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Microbiology Exam 1 > Virology > Flashcards

Virology Flashcards

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Biology 101 flashcards
1
Q

What are viruses?

A

Acellular, obligate intracellular parasites known to infect every type of cell. They are considered nonliving and cannot live outside a host cell.

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2
Q

General Characteristics of Viruses?

A
  • Obligate intracellular parasites of living cells
  • Lack a metabolic system & must obtain energy from host cells (No ADP or ATP, free amino acids, or sugars. Lack enzymes/machinery for synthesizing proteins, must reproduce inside a host cell.)
  • Multiply by taking control of the host cell’s processes & regulating the synthesis and assembly of new viral particles
  • Most viruses only infect a limited number of cell types
  • Viruses infect every type of cell
  • Protected from much of the hosts immune response
  • Contain either DNA or RNA.
  • Genome encodes info needed for viral replication & synthesis of progeny virions.
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3
Q

What are the size of viruses?

A

Animal- 22nm-450nm

Require an Electron Microscope to view

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4
Q

How are viruses different from other pathogens?

A

Acellular, reproduce via assembly process, haploid (except retroviruses), contain EITHER DNA or RNA, lack organelles/cytoplasm/nucleus/nucleoid.

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5
Q

The genome of the virus is surrounded by?

A

An outer protein coat (Capsid). And sometimes an envelope.

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6
Q

What is an envelope?

A

A lipid membrane derived from the host cell (either the cell membrane or internal organelle membrane), which contains glycoproteins of viral and host cell origins.

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7
Q

True or False? 13 of the 19 families of animal viruses are enveloped.

A

True

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8
Q

Most Enveloped Viruses cannot survive in the GI tract

A

……

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9
Q

The capsid is made up of identical protein subunits called…..

A

Capsomers.

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10
Q

What are the two symmetrical nucleocapsid structures found among medically important human and animal viruses?

A

Helical and Icosahedral

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11
Q

How are the Nucleocapsids of helical viruses arranged?

A

They are tightly wound and rigid in naked viruses, nucleocapsids of enveloped viruses are looser.

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12
Q

Icosahedral capsids have ____Triangular faces and ____corners.

A

20 Triangular faces and 12 corners.

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13
Q

What is the function of the capsid and envelope?

A

To protect the virus core, which contains the genome.

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14
Q

The viral envelope plays the following roles….

A

Host Cell recognition and binding to host cell upon infection. Capsid proteins fulfill these roles in the absence of an envelope.

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15
Q

Capsid+Genome=

A

Nucleocapsid

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16
Q

True or False. A virus contains DNA and RNA?

A

False. DNA or RNA.

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17
Q

DNA Viral Genomes can exist as…..

A

Single Stranded Linear (+ or -), Double Stranded Linear, or Double Stranded Circular.

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18
Q

RNA Viral Genomes can exist as…..

A

Single Stranded Linear (+ or -), Single Stranded Negative Sense Segmented, Single Stranded Circular Negative Sense, or Double Stranded Linear Segmented.

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19
Q

Why are virus genomes small?

A

Physically not enough space.

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20
Q

Describe “Strain”, “Type”, and “Variant”.

A

Strain- Same virus but isolated form different patients or geographical locations.

Type- Same virus but responding differently to antibody detection (serotypes)

Variant- Virus whose phenotype differs from wild-type (genetic mutation is not known)

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21
Q

Spontaneous mutations occur often in viral genomes. What are their rates of incidence? And why do RNA viruses have a higher rate?

A

DNA Virus- 1/10^-9

RNA Virus- 1/10^-3

RNA dependent RNA polymerases are typically more error prone than their DNA counterparts.

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22
Q

All RNA viruses encode an RNA-dependent RNA polymerase EXCEPT…..

A

Retroviruses (RNA Dependent DNA Polymerases)

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23
Q

Reverse transcriptase have a rate of error of……

A

One per cycle

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24
Q

What are the two methods of recombination?

A

Intramolecular recombination by strand breakage and religation or strand switching (occurs in all viruses that use a DNA intermediate)

Intramolecular recombination by copy-choice, a viral polymerase switches template strands during replication. (Occurs only in RNA)

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25
Q

Reassortment is…..

A

Exchange of genetic material between two segmented genomes. (Commonly seen in Influenza viruses each year)

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26
Q

How is viral genetic diversity relevant to human disease?

A

Drug resistance, escape anitbody recognition, or recognize a new host.

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27
Q

The life cycle of an animal virus includes the following steps…..

A 
Recognition of host cell,
Attachment,
Penetration,
Uncoating,
Synthesis of nucleic acids and proteins,
Assembly,
Release from host cell.
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28
Q

People who will get an A on this exam…

A

Karin Hwang

Terry Parsons!

Sarah Stamper

William Gunther

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29
Q

The viral attachment protein for binding to a cellular protein is usually a ____ if the virus is enveloped, or a ____ if the virus is naked.

