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VP - Microbio > Wk 11/12 > Flashcards

Wk 11/12 Flashcards

1
Q

T/F: Viruses are definitely considered to be a part of the tree of life and a living thing, even though they don’t have a metabolism and standard cellular organelles of their own.

A

False, it is not a definitive thing, and they are non living entities (?!)

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2
Q

T/F: Loeffler and Frosch developed the first proof of viral infections in animals, while Dimitri Ivanosky used diseased tobacco plants to discover filterable infectious agents within them.

A

True

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3
Q

Discuss the general properties of viruses (relative/general size, facultative or obligate intracellular parasite, survival rate outside of host cells)

A

Small and filterable
Obligate intracellular parasites (hijack and utilize cellular metabolism to make energy or proteins)
Survive hours to days outside host cells - reduced infectivity with increased time outside host cells

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4
Q

T/F: many viruses have shown to be host specific but when selecting a host range, it is determined by virus requirements for attachments to host cell

A

True

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5
Q

Define giant viruses and provide two examples.

A

Viruses whose viral particle magnitude, structure, genome length, and complexity are larger than standard virus families
Ex. Mimivirus, medusavirus

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6
Q

In a general virus structure, what can a naked virus versus an enveloped one include?

A

Naked: nucleic acid, capsid, capsomer
Enveloped: All with envelope (w/ proteins, glycoproteins) and envelope spikes

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7
Q

Describe the difference between the viral genome and nucleocapsid.

A

Viral genome: viral RNA or DNA
Nucleocapsid: capsid + viral genome

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8
Q

What is the difference between capsid and capsomer?

A

Capsid: the protein shell that encases the viral genome that can exist in different symmetries with the function to protect, antigenic sites, and attachment to host cells
Capsomer: Basic subunit protein of the capsid

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9
Q

What is the structure and purpose of the envelope of a virus?

A

Structure: outer membrane of a lipid bilayer with embedded (glyco)proteins surrounding protein capsid
Purpose: facilitate virus entry to host cells, helps virus to adapt fast and evade host immune system

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10
Q

Define virion

A

Complete virus particle with RNA or DNA core with a protein coat, sometimes with an envelope and is the extracellular infective form of a virus

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11
Q

Define virus

A

Any aspect of the infectious agent including, infectious (virion) or inactivated virus particle, or viral nuclei acid and protein in the infected host cell

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12
Q

Define viroid

A

Infectious particle smaller than any of the known viruses, but AN AGENT OF CERTAIN PLANT DISEASES
Small circular RNA molecule, lacking the protein coat of a virus

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13
Q

What are four ways in classifying viruses?

A

Presence of envelope, capsid symmetry, nucleic acid, and genome architecture

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14
Q

T/F: enveloped viruses are the only type of viruses exist.

A

False, they can get naked as well ;)

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15
Q

What are the three types of capsid symmetry?

A

Helical, isohedral, and complex

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16
Q

Describe the helical capsid symmetry. Explain the difference between animal and plant viruses with helical nucleocapsids.

A

Description: capsomeres and nucleic acid are wound together and form a helical or spiral tube
Animal viruses are always enclosed within a lipoprotein envelope, while plant viruses commonly have naked helical nucleocapsids

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17
Q

How is the isohedral capsid symmetry formed?

A

(5) protomeres aggregate to form capsomers which are either hexons or pentons

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18
Q

Why can viruses be considered to have a complex capsid symmetry? Name two examples

A

Virions are composed of several parts each with separate symmetries and shapes.
Ex; bacteriophage (icosahedral head and helical tail) and pox virus

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19
Q

Explain the differences between DNA and RNA viruses

A

DNA: very stable, usu 2x helix, accurate replication, larger genomes
RNA: less stable, mixture of ss and ds, error prone replication

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20
Q

What is sense in terms of genome architecture? Differentiate between positive and negative sense.

