mico chapter 6

Which of the following suffixes would be used to describe a viral family?

-viridae

Cells can only contain which of the following types of genomes?

A double-stranded DNA genome

Bacteriophage

A virus that infects bacteria

pairs for DNA

A-T G-C

Which of the following is a major difference between bacteriophages and animal viruses?

Animal viruses enter the host cell; bacteriophages inject their genome into the host without entering. -bacteriophage replication involves injection of naked nucleic acid into the host cell.

Which of the following methods is used to cultivate bacteriophages in the laboratory setting?

Bacteriophages are cultivated in bacteria in liquid broth or on solid medium.

What are the leading contributors to viral genome evolution and what are their potential effects on viral features?

Because of their relatively quick replication time and the large quantity of virions released within a host, viruses exhibit a faster rate of genomic change than do living infectious agents. Reassortment events also contribute to viral evolution. Reassortment may occur when two different viral strains coinfect a single host cell; their genomes can mix and generate new viral strains -Viral genetic reassortment is most likely to occur when different viral strains infect the same cell Beneficial mutations may allow the virus to escape host immune system detection, broaden host range, expand tropism (the type of cells or tissues the virus infects), or make the virus more infectious so that it is more easily spread from one host to the next. The effects of spontaneous mutations and recombination in viral evolution are classically modeled in influenza viruses.

mechanisms of an antiviral drug?

Blocking viral attachment Blocking viral penetration Blocking uncoating

Describe the features and functions of viral capsids, spikes, and envelopes.

Capsid: The protein shell that packages and protects the genome and also accounts for the bulk of a virion's mass -A capsid's shape is based on how the individual three-dimensional subunits, called capsomeres, are arranged. Spikes: protrude from the viral capsid or, if present, from the viral envelope. These glycoprotein extensions help viruses attach and gain entry to host cells. -Because they only bind to specific factors on a given host cell, spikes have an important role in determining what species and tissues the virus can infect, similar to how a lock and key must match -Spikes may be recognized by the host immune system that mounts an immune response to them. Envelope: A lipid-based coating that surrounds the capsid of some animal viruses -Enveloped viruses develop by budding from the host, taking a portion of the cell membrane with them as a coating when they go. often comprised of the host cell membrane.

prion diseases is found in deer and elk?

Chronic wasting disease

Assume a new enveloped RNA virus is causing an epidemic. Which of the following types of antivirals could be used to prevent the spread of or control the disease?

Detergents Interferon Nucleoside analogs

viral genome arrangements

Double-stranded RNA Segmented RNA Single-stranded DNA Linear DNA

HIV

HIV infects helper t cells t cells serve as a mediator between innate and adaptive immune systems which leads to aids is a chronic infection

virus and cancer links

Human herpes virus 8: Kaposi sarcoma Hepatitis B virus: liver cancer Human papilloma viruses: cervical cancer

Which of the following is oncogenic?

Human papilloma viruses

Which of the following oncogenic viruses may integrate into the host genome?

Human papilloma viruses (HPVs)

What is the fate of the prophage during the lysogenic stage?

It is copied every time the host DNA replicates.

Which of the following DNA virus families includes the viruses that cause warts and cervical cancer in humans?

Papillomaviridae

Which of the following is a potential feature of an animal virus (select all that apply)?

Presence of an envelope Presence of a naked icosahedral capsid Ability to integrate into the host cell's genome Ability to cause host cell lysis Ability to build DNA from an RNA template

RNA viruses are able to mutate more rapidly than DNA viruses because _______________.

RNA polymerases do not have proofreading capabilities

An RNA virus with an antisense or negative strand must have what enzymes to replicate?

RNA-dependent RNA polymerase

What part of the nervous system is most affected by fatal familial insomnia?

Thalamus

Why is there a need to be vaccinated with a new flu shot every year?

The RNA genome of influenza mutates frequently, causing minor changes to HA and NA spikes. This is referred to as antigenic drift.

How might phage conversion give a virus an evolutionary advantage?

The bacterium with the new trait might survive better, carrying the virus with it as a prophage.

How is the lytic cycle different from the lysogenic cycle with respect to the infected host cell?

The host cell dies during the lytic stage.

Where does the name "scrapie" come from?

The prion disorder causes infected sheep to scrape against objects until their skin is raw.

How do DNA viruses use their genomes to make mRNA?

