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Microbiology > Chapter 6: Viruses and Prions > Flashcards

Chapter 6: Viruses and Prions Flashcards

1
Q

Viruses

A

submicroscopic (itty bitty); always infectious; acellular; obligate intracellular pathogens

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2
Q

Zoonotic Infections

A

infections/viruses that was originally in an animal and then spread to humans

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3
Q

Bacteriophages

A

or phages; viruses that infect bacteriaA

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4
Q

Animal Viruses

A

viruses that infect animals and humans

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5
Q

Virion

A

single, infectious virus particle; have an exterior protective protein capsid; contain genetic material (DNA or RNA)

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6
Q

Capsid

A

protein shell that packages and protects the genome; accounts for the bulk of a virions mass; made of capsomere subunits

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7
Q

Helical Capsids

A

look like a hollow tube

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8
Q

Icosahedral Capsids

A

look like three dimensional polygons

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9
Q

Complex Capsids

A

deviations from these two structures

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10
Q

Bacteriophages exhibit a complex capsid structure…

A

usually have capsids with icosahedral symmetry; often their capsids are associated with additional complex structure tha enable them to inhect their genome into target cells

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11
Q

Enveloped VIruses

A

have a lipid based envelope that surround the capsid; arise from budding off the host cell (take a portion of the phospholipid bilayer with them)

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12
Q

Naked Viruses

A

or nonenveloped; lack an envelope; arise from lysing (bursting) the host cell

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13
Q

Animal viruses are either…

A

enveloped or naked

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14
Q

Bacteriophages lyse cells so…

A

they are always (usually) naked

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15
Q

Spikes

A

or peplomers; may protrude from the viral capsid or envelope; glycoprotein extensions that help viruses attach and gain entry to host cells; only bind to specific factors on a given host cell (host specificity and tissue tropism)

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16
Q

Tissue Tropism

A

the ability for a virus to infect one type of tissue/ cell (say lung) and then migrate and infect other parts (say skin cells)

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17
Q

Influenza A Spikes

A

hemagglutinin (HA); neuraminidase (NA)

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18
Q

Viral Genes Encode

A

capsomere proteins; enzymes needed for viral replication; structural factors

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19
Q

Viral Genomes can either be…

A

RNA or DNA; single or double stranded; single or segmented sections; circular or linear

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20
Q

What is the goal of all viruses?

A

to get a host cell to make viral proteins, so more virions can be built

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21
Q

Double Stranded DNA Virus

A

dsDNA; viral DNA is transcribed using host RNA polymerases; mRNA is then translated into protein

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22
Q

Single Stranded DNA Viruses

A

ssDNA; converted to a double stranded form before transcription

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23
Q

Single Stranded Positive RNA

A

ssRNA+; ssRNA genome functions as an mRNA; directly translated by host cell ribosomes

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24
Q

Single Stranded Negative RNA

A

ssRNA-; RNA genome is complementary to mRNA; transcribed into mRNA by RNA dependent RNA polymerases (RdRPs)

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25
Q

Single Stranded Retroviruses

A

RNA genome is made into DNA by reverse transcriptase; DNA is usually inserted into the host DNA; DNA is then transcribed into mRNA

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26
Q

Double Stranded RNA Genome

A

dsRNA; transcribed to make mRNA; requires RNA dependent RNA polymerases

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27
Q

Why did viruses exhibit a faster rate of genomic change than living infectious agents?

