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BIOL 121 - Impact Of Microbes > Virus > Flashcards

Virus Flashcards

1
Q

What is a virus

A

A simple, miniscule, infectious, obligate intracellular parasite comprising of genetic material (RNA or DNA) surrounded by a protein coat (capsid) and/or an envelope derived from a host cell membrane

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2
Q

Genetic material of virus

A

Virus contain either DNA or RNA genomes, (double stranded or single stranded)

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3
Q

Intracellular parasite definition

A

Virus have to have a living host to replicate/reproduce and require cellular machinery to do this

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4
Q

Relative size of virus

A

Usually they’re 20-300nm, they’re very small! And can only be seen through an electron microscope

However there are giant virus, which can be seen under a light microscope

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5
Q

Giant virus example

A

Pandoravirus
> 1000nm length. Biggest virus known so far, 2.9 MB genome in size. Enclosed 2556 gene

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6
Q

Virus exist in what 2 states?

A

Extracellular Virion (outside the host cell) - for transmission

Intracellular Virus (after infecting the host cell) - for replication

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7
Q

Tools that can be used to view vital structure

A

Electron microscope

X-ray crystallography

Cryo-electron microscopy

Nuclear magnetic resonance spectroscopy (NMR)

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8
Q

Structure of virus (The nucleocapsid)

A

Outside of cell: virus particles = virion

Capsid (protein coat/shell) (made up of many protein subunits = capsomers)

Nucleic acid (DNA or RNA)

Additional: Capsomers can either be identical or (more often) the capsid will be composed of a mixture of structurally distinct capsomers

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9
Q

Shapes of virus (capris symmetry)

A

Helical - capsomers bond together in a spiral fashion

Polyhedral - capsid is roughly spherical

Binal (complex) - neither helical nor polyhedral forms, have irregular shapes, or have complex structures. May consist of both helical and isometric symmetries

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10
Q

Functions of the capsid

A

Protects nucleic acid from digestion by enzymes

Enables penetration of the host cell membrane to inject the infectious nucleic acid into the cells cytoplasm

Allow the virion to attach to a host cell

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11
Q

Naked/non-envelope vs enveloped virion

A

Enveloped has an envelope layer, (most infect humans) enables an extra layer of protection so they’re usually acquired by the host

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12
Q

What groups of organisms can be infected by virus

A

All groups of cellular organisms are infected by viruses:

Bacteria
Protozoa
Algae
Fungi
Plants
Animals
Virophage

Each virus only infects a specific host or group of hosts, not all!

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13
Q

Viruses of bacteria: Bacteriophages

A

More than 10^30 bacteriophage particles in the world waters

They weigh about a femtogram (10^-15grams)

The length of head-to-tail joining of 10^30 phases = 1.25x10^21 km = 100 million light years

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14
Q

Bacteriophages: genomes

A

Only a few with envelopes
Most had dsDNA
Many are complex

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15
Q

Replication cycle of bacteriophage step 1

A

Adsorption: attachment of specific receptors

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16
Q

Replication cycle of bacteriophage step 2

A

Penetration: entry of DNA

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17
Q

Replication cycle of bacteriophage step 3

A

Replication: synthesis of viral nucleic acids and protein

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18
Q

Replication cycle of bacteriophage step 4

A

Assembly and packing of new virions

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19
Q

Replication cycle of bacteriophage step 5

A

Release: release of new virion (lysis)

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20
Q

Replication cycle of bacteriophage step 6

A

Re infection: infect another cell

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21
Q

Lytic and temperate bacteriophages

A

Bacteriophage T4 is virulent and kills the host: it’s a lytic phage

Many bacteriophages have a alternative life cycle where they don’t kill the host: temperate phages or lysogenic phages

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22
Q

What happens after infection of a temperate phage

A

The genome can intergrate into the host’s chromosome; it is then termed a “prophage”

These produce a depressor protein
Repressive blocks lytic genes

The prophage replicates with the host chromosome: lysogeny or lysogenic cycle

The bacterial hosts that harbour a prophage are termed lysogens, (they are immune against infection with the same phage because of the repressor

Stresses initiate induction to resume lytic cycle

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23
Q

Why do we care about virus,

A

They’re a “planetary force” (10million viruses in one drop of seawater)

They keep control of “bacteria”

They’re primarily known for impact on health

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24
Q

Define virus

A

Intracellular replicative form of particle

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25
Q

Define virion

A

Complete infectious virus particle

26
Q

Define capsid

A

Protein coat that surround nucleic acid

27
Q

Define nucleocapsid

A

Nucleic acid plus capsid

(May be enclosed inside an envelope containing proteins encoded by the virus)

28
Q

Define Naked viruses

A

Lacking an envelope

29
Q

Define structural subunits

A

Smallest equivalent building units of the capsid

30
Q

Define capsomere

A

Structural protein units that made up the capsid

31
Q

What are the two main methods for taxonomy of virus?

