic drift in influenza viruses?

Small changes in glycoproteins that evade the host immune system.

What is antigenic shift in influenza viruses?

Gene exchange between different influenza viruses leading to new strains.

What is the impact of HIV on the immune system?

It infects helper T cells, leading to a weakened immune response.

What is AIDS?

A cluster of symptoms that occur when CD4 T cell levels are very low.

What are some common symptoms of HIV infection?

Fever, fatigue, swollen lymph nodes, and other flu-like symptoms.

What is the global impact of HIV?

It has claimed over 40 million lives and continues to spread globally.

What are oncogenes?

Genes that can transform normal cells into cancerous cells.

What is the role of viral proteins in oncogenesis?

They can inhibit tumor suppressors or transform host cells.

What is a persistent viral infection?

An infection that occurs gradually over a long period and is generally fatal.

What is an example of a latent viral infection?

Cold sores caused by herpesvirus or shingles from Varicella.

How does the immune system respond to acute viral infections?

Through inflammation and specific immune responses including antibodies and T cells.

What are the two viral families that have double-stranded DNA and are non-enveloped?

Adenoviridae, Polyomaviridae

What are the two viral families that have double-stranded DNA and are enveloped?

Poxivirdae, Herpesviridae

What viral family has single-stranded DNA and is non-enveloped?

Parvoviridae

What viral family has double-stranded DNA and is non-eneveloped?

Reoviridae

What are two viral families that have single-stranded RNA, + strand and are non-enveloped?

Picornaviridae, Hepeviridae Caliciviridae

What are three viral families that have single-stranded RNA, + strand and are enveloped?

Coronaviridae, Togaviridae Matonaviridae, and Flaviviridae

What are three viral families that have single-stranded RNA, - strand and are enveloped?

Paramyxoviridae, Rhabdoviridae, and Filoviridae

What viral family has single-stranded RNA, - strand and is a virusoid or satellite RNA?

Deltaviridae

What are three viral families that have multiple strands of RNA and are enveloped?

Orthomyxoviridae, Arenaviridae, and Peribunyaviridae

What viral family has single-stranded RNA, produce DNA, and is enveloped?

Retroviridae

What viral family has double-stranded DNA, use reverse transcriptase, and is enveloped?

Hepadnaviridae