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MED-109 Biology II > topic 8: viruses > Flashcards

topic 8: viruses Flashcards

1
Q

what are viruses defined as and why?

A
  • defined as non-cellular infectious particles
  • because they do NOT consist of cells (do not fit the definition of a living organism)
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2
Q

what is the approximate size of viruses?

A

10 - 300 nm diameter

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3
Q

define viruses

A

obligate intracellular parasites:
- depend on the host cells for their replication
- use enzymes of the host cells in order to replicate

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4
Q

what are the characteristics of viruses?

A
  • obligate intercellular parasites
  • can infect both eukaryotes and prokaryotes
  • bacteriophages
  • important pathogenic agents in both animals and plants
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5
Q

what are bacteriophages (phages)?

A

viruses that infect only prokaryotes (bacteria)

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6
Q

compare the sizes of eukaryotes, prokaryotes, and viruses

A

virus - 0.05μm
phage - 0.1μm
bacterium - 1-10μm
eukaryotic cell - 10-100μm
** bacteria is around 10-100x smaller than eukaryotic cells
** viruses are much smaller than both prokaryotic & eukaryotic cells

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7
Q

what is the essential structure of a virus? what is an additional structure that some viruses have?

A

essentially made from:
(1) nucleic acid (DNA or RNA)
(2) a protein capsid
additional structure:
(3) envelope (an external protective layer)

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8
Q

what is a capsid? what is it responsible for?

A
  • a protein coat
  • encapsulates the nucleic acid and protects the viral genome from nucleases
  • may have fibers that assist the attachment of the virus to the host cell
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9
Q

what is the function of an envelope? what does it consist of?

A
  • consists of membrane
  • carries glycoproteins
  • is required during the exit of viruses from cells that they infect
  • only present in enveloped viruses
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10
Q

viral genomes may consist of?

A
  • single or double-stranded DNA
  • single or double-stranded RNA
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11
Q

what are the 2 types of viruses that can exist based on the type of nucleic acid they contain?

A
  • DNA viruses
  • RNA viruses
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12
Q

capsids are built from protein subunits called?

A

capsomeres

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13
Q

what are the types of shapes or symmetry that a capsid can have?

A
  • icosahedral (spherical) symmetry
  • helical symmetry
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14
Q

regarding viral capsid structures, what type of capsid structure do each of the following have:
(1) tobacco mosaic virus (TMV)
(2) adenoviruses
(3) influenza viruses
(4) bacteriophage T4

A

(1) non-enveloped, helical capsid
(2) non-enveloped, icosahedral capsid
(3) enveloped, helical capsid
(4) non-enveloped, icosahedral capsid

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15
Q

what type of nucleic acid do each of the following have:
(1) tobacco mosaic virus (TMV)
(2) adenoviruses
(3) influenza viruses
(4) bacteriophage T4

A

(1) RNA virus
(2) DNA virus
(3) RNA virus
(4) DNA virus

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16
Q

most animal viruses are _____, unlike most plant viruses which are _____

A
  • enveloped
  • non-enveloped
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17
Q

ALL phages are _____

A

non-enveloped

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18
Q

what does the viral envelope contain?

A

viral glycoproteins which bind to specific receptor molecules on the surface of the host cell

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19
Q

what function does the viral envelope help with?

A
  • it helps the virus infect their host cells
  • envelope fusion with host cell membrane
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20
Q

what is the origin of viral envelopes?

A

they are derived from the host cell’s membranes (mainly the plasma membrane but can be the nuclear membrane)

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21
Q

how does specificity of a bacteriophage work?

A

different types of phages infect specific different bacteria types

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22
Q

when is the viral envelope formed?

A
  • during the exit of the viral particles from the host cells
  • therefore, they contain a combination of viral and host cell molecules
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23
Q

describe the structure of a phage

A
  • capsid head
  • protein tail
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24
Q

what is the function of the phage capsid head?