A
  1. International committee of taxonomy of viruses:
    - rebranded in 1971; established by Federation of European Microbiology Societies Virology Division
  2. Baltimore system of virus classification
    - the system was developed by David Baltimore

(These classifications are being used together - before these, there was no consistent way of classifying virus)

32
Q

What is the primary aim of ICTV criteria for taxonomy of virus?

A

To develop, refine and maintain a universal virus taxonomy.

Collection and comparison of characters that distinguish one virus from another:

  • Phenotypic:
    Molecular comparison of genome
    Virion/capsid structure
    Presence of an envelop
    Host range
    Pathogenicity
  • Genotypic:
    Sequence similarity
    Gene contents
    Gene synteny
    Gene expression system
    Phylogenetic relationships
33
Q

What is the order of taxonomy virus groups, highest level to lowest level?

A

Realm
Kingdom
Phylum
Class
Order
Family
Genus
Species

34
Q

What is Baltimore System of Virus Classification?

A

It explains that regardless of the genome, every viral genome must make mRNA that can be read by host ribosomes.

35
Q

Key definitions: Bases for Baltimore Classification System

A

The mRNA is always the (+) single strange (+ssRNA). the mRNA is ribosome ready; it can directly be translated into proteins

-ssRNA: complementary to +ssRNA

dsRNA: +ssRNA and -ssRNA

DNA of equivalent polarity to cellular DNA is also the + strand (+dsDNA of virus)

DNA complements of + strands (ds+DNA) are - strands (-ssDNA)

36
Q

How many genome can a virus carry?

A

7

While they represent infinite complexity of infection, they carry a finite number of genomes: dsDNA, gapped daDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, +ssRNA with DNA intermediate

37
Q

What possible ways can virus infect cells?

A

Transformation into tumor cell (stops cancer suppressor genes within the cell)

Lysis; death of cell and release of virus (eg Ebola causes the individual to spit blood as a result)

Persistent infection; slow release of virus without cell death (eg HIV - however if come into contact with another infection, it becomes lytic and causes AIDS)

Latent infections; virus present but not causing harm, later emerges in lytic infection (eg fever which can cause sores)

38
Q

What are the 6 steps of a virus life cycle?

A

Entry includes:
1. Attachment
2. Uncoating

Replication includes:
3. Replication
4. Biosynthesis

Exit includes:
5. Assembly
6. Budding

39
Q

Virus life cycle: 1. Attachment

Receptor-Viral Protein Interface: What virus can attach to what receptor?

A

All virus require receptor to attach; exception include fungal viruses (no extracellular phase) and plant (enter by mechanical damage)

  • Different virus bind to receptors.
  • Virus of same family might bind to different receptors
  • One virus may bind to multiple receptors
40
Q

Virus life cycle: 1. Entry

How viruses enter cells?

A
  1. Injection of nucleic acid
  2. Fusion of envelope with host membrane
  3. Endocytosis
41
Q

Virus life cycle: 2. Replication of viruses (purposes)

A
  1. Viral proteins - synthesis of mRNA (unanimous)
  2. Viral genome - generation of viral genetic material (virus-dependent)
42
Q

Virus life cycle: 3. exit
and where does the envelope come from?

Envelope virion vs Naked virion?

A

Enveloped:
Surface proteins bud onto the cell membrane and push through it as the viral capsid joins the viral proteins at the cell membrane surface. This is released from the cell in an envelope.

Naked:
Naked viruses release results in cell lysis (bursting of the cell)

43
Q

There are at least 200 disease caused by virus in human, name some older diseases and re-emerging ones?