A

quick replication time; large quantity of virions are produced; RNA genomes mutate more than DNA (DNA polymerases have proofreading capabilities and RNA polymerases do not)M

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28
Q

Mutations can be…

A

neutral, beneficial (rarely), or deleterious (normally)

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29
Q

Attenuated Strains

A

genetic changes that limit infectivity; used in vaccines

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30
Q

Beneficial Mutations may allow the Virus to…

A

escape host immune sustem detection; broaden host range; expand tropism (the type of cells or tisses the virus infects); increase infectivity

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31
Q

Reassortment

A

may occur when two different viral strains coinfect a single host cell; leads to new viral strains; ex) influenza virus;

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32
Q

Antigens

A

things that trigger the immune system response; such as spikes on a virus

33
Q

Antigenic Drift

A

frequent and small changes; for influenza it changes HA and NA spikes; eventually leads to a different enough virus that the immune system does not have antibodies to

34
Q

Antigenic Shift

A

major genetic reassortment; does not take a long time it is sudden; can lead to increased infectivity or expanded host range; people have no residual immune protection from infections or vaccinations because it is a new strain; sets the stage for a pandemic

35
Q

Viruses are grouped by the following properties…

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)

36
Q

Host Range

A

refers to a collection of species that a virus can infect; some viruses infect more than one species, while others infect only one species; ex) measles can only infect humans

37
Q

Tropism

A

refers to the tissues or cell specificity (due to viral surface factors); some viruses can infecct a wide range of host cells or tissues (broad tropism); other virsues can infect only one type of host cells or tissue (narrow tropism)

38
Q

What viruses are the smallest?

A

rhinoviruses and polioviruses; 30nm

39
Q

What is one of the largest viruses?

A

pithovirus; length of 1500nm

40
Q

What is the highest taxon for viruses?

A

phylum; they do not have a domain or kingdom

41
Q

Bacteriorphage Lytic Replication

A

1) Attachment (adsorption, phage binds); 2) Penetration (Entry, phage inhect genetic material); 3) replication (synthesis, commandeers host cell); 4) Assembly (maturation, genome packed and structures assemebled); 5) release (host cell lyses and new phages released)

42
Q

Lysogenic Replication

A

done by temperate phages; attachment; penetration; phage genome is oncorporated into host cell genome forming a prophage; as the cell divides it copies the prophage; host cell is stressed, the prophage may excise itself from host (bc it will die if the host dies); phage enters the lytic repliation pathway

43
Q

What are the 6 steps of Animal Virus Replication

A

attachment, penetration,m uncoating, replication, assembly, and release

44
Q

Acute Infections

A

viruses infect a host cell and new virions are made immediately

45
Q

Persistent INfections

A

virsues have replication strategies that allow them to avoid immune system clearance; chronic or lantent

46
Q

Chronic Infections are characterized by…

A

continous release of virions over time (months or years); slow progressions of disease

47
Q

Provirus

A

integration of viral genome into the host cell

48
Q

Latent Infections

A

distinguished by flare-ups with intermittent periods of dormancy (latency); during flare up- virions are shed, person experiences symptoms; flare ups can be triggered by stress (fever, sunburn, hormone level changes)

49
Q

Herpesviridae Family

A

notorious for causing latent infections; Human herpes virus 1 causes cold sores; HSV 2 causes genital herpes; Variculla zoster virus (HHV3) causes chicken pox and shingles

50
Q

Oncogenic Viruses

A

cause 10-15% of cancers; cause cancer by stimulating uncontrolled host cell division and/or decreasing host cell responsiveness to death signals; ex) human papilloma viruses (HPVs) and Human T-Lymphotropic Viruses

51
Q

Growing Bacteriophages

A

can be grown in the lab with realitve ease

52
Q

Plaque Assays

A

bacteria are gown on a petri plate; pahge infect cells then lyse out of the cell; infect adjacent cells; lysed cells leave a clear zone (plaque)

53
Q

Plaque Forming Units

A

are the quanity of bacteriophages in an initial volume of sample

54
Q

Viral Titer

A

the quantity of virus present in a given volume of sample

55
Q

Growing Animal Viruses

A

animal viruses are more difficult to cultivate than bacteriophages; most animal virsues are grown using tissue culture techniques; live anime hosts (mice, rats, guinea pigs) may be required to support growth of some viruses; embryonted eggs (fertilized eggs) are also useful for growing certain viruses

56
Q

Specificity

A

means that the test only detects the virus(es) of interest (no false positives)