A

Sense: polarity of the genome in relation to mRNA (5’ —> 3’)
Positive: genetic material has same polarity as viral mRNA (no need for transcription , direct translation into proteins)
Negative: genetic material is complementary to mRNA (transcription before translation)

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21
Q

Define Baltimore classification.

A

Clusters viruses into 7 groups depending on replication strategy of mRNA

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22
Q

What is a reservoir?

A

Habitat or population in which an infectious agent normally lives, grows and multiplies; can maintain pathogens over time; in animals, humans, environment

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23
Q

What are some misconceptions about reservoirs?

A

Not all sick animals are reservoirs, reservoir does not mean “not ill,” an individual can be killed by the agent, but the population maintains the agent

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24
Q

What are the 7ish examples of routes of transmission?

A

Abiotic environmental factors, animal vectors, direct contact, indirect contact, droplets, airborne, fecal/oral

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25
Q

What is the difference between the airborne versus droplet route of transmission?

A

Airborne: can float in air for hours, can be inhaled, <5-100um
Droplet: can travel less than 1m, cannot be inhaled, >100 um

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26
Q

What are four ways diseases can be transmitted?

A

Horizontal transmission, vertical transmission, zoonotic, cross-species transmission

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27
Q

Describe the viral genome (what do their genes code for?)

A

Contains only few genes, genes encode for structural components (capsid components), genes encode for enzymes necessary in the virus cycle, mainly for nucleic acid synthesis

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28
Q

T/F: viruses are facultative intracellular parasites, and can make energy and proteins by themselves. Their proteins and enzymes are synthesized and functional both inside and outside of the host cell, and do not need to be supplied by the host cell

A

False, they are obligate intracellular parasites. They need to be supplied by the host cell in order to make energy and proteins, making them only functional inside the host cell

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29
Q

List the viral replication cycle in order

A
  1. Attachment, 2. Penetration, 3. Uncoating, 4. Replication, 5. Assembly, 6. Release
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30
Q

Describe the first step of the viral replication cycle: attachment/adsorption.

A

The process of attachment of the virion to the host cell surface
Interactions between capsid (glycol)proteins or envelope spikes and host cell receptors determine host specificity and tissue specificity of viruses
Receptors: selectively bind specific substance and mediate it’s entry or action into the cell
Viruses have evolved to use host cell receptors where animal ones have attachment sites distributed all over the cell surface

31
Q

Describe the second step of the viral replication cycle: penetration/entry (definition, dependent on)

A

The process of bringing the viral genome to the other side of the host cell’s plasma membrane by entry of (a portion of) the virion
Dependent on energy and temperature

32
Q

A host cell is classified as susceptible to virus if a virus can enter the cell. What are the three mechanisms a virus can enter?

A

Endocytosis, membrane fusion, direct penetration

33
Q

Define endocytosis

A

Process in which the virus gains entry into the host cell without passing through the cell membrane via active transport

34
Q

Define membrane fusion (definition, mediated with or without pH, type of viruses susceptible to this)

A

Process of merging fusion of the virus envelope with the host cell lipid bilayer membrane
Mediated by pH independent fusion proteins or pH dependent fusion proteins that are anchored on the virus surface
Only for enveloped viruses

35
Q

Define penetration (definition, what mediates a pore’s location, restricted to which viruses)

A

Def: process of viral genome injection into the host cell’s cytoplasm after initial attachment
Pore-mediated: relation of pore in host membrane mediated by viral pore-forming peptide associated in viral capsid
Restricted to naked viruses AND viruses which genome is required for infection

36
Q

Describe the third step of the viral replication cycle: uncoating

A

The process of capsid protein removal and release of viral genome in the host cell
Disassembly of the capsid in a programmed multi step process mediated by cell pH and lysosomal enzymes

37
Q

T/F: large viruses have their own uncoating enzymes, and there is a loss of infection for virions

A

True

38
Q

Describe the fourth step of the viral replication cycle: replication/synthesis.

A

The genomic expression the viruses, using host cellular machinery to replicate and make functional and structural proteins

39
Q

In addition to Baltimore classification, what key enzymes are important for replication/synthesis in viruses and why?