A

Older: Rabies, polio, smallpox, warts, etc

Re-emerging: Dengue fever, monkeypox, Avian flu, etc

44
Q

What type of virus is Rabies?

A

Older disease: Rhabdoviruses;
Group V Virus (-ssRNA)

45
Q

How does the rabies virus enter/infect the patient?

A

Infection of humans via saliva of infected animal

Virus enters PNS migrates to CNS to the brain

Causes swelling of brain, almost always results in death

46
Q

What are the two forms of rabies disease?

A

Furious Rabies (80%-90% of cases, change in behaviour and voice, paralytic stage, death)

Dumb Rabies (10-20% of cases, predominantly paralytic, lapse into stage of sleepiness, death in 3 days)

47
Q

Monkeypox is group I virus, dsDNA.

Firstly identified?

A

In 1958 in monkeys in Denmark,
first human case was reported in 1970 in a child in DRC, Africa.

48
Q

What are the 2 distinct classes of monkeypox?

A

Congo basin / Central African Clade (clade 1)

West African clase (clade 2, IIa, IIb)

49
Q

How can monkeypox be transmitted?
(Animal-to-human)

A

Animal-to-human

  • transmission occurs via bites / scratches from infected animal
  • Preparation and handling of infected animal products (bushmeat) may also result in transition
50
Q

How can monkeypox be transmitted?
(Human-to-human)

A

Human-to-human

  • transmission is thought to occur via direct skin-to-skin contact with lesions on the skin
  • Through indirect contact with contaminated fomites, such as bedding or clothing
51
Q

What are viroids?

A

Infectious agents that resemble virus.

They only infect plants

51
Q

Features of viroids?

A
  • Smallest known pathogens
  • Small, circular ssRNA
  • Extracellular forms naked - no capsid
  • Resistant to proteases and nucleases
  • Only infect plants
  • Do not encode proteins
  • Mode of action is unknown but replicate autonomously
51
Q

What are obelisks?

A

A new class of viroid-like elements that are first identified in human oral and stool metatranscriptomic data

They form their own distinct phylogenic group with no detectable sequence or structural similarity to known biological agents

52
Q

Properties of obelisks

A
  1. apparently circular ~1kb (1000nt) genome
  2. predicted rod-like secondary structures
  3. open reading frames coding for a novel protein superfamily, which are called “Oblins”
53
Q

What is a prion?

A

Small proteinaceous infectious particles which resist inactivation and contain no genetic material

54
Q

What are prion diseases often called?

A

Spongiform Encephalopathies

55
Q

How does Spongiform Encephalopathies disease occur?

A
  • Cellular prion localize on the neurones synapses between neurones / facilitate uptake of copper into the cell.
  • caused by accumulation of the misfolded protein scrapie prion protein

(Its uncertain how disease is actually caused. Most likely: infection with prion protein produces more copies of prion protein, leading to disease.)

56
Q

Example of disease caused by prions in animals?

(there are two, you just need to say one)

A

EG: Scrapie in sheep.
- Degenerative, fatal disease of CNS.
- Clinical signs: ataxia and recumbency
- No treatment
- Selective breeding for genetic resistance, surveillance and depopulation are primary means of controlling the disease

EG: BSE (bonvine spongiform encephalopathy) in cattle
- Mad cow disease due to animals’ erratic behaviour
- 4 million cows killed during eradication programme in YK
- 3 different presentations: classical, H-type atypical and L-type atypical
- Classical BSE can be transmitted to humans by consuming infected meat (causes CJD; Creutzfeldt-Jakob disease)

57
Q

Disease caused by prions in human example?

Just need one!

A

EG: Kuru; meaning “trembling”
Reported in ‘Fore’ tribe of Papua New Guinea via ‘funerary cannibalism’

EG: CJD; Creuzfeld-Jakob Disease
- Those affected lose ability to think and move properly and suffer memory loss. It’s always fatal, usually within 1 year of onset.

58
Q

What are the different types of CJD (disease caused by prions) that affect human?

A
  • Sporadic CJD = Most common type
  • Familial/inherited CJD = Rare genetic condition where one of the genes a person inherits from their parents
  • Variant CJD = likely to be caused by consuming meat from a BSE cow
  • Latrogenic CJD = infection is accidentally spread from someone with CJD through medical/surgical treatment

BIOL 121 - Impact Of Microbes (4 decks)

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