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Microbiology > Chapter 6-Viruses and Prions > Flashcards

Chapter 6-Viruses and Prions Flashcards

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Biology 101 flashcards
1
Q

Define: virus

A

-submicroscopic, infectious agents

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2
Q

Define: virion

A

-single,infectious virus particle

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3
Q

Define: virology

A
  • the study of viruses
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4
Q

Define: bacteriophage

A

-viruses that infect bacteria

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5
Q

Define: pandemic

A
  • worldwide outbreak of disease
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6
Q

Define: Hemagglutinin

A
  • glycoproteins which cause red blood cells to agglutinate or clump together
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7
Q

Define: Neuraminidase

A

-an enzyme that catalyzes the breakdown of glycosides

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8
Q

Define: attenuated strain

A
  • genetic changes that limit infectivity
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9
Q

Define: prophage

A
  • in the lysogenic pathway, the result of the phage genome being incorporated into the host cells genome
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10
Q

Define: provirus

A

-formed when some viruses that cause persistent infections integrate their genome into the host cell

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11
Q

Define: reverse transcriptase

A
  • virally encoded enzyme that enables retroviruses to use their single stranded RNA genome to direct formation of DNA

*basically special enzymes that carry out reverse transcription

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12
Q

Steps of viral replication

A

Attachment: naked viruses attach to host cell membranes through capsid proteins

Penetration: enveloped viruses enter through endocytosis or membrane fusion while naked viruses enter by endocytosis

Uncoating: capsid is digested by enzymes in the endocytic vesicle or cytoplasm, or nucleus

Replication: genome is replicated and viral proteins are made

Assembly: new virions are formed

Release:

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13
Q

*know table 6.1

A
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14
Q

*Be able to diagram and label the parts of an enveloped and non-enveloped virus

*know the function of the parts of a virus

A

capsid: protein shell that packages and protects the genome (also accounts for the bulk of a virions mass)
capsomere: 3D subunits that account for a capsids shape
genome: entire collection of genetic material in a cell or virus
spikes: peplomers that protrude from the viral capsid or viral envelope
envelope: lipid based; surrounds the capsid

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15
Q

How are viruses classified?

A
  1. ) type of nucleic acid present (DNA or RNA)
  2. ) capsid symmetry (helical, icosahedral, or complex)
  3. ) presence or absence of an envelope
  4. ) genome architecture (ssDNA, ssRNA, etc.)
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16
Q

What is antigenic drift?

A
  • changes to the HA and NA spikes
  • minor changes
  • 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
17
Q

What is antigenic shift?

A
  • major genetic reassortment
  • broader mutations that lead to viral strains with new features, such as increased infectivity or expanded host range
18
Q

What is viral genome reassortment?

A

-when different viral strains coinfect a host cell, their genomes mix and can generate new viral combinations

19
Q

Lytic Replication (cycle)

*type of bacteriophage replication

A

-this pathway kills the host cell as newly made bacteriophages are released

20
Q

Lysogenic Replication (cycle)

*type of bacteriophage replication

A
21
Q

How is bacteriophage replication different from viral replication in animal cells?

A
  • bacteriophages have a lytic or lysogenic cycle
  • bacteriophages inject DNA into the host cell, while animal viruses enter via endocytosis or membrane fusion
  • bacteriophages do not go through uncoating
22
Q

What is an acute infection?

A

-viruses infect a host cell and new virions are made (nonpersistant)

23
Q

What is a chronic infection?

A
  • continuous release of virions over time and a slow progression of disease (persistent)
  • HIV
24
Q

What is a latent viral infection?

A
  • flare ups with intermittent periods of dormancy (persistent)
  • herpesviridae
25
Q

How does HIV replicate in human cells?