A

encloses their nucleic acid (commonly DNA)

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25
Q

what are two contributing factors in the differences in both replication and transcription processes in viruses?

A

(1) enveloped vs. non-enveloped viruses have differences
(2) DNA viruses vs. RNA viruses have differences

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26
Q

what is the function of the phage protein tail?

A

has fibers that facilitate the attachment of the phage to the host cell

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27
Q

what does it mean for viruses to be obligate intracellular parasites?

A

they can only replicate within a host cell

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28
Q

what are the stages of the viral replicative cycle?

SOSS

A

(1) attachment
(2) penetration (entry of virus into cell)
(3) uncoating (of viral genome)
(4) replication
(5) gene expression
(6) assembly
(7) release (exit)
(8) maturation (only for enveloped viruses)

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29
Q

what are some differences in the replicative cycles of enveloped vs. non-enveloped viruses?

A
  • penetration into the host cell
  • release from the cell
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30
Q

describe the virus life cycle

A
  • viruses are infectious particles that take over the operation of a cell to manufacture new viruses
  • they are very specific in the type of cells they infect
  • they use the pattern of protein receptors on a cell’s surface to target cells for infection
  • in the case of a DNA virus, it is rather simple compared to the DNA inside a host cell, only containing the info needed to manufacture new virus parts
  • once inside, the instructions in the DNA are transcribed to RNA, the protein-making machinery then translates this into the components of a new virus
  • once new viruses are assembled, when ready they emerge from the cell, killing it
  • some retain parts of the host membrane, forming an envelope around themselves (enveloped viruses) for protection
  • every new virus is capable of infecting another host cell, repeating this process
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31
Q

regarding virus specificity, what do viruses depend on in their ability to infect a specific cell?

A

the type of cell-surface receptors of the target cell

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32
Q

what do anti-viral drugs do in regards to the viral life cycle?

A

they target points in the life cycle of the virus, preventing it from replicating

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33
Q

describe step (1): attachment of the virus to the host cell, in both enveloped and non-enveloped viruses

SOS

A
  • enveloped viruses: glycoproteins on the viral envelope attach on receptors on the plasma membrane of the host
  • non-enveloped viruses: fibers or spikes on the viral capsid attach on the host cell membrane
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34
Q

describe step (2): viral entry to the host cell (penetration), in both enveloped and non-enveloped viruses

SOS

A
  • enveloped viruses: mostly by membrane fusion (of the viral envelope with host cell plasma membrane)
  • non-enveloped viruses: by endocytosis
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35
Q

describe step (3): uncoating of the viral genome

SOS

A

capsomeres fall apart
(catalyzed by lysosomal enzymes)

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36
Q

what processes does step (4): virus replication in the host cell include?

A
  • replication of the viral genome in the host cell
  • replication of the viral proteins in the host cell
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37
Q

there are different replication mechanisms for viruses based on?

A

their viral genome type

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38
Q

what are the 4 types of viruses based on their nucleic acid?

A
  • double stranded DNA viruses (ds DNA)
  • single stranded DNA (ssDNA)
  • double stranded RNA (ds RNA)
  • single stranded RNA (ss RNA)
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39
Q

what type of RNA has 3 types? what are they?

A

single stranded RNA viruses have 3 different types:
- positive sense RNA genome (5’ - 3’ RNA) viruses
- negative sense RNA genome (3’ - 5’ RNA) viruses
- retroviruses

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40
Q

what are retroviruses?

