BIOD 171 Module 6 Review

Describe the basic steps of the viral life cycle.

1. Attachment: Viral receptors bind to host proteins on the surface of the cell. 2. Entry: The virus fuses with the host membrane and enters the cell 3. Uncoating: (where applicable) the viral capsid disassembles 4. Replication: The viral genome provides the 'blueprint' to make copies of itself 5. Exit: New viruses are produced and leave the cell 6. New infection: Newly produced viruses leave the host cell and go on to infect new cells. The process outlined above now restarts.

Place the following viral life cycle steps in order beginning with viral attachment and provide a description of each step.

1. Attachment: Viral receptors bind to host proteins on the surface of the cell. 2. Entry: The virus fuses with the host membrane and enters the cell 3. Uncoating: (where applicable) the viral capsid disassembles 4. Replication: The viral genome provides the 'blueprint' to make copies of itself 5. Exit: New viruses are produced and leave the cell 6. New infection: Newly produced viruses leave the host cell and go on to infect new cells. The process outlined above now restarts.

What is a bacteriophage?

A bacteriophage is simply a virus (phage) that infects bacteria.

Describe the two basic components of a virus.

A virus has (1) genomic material comprised of either DNA or RNA and (2) a capsid, a membrane-like protective structure that contains the genetic material, similar to the nucleus of a eukaryotic cell.

What linear, double-stranded, enveloped DNA virus is the first virus (as of October 26, 1977) to be declared eradicated?

Although once a major cause of death in the world, a smallpox vaccine was developed in 1796 by Edward Jenner. Global vaccination efforts have prevented smallpox from appearing in humans since October 26, 1977, making smallpox the first infectious disease ever to be eradicated.

What is an obligate intracellular parasite?

As an obligate intracellular parasite, viruses cannot (obligate) replicate unless inside (intracellular) a living host cell. As a parasite, a virus depends on its living host to provide the framework (proteins, etc) to replicate—to make additional copies of itself.

A virus that infects bacteria is called a _____ and contains a _____-sided polygon capsid.

Bacteriophage 20

What structural aspects make bacteriophages distinct from viruses that infect either animals or plants?

Bacteriophages possess an icosahedral capsid head group and a helical tail. Attached to the tail are fibrous extensions or 'legs' that aid in binding host cells. Notably, this particular structural arrangement has not been observed among viruses that infect either animals or plants.

The HIV surface glycoprotein gp41 binds what host cellular receptor?

CXCR4

A patient diagnosed with German measles may additionally experience what disease?

Conjunctivitis and influenza-like symptoms A patient may experience a combination of symptoms such as fever, flu-like symptoms (influenza), cough, conjunctivitis, and a red blotchy skin rash

What type of microscope would be used to study the shape of a viral capsid?

Due to its size (~30-150 nm) most viral capsids must be visualized via electron microscopy.

Describe the appearance of a bacterial culture infected with virus at the time of infection versus later once viral replication is occurring at a high rate.

During the initial inoculation of virus and bacteria, the media has a high degree of turbidity (cloudiness). However, as the lytic cycle progresses and more and more bacterial cells are destroyed, the culture media turns from turbid to clear, as turbidity is a function of the number of intact bacterial cells present in the media. Thus, as bacterial cell numbers decrease due to lysis, the media becomes clearer.

True or False: Structurally, bacteriophages are similar to viruses that infect animals.

False: Bacteriophages have a distinct composition and structure.

True or False: You would expect to see a viral envelope on a virus infecting a bacterial cell.

False: The overwhelming majority of animal viruses are enveloped whereas the majority of plant or bacteria-infecting viruses are not.

True or False: Because the genome is contained within an enclosed space (music like the nucleus of a cell), viruses are classified as eukaryotic.

False: viruses are neither eukaryotic nor prokaryotic

What must happen before viral replication of its genome can occur?

For all viruses, the genome is replicated following attachment and entry, never before.

Describe the composition of HIV.

HIV contains two copies of single-stranded, linear RNA that is enclosed by a capsid. The conical capsid surrounds the two RNA strands and is comprised of ~2,000 copies of the viral protein p24. A viral envelope derived from the cell host membrane then surrounds the viral capsid. Within this envelope are two key glycoproteins, gp120 and gp41, which are essential for viral binding and entry into the host cell.

Which subtype of Influenza is the most virulent?

Influenza A

Explain why the flu shot given each year may not be 100% effective at preventing the flu?

It is possible to receive a flu vaccine and yet (unfortunately) still get the flu in the same season if you are exposed to a viral strain that was not included in the vaccine. There are a large number of variants and the flu vaccine is unable to vaccinate against all subtypes. Medical researchers predict and then distribute flu vaccines based current trends and the available data releases to the most common circulating strains. Unfortunately, this model is not always 100% accurate.

Describe the main differences between lytic and temperate phages.

Lytic bacteriophages replicate within the host bacteria until it ruptures, whereas temperate (or lysogenic) phages primarily exist in a non-replicative state that does not kill the host cell Lytic phages replicate all viral proteins needed for the assembly of new virus particles whereas lysogenic phage genomes are integrated into the host genome but production of viral proteins is suppressed.

Which of the following cannot be spread via airborne particles:

Measles, mumps and rubella can all be spread via airborne particles formed while coughing, sneezing, etc.