A

Reverse transcriptase: transcript + sense mRNA to ds DNA
RNA dependent RNA polymerase: form + sense mRNA to - sense mRNA and vice versa
DNA Polymerase: form DNA copies from DNA

40
Q

mRNA synthesis is essential for viral protein synthesis. How does DNA viruses and RNA viruses differ in their mRNA synthesis and what are examples of exceptions for each?

A

DNA viruses: mRNA synthesis and replication in nucleus using host cell’s DNA-dependent RNA polymerase (exception: Pox virus - due to size)
RNA viruses: mRNA synthesis and replication in cytoplasm (exception: retroviruses, influenza viruses)

41
Q

In replication/synthesis, what is the difference in early and late protein synthesis?

A

Early: synthesis of enzyme polymerase which makes many copies of genetic material of progeny viruses
Late: synthesis of capsid and/or envelop proteins

42
Q

What are the differences in genomic expression between taxonomic groups of viruses?

A

Strandedness & Sense
Location of production of mRNA

43
Q

Describe the fifth step of the viral replication cycle: assembly and maturation. Where would it get packaged and which organelle holds that role?

A

Process of packing the viral genome and proteins into new virions following a specific order
In nucleus, cytoplasm , and/or cell membrane
Role of golgi

44
Q

Describe the last step of the viral replication cycle: release/shedding. (List the 3 mechanisms and what type of virions does which mechanism)

A

The process of expulsion and release of progeny virions following replication in infected host cells
Mechanisms: budding (enveloped virions), exocytosis, cell lysis (naked virions)

45
Q

T/F: most bacteriophages require cell lysis to be released from the infected cell

A

True

46
Q

What are the steps the life cycle of DNA viruses?

A

1) virions attaches to host cell
2) virion enters cells and its DNA is uncoated
3) a portion of viral DNA is transcribed, producing mRNA that encodes “early” viral proteins
4) viral DNA is replicated and some viral proteins are made
5) late translation; capsid proteins are synthesized
6) virions mature and are released

47
Q

Why is Pox virus an exception to the life cycle of DNA viruses?

A

Large viruses, more gene,s, carry their own RNA polymerase, produced mRNA in the cytoplasm

48
Q

What is the difference between plus sense versus minus sense single strand RNA virus in their life cycle?

A

Plus: fastest way to do translation/transcription, as you can immediately start translation
Minus: first needs to be transcribed towards +sense mRNA

49
Q

What are the exceptions to the life cycle of RNA viruses and why?

A

Influenza: viral DNA enters the nucleus
Retroviruses: reverse transcriptase & viral DNA enters host’s nucleus and integrate as a provirus

50
Q

In the third life cycle of bacteriophages, it can either be lytic or lysogenic. Define the lytic cycle.

A

phage infects the cell —> phage DNA circularizes remaining separate form the host DNA —> phage DNA replicates and phage proteins are made. New phage particles are assembled —> cell lyses, releasing phage

51
Q

In the third life cycle of bacteriophages, it can either be lytic or lysogenic. Define the lysogenic cycle. What makes it different from the lytic cycle?

A

Phage infects a cell —> phage DNA becomes incorporated into the host genome —> cell divided and propagate is passed on to daughter cells —> under stressful conditions, the phage DNA excised from the bacterial chromosome and enters the lytic cycle

52
Q

Compare prophages and proviruses

A

Prophage: virus genome of bacteriophage that is integrated into the DNA of a host cell; in life cycle of bacteriophages
Provirus: virus genome that is integrated into the DNA of a host cell

53
Q

When referring to the mechanism of cell injury, what are the results we can see viral infections have on host cells?

A

Inhibition (host cell nucleic acid synthesis, RNA transcription, protein synthesis), cytopathic effect, neoplasticism transformation, drive host cell to apoptosis, non-cytocidal changes

54
Q

What are the three general effects viral infections can have on host cells?