A
  • a type of ss RNA virus
  • has positive sense RNA genome (5’ - 3’)
  • replicate through the enzyme reverse transcriptase (converts RNA to DNA)
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41
Q

describe the replication of viral genome process (of step 4) in the host cell for DNA vs RNA

SOSSSSSS

A

DNA viruses:
- use the same mechanisms as the host cells (have the same genome as us)
- ss or ds viral DNA replicates using the host DNA polymerase
- viral DNA replicates using host DNA polymerase to produce viral cDNA (multiple copies)
- cDNA = copy DNA

RNA viruses:
- use different mechanisms than the host (cannot use our enzymes)
- all RNA viruses use the same enzyme, except retroviruses
- retroviruses use the viral enzyme reverse transcriptase to produce viral cDNA, THEN use the host RNA polymerase to produce the viral RNA copies
- other RNA viruses (+ and - sense) use the viral enzyme RNA-dependent RNA polymerase to replicate and produce viral RNA copies

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42
Q

describe the viral protein production process (of step 4) in the host cell (transcription + translation) for DNA vs RNA

SOSSSSSS

A

DNA viruses:
- viral mRNA is produced from viral DNA using the host cell RNA polymerase
- viral DNA uses hot RNA polymerase for transcription to produce viral mRNA, then uses host cell ribosomes to produce viral proteins (translation)

RNA viruses:
- the viral RNA serves as either:
(i) mRNA (positive sense RNA viruses)
(ii) as template for production of viral mRNA (negative sense RNA viruses) using viral RNA-dependent RNA polymerase
- this is because viruses with a 3’ - 5’ RNA genome need to be converted into their complementary strand (5’ - 3’) to serve as mRNA
- as for translation, the viral mRNA is translated into the viral proteins using the host ribosomes and the translation machinery of the host cell
- (+ sense): viral RNA –> produce viral proteins using ribosomes
- (- sense): viral RNA –> viral mRNA using RNA-dependent RNA polymerase –> produce viral proteins using ribosomes

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43
Q

what is the only process taking place in RNA viruses where the host machinery is used?

A

translation

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44
Q

compare host and viral enzymes

A

(1) host DNA polymerase:
- DNA dependent DNA polymerase
- uses DNA as a template to synthesize a new DNA strand
- DNA –> DNA

(2) host RNA polymerase:
- DNA dependent RNA polymerase
- uses DNA as a template to synthesize a new RNA strand
- DNA –> RNA

(3) viral RNA polymerase:
- RNA dependent RNA polymerase
- uses RNA as a template to synthesize a new RNA strand
- RNA –> RNA
- used by (+ and - sense) RNA viruses to replicate their viral genome
- used by ONLY (-) sense RNA viruses to produce their viral proteins

(4) viral reverse transcriptase:
- RNA dependent DNA polymerase
- uses RNA as a template to synthesize a DNA strand
- RNA –> DNA
- used by retroviruses to replicate their viral genome

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45
Q

describe step (5): viral assembly

A
  • the viral proteins (capsomeres) assemble to produce the new capsids
  • the capsids then encapsulate the new viral genomes to produce the new viral particles
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46
Q

describe step (6): viral release (exit) from the cell, in both enveloped and non-enveloped viruses

A
  • enveloped viruses: released by budding, then acquire an envelope through a process called maturation

non-enveloped viruses: released by lysis of the host cell using lysosomal enzymes
(the membrane breaks open and the new viral particles are released)

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47
Q

how is the host cell destroyed after the release of the virus?

A
  • the change in permeability of the plasma membrane (due to the presence of the viral proteins)
  • inhibition of the host cell gene expression (the virus “steals” the host enzymes), the cell has no more machinery to do its own protein synthesis, and dies
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48
Q

what is the only exception to the central dogma of transfer of genetic information?

A

retroviruses
- retroviruses dogma: RNA –> DNA –> RNA –> protein

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49
Q

what is an example of a retrovirus, and what disease does it cause?

SOS

A
  • HIV (human immunodeficiency virus)
  • HIV is the retrovirus that causes AIDS (acquired immunodeficiency syndrome)
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50
Q

what type of cells does HIV infect?

