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agents of infectious disease > 15-22 virology > Flashcards

15-22 virology Flashcards

1
Q

what is the current definition of a virus?

A

a genetic element that is protected by a protein coat and cannot replicate independently of a living cell

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2
Q

what are the general features of viruses?

A
  • contain DNA or RNA
  • do not divide by binary fission
  • they are obligate intracellular parasites
  • small
  • simple structure
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3
Q

what replication phase are viral components produced in?

A

the viral eclipse phase

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4
Q

what technology can be used to target viruses?

A
  • siRNA
  • CRISPr
  • vaccines
  • novel therapies
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5
Q

what is the basic structure of a virus?

A
  • contain DNA or RNA surrounded by a protein capsid
  • some viruses possess a viral envelope that surrounds the capsid - it is derived from the host cell
  • all viruses have viral attachment proteins which help the virus recognise, bind, and enter the host cell
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6
Q

define what a virion is

A

the complete virus particle

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7
Q

how do viruses recognise their target cells

A

by their cellular receptors

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8
Q

what does the viral genome encode?

A
  • structural proteins including capsids and VAPS
  • non structural proteins including proteins for: viral replication, pathogenesis, transformation, modulation of host defences
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9
Q

what does the viral genome not encode?

A
  • the complete protein synthesis machinery
  • proteins involved in cell wall production or membrane biosynthesis
  • centromeres or telomeres found in standard host chromosomes
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10
Q

what is a capsomere?

A

the viral subunits of the capsid

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11
Q

what is the use of viral particles being stable?

A

it protects the viral genome

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12
Q

what is the use of viral particles being unstable?

A

it facilitates the delivery of the viral genome into the host cell to dissociate on infection

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13
Q

how is the stable structure of viral particles achieved?

A
  • symmetrical arrangement of identical virus protein subunits provide maximal contact
  • each subunit has identical bonding contacts with its neighbours
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14
Q

how is the unstable structure of viral particles achieved?

A
  • the contact is not covalent
  • the structure can be dissociated or taken apart once the virus attaches to the host cell to release the genome
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15
Q

what shapes can the capsid structure be?

A
  • helical - the capsid look like a coil and the virus looks like a rod
  • icosahedral - the capsid has an icosahedral shape and the viruses look like spheres or cocci
  • complex - a capsid with a combination of helical and icosahedral arrangements or no specific arrangement
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16
Q

how is the viral envelope acquired?

A
  • when the virus exits the infected cell, it pushes out of the cellular membrane, acquiring the envelope, endoplasmic reticulum membrane, and nuclear membrane
  • the VAPs are located within this envelope
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17
Q

is the viral envelope sensitive to environmental conditions?

A

yes, including heat, soap, detergents, and stomach acidity

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18
Q

what are the disadvantages of classing viruses based on the diseases they cause?

A
  • focuses on some viruses and ignores others
  • a single virus may cause more than one disease
  • viruses infect more than one host
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19
Q

how can viruses be classified based on virus particle morphology and nucleic acid?

A

-> nucleic acid
- type of nucleic acid
- single or double stranded
- linear, circular, single molecule, or segmented
- negative or positive polarity
-> capsid symmetry
- icosahedral, helical, or complex
-> presence of absence of lipid envelope

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20
Q

what is the systematic taxonomy scheme used for viruses?

A

order -> family -> subfamily -> genus -> species -> member

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21
Q

what are the 7 viral genome types in the baltimore classification?

A

1 - dsDNA
2 - ssDNA +ve strand
3 - dsRNA
4 - ssRNA +ve
5 - ssRNA -ve
6 - ssRNA -> ssDNA -ve
7 - gapped dsDNA

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22
Q

describe the basic structure of viroids

A
  • novel agents of disease in plants
  • contains a single circular ssRNA molecule as infectious material
  • no protein components
  • smallest self replicating pathogen known
  • up to 70% of the nucleotides in the genome RNAs are based paired
  • rod shaped or dumb-bell shaped
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23
Q

what are prions?

A
  • agents of infection in diseases which are characterised by slow, progressive neurological degeneration that are fatal
  • no nucleic acid
  • they replicate slowly in hosts
  • they are abnormal forms of normal cellular proteins
  • they induce changes in the shape of their normal homologues
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24
Q

what is viral tropism?

A
  • the specificity of a virus to a specific host
    there is:
  • cellular tropism
  • tissue tropism
  • host tropism
25
Q

how can enveloped viruses enter the host cell?

A

they can either:
-> fuse with the plasma membrane
- they fuse directly with the plasma membrane via fusion proteins
- the genetic material and capsid are immediately delivered to the cytoplasm of the cell
-> fuse via endosomes
- occurs at a low pH
- the virus is taken up by invagination of the membrane into endosomes
- the pH inside the endosome decreases, so fusion of the viral envelope with the cell membrane can now occur, resulting in delivery of virion components into the cell cytoplasm

26
Q

how do non enveloped viruses enter the host cell?

A
  • endocytosis via the endosomal membrane
  • direct entry
27
Q

how does the virus uncoat and where is the contents delivered?

A
  • the capsid destabilizes to release the contents into the cytoplasm
  • DNA viruses must deliver DNA into the nucleus
  • RNA viruses must deliver RNA into the cytoplasm?
28
Q

which virus does not deliver DNA into the nucleus?

A

poxiviruses

29
Q

which virus does not deliver RNA into the cytoplasm?

A

influenza

30
Q

how are the new viral protein and nucleic acids packaged?

