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Viruses Flashcards

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Biology 101 flashcards
1
Q

Describe a virus.

A
  • Nucleic acid surrounded by a protein coat
  • Replication is host dependent
  • Intracellular and extracellular phases
  • Infect humans, plants, protozoans and bacteria
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2
Q

What is the ‘city’ virus method?

A

Change quickly to escape being recognizable to the body’s immune system

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3
Q

What is the ‘buy what I can afford’ virus method?

A

Old enough to have developed safe ways to evade detection by the immune system

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4
Q

What is the ‘infect whatever moves’ virus method?

A

Infect as much and as quickly as they can

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5
Q

What is the extracellular phase of a virus?

A

Virion

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6
Q

What is the general virion structure?

A
  • Nucleic acid surrounded by protein capsid
  • Capsid form is highly repetitive
  • Some surrounded by a membrane = enveloped virus
  • No membrane = naked virus
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7
Q

How do viruses attach to host cells?

A
  • mediated by protein spikes on the surface

- Bind to host surface molecules often glycoproteins

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8
Q

How does an enveloped virus enter?

A
  • Membranes fuse, endosytosis, release viral capsid, enveloped bcomes naked
  • Endocytosis, outer membrane fuse with virus membrane, naked membrane is released, can borrow membrane, budding
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9
Q

What are the consequences of viruses?

A
  • Multiplication, lytic infection
  • Transform into a tumor cell
  • Slow release without cell death
  • Virus infection but not causing har,
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10
Q

What are the different genome based categories of viruses?

A
  1. Double stranded DNA (dsDNA)
  2. Single stranded RNA (ssRNA)
  3. Double stranded RNA (dsRNA)
  4. Retroviruses
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11
Q

How do dsDNA viruses replicate?

A
  1. Viral DNA transported in host nucleus
  2. Host RNA converts viral DNA to viral mRNA
  3. Viral mRNA translated to viral proteins
  4. Viral DNA replicated by host DNA polymerase
  5. Viral genome and proteins assemble and are released
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12
Q

What are some examples of dsDNA viruses?

A

Herpesviruses - herpes simplex, chickenpox. Papillomaviruses - warts. Poxviruses - smallpox.

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13
Q

What are the two different categories of ssRNA viruses?

A

Positive strand and negative strand.

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14
Q

How do positive strand ssRNA viruses replicate?

A
  1. Cytoplasmic ribosomes translate viral mRNA to proteins
  2. Viral synthetase replicates the viral RNA genome
  3. Viral proteins from the capsid ecapsulate the replicated RNA genomes forming new virions
  4. New virions bud from the infected cell
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15
Q

What are some examples of positive strand ssRNA viruses?

A

Picornoviruses: polio, rhinovirus (cold), hepatitis A.

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16
Q

How do negative strand ssRNA viruses replicate?

A
  1. Virus is endocytosed
  2. RNA negative strand converted to mRNA positive using viral RNA polymerase in the nucleus
  3. RNA replication happens in the nucleus
  4. mRNA is translated in cytoplasm to produce viral proteins
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17
Q

What are some examples of negative strand ssRNA viruses?

A

Rhabodoviruses: rabies. Orthomyxoviruses: influenza

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18
Q

How do dsRNA viruses replicate?

A
  1. Late structural proteins assemble into developing inner core
  2. Ten viral mRNA gene segments are inserted into inner core
  3. Negative RNA strand is copied on viral mRNA to replicate dsRNA genome
  4. Inner core is used for mRNA transcription and virion progeny production
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19
Q

What are some examples of dsRNA viruses?

A

Reoviruses: reovirus, rotavirus.

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20
Q

How do retroviruses replicate?

A
  1. Bind and viral envelope proteins fuse to specific host cell receptors so the virus can enter
  2. Virion is uncoated
  3. Viral reverse transcriptase reverse transcribes one RNA strand in ssDNA and then into dsDNA.
  4. Enters nucleus
  5. Viral DNA integrates into host DNA - provirus is formed
  6. Transcription of viral DNA to viral mRNA
  7. Synthesis of HIV polyproteins
  8. Processing of HIV polyproteins by the viral protease and generation of mature function proteins
  9. Encapsidation of viral ssRNA
  10. Budding of virions
  11. Release of virions
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21
Q

What are some examples of retroviruses?

A

HIV; AIDs. HTLV-1: leukemias.

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22
Q

What are non-eukaryotic viruses?

A
  • Bacteriophages (viruses that infect bacteria)
  • Mostly dsDNA viruses
  • Most common and bipodiverse entities
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23
Q

What are some applications of non-eukaryotic viruses?

A

Medicine. Biology. Anti-terrorism.

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24
Q

What are the different types of non-eukaryotic viruses?

A

Latent/temperate - Lambda. Lytic -T4.

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25
Q

How does T4 bacteriophage infect E. coli?

A

Attach and inject material in the bacterial cytoplasm

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26
Q

What are the stages of the Lytic Phage?

A
  1. Attachment
  2. Penetration
  3. Transcription
  4. Replication of phage DNA, synthesis of proteins
  5. Assembly
  6. Release
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27
Q

What are the stages of the Temperate Phage?

A
  1. Attachment
  2. Linear phage DNA circularises
  3. Replication or integration
  4. New virions formed
  5. Cell lyses releasing phage virions
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28
Q

What type of virus is smallpox?

A

DNA virus

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29
Q

What are the key features of smallpox?