A

T helper cells, also known as CD4

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51
Q

describe the retrovirus replicative cycle

SOS

A

(1) attachment and entry: the viral glycoprotein (gp120) binds to host cell receptor (CD4)

(2) reverse transcriptase: viral enzyme converts the viral RNA into cDNA

(3) integrase: viral enzyme integrates the viral genome into the host genome => the retrovirus cDNA produced is inserted (integrated) at random into the host genome as a provirus

(4) the host’s RNA polymerase transcribes the proviral DNA into RNA molecules

(5) the viral RNA molecules function:
- as mRNA for synthesis of viral proteins
- as genomes for new virus particles released from the cell

(6) protease: viral enzyme cuts and cleaves the viral polypeptide produced by translation => enables assembly and release from the cell
(functional proteins need to be cleaved)

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52
Q

what is a provirus?

A

the genetic material of a virus as incorporated into, and able to replicate with, the genome of a host cell

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53
Q

what are the 3 viral enzymes?

SOS

A

the retroviral RNA genome encodes for three enzymes essential for virus replication:

(1) reverse transcriptase: responsible for the conversion of the single-stranded genomic RNA into double-stranded proviral DNA

(2) protease: converts the immature virion into a mature virus through the cleavage of precursor polypeptides

(3) integrase: inserts the proviral DNA into the host cell genome

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54
Q

what is integrase?

A
  • an enzyme found in HIV (and other retroviruses)
  • HIV uses integrase to insert (integrate) its viral DNA into the DNA of the host CD4 cell
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55
Q

viruses do not consist of cells, are not classified as microorganisms, but as ?

A

pathogens

56
Q

what is believed to be the origin of viruses?

SOS

A

nucleic acid fragments released

57
Q

what are the possible sources of viral genomes?

A

plasmids, bacterial and yeast DNA, transposons (small mobile DNA segments)

58
Q

what is pathogenicity?

A

the ability for organisms to cause pathogenic diseases

59
Q

what are the different mechanisms where viruses may damage or kill host cells?

A

(1) cause the release of hydrolytic enzymes from lysosomes => cell lysis
(2) cause the infected cells to produce to toxins that lead to disease symptoms
(3) have toxic macromolecules (e.g. such as envelope proteins) and/or change the permeability of the plasma membrane (due to the presence of vital proteins)
(4) inhibition of the host cell replication machinery

60
Q

what is cell lysis?

A

the destruction of the plasma membrane so that the viruses are released

61
Q

which of the mechanisms of virus pathogenicity applies to only non-enveloped viruses?

A

viruses causing the release of hydrolytic enzymes from lysosomes => cell lysis

62
Q

which of the mechanisms of virus pathogenicity applies to only enveloped viruses?

A

having toxic macromolecules and/or changing the permeability of the plasma membrane

63
Q

which of the mechanisms of virus pathogenicity applies to both enveloped and non-enveloped viruses?

A
  • causing the infected cells to produce toxins that lead to disease symptoms
  • inhibition of the host cell replication machinery
64
Q

what are vaccines?

A

harmless derivates of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen (to produce antibodies)

65
Q

what do vaccines commonly consist of?

A

of dead or inactivated pathogens or their products (e.g. proteins/nucleic acids)

66
Q

why are vaccines important?

A
  • important control measure as viral infections cannot be treated by antibiotics
  • vaccines can prevent certain viral illnesses (and certain bacterial illnesses)
67
Q

what are emerging viruses?

A

those that suddenly become apparent

68
Q

what are examples of emerging viruses?

A

(1) the 2009 flu out break (pandemic) caused by the influenza virus strain H1N1
(2) the current COVID-19 pandemic by the coronavirus SARS-CoV-2

69
Q

what are flu epidemics caused by?

A

new strains of influenza virus to which people have little immunity

70
Q

how can new viral diseases emerge?

A
  • when viruses spread from animals to humans
  • viral strains that jump species exchange genetic material with other viruses to which humans have no immunity
71
Q

what can these new strains cause?

A

pandemics (global epidemics)

72
Q

what is an example of a pandemic caused by a virus spread from animals to humans?

A

the 2009 flu pandemic was likely passed to humans from pigs => it was originally called the “swine flu”

73
Q

what is SARS-CoV-2?