The viral DNA is transcribed using host cell RNA polymerases, and the resulting mRNA is then translated into protein. If the virus is a single-stranded DNA virus (ssDNA), then it is converted to a double-stranded form before transcription is performed.

What would be the fate of a lytic bacteriophage if the host cell died prior to the assembly stage?

The virus would not be able to infect new hosts.

oncoviruses:

Their viral genome is maintained episomally in the cell. They stimulate cells to undergo cell division. They tend to integrate into the host cell genome.

Which of the following best describes the genomes of influenza, measles, Ebola, and rabies viruses?

They each have an RNA genome that is complementary to mRNA.

How is iatrogenic Creuzfeldt-Jakob disease (CJD) contracted versus variant CJD?

Variant CJD is caused by a prion that has a different protein sequence than other CJDs (mad cow ). accidental transmission of CJD to a patient as a result of a medical intervention (Iatrogenic)

Which of the following best describes a prophage?

When a phage genome is integrated into the host cell's chromosome -Lysogenic viral DNA which has integrated into the host genome

another term for a virus attaching to the host cell

adsorption

Zika virus is best described as a(n) _________ virus with a ________ genome.

enveloped, ssRNA+

Name the virus families that are medically important in humans.

figure 6.8

What is meant by host range and tropism?

host range: the collection of species that a pathogen can infect tropism: the type of cells or tissues the virus infects. The preference of a pathogen for a specific host cell.

Which enzyme is responsible for breaking down a host bacterium's cell wall so that the virus can leave the cell?

lysozyme

The most common drugs that block replication are ________.

nuceloside analogs

The definition of lysogeny is

phage DNA is incorporated into host cell DNA

anti-HIV drugs

protease inhibitors azidothymidine enfuviritide

Retroviruses produce mRNA by:

using reverse transcriptase to convert single- stranded RNA (ssRNA) to double-stranded DNA (dsDNA) and then using the dsDNA for transcription.

What is the primary reason that viruses are not considered alive?

viruses are not cells, they are acellular which mean nonliving. viruses are obligate intracellular parasite

Which type of method is used to determine if a prior exposure to a virus occurred?

Latex agglutination test

Why don't bacteriophages have the animal virus life cycle stage of "uncoating"?

Uncoating is characterized by the release of the genome from the capsid after the virion enters the cell. Bacteriophages do not enter the host cell but inject the genome from outside the cell.

Nucleic acid detection techniques:

can detect new viruses and early-stage infections that antibody-antigen tests are likely to miss.

What are the naming conventions for viruses?

table 6.2 Order, Family, Subfamily, Genus, Species, common name

phage conversion

- the ability to confer new pathogenic properties to bacterial cells -Phage conversion can provide new pathogenicity factors to a bacterium, such as the capacity to make certain toxins. Prophages sometimes provide bacteria with genes that encode pathogenicity factors through phage conversion -Ex: Corynebacterium diphtheria, Clostridium botulinum, e. coli

Virons

-A single, infectious, fully developed virus particle -All virions have an exterior protective protein capsid, packed with genetic material (DNA or RNA). -They are composed of nucleic acid, proteins and maybe an envelope 1-nucleic acid: in the form of RNA or DNA. Single or double stranded. can be circular, segmented or linear 2-protein types include: capside (protein coat made of capsomeres) or spikes which protrude out from capsid or envelope. (ex: hemagglutinin HA attachment. Neuraminidase NA release ) 3- might have an envelope: phospholipids or plasma membrane covering derived from infected cell as it buds

What criteria are used to classify viruses?

-Type of nucleic acid present (DNA or RNA) -Capsid symmetry (helical, icosahedral, or complex) -Presence or absence of an envelope -Genome architecture (ssDNA, ssRNA, etc.)

Retrovirus replication

1) Attachment and penetration: HIV attaches to host cell via fusion 2) Uncoating 3) reverse transcription: upon entry, HIV genome is reverse transcribed by viral reverse transcriptase 4) viral integration: DNA version of the HIV genome integrates into the host genome to make provirus 5) replication: provirus is transcribed to make viral genome and translated to make viral proteins 6)assembly 7)release: HIV provirus directs the production of new virions, which bug from the host cell Retroviruses like HIV are notorious for forming a provirus in infected cells and then remaining silent for years before releasing sufficient virions to destroy the host's immune system Figure 6.17

4 things that can lead to mutation

1) lack of proofreading by RdPP's 2) reassortment: 2 different strains can coinfect a single host and genomes mix 3) antigenic drift 4) antigenic shift

Which of the following would be the first step in the biosynthesis of a virus with reverse transcriptase?

