Microbiology Ch.6 Viruses and Prions Study Guide

Define virus.

Nonliving/noncellular entities that can infect animal, plant, or bacterial cells; can have a DNA or RNA genome.

Can viruses synthesize their own nucleic acids and proteins apart from a host?

No

Viruses are obligate intracellular pathogens. What does this mean?

disease causing microbes that must invade living cells and hijack their biochemical and cellular tools to replicate

What is a virus that infects a bacterium called? What is a virion?

bacteriophages; a singe infectious virus particle

What is a capsid and what macromolecule makes up the capsid?

the protein shell that packages and proteins a virion's genome, accounts for bulk of virion mass; protein capsomeres

What is a capsomere?

three-dimensional protein subunits that make up capsids

List three general virus capsid shapes

helical, icosahedral, complex

What macromolecule comprises the viral envelope?

lipids

What is a naked virus?

viruses that lack an envelope

Where does an enveloped virus obtain its envelope?

develop by budding from the host, taking a portion of the cell membrane with them as a coating when they go

What is another term for viral spikes?

peplomers

What macromolecules make up viral spikes?

glycoproteins

What part of the virus binds to specific factors on a host cell which determines the exact cell type a virus can infect?

spikes

The influenza virus that causes swine flu is called H1N1. Name the glycoproteins that produce "HA" and "NA" spikes, which are represented by the letters H and N, respectively, in H1N1.

hemagglutinin (HA) and neuraminidase (NA) spikes

In general, can a single virus's genome contain both DNA and RNA?

not usually

Which type of single-stranded RNA virus genome functions directly as mRNA?

sSRNA+

What enzyme is used by single-stranded antisense RNA (ssRNA-) viruses to make mRNA from an RNA template?

RNA-dependent RNA polymerases (RdRPs)

What is the function of the enzyme reverse transcriptase?

builds a double-stranded DNA using the single-stranded viral RNA genome as a template

Why do RNA viruses mutate more quickly than DNA viruses?

RNA polymerases , which copy RNA, don't have the proofreading capabilities of DNA polymerases

Do attenuated virus strains cause disease in healthy, non-immunocompromised hosts?

no, but they do stimulate an immune response

Define tropism

preference of a pathogen for a specific host (and even a specific tissue within the host)

The influenza virus undergoes processes called antigenic drift and antigen shift. Define these two processes and describe the outcome of each using the example of influenza. ANTIGENIC DRIFT

minor changes to HA and NA spikes resulting from frequent mutation of the influenza RNA genome (epidemic outbreaks)

The influenza virus undergoes processes called antigenic drift and antigen shift. Define these two processes and describe the outcome of each using the example of influenza. ANTIGENIC SHIFT

often lead to viral strains with new features such as increased infectivity or expanded host range (influenza pandemic)

The Pfizer and Moderna SARS-CoV-2 vaccines use which immunization strategy?

mRNA vaccinations

What viral protein is coded for by Pfizer and Moderna SARS-CoV-2 vaccines, which is then produced by the host?

spike protein

The Johnson and Johnson SARS-CoV-2 vaccine use which immunization strategy?

vector vaccine

Define host range.

collection of species that it can infect

Certain viruses, like Ebola, are said to have a broad tropism. What does that mean?

can infect a wide range of host cells or tissues

True or False: If the answer is "false", correct the statement.

Viruses are not classified into domains. Their highest taxonomic classification is kingdom

False, viruses are not assigned to domains or kingdoms; phylum level is highest taxon for viruses

In bacteriophage, what type of replication kills the host cell when new phage are released?

lytic replication pathway

What is a prophage?

phage genome incorporated into the host cell genome

What is the medical importance of phage conversion?

the ability to confer new pathogenic properties to bacterial cells

List the six steps of animal virus replication in the order they occur and briefly describe what occurs during each step.

1. attachment- viral surface proteins interact w/ host plasma membrane proteins

2. penetration- occurs by fusion or endocytosis

3. uncoating- genome released from capsid

4. replication- genome is replicated and viral proteins are made

5.assembly- new virions are assembled

6. release- virions are released by budding or lysis

Define acute infection.

short-term infections quickly cleared by the immune system (common cold and influenza)

Define persistent infection.

chronic or latent infections caused by persistent viruses that remain in the host cell for long period of time (weeks to a lifetime)

What is a provirus

viruses that cause persistent infections integrate their genome into a host cell

What is one of the most important advances in HIV treatment for healthcare providers who may have been exposed to HIV?

postexposure prophylaxis (PEP)

What is a latent infection?

infection in which the host is asymptomatic

Which virus causes the latent infection called cold sores?

Human Herpes Virus (HSV-1)

Which virus causes chickenpox? Which virus causes the latent infection called shingles?

varicella-zoster virus (HHV-3) causes chickenpox and shingles

What are oncogenic viruses?

viruses that cause cancer

According to the U.S. Centers for Disease Control and Prevention (CDC) what percentage of all cervical cancer cases are linked to HPV?