A
  • severe acute respiratory syndrome coronavirus 2
  • the virus strain that causes the respiratory illness named Coronavirus Disease 2019 (COVID-19)
74
Q

what type of virus is SARS-CoV-2?

A

an enveloped positive-sense ssRNA virus

75
Q

what is the zoonotic origin of SARS-CoV-2?

A

current hypothesis is to have passed from bats via an intermediate host to humans

76
Q

what are the only currently approved antiviral drugs?

A
  • remdesivir
  • molnupiravir
    -paxlovid (nirmatrelvir +ritonavir)
77
Q

describe COVID-19

A
  • Corona Virus 2019
  • common symptoms: include fever, cough, fatigue, shortness of breath, loss of smell + taste, loss of appetite, sputum production, muscle & joint pain
  • complications: pneumonia, multi-organ failure, or cytokine storm
  • transmission: air-borne (via respiratory droplets)
78
Q

what are the diagnostic methods involved in COVID-19?

A

(1) real-time reverse transcription polymerase chain reaction (rRT-PCR)
(2) antigen tests (rapid tests/self tests)

79
Q

describe the mechanism of rRT-PCR

A
  • from a nasopharyngeal swap sample
  • includes viral particles => viral RNA detection
  • amplifies the viral cDNA to produce many copies
  • highly sensitive method as it detects viral DNA (detects viral nucleic acid NOT the viral capsid protein)
80
Q

describe the mechanism of antigen tests

A
  • viral antigen detection from nasal/nasopharyngeal swab
  • detects viral proteins (surface glycoproteins)
  • not as sensitive as it doesn’t multiply the viral protein
81
Q

which method is more likely to produce false negatives?

A

antigen tests

82
Q

how does PCR amplify viral DNA to produce many copies?

A
  • viral RNA –> reverse transcriptase –> cDNA –> DNA polymerase –> cDNA (35-40 copies)
  • first detects viral RNA with a non-viral enzyme (reverse transcriptase in this case is not viral, as COVID is not a retrovirus)
  • reverse transcriptase converts the viral RNA to DNA which is amplified using DNA polymerase
  • both reverse transcriptase and DNA polymerase are commercially available
83
Q

what types of treatment for COVID-19 are there?

A

(1) anti-viral drugs
(2) anti-inflammatory drugs
(3) neutralising antibodies

84
Q

what are the types of anti-viral drugs used for COVID-19 treatment?

A

(1) remdesivir - the USA and UK gave Emergency Use Authorization for it in critically ill COVID-19 patients
(2) molnupiravir - was also approved by them only for cases where remdesivir cannot be used (ex: patients with severe asthma)
(3) paxlovid - approved use in EU
(4) other antiviral drugs under clinical trials

85
Q

what is the mode of action for the anti-viral drugs remdesivir and molnupiravir?

A

viral RNA polymerase inhibitors-nucleoside analogues
- inhibit viral RNA polymerase
- block viral replication

86
Q

what is the mode of action for the anti-viral drug paxlovid?

A

Pfizer protease inhibitor
- blocks the protease in COVID
- which inhibits post-translational modification

87
Q

IF anti-viral drugs are not sufficient, we

A

proceed with using anti-inflammatory drugs and neutralising antibodies

88
Q

what are the types of anti-inflammatory drugs used for COVID-19 treatment?

A

(1) dexamethasone
- corticosteroid drug with anti-inflammatory and immunosuppressive function
- used for patients requiring oxygen support only

89
Q

what drug would you give a COVID patient with serious condition, requiring oxygen support?

A

dexamethasone

90
Q

what are the types of vaccines used for COVID-19?

A

(1) Pfizer/Moderna
(2) Novavax
(3) Johnson & Johnson/Astra Zeneca
(4) Valneva

91
Q

which of the COVID-19 vaccines are considered new technology?

A

Pfizer, Moderna, Johnson & Johnson, Astra Zeneca

92
Q

what is the mode of action in Pfizer/Moderna vaccines?