A complementary strand of DNA must be synthesized from an RNA template.

acute, latent and chronic infections

Acute: (short duration like the common cold)The first of three broad stages in HIV infection; usually marked by flu-like symptoms that resolve within a few weeks. In this stage of infection, the virus enters the body, circulates the blood, and infects an array of white blood cells (especially T-helper cells) -viral replication peaks, followed by immune clearance of the virus. Latent: Infection in which the host does not have sign or symptoms; if conditions are right, the agent can cause an active illness; infections that may be distinguishable by flare-ups with intermittent periods of dormancy. Chronic: characterized by continuous release of virions over time and a slow progression of disease. Disease is not evident but can still be passed on to others. (hepatitis: you don't have symptoms for a very long time so you are not aware you have it)

Define antigenic shift and antigenic drift and describe how they influence influenza evolution and outbreaks.

Antigenic shift: A major genetic reassortment that dramatically changes the virus; often leads to viral strains with new features; leads to influenza pandemic Antigenic drift: minor genetic changes in a virus (small change in surface antigens ) that lead to the influenza epidemic -allow the virus to evade a quick antibody response by making the new strains different enough to go unrecognized by the immune system—even if the host had a prior interaction with a related strain

What are the steps in animal virus replication and what occurs in each step?

Figure 6.12 1)Attachment: Naked viruses attach to host cell membranes through capsid proteins. Other viruses (both naked and enveloped) use spikes. As described earlier, specificity of this binding is why viruses exhibit host range and tissue tropism. This makes attachment proteins a target for drug therapy to limit or prevent infection. One drug called maraviroc (Sezentry) works by blocking HIV's attachment to host cell proteins. 2)Penetration (Entry): Enveloped animal viruses enter the host cell through endocytosis or membrane fusion. Naked viruses mainly enter by endocytosis. In membrane fusion, the cell's plasma membrane and the viral envelope blend together, releasing the viral capsid into the cytoplasm. In endocytosis, viral binding to host cell surface receptors triggers uptake of the virus into vesicles. 3)Uncoating: Unlike bacteriophage capsids, animal virus capsids enter the host cells. The capsid is then entirely or partially broken down, releasing the viral genome. This uncoating varies by process and location. A virus that entered by endocytosis usually has its capsid digested away by enzymes in the endocytic vesicle. Poliovirus is an exception: It enters via endocytosis, but spits out its genome through a pore that forms in the capsid and the surrounding endocytic vesicle.5 Viruses entering by fusion may have their capsid degraded by enzymes in the host cell cytoplasm (Figure 6.14). Many DNA viruses don't undergo uncoating until their capsid is safely delivered to the host nucleus. 4)Replication (Synthesis): As stated earlier, DNA viruses import their genome into the host cell nucleus to be transcribed and replicated. The resulting mRNA is then shipped from nucleus to cytoplasm, where it is translated to make viral proteins. Most RNA viruses direct genome replication and protein synthesis from the cytoplasm, never entering the nucleus. Notable exceptions include the orthomyxoviruses (which cause influenza) and retroviruses such as HIV, which are RNA viruses but have a replication process that takes place in the nucleus. 5)Assembly: Sometimes new capsids are partially built and packed with the viral genome before finishing and sealing them. However, usually the capsid assembles around the genome. Enveloped viruses often require viral proteins to be embedded in the host cell plasma membrane before virion release. 6)Release: Newly assembled enveloped viruses are released by budding off the host cell or lysis. As they do so, they usually take a portion of the cell's plasma membrane, enriched with viral surface proteins, with them (Fig. 6.15). Naked viruses rupture the host cell during release, usually killing the cell.

You are comparing the size of different viruses. You are specifically interested in the size of the following viruses: Ebola virus, Poliovirus, Rhinivirus, and Pithovirus. Which of these viruses would be the smallest, and which the largest?

Poliovirus is the smallest; Pithovirus the largest.

What are prions and what diseases do they cause?