90%

Which two retroviruses form proviruses and can quietly persist in host cells for more than a decade before emerging to cause leukemia or lymphoma?

HTLV-1 and HTLV-2 (human T lymphotropic viruses)

What is a plaque? In theory, what does one plaque represent?

clear zones on the growing plate of bacteria; a single bacteriophage in the initial sample

What is a concern when vaccines are made from virions purified from fertilized chicken eggs?

People allergic to eggs can't be vaccinated with those types of vaccines

Define specificity in reference to diagnostic testing methods

the diagnostic test reliability detects only the virus(es) of interest w/o producing false-positive results

Define sensitivity in reference to diagnostic testing methods

the test detects very low levels of the target to limit false-negative results

What type of immunoassay adheres viral antigen to latex beads to determine if a patient sample contains antibodies made to the virus? (Remember, the test could also use antibody-coated latex beads to test if the patient's sample has the antigen that is specific to the antibody).

latex agglutination test

What type of immune assay adheres an antigen or antibody to a surface and usually changes color if binding occurs?

ELISA assay

Immunoassays such as agglutination and PCR have limitations. One limitation is seroconversion. What is a seroconversion window?

the period following infection for detectable antibodies to develop

What do PCR tests amplify? What does the acronym PCR stand for?

polymerase chain reactions amplify specific parts of a genetic sequence

What can't a viral infection be treated with antibiotics?

antibiotics are designed to target bacterial cell structures and biochemical processes

When developing drugs, what is selective toxicity and why is it important?

an antiviral that stops the pathogen but leaves host cells unharmed to be an effective drug rather than poison

What two categories of testing options are currently used to detect active SARS-CoV-2 infections?

reverse transcription-PCR (RT-PCR) test and antigen tests

What does the RT-PCR test detect?

detects the genetic material of SARS-CoV-2 (viral RNA)

What does the antigen test detect?

detects SARS-CoV-2 proteins

Which test is the "gold standard" test when detecting SARS-CoV-2 infection?

RT-PCR test

Define postexposure prophylaxis.

a prevention treatment applied after an exposure to limit infection

What are prions?

infectious proteins

What is the current theory explaining how normal prion proteins become misfolded?

the misfolded, infectious version of the prion protein makes contact w/ the normal version, causing changes to a normal protein's shape

Why are diseases caused by prions called spongiform encephalopathies?

as the brain tissue deteriorates, spongy holes are left in the tissue

Name two spongiform diseases that occur when a child inherits a parental gene that encodes a mutated form of the prion protein.

Gerstmann-Sträussler-Scheinker syndrome and fatal familial insomnia

Which type of acquired Creutzfeldt-Jakob disease (CJD) has been given the name mad cow disease?

Variant CJD

What is sporadic CJD linked to?

A spontaneous mutation in the normal cellular prion protein affecting 200-400 people in the U.S. every year

How does a person acquire iatrogenic CJD?

Contaminated surgical instruments or tissue transplants derived from infected cadavers

Several neurodegenerative diseases have been associated with misfolded proteins in the brain but are not considered spongiform encephalopathies. List three of them.

Alzheimer's, Parkinson's, and amyotrophic lateral sclerosis (ALS)

Bacteriophages use different mechanisms for host cell infection and viral replication. During the lytic replication pathway, bacteriophages infect the host bacterial cells and immediately build new virions. During which of the key steps is the genome packed into the capsid and phage structures put together?

Assembly

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

Latex agglutination test

Nucleic acid detection tecniques:

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

In a(n) _______ infection, viral replication peaks, followed by immune clearance of the virus

acute

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

Which of the following acellular agents do not have any genetic material and therefore do not replicate?

prions

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

integration

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

Which of the following are true about SARS-CoV-2?

SARS-CoV-2 causes Covid-19

the genome of SARS-CoV-2 undergoes mutations

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

Human T-lymphotropic viruses (HTLVs)

Human papilloma viruses (HPVs)

Which of the following statements are incorrect about the transmission of Creutzfeldt-Jakob disease?

-Creutzfeldt-Jakob disease is never inherited.

-Creutzfeldt-Jakob disease can be transmitted through respiratory droplets.

The protein shell that packages and protects the genome and also accounts for the bulk of a virion's mass is called a

capsid

Which of the following statements incorrectly describes viral spikes?

Lipid-based spikes make up the envelope that surrounds the capsid

The most common drugs that block replication are

nuceloside analogs

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

-viridae

Which of the following terms is used to describe the shape of a virus?

icosahedral

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

a double-stranded DNA genome

Viruses do not infect which of the following organisms?

viruses can infect all forms of life

Why are you supposed to get a new flu shot every year?

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

Which of the following is not a property used to group viruses?

unicellularity versus multicellularity

Which of the following is not a mechanism of an antiviral drug?

blocking viral ribosomes

Which of the following would be the best general description of a "virus"?

viruses are acellular infectious agents