A

mRNA vaccines
- use the host cell ribosomes & translation machinery to produce viral proteins, and the immune system recognizes foreign antigens and produces antibodies

93
Q

what is the mode of action in Novavax vaccine?

A

protein subunit
- includes the actual viral surface glycoproteins, and also causes antibody production
- old technology

94
Q

what is the mode of action in Johnson & Johnson/Astra Zeneca vaccines?

A

vector vaccines
- carrying viral genes
- carry COVID-19 DNA (SARS-CoV-2 DNA) with transcription converted into mRNA, with translation converted to protein, then leading to formation of antibodies

95
Q

what is the mode of action in Valneva vaccine?

A

whole inactivated virus vaccine
- they cheat our immune system to think we are infected, to produce antibodies

96
Q

what are the major human viral diseases?

A
  • adenoviruses
  • coronaviruses
  • rhinoviruses
  • enteroviruses
  • herpesviruses
  • ebola virus
  • human immunodeficiency virus (HIV)
  • human papilloma virus (HPV)
  • poliovirus
  • mumps, measles, and rubella viruses
  • hepatitis viruses
  • influenza virus
  • prions
97
Q

what are the major human viral diseases that cause common cold?

A

adenoviruses, coronaviruses, rhinoviruses, enteroviruses

98
Q

what do herpesviruses include?

A

(1) Herpes simplex viruses (HSV-1 and HSV-2)
(2) Varicella Zoster virus (VZV)
(3) Epstein-Barr VIrus (EBV)
(4) Cytomegalovirus (CMV)

99
Q

what do Herpes simplex viruses cause?

A

HSV-1 : oral infection (blisters; cold sores)
HSV-2 : genital infection (blisters; genital sores)

100
Q

what does Varicella Zoster virus cause?

A
  • causes chicken pox (in children)
  • shingles (herpes zoster in adults)
101
Q

what does Epstein-Barr virus cause?

A
  • causes infectious mononucleosis (kissing disease)
  • may also cause Burkitt’s lymphoma and nasopharyngeal carcinoma
102
Q

what does cytomegalovirus cause?

A

causes CNS infections (hearing loss, encephalitis)

103
Q

what does ebola virus cause?

A

hemorrhagic fever (fatal)

104
Q

what does human immunodeficiency virus (HIV) cause?

A

causes AIDS

105
Q

what does human papilloma virus (HPV) cause?

A
  • cervical warts (types HPV-16 / 18)
  • genital warts (benign papillomas; types HPV-6 / 11)
106
Q

what type of transmission causes HPV?

A

sexually transmitted disease

107
Q

what are the prevention measures used for HPV?

A

(1) vaccination
- vaccine Gardasil (HPV 16/18/11/6)
- vaccine (HPV 16/18)
(2) pap test
- cervical smear => detection of morphological abnormalities
- e.g. cervical dysplasia

108
Q

what does poliovirus cause?

A

poliomyelitis

109
Q

what are the prevention measures used for poliovirus?

A

Sabin or Salk vaccines

110
Q

what do mumps, measles, and rubella viruses cause?

A

mumps, measles, and rubella respectively

111
Q

what are the prevention measures used for mumps, measles and rubella?

A

MMR vaccine

112
Q

what do hepatitis viruses cause? (what is hepatitis)

A

liver inflammation

113
Q

what are the two major forms of hepatitis?

A

(1) acute hepatitis => jaundice
(2) chronic hepatitis => cause liver cirrhosis and hepatocellular carcinoma

114
Q

what are the major hepatitis viruses?

A

(1) hepatitis A virus (HAV)
(2) hepatitis B virus (HBV)
(3) hepatitis C virus (HCV)

115
Q

describe hep A virus

A
  • type: RNA virus
  • transmission: food-borne
  • vaccine: available
116
Q

describe hep B virus

A
  • type: DNA virus
  • transmission: blood, other biological fluids (sexually transmitted)
  • vaccine: available
117
Q

describe hep C virus

A
  • type: RNA virus
  • transmission: blood or sexually
  • vaccine: NOT available, not developed yet
118
Q

how does HIV infect the body?