A

Glycoprotein if enveloped, Surface peptide if naked.

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30
Q

Receptor molecules on host cells are usually…..

A

Glycoproteins (specific) or Glycolipids.

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31
Q

The interaction of a viral attachment protein with a cellular receptor protein establishes the _____ of a virus.

A

Tropism. Specificity of a certain cell type. Hep. A has a tropism for hepatocytes.

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32
Q

How do naked viruses attach to their host cells?

A

Direct interaction between viral capsid proteins and the host cell receptor. (This presents a problem for curing the common cold, because the ligand on rhinovirus is inaccessible to antibodies.)

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33
Q

How do enveloped viruses attach to their host cells?

A

Viral “spikes” extend from the virion surface. One of them is a ligand for the host cell receptor.

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34
Q

Penetration can be by 3 ways…..

A

Direct Penetration, Fusion, or Endocytosis.

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35
Q

Direct Penetration is seen only in…..

A

Naked Viruses. Capsid remains extracellular while the genetic material enters the host cell.

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36
Q

Fusion is seen only in…..

A

Enveloped Viruses. The viral envelope merges with the host cell, both capsid and genome enter the host cell.

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37
Q

Endocytosis is seen in both Naked and Enveloped viruses.

A

…….

38
Q

Now I’m standing alone in a crowded room, and we’re not speakinnnnn.

A

And I’m dying to know is it killing you, like it’s killin me yeahhhhhhh.

39
Q

Which type of viruses commonly keep the genetic material in the cytosol for replication and gene expression after uncoating?

A

RNA Viruses

40
Q

Which type of viruses commonly transport the genetic material to the nucleus for replication and gene expression after uncoating?

A

DNA Viruses

41
Q

Describe the production of mRNA from DNA Genomes.

A

+ssDNA—>Synthesis of - strand—->+-dsDNA intermediate OR +-dsDNA —–>Transcription of - strand—–> +mRNA

42
Q

Describe the production of mRNA from RNA Genomes.

A

+-dsRNA—>Transcription of - strand —->+mRNA

+ssRNA—-> +mRNA

-ssRNA—-> Transcription of - strand —-> +mRNA

+ssRNA —-> Reverse Transcriptase makes DNA—-> -ssDNA —-> Replicase copies - strand —-> +-dsDNA Intermediate —-> Transcription of -strand —->+mRNA

43
Q

Where is mRNA translated?

A

Cytoplasm

44
Q

dsDNA viruses typically replicate in the nucleus, with the exception of…..

A

Poxviridae (cytosol)

45
Q

ssDNA viruses replicate in….

A

Nucleus, via a dsDNA intermediate

46
Q

T or F. DNA genomes are replicated by direct DNA–>DNA copying by either viral or cellular DNA polymerases.

A

True

47
Q

Non retrovirus RNA genomes are replicated by direct RNA–>RNA copying and require a…..

A

Viral Replicase enzyme (RNA Dependent RNA Polymerase)

48
Q

Retroviral RNA replication includes an RNA–>DNA step that requires a……

A

Reverse Transcriptase enzyme.

49
Q

What are inclusion bodies?

A

Compact masses of viruses that may be present in the nucleus or cytoplasm of the host cell.

50
Q

Before progeny virus particles assemble and leave the infected cell, each virion needs to contain:

A

Viral nucleic acid, accessory proteins, and viral enzymes required for infection.

51
Q

How are icosahedral virions assembled?

A

Spontaneously into an empty capsid due to a packaging sequence in the genome

52
Q

How are helical virions assembled?

A

Using a Pac site in which capsomer subunits bind to begin the process of assembly. It then proceeds spontaneously.

53
Q

What occurs during the maturation phase that, if not done, will result in the virus being noninfectious?

A

Processing of protein precursers into their final products through protease activity.

54
Q

Release of the virions from the host cell occurs via what 3 mechanisms?

A

Budding, Cell Lysis, or Exocytosis.

55
Q

What is Budding?

A

Virions distend through a membrane, becoming enveloped. This takes place through the plasma membrane, nuclear membrane, ER, or vesicles. This takes place in enveloped viruses and incorporates both viral and host cell proteins

56
Q

What is Cell Lysis?

A

When the cell becomes overwhelmed by viral load and bursts. Used by naked viruses.

57
Q

What is Exocytosis?

A

Occurs in both naked and enveloped viruses. Similar to budding, but the virions do NOT gain a part of the cell membrane. Enveloped viruses that obtain their envelope from an internal membrane exit via this method.

58
Q

What happens if a virus encounter a non permissive cell?

A

No infection. Lack of appropriate receptors.

59
Q

What are the three broad types of viral infections?

A

Abortive, Acute/Lytic, Persistent.

60
Q

Describe an abortive infection.

A

A virion enters a cell, but does not proceed through all the steps of replication. Mature virions are not produced.

61
Q

Describe an Acute/Lytic infection.

A

Rapid onset, period of disease, clearance of virus. Usually result in the death of the host cell.