57
Q

Sensitivity

A

means the test detects very low levels of the target (no false negatives)

58
Q

Agglutination Tests

A

purified antibodies linked to tiny latex beads; mixed with the sample; antibodies bind the viral antigen; beads agglutinate

59
Q

Latex Agglutination Tests

A

viral antigens linked to tiny latex beads; mixed with the sample; patient antibodies bind the viral antigen; beads agglutinate

60
Q

Enzyme Linked Immunosorbent Assays (ELISA)

A

can be adapted to detect either anitgens or antibodies in a sample; target adheres to a surface; change of color indicated binding

61
Q

Limitations of ELISA and Agglutination Assays

A

sample being tested must be a liquid; antigens must be fairly well characterized; virsues can undergo an antigenic shift making it no longer detectable; takes time to build up detectablt anitbodies (seroconversion window) ; therefore it is helpful to use a combination of detection methods

62
Q

Detecting Viral Genetic Material

A

to perform the test: collect a clinical sample (sputum, blood, cerebrospinal fluid or tissue); DNA and RNA are extracted; very specific segments of viral nucleic acid are detected by fluorescent-labeled probes, sequencing, PCR (polymerase chain reaction)

63
Q

Difficulties when designing antiviral drugs

A

viruses are obligate intracellular pathogens; antivirals should be slectively toxic; viruses have fewer chemically distinct targets than living pathogens

64
Q

Antiviral Drugs treat but do not cure

A

only limit infections rather than cure them; there are a few effective antiviral agents; prevention of serious viral disease through vaccination is important; vaccines train the immune sys to recognize viruses and are an effective means to limit infection

65
Q

Postexposure Prophylaxis

A

laboratory-prepared mixture of injectable antibodies prevents viruses from binding and entering host cells; used shortly after suspected exposure; used to treat rabies and HIV

66
Q

Docosanol

A

blocks viral entry into host cells; ised to treat cold cores caused by HHV-1

67
Q

Palivizumab

A

injectable antibody preparation; blocks fusion of the respiratory syncytial virus (RSV)

68
Q

Nuceloside Analogs

A

block replication; at least a dozen drugs in this class; activated into compounds that mimic normal nucleotides (A,G, C, T, and U); chemical dead end for nucleic acid replication

69
Q

Acyclovir

A

example of nucleoside analogs; inhibits DNA replication; effective agianst HHV-1, 2 or caricella zoster vrius

70
Q

Ribavirin

A

example of nucleoside analogs; targets RNA polymerases; effective against respiratory syncytial virus and hepatitis C virus

71
Q

Nucleoside Reverse Transcriptase Inhibitors

A

NRTIs; target reveerse transcriptase enzymes; azidothymidine

72
Q

Anitsense Antivirals

A

shorts sequences of nucleotides complementary to the viral RNA; bind to viral RNA inhibiting translation; targeted RNA is destroyed by cellular enzymes; ex) vitrave

73
Q

Interferons

A

naturally occuring substances released by cells in response to viral infections; signla the presence of a virus; neighboring, uninfected cells make defensie changes that limit viral entry and replication; can be produced in the lab and adminitered to help limit the pregression of certain viral infections

74
Q

Oseltamivir and Zanamivir

A

tamiflu and relenza; prevent influenza a and B virions from budding off the host cell curface

75
Q

Prions

A

infectious proteins; no genetic material; do not replicated; cause transmissible spongiform encephalopathies (TSEs)

76
Q

Types of Spongiform Encephalopathies

A

can be inherited or acquired; gerstmann straussler schienker syndrome; fatal familial insomnia (both inherited); creuzfeldt jakob disease (CJD)

77
Q

Some Neurodegenerative Disease exhibit Prion-like Features

A

been associated with misfolded proteins in thebrain; alsheimers disease; parkisons disease; amyotrophic laterla sclerosis

78
Q
A

Microbiology (9 decks)

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