A
  • infects the T-helper lymphocytes
    (T h-cells)
  • viral glycoprotein gp120 attaches to the CD4 receptor on the surface of T-helper cells
  • causes AIDS
119
Q

what are two ways AIDS is manifested as?

A

(1) opportunistic infections
- e.g. candidiasis, toxoplasmosis, pneumonia
(2) malignant tumors (cancers)
- Kaposi sarcoma: malignant tumors of the epithelial cells of the blood vessels
- Burkitt’s lymphoma: B-cell cancer

120
Q

what are the different transmission types of HIV?

A
  • sexual intercourse (through sperm/vaginal fluids)
  • blood (e.g. by infected needles/syringes, blood transfusions)
  • mother to child (during pregnancy, birth or breast feeding)
121
Q

describe the detection of HIV

A
  • window period: the virus cannot be detected yet (due to the low levels in the blood) but can still be transmitted to other people
  • detection: the virus can be detected in blood 3-6 weeks after window period (suspected infection date) depending on the detection method
122
Q

what are the diagnostic methods with HIV?

A
  • detection of anti-HIV antibodies in the blood using ELISA (6-8 weeks after infection)
  • detection of viral RNA in the blood using RT-PCR (3 weeks after infection)
123
Q

what are the therapeutic strategies used with AIDS?

A
  • no cure for HIV
  • no vaccine due to high mutation rates of virus
    treatment strategies:
  • HAART: highly active anti-retroviral therapy, which is a combination of different types of antiretroviral drugs
124
Q

what are common problems associated with antiretroviral drugs?

A

toxicity, resistance

125
Q

what are the antiretroviral drug types used in AIDS?

A

(1) nucleotide analogues
- inhibit the viral RNA replication by being incorporated into the growing cDNA chain
(2) non-nucleotide analogues
- inhibit the activity of reverse transcriptase
(3) protease inhibitors
- inhibit the HIV protease which is responsible for the viral polypeptide cleavage and hence the maturation of the virus particles

126
Q

what is an example of a nucleotide analogue antiretroviral drug used in AIDS

A

AZT (azido-deoxy-thymidine)
- the next nucleotide cannot be incorporated into the growing DNA chain due to the presence of nitrogen (N3) instead of -OH
=> inhibits the viral RNA replication

127
Q

what is polymorphism of HIV?

A

it mutates at a very very high rate

128
Q

what are non-conventional viruses?

A

viruses that do not have the characteristic virus structure
(capsid + nucleic acid), so they lack one or the other

129
Q

what are viroids?

A
  • viruses without a protein capsid (only contains nucleic acid)
  • infectious nucleic acids that replicate in tissues
    => plant pathogens (mostly)
130
Q

what are prions?

A
  • viruses without nucleic acids (PROTEINS only)
  • small infectious proteins that replicate in tissues
    => animal pathogens
131
Q

describe viroids

A
  • small circular RNA molecules
  • infect plants => disrupt their growth
132
Q

describe prions

A
  • slow-acting indestructible infectious proteins
  • prions propagate by converting normal proteins into the prion version => aggregation in tissues
  • causes: serious CNS infections (spongiform encephalopathies)
133
Q

what are examples of prion diseases?

A
  • Scrapie disease in sheep
  • mad cow disease
  • Creutzfeldt-Jakob disease in humans
134
Q

what does a “prion version” of a normal protein entail?

A

a different 3D conformation

135
Q

describe mad cow disease

A
  • infects cattle (e.g. cows)
  • transmitted to humans by consumption of contaminated beef (COOKING DOES NOT DESTROY THE PRIONS)
  • causes Creutzfeldt-Jakob disease (CJD) in humans
136
Q

describe Creutzfeldt-Jakob disease

A
  • fatal CNS infection by prions
  • symptoms: ataxia, memory less, convulsions, coma

MED-109 Biology II (10 decks)

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