A

Abnormal cell growth, cell damage/death (lysis, cell membrane alteration, apoptosis), no apparent changes (persistent, latent, immuno-suppression)

55
Q

What are the two types of viruses with specific host range and effect?

A

Bacteriophages: viruses that infect bacteria and can kill bacteria; applied in phage therapy
Oncolytic viruses: viruses that infect and kill cancer elks through oncolysis; applied in cancer therapy through stimulation of host anti-tumor immune response

56
Q

In a viral growth curve, the timing of a one step growth cycle varies depending on virus and host. What is the difference in growth of bacterial viruses versus animal viruses.

A

Bacterial: 20-60min
Animal: 8-40hr

57
Q

Define the eclipse period of the viral growth curve. What stage(s) of the viral replication cycle does this happen

A

Infectivity of the virus disappears during uncoating and replication stage

58
Q

Define the latent period of the viral growth curve. What stages of the viral replication cycle are seen here?

A

Replication of viral nucleic acid and protein. Uncoating, replication, reassembly/maturation (kinda)

59
Q

Define the maturation period of the viral growth curve

A

Assembly of viral genome and protein into mature virus particles. If at this time cells are broken, active virus can be detected

60
Q

Define viremia and the difference between passive and active viremia

A

Viremia: spread of viruses via bloodstream
Passive: direct inoculation of virus into host’s bloodstream and no replication at site of entry (ex contaminated syringe, bite of arthropods)
Active: viremia following virus replication in host

61
Q

Compare primary and secondary viremia

A

Both are subcategories of active viremia
Primary: spreading into the blood from infected area
Secondary: spreading to other organs/tissues

62
Q

What are the five patterns of infection in a host?

A

Acute, latent, chronic, persistent, persistent slow

63
Q

Compare acute, latent and chronic infection

A

Acute: rapid onset of disease and symptoms
Latent: virus remains in asymptomatic host cell for long periods
Chronic: often with persistent shedders that have constant or intermitted shedding, can go unnoticed

64
Q

Describe the difference between persistent infections versus persistent slow infections in a host

A

Persistent: after initial viral infection proliferation is ceased but viral genome not fully eradicated
Persistent slow: characterized by a long incubation period followed by progressive disease

65
Q

T/F: threshold level of virus is required to activate innate immune response

A

False; activate adaptive immunity

66
Q

Why is diagnosis of viral infections necessary?

A

Viral disease diagnosis, screen of blood donors, proper management of diseases, early detection of epidemics

67
Q

Although sampling depends on disease, virus type, host species, and diagnostic test, where can we sample from?

A

Blood, sputum/bronchial washes, feces, cerebrospinal fluid, biopsy/necropsy tissues

68
Q

What are the four methods for lab diagnosis of a virus?

A

Virus culture and isolation, detection of virus specific antibodies, detection of viral antigen, detection of viral genome

69
Q

T/F: viruses can grow on artificial media as they do not need host cells to replicate

A

False

70
Q

List and define the three cell lines

A

Primary: derived from tissues, die after few generations
Diploid: developed from human embryos, grow for 100 generations
Continuous: transformed (cancerous) immortal cell lines (ex HeLa, Vero)

71
Q

What are the purpose of embryonated chicken eggs

A

Cells that support virus growth; used for virus isolation, identification & production of vaccines
Not all viruses will grow in tissues of ECE, but many can adapt to it

72
Q

What is candling?

A

Method using bright light behind the egg to study growth and development of embryo inside

73
Q

What is the difference between TCID50, LD50, ID50?

A

TCID50: tissue culture infectious dose; # of VIRUSES required to cause infection in 50% of cell culture
LD50: 50% lethal dose; # of MICROBES or amount of TOXIN required to cause terminal acute infections in 50% of animals infected
ID50: 50% infectious dose; number of MICROBES required to cause infection in 50% of animals

74
Q

What are the 4 ways used for virus detection in diagnosis of viral infections

A

Electron microscopy, fluorescent antibody staining, immunohistochemistry, virus induced cytopathic effects

VP - Microbio (5 decks)

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