A
  • each nucleic acid copy is packaged in viral capsid proteins
  • usually occurs in the cytoplasm
  • helical and icosahedral complexes assemble around the viral nucleic acid
  • complex capsids first assemble into empty capsule structures (procapsid) using scaffolding proteins. scaffolding proteins are then removed and replaced by viral NA
31
Q

how is the new virus released?

A
  • naked viruses usually lyse the cells, causing them to burst and release the new virions
  • enveloped viruses bud from the cells, acquiring their envelope from the host cell membrane
32
Q

how do dsDNA viruses replicate?

A

to produce viral proteins - dsDNA is transcribed by RNA polymerases to produce viral mRNA that is read and translated by the host ribosome
replication of viral DNA - the genome is replicated by DNA polymerases

33
Q

how do ssDNA viruses replicate?

A
  • it is first replicated by host DNA polymerase to produce dsDNA - this is transcribed by host RNA polymerase to produce viral mrna to make proteins
  • viral DNA is just replicated as normal by host DNA polymerase
34
Q

how is gapped dsDNA replicated?

A
  • the genome is first repaired by cellular DNA repair polymerases to remove the RNA piece with the protein and to fill the gap in the DNA - this is now recognised by host RNA polymerase to produce viral mRNA to make proteins
  • some mRNAs are used as templates to produce incomplete dsDNA using RT
  • A DNA strand is produced by RT, which is then used again to product a tDNA strand that is incomplete and contain RNA and RT itself
35
Q

what does RT stand for?

A

reverse transcriptase

36
Q

how are ssRNA+ genomes replicated?

A
  • the genome is translated straightaway by the ribosomes to viral proteins including replicase
  • RNA replicase is then used to replicate the viral genome
37
Q

how are ssRNA- genomes replicated?

A
  • RNA must first be replicated to tRNA using carried RNA replicase
38
Q

how is dsRNA replicated?

A

in the same way as ssRNA-

39
Q

how is ssRNA+ sense with DNA intermediate (retrovirus) replicated?

A
  • RT is carried and converts ssRNA to dsDNA
  • the dsDNA copy is delivered to the nucleus and is integrated into the host DNA using integrase
  • now, when the cell replicates its own DNA, the viral dna is also transcribed to produce viral mRNA
40
Q

what are cytopathic effects?

A

distinct observable cell abnormalities due to viral infection

41
Q

what is hemadsorption?

A
  • cells infected with certain viruses acquire the ability to bind to and adsorb red blood cells
  • many viruses contain haemagglutinin surface glycoproteins
42
Q

which viruses are capable of hemadsorption?

A
  • influenza
  • measles
  • mumps
43
Q

what are the main stages of the viral single step growth curve?

A

1 - inoculation - inoculum of virus binds to cells
2 - eclipse - virions penetrate the cells
3 - burst - host cells release many viral particles
4 - burst size - the number of virions released per bacterium

44
Q

define what is meant by susceptible cells

A

a cell that expresses the specific receptors that are recognised by a specific virus through specific VAPs

45
Q

define what is meant by a permissive cell

A

a cell that contains the proteins and molecules within the cell that are necessary for replication to occur

46
Q

what are common portals of entry in the body?

A
  • the skin
  • the respiratory tract
  • the GI tract
  • the genital tract
47
Q

what is a localised infection?

A

when the virus infects and replicates only within cells at the site of infection

48
Q

what is meant by systemic infection?

A

when the virus infects the initial site of entry and replicates locally to spread to other sites within the body

49
Q

define what is meant by pathogenesis

A

the ability/capacity of a virus to cause disease

50
Q

define what is meant by virulence

A

a quantitative or relative measure of the pathogenesis of the infecting virus

51
Q

how can viruses carry out direct killing?

A
  • poliovirus kills neurons, causing paralysis of muscles innervated by those neurons
  • ebola virus damages endothelial cells, causing haemorrhage
52
Q

what is virus induced transformation?

A
  • cancers associated with some viral infections are due to indirect effects, such as immune suppression
  • some viral infection directly promotes tumour development
53
Q

define what is meant by a vaccine

A

a biological product that can be used to safely induce an immune response that confers protection against infection and/or disease on subsequent exposure to a pathogen

54
Q

what is a live attenuated vaccine? what are its advantages and disadvantages?

A
  • it is a vaccine which contains the whole virus that has been weakened or attenuated to produce an immune response similar to that during natural infection
    pro - tends to create a strong and lasting immune response
    cons - may not be suitable for immunocompromised individuals
55
Q

what is a killed/inactivated vaccine? what are its advantages and disadvantages?

A
  • it is a vaccine which contains the whole virus which has been killed or altered so it cannot replicate
    pros - may be suitable for immunocompromised individuals
    cons - doesn’t create a strong and lasting immune response
56
Q

what is a subunit vaccine? what are its advantages and disadvantages?

A
  • it is a vaccine which does not contain the whole virus but instead contains one or more specific component or antigen usually from the surface of the virus
    pro - may be suitable for immunocompromised individuals
    cons - doesn’t create a strong and lasting immune response
57
Q

what is a nucleic acid vaccine?

A
  • vaccines which do not provide the viral protein/antigen and instead provide the genes that encode for the specific viral antigens to host cells
  • these genes are then expressed by the host cells to produce the viral antigen, stimulating an immune response against it
58
Q

why is there a limited number of marketed antiviral drugs?

A
  • many compounds that interfere with virus growth cause adverse effects in the host
  • some medically important viruses cant be propagated, have no animal models, or are very dangerous
  • antiviral drugs must be potent to completely inhibit viral replication
  • many acute viral infections are short lived

agents of infectious disease (4 decks)

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