Prions: infectious proteins that can cause a disease such as transmissible spongiform encephalopathies; prions are transmissible by transplant or ingestion; some prions diseases are inherited. -do not have any genetic material and therefore do not replicate? Other diseases in humans include: CJD(linked to bovine spongiform encephalopathy in humans), Kura(from cannibalism also known as laughing disease) Gerstmann-Straussler-Schienker syndrome Sporadic Creuzfeldt-Jakob Disease Variant Creuzfeldt-Jakob Disease diseases in cows: bovine spongiform encephalopathies(BSE) When humans eat infected cows they may contract CJD

Protease Resistant Protein (PrP)

Prp:An enzyme that breaks down proteins. can not be broken down by typical proteases PrPc: type of Prp located in neurons and glial cells PrPc is converted to PrPsc which leads to brain damage (spongiform encephalopathy) PrPsc is necessary for replication of a prion resistant to high temps (autoclaves) and disinfectants when proteins change shape it can lead to diseases such as: alzheimer's, parkinson's, mad cow etc.

What are four ways that RNA viruses may make mRNA?

The RNA genome functions as an mRNA: A single-stranded RNA genome may be in a form that can be directly translated by host cell ribosomes in the cytoplasm. These are single-stranded, positive, or sense-stranded RNA (ssRNA+) viruses. They include the causative agents of polio, rubella, West Nile encephalitis, and dengue fever. The RNA genome is complementary to mRNA: This group of RNA viruses encompasses a wide variety of pathogens, including the causative agents of influenza, measles, Ebola, and rabies. These single-stranded, antisense, or negative-stranded RNA (ssRNA-) viruses have an RNA genome that is complementary to mRNA. Consequently, their RNA genome must be transcribed into a readable mRNA format before translation. This is accomplished by virally encoded enzymes called RNA-dependent RNA polymerases (RdRPs). Unlike host cell RNA polymerases that build new RNA from a DNA template, RdRPs build new RNA from an existing RNA template. The RNA genome makes DNA, which is then transcribed to make mRNA: Using the virally encoded enzyme called reverse transcriptase, retroviruses use their single-stranded RNA genome to direct formation of DNA. (See Chapter 5 for more on reverse transcription.) The DNA is usually inserted into the host genome and then transcribed in the nucleus, and the resulting mRNA is translated. HIV (the virus that causes AIDS) as well as other human T-cell leukemia viruses (HTLVs) carry out reverse transcription and operate through a DNA intermediate. The double-stranded RNA genome is transcribed to make mRNA: If the virus has a double-stranded RNA (dsRNA) genome, then the RNA has to be unwound, so that RNA polymerases can transcribe it into an mRNA format. The process resembles that of a double-stranded DNA virus, but instead of using host cell RNA polymerases, virally encoded RNA-dependent RNA polymerases are required. Rotaviruses, which cause severe diarrhea, are an example of dsRNA viruses.

Lysogenic Cycle pathway of replication FOR bacteriophage (temperate)

The first two steps of the lysogenic cycle, attachment and penetration, are the same as in the lytic pathway. However, following penetration, the phage genome is incorporated into the host cell genome, forming a prophage. As the infected bacterial cell divides, it copies its own genome as well as the prophage's genome. Therefore, a single infection event ultimately results in many cells carrying the bacteriophage's genome. If a host cell carrying a prophage is stressed, the prophage may excise itself from the host genome and enter the lytic replication pathway. This "abandon ship" approach allows the bacteriophage to replicate and find a new host before its current host cell dies.

You are studying an unknown virus that does not perform transcription to make viral proteins. Which of the following characteristics must also be true for this unknown virus?

The virus has a positive, sense-stranded RNA genome.

properties used to group viruses?

Type of nucleic acid present (DNA or RNA) Capsid symmetry (helical, icosahedral, or complex) Presence or absence of an envelope Icosahedral shaped; May appear spherical, but are three-dimensional polygons

describe enveloped virus replication?

Viral proteins embedded in the plasma membrane Release through budding Penetration through membrane fusion

Why do RNA viruses evolve faster than DNA viruses?

because RNA polymerases, which copy RNA, do not have the proofreading capabilities of DNA polymerases. As a result, DNA viruses may mutate once per thousand rounds of genome copying, while RNA viruses may mutate as frequently as once every round of genome copying.

Compare and contrast production of viral proteins for dsDNA viruses and ssRNA+ viruses.

dsDNA genomes can express genes using the normal host machinery, RNA polymerase and ribosomes. ssRNA+ genomes can be used directly as mRNA by the ribosome.