A
26
Q

How are viruses grown in the laboratory? (Bacteriophages)

A

Plaque assays

  • bacteria are grown on a petri plate
  • phage infects cell then lyse out of the cell
  • infect adjacent cells
  • lysed cells leave a clear zone

*each plaque represents a bacteriophage

Plaque forming units: quantity of bacteriophages in an initial volume of sample

Viral titer: quantity of virus present in a given volume of sample

27
Q

How are viruses grown in the laboratory? (Animal Viruses)

A
  • more difficult to cultivate than bacteriophages
  • most are grown using tissue culture techniques
  • live animal hosts may be used to support growth of some viruses
  • embryonated eggs are useful for growing certain viruses
28
Q

What is an oncogenic virus? What cancers does it cause?

A
  • virus that causes cancers
  • cause cancer by stimulating uncontrolled host cell division and/or decreasing host cell responsiveness to death signals
    ex. )
  • Human papilloma virus (HPV)
  • Human T-lymphotropic virus (HTLV)
29
Q

Agglutination Test

A
  • purified antibodies linked linked to tiny latex beads
  • mixed with the sample
  • antibodies bind the viral antigen
  • beads agglutinate
30
Q

Latex Agglutination Test

A
  • viral antigens linked to tiny latex beads
  • mixed with the sample
  • patient antibodies bind the viral antigen
  • beads agglutinate
31
Q

ELISA Test

A
  • can be adapted to detect either antigens or antibodies in a sample (early or later infections)
  • target adheres to surface
  • change of color indicates binding
32
Q

DNA Test

A
33
Q

How do antiviral drugs work?

A
  • antiviral drugs treat infections but don’t typically cure them
  • vaccinations are an effective means for limiting infection
  • viruses are obligate intracellular pathogens
  • antivirals should be selectively toxic
  • viruses have fewer chemically distinct targets than living pathogens
34
Q

Antiviral Drugs

A

Drugs that block viral attachement, penetration and uncoating

Postexposure prophylaxis

  • laboratory prepared mixture of injectible antibodies prevents viruses from binding and entering host cells
  • used directly after exposure
  • used to treat rabies and HIV

Docosanol

-blocks viral entry into host cells

-used to treat cold sores caused by HHV-1

Palivizumab

  • injectable antibody preparation
  • blocks fusion of the respiratory syncytial virus (RSV)
35
Q

Antiviral Drugs-

A

Drugs that target viral replication, assembly, and release

Nucleoside analogs

  • block replication
  • activated into compounds that mimic normal nucleotides
  • chemical dead end for nucleic acid replication
    ex. )Acyclovir-inhibits DNA replication of HHV-1, HHV-2

Ribavirin-targets RNA polymerases syncytial virus, hepatitis C

Nucleoside reverse transcriptase inhibitors

-targer reverse transcriptase enzymes

(AZT)

Antisense antivirals

-short sequences of nucleotides complementary to the viral DNA

  • bind to viral RNA inhibiting translation
  • targeted RNA destroyed by cellular enzymes
  • ex.) Vitravene

Interferons

  • signal the presence of a virus
  • neighboring, uninfected cells make defensive changes to limit viral entry and replication

seltamivir (Tamiflu) and zanamivir (Relenza)

-Prevent influenza A and influenza B virions from

budding off the host cell surface

36
Q

What is a prion?

A

–Infectious proteins; no genetic material

–Do not replicate

–Cause transmissible spongiform encephalopathies

(TSEs)

37
Q

Prion Infections

A

Gerstmann-Straussler-Schienker syndrome (Genetic)

•

Creuzfeldt-Jakob disease (CJD)

–

Consumption of contaminated meat

•

Chronic Wasting Disease- (Deer, Elk)

MT- S f Billings >50 deer tested positive 2017

N of Chester 3 deer tested positive

Spread thru urine, saliva, central nervous system

tissue, direct contact (feces?)

Not passed to humans?

•

Scrapie- Sheep

38
Q

How are prions spread/ treatments?

A

Death of the host occurs from

nerve cell death leading to

sponge-like holes in brain tissue.

–

Symptoms include:

dementia.

weakened muscles.

loss of balance.

–

This results from insoluble

aggregates of abnormal prions in

the brain.

•

The human form of TSE is called

variant CJD (Creutzfeldt-Jakob

disease)

Microbiology (10 decks)

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