62
Q

Describe a persistent infection.

A

Lingers, not readily cleared by the immune system.

63
Q

What are the 3 types of persistent infections? Describe them.

A

Chronic Infection: Can be lifelong, continuous shedding of virions.

Latent Infection: Intermittent periods of viral replication and shedding with long periods of dormancy.

Transforming: Virus causes the cell to lose growth control, usually by overexpression of growth factors. May lead to tumor formation.

64
Q

Describe the Cytopathic response in response to the following viruses- Smallpox, Herpes Simplex, Adenovirus, and Polio.

A

Smallpox- Cells round up, inclusion bodies in cytoplasm.

Herpes Simplex- Multinucleated Syncytia, inclusion bodies in nucleus.

Adenovirus- Clumping of cells, nuclear inclusions.

Polio- Cell lysis

65
Q

Describe the Cytopathic response in response to the following viruses- Reovirus, Influenza, Rabies, Measles.

A

Reovirus- Cell enlargement, vacuoles and inclusions in cytoplasm

Influenza- Cells round up

Rabies- Cytoplasmic inclusions

Measles- Multinucleated Syncytia. (Syncytia= Fusion of infected cell with neighboring cell)

66
Q

What are the basic steps of a viral infection?

A

Entry into host, Immune evasion, Entry into cells/primary replication, Spread within host, Cell injury/clinical illness, Shedding.

67
Q

Most viruses enter the host through what? (Hint- Covers 90% of our bodies)

A

A mucosal surface.

68
Q

Localized infections occur where?

A

Site where the virus entered the host.

69
Q

Generalized infections occur where?

A

They spread beyond the point of entry to infect additional tissues or may become systemic.

70
Q

What is the most common point of entry for virions?

A

The respiratory tract.

71
Q

The alimentary tract (GI) is a common portal of entry for viruses. Viruses that enter via this route are typically what kind?

A

Naked, since bile disrupts the lipid bilayer of enveloped viruses.

72
Q

What are a few ways viruses can enter through the skin?

A

Minor abrasions (Herpes simplex, poxviruses), Insect bites (West Nile), Needles (Hep B/C, retroviruses, Cytomegalovirus, Epstein-Barr, Ebola)

73
Q

The genital tract is a route of entry for some viruses. Which cause localized infections and which caused generalized?

A

Localized- Herpes Simplex, Papillomaviruses

Generalized- HIV, HTLV, Hep B/C

74
Q

The Conjunctiva is less resistant to viral infection than skin, but how does it prevent infection?

A

Lysozyme, IgA in tears, blinking of the eyelids.

75
Q

How does a virus avoid detection via inhibiting antigen presentation?

A

Downregulating expression of MHC class I so the host cell cannot present viral antigens to T cells.

76
Q

What is antigenic variation?

A

The ability of a virus to change or remove certain surface proteins to avoid antibody binding from previous infections. The host no longer recognizes the virus.

77
Q

Describe molecular mimicry.

A

Viruses can make surface proteins very close to the host proteins, this can trick the immune system into believing a virus is a “self” molecule.

78
Q

Places like the eye, brain, ovary, and testes are also known as what?

A

Privileged sites. Locations with little immune protection.

79
Q

Why do papillomaviruses have a long incubation period?

A

They infect the basal layer of the epidermis, becoming keratinized as they mature.

80
Q

Presence of virus in the bloodstream is called?

A

Viremia

81
Q

When a primary viremia transfers to an organ, this liberates more viruses that spread via…..

A

Secondary viremia

82
Q

How can HIV be transferred to a fetus?

A

In-Utero, during birth, or through breast feeding.

83
Q

Parvovirus and Variola can both cross the placenta. What happens to the fetus?

A

Fetal death/abortion

84
Q

Cytomegalovirus and Rubella both cross the placenta. What happens to the fetus?

A

Congenital defects. Deafness, blindness, heart/brain defects.

85
Q

The TORCH panel is a blood test that measures antibodies for a group of organisms that cause birth defects. What are they?

A

Toxoplasma

Other (Syphilis, HBV, coxsackie, EBV, VZV, human parvovirus)

Rubella

Cytomegalovirus

Herpes Simplex

86
Q

The level of clinical illness usually correlates to what?

A

The amount of damage done by the virus.

87
Q

The amount of damage done by a virus depends on its…..

A

Virulence

88
Q

The relative capacity of a pathogen to infect and harm a host cell.

A

Virulence

89
Q

Localized infections typically _____ at the site of entry.

A

Shed (Ex. Viral pneumonia is shed by coughing, herpes spreads vial epithelial lesions)

90
Q

_____is shed in stools and is present before the onset of illness.

A

Poliovirus

91
Q

How is HIV primarily shed?

A

Body fluids

92
Q

In a generalized disease, the virus spreads through blood and along _____ to the peripheral nerves.

A

Axons

Microbiology Exam 1 (5 decks)

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