An accidental needle stick occurs during routine treatment of what an HIV-positive patient who arrives at your clinic. Immediate administration of can block viral entry.

enfuvirtide

Which of the following events might trigger induction of a temperate bacteriophage?

exposure to UV light

Lytic Cycle pathway of replication FOR bacteriophage (virulent)

figure 6.10 1) Attachment (adsorption): Since viruses can't move on their own, the bacteriophage and host cell usually come together from random contact. Bacteriophage tail fibers help the virus adhere to the specific protein on the bacterial cell wall surface. The specificity of these interactions means that certain bacteriophages only infect certain bacteria. 2) Penetration (entry): Like a hypodermic needle, the bacteriophage injects genetic material into the cell, through the host's cell wall and plasma membrane. The empty capsid remains outside the cell. (viral Dna is introduced to the cell) 3) Replication (synthesis): Once the viral genome is inside, the bacteriophage commandeers host cell factors to transcribe and translate viral genes. Among the early viral proteins that get made are DNAases (DNA-degrading enzymes) that break up the host cell's DNA. The viral genome also encodes proteins to build new phage particles and enzymes that will copy the viral genome. 4) Assembly (maturation): Once all the parts of the bacteriophage are replicated, viral factors pack the viral genome into the capsid and the remaining phage parts are assembled. Hundreds to thousands of new bacteriophages may be generated in this step. 5)Release: Bacteriophages encode an enzyme called lysozyme, which breaks down host cell walls and causes bacterial cell lysis (bursting) once the newly assembled phages are mature. The released bacteriophages can then infect other cells. The envelope of a virus is acquired in this stage

What are the possible genomic variations for viruses?

figure 6.4 viruses can have either an RNA- or DNA-based genome (but usually not both),3 and the nucleic acid present can be either single or double stranded. viral genome can exist in diverse arrangements. It may be spread over multiple segmented sections, or it could be a single circular or linear molecule

The avian influenza virus host range includes all of the following

humans geese swine

Which of the following steps is found in the lysogenic replication pathway but not in the lytic replication pathway?

integration

An effective treatment for hepatitis B and hepatitis C is

interferon-alfa

When a virus has an envelope it:

it likely escapes its host cell by budding.

What happens to naked viruses?

naked viruses lyse (burst) out of host cells and do not coat themselves in an envelope. Animal viruses may be either enveloped or naked. Because all bacteriophages lyse host cells, these complex-shaped viruses are therefore always naked.

A virus that can only infect humans would best be described as having a ______________.

narrow host range -includes: Zika virus hepatitis B virus human T-lymphotrophic viruses

Mutations of virus

neutral: does no harm or help to the virus beneficial: allows virus to escape immune system detection -broadens hosts range -expands its tropism so it can target different cells. -increases infectivity to increase speed deleterious: results in attenuated (decreases infectivity but still provokes an immune response in the host) virus. -a lot of vaccines are attenuated viruses

Growth of bacteriophages on a lawn of bacteria is indicated by the presence of _

plaques

All of the following explain why viral genomes evolve rapidly

reassortment events cause rapid viral evolution. RNA viruses have a high mutation rate. quick replication time of viruses.

anti-influenza drugs

rimantadine oseltamivir amantadine

How do viruses differ from prokaryotes and eukaryotes?

see table 6.1 viruses are incapable of synthesizing their own components, such as nucleic acids or proteins, without the help of the host cells they infect. -Unlike prokaryotes and eukaryotes, viruses are not considered alive. -Unlike prokaryotes and eukaryotes, viruses are incapable of replicating independently from a host cell. -Unlike prokaryotes and eukaryotes, viruses are classified as acellular particles. Viruses: Protein capsid with nucleic acid. Eukaryotes: May be viewed with light microscopy. Prokaryotes: Cells without nuclei or membrane-bound organelles. Eukaryotes: Division using mitosis and meiosis. Viruses: DNA or RNA genome. Prokaryotes: May be viewed with light microscopy.

Frequent mutations in Influenza A change the protein makeup of hemagglutinin (HA) and neuraminidase (NA) __________.

spikes

The rabies virus primarily affects the nervous system. The specificity that the rabies virus has for neuronal host cells is primarily dictated by __________________________.

the spikes that protrude from its viral envelope