Which of the following diseases does a linear, single-stranded RNA virus cause?

Measles, mumps, and rubella

What disease displays as a secondary characteristic swelling of the testes/ovaries and pancreas?

Mumps. A patient infected with mumps (aka epidemic parities) has primary swelling in the paranoid (salivary glands) located in the neck but also may have secondary swelling in the testes/ovaries and pancreas

A drug company is trying to develop a new drug that will inhibit the release of newly produced viral particles. Would the drug company target hemagglutinin proteins or neuraminidase proteins? Why?

Neuraminidase (N) proteins are directly involved in the budding and release of new viral particles and would thus be the correct target. Hemagglutinin (HA) proteins would not be advisable targets as they are directly involved in viral attachment and entry into the host cell.

Can viruses be classified as either prokaryotic or eukaryotic microorganisms?

No. Viruses are neither prokaryotic nor eukaryotic.

What small (~30nm) single-stranded, non-enveloped RNA virus targets the CNS (central nervous system), causing potentially catastrophic damage to motor neurons?

Polio also known as poliomyelitis

To what family of viruses does rubella come from and how is it transmitted?

Rubella virus belongs to a family of viruses called Togaviridae. Rubella is transmitted via air-borne particles such as when a person coughs.

What is the common name for rubeola, and is it a DNA or RNA virus?

Rubeola is commonly referred to as the measles and belongs to the family of viruses called Paramyxovirus. Rubeola viruses are RNA viruses with a genome ~ 15,000 nucleotides long.

What disease state emerges as a viral reactivation of a prior infection with the varicella virus?

Shingles, also known as Herpes zoster, is due to the reactivation of the varicella-zoster virus (VZV). Because VZV lies dormant in inactive nerve cells, its reactivation typically results in painful blisters. However, unlike the initial chickenpox rash, the blisters are localized and limited to small areas.

What linear, double-stranded, enveloped DNA virus is the first virus (as of Oct. 26, 1977) to be officially declared eradicated?

Smallpox or the Variola Virus

Describe the main underlining differences between the Salk and Sabin polio vaccine

The Salk vaccine contained an inactivated form of the virus and was injected while the Sabin vaccine contained a live attenuated (weakened) form of the virus and was administered orally

What is a viral capsid?

The capsid is a membrane-like protective structure that contains the genetic material, similar to the nucleus of a eukaryotic cell.

An individual infected with HIV is placed on anti -retroviral medication. What is the general purpose of this medication?

The drug is intended to inhibit the process of reverse transcription, stopping the virus from creating the complementary DNA strand it usually does. You effectively block the production of new viruses by preventing its integration and replication

What is the viral envelope, and what does the presence (or absence) of it tell you about the type of virus?

The envelope surrounds the viral capsid, is derived from the host cell membrane and serves as an additional barrier to the external environment. The overwhelming majority of animal viruses are enveloped whereas the majority of plant or bacteria-infecting viruses are not.

A person who has neither previously had chickenpox nor been administered the VZV vaccine is exposed to someone with an active VZV (shingles) outbreak and becomes infected. Explain why (or why not) the person will only develop shingles.

The infected individual will not develop shingles, but will develop chickenpox. Unvaccinated and unexposed individuals must first develop chickenpox, as shingles is the reactivation of the dormant VZV virus from the chickenpox infection

Which viral replicative process results in the destruction of the host cell?

The lytic replication cycle occurs when a bacteriophage replicates within a host until it ruptures, effectively destroying the host bacterial cell. The phrase lytic stems from 'lysis', meaning to rupture or disintegrate (breakdown) a cell.

How does the viral envelope both aid in cell entry as well as hide it from being detected by the immune system?

The viral envelope contains the necessary proteins required for interaction with host cells. As the envelope is derived from the host cell membrane, this camouflages the virus and lowers the likelihood of immune detection by making it appear similar to the normal biological host cell.

What are the two key glycoproteins found in the influenza virus?

The viral envelope contains two key glycoproteins, hemagglutinins (HA) and neuraminidase (N). Hemagglutinins are heavily involved in the entry of the viral particle into a host cell, while neuraminidase proteins are involved in the budding and release of new viral particles from the host cell.

True or False: A patient infected with rubella is considered infectious one week before and after the appearance of the trademark rash.

True

True or False: The development of shingles is most often seen in an older adult populating >60 years old

True

True or False: The viral capsid of HIV is cone shaped and contains 2,000 copies of the viral protein p24

True

True or False: Unlike chickenpox, the blisters that appear with shingles are localized and limited to small areas.

True

True or False: Viral replication occurs after it attaches and enters the host cell.

True: The viral genome is never replicated before attachment and entry.

Rank the following viruses based on their size from largest to smallest:

Variolavirus (-200nm) > Orthomyxovirus (100-150nm) > Poliovirus (-30nm)

You go to visit a friend who has chickenpox. While visiting what are 2 things you will be sure to avoid so that you don't also become infected?

You would want to be sure to keep a distance especially if your friend is coughing or sneezing as chickenpox can be transmitted through air-borne droplets (sneezing/coughs). You would also be absolutely certain to avoid direct contact with the blisters of an infected individual

The envelope surrounds the _____ of some viruses.

capsid