A
  • Human disease
  • Person to person
  • Starts as respiratory infection
  • High rate of mortality
  • Now eradicated
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30
Q

Why was eradication of smallpox possible?

A
  • Because it was exclusive to humans
  • No hidden carriers so obvious who had the disease
  • Only one serotype
  • Vaccination was 100% successful
31
Q

What type of virus is human herpesvirus?

A

dsDNA, with large genomes

32
Q

What are the key features of herpesvirus?

A
  • Lifelong infections
  • Different cycles, latent and lytic
  • HSV 1 and HSV 2
33
Q

What is the latent cycle?

A

Few viral proteins expressed and no virions produced

34
Q

What is the lytic cycle?

A

All viral proteins expressed and virions produced to infect new cells

35
Q

What is HSV1?

A

Infects nerves cells. During primary infection and reactivation it manifests as ‘cold sores’. Reactivates due to stress.

36
Q

What is HSV2?

A

Genital

37
Q

What type of virus is polio virus?

A

Positive strand ssRNA. Linear genome.

38
Q

How big is the polio virus?

A

Small (28nm). Genome codes only 4 proteins

39
Q

How does polio affect people?

A

Poliomyelitis - oral - infects the gut and then invades the blood. Targets nerve cells and destroys them leading to paralysis of infected tissue.

40
Q

What are the two types of vaccines?

A

Inactivated (dead) and attenuated

41
Q

What is the inactivated vaccine for polio?

A

Treated with formaeldehyde. Prevents entry to nerve cells. Still infects the gut.

42
Q

What is the attenuated vaccine for polio?

A

Cell culture - lives but doesn’t cause pathology. Induces immunity in the gut and prevent infection

43
Q

What are the advantages of an inactive polio vaccine?

A

Effective. Can be incorporated into routine immunizations. Good stability in transport and storage. No risk for poliomyelitis in recipients and contacts. Safe for immunodeficient individuals.

44
Q

What are the disadvantages of an inactive polio vaccine?

A

Does not induce gut immunity. Booster vaccines required. Administered as injection. Higher community vaccination levels required.

45
Q

What are the advantages of an attenuated polio vaccine?

A

Effective. Lifelong immunity. Induces antibody response to natural infection. Administration - oral. No booster vaccines. Indirect community immunization.

46
Q

What are the disadvantages of an attenuated polio vaccine?

A

Vaccine induced poliomyelitis. Spread to contacts without consent. Unsafe for immunodeficient individuals.

47
Q

What are the different serotypes of influenza?

A

A, B and C

48
Q

What is the most serious serotype of influenza?

A

C

49
Q

What type of virus is influenza?

A

Negative ssRNA

50
Q

What is meant by nucleoprotein?

A

Helical

51
Q

What is meant by polymorphic?

A

No defined shape

52
Q

What are the two enveloped forms of influenza?

A

Hemagglutinin and Neraminidase

53
Q

What is Hemagglutinin?

A

Attaches to host receptors

54
Q

What is Neuraminidase?

A

Breaks down sialic acid to allow budding

55
Q

What is antigenic drift in influenza?

A

Minor mutations. Replicates and copies genome. Each times its copied there are small mutations. Accumulation of genetic change. RNA doesn’t have proofreading mechanisms like DNA

56
Q

What is antigenic shift in influenza?

A

Major re-assortment. Unique to influenza A, Huge jump in genetic change. Entire section of the genome changes.

57
Q

How many different HA are there?

A

15

58
Q

How many different NA are there?

A

9

59
Q

What are epidemics the result of?

A

Antigenic drifts

60
Q

What pandemics the result of?

A

Antigenic shifts

61
Q

Where do many flu viruses come from?

A

Birds and pigs

62
Q

What is the pathogenic strain of flu?

A

H5N1

63
Q

What are the anti-influenza drugs?

A

Amantadine. Oseltamivir.

64
Q

How does Amantadine work?

A
  • Targets M2 protein on envelope
  • Stops uncoating of virus in cell
  • Some strains resistant to M2
65
Q

How does Oseltamivir work?

A

Targets Neuraminidase on envelope. Stops budding of the virus.

66
Q

Describe the vaccine for influenza.

A
  • Kill vaccine compromised of at least 3 strains
  • Need to predict future strain
  • Recombinant HA vaccine
67
Q

What type of virus is HIV?

A

Retrovirus (RNA virus which replicates through a DNA intermediate) Enveloped virus

68
Q

What are the different types of HIV?

A

HIV 1 - 99% of infections. HIV 2 - less virulent.

69
Q

What are the 3 regions of the HIV genome?

A
  1. Gag - internal structural proteins
  2. Pol - reverse transcriptase and integrase
  3. Env - envelope protein
70
Q

Describe Budding.

A

Smal projection in the shape of a bud is formed. Nucleus divides. One daughter passes into bud and another bud is formed.

71
Q

What is SIV?

A

Simian Immunodeficiency Virus - infects apes - this is where HIV originated

72
Q

How does HIV work?

A
  1. Infects cells of the immune system
  2. Destroys immune cells, impairs function and reduces numbers
  3. Weakens immune system
  4. Inability to battle secondary infections leads to disease and death
73
Q

How is HIV transmitted?

A

Exchange of bodily fluid

74
Q

What are high risk activities for people with HIV?

A

Drug use. Unprotected sex. Blood transfusions.

Microbiology (8 decks)

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