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Microbiology > Viruses > Flashcards

Viruses Flashcards

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Biology 101 flashcards
1
Q

what are the general characteristics of viruses?

A
  • obligatory parasites - they need to hijack host machinery to replicate
  • small
  • made of nucleic acid genome which is surrounded by a protein coat (capsid) and a lipid envelope
  • they can infect all living organisms, even other viruses (virophages)
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2
Q

what is the virus nucleic acid genome comprised of?

A
  • DNA = ss or ds
  • RNA = ss (+/-), or ds
  • usually between 2-20kbp
  • minimal genetic info is needed as they hijack host machinery
  • ds>ss, DNA genome > RNA genome
  • organised usually as one molecule which can be fragmented
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3
Q

what is the composition and structure of the viral capsid?

A
  • made of capsomer proteins
  • highly ordered structure which can be self-assembled

isosahedral symmetry - spherical viruses
- shape is dependent on no. of subunits on each fase

helical symmetry - rod viruses
- nucleic acid filments bind to capsomers which hold genome togeter

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4
Q

what is the composition and role of the lipid envelope?

A
  • made of lipid bilayer with glycoproteins from host (viral encoded)
  • can take glycoproteins from host cell

role: allows entry into host cells - fusion and endocytosis

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5
Q

what are examples of complex viruses?

A

Bacteriophages:

  • contain a mixture of isosahedral and filamentous structures
  • tail can contract and disperse genetic material into the cell

Non-symmetricral viruses e.g. poxyviridae (smallpox)

archaea phages: long rod shaped

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6
Q

What is the overview of the Baltimore classification?

A

Group I, II and VII: DNA viruses
Group III, IV, V and VI: RNA viruses

takes into account:

  • nature of the genome: RNA/DNA
  • type of RNA/DNA: ss, ds and polarity
  • the genome replication mechanism
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6
Q

what do viruses need to be able to invade the host?

A

positive mRNA

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7
Q

what is the genome and replication machinery of Class I?

A
  • dsDNA
  • classical semiconservative replication
  • transcribe minus strand to produce +mRNA
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7
Q

what is the genome and replication machinery of Class II?

A
  • ssDNA (+)

- classical semiconservative, synthesise other strand to produce dsDNA. then transcribe minus strand to produce +mRNA

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8
Q

what is the genome and replication machinery of Class III?

A
  • dsRNA

- transcribe the minus strand to produce +mRNA

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9
Q

what is the genome and replication machinery of Class IV?

A
  • ssRNA (+)

- can be directly translated as +mRNA

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10
Q

what is the genome and replication machinery of Class V?

A
  • ssRNA (-)

- minus strand is transcribed to produce +mRNA

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11
Q

what is the genome and replication machinery of Class VI?

A
  • ssRNA (+) retrovirus

- reverse transcribed to produce dsDNA, and then minus strand is transcribed to produce +mRNA

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11
Q

what is the genome and replication machinery of Class VII?

A
  • dsDNA

- transcription followed by reverse transcription

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12
Q

What kind of virus is HPV16 and what effects does it have on human health?

A
  • dsDNA - Class I
  • Papillomavirus - warts, cervical cancer
  • no lipid envelope
  • genome size = 5.3-8kbp
  • 90% of cervical, 85% vulvar and 80% vaginal HPV related cancers in women
  • 90% genital warts in men and women
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13
Q

What kind of virus is is adeno-associated virus and what effects does it have on human health?

A
  • ssDNA = class II
  • adeno-associated virus
  • no lipid envelope
  • genome size = 5kbp
  • harmless to humans
14
Q

What kind of virus is rotavirus and what effects does it have on human health?

A
  • dsRNA = class III
  • reovirus
  • no lipid envelope
  • genome size = 18-31kbp
  • 2 million hospitalisations world wide 1986-2000
  • rotavirus vaccine protects against 90% of the strains in UK
15
Q

What kind of virus is aphtovirus and what effects does it have on human health?

A
  • (+) ssRNA = class IV
  • foot and mouth disease virus
  • no lipid envelope
  • genome size = 7.5kbp
  • over 4 million cattle killed in 2001
16
Q

What kind of virus is the flu virus and what effects does it have on human health?

A
  • (-) ssRNA = class V
  • influenza virus
  • has a lipid envelope
  • genome size = 12-15kbp
  • 1918 pandemic killed 20-100 million
  • killed 3-5% of world population 1918-20
17
Q

What kind of virus is AIDS and what effects does it have on human health?

A
  • reverse (+) ssRNA retrovirus = class VI
  • HIV
  • has a lipid envelope
  • genome size = 9.7kbp
  • causes AIDS which is progressive failure of immune system, kill CD4 cells, macrophages and dendritic cells
  • 37 million have died from HIV to date
18
Q

What kind of virus is cirrhosis and what effects does it have on human health?

A
  • reverse dsDNA = class VII
  • hepatitis B virus - causes liver cancer
  • has a lipid envelope
  • genome size = 3.1kbp
19
Q

what is the life cycle of bacteriophages?

A
  1. attachment: tail fibres interact with cell-surface proteins and form irreversible contact
  2. Genome injection: contractile tail injects genome through hole in envelope into cytoplasm via hydrolysis of peptidoglycan
  3. production of nucleic acids and proteins via epistome which uses host machinery
  4. maturation: progeny viruses assemble in cytoplasm
  5. release: phage proteins destabilise membrane and form endolysin pores in peptidoglycan layer to leave the cell
20
Q

what are temperate phages?

A
  • they can enter virulent stage or dormant stage
  • stage 1 and 2 (attachment and injection) are the same
  • genome integrates into host cell and is maintained over generations
  • phages can multiply in non-harmful way
  • they can revert to virulent phase by stress which causes cell machinery to enter lytic process
21
Q

how do DNA viruses replicate?

A
  • virus has a capsid (no envelope)
  • capsomers interact with cell surface proteins and virus is engulfed by endocytosis
  • viruses are uncoated and release genome into nucleus for transcriptioon of +mRNA
  • viral mRNA enters cytoplasm for translation to form viral proteins
  • virions assemble and are released
22
Q

how do RNA viruses replicate?

A
  • viral RNA enters cytoplasm and can be transcribed to form correct polarity, or directly used in translation if +
23
Q

how do retroviruses (class VI) replicate?

A
  • viruses attach to host cell membrane via glycoproteins
  • ssRNA genome enters the cell with reverse transcriptase, integrase and protease
  • reverse transcriptase copies viral RNA into dsDNA
  • integrase transports viral DNA into chromosomes which can then remain dormant
  • viral DNA is transcribed to produce viral mRNA which is translated into viral proteins to form more HIVs
24
Q

how are dsDNA viruses packaged?

A
  • encapsulation is coupled with maturation of the replicative genome
25
Q

how are ssDNA viruses and retroviruses packaged?

A
  • electrostatic interactions between capsid proteins and RNA genome
  • promote cooperative assembly of capsomers
26
Q

how are fragmented genomes packaged?

A
  • genomic fragments in complex with proteins are in pairs before encapsulation

Microbiology (8 decks)

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