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Immunology & Virology > Week 2 Module 1 > Flashcards

Week 2 Module 1 Flashcards

1
Q

What’s the difference between a virus and a virion?

A

-A virus is inside a host cell, whereas a virion is in extracellular form and mature virus outside of cell

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2
Q

What is a naked virus?

A

-A virus that has no envelope

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3
Q

What is an enveloped virus?

A
  • A virus that has a lipoprotein membrane around nucleocapsid
    -Typically infect animal cells and use proteins on envelope for attachment
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4
Q

What is a nucleocapsid?

A

-Capsid + nucleic acid

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5
Q

Are all animal viruses enveloped?

A

-Not all animal viruses are enveloped
-Enveloped and naked viruses can infect animal cells
-All enveloped viruses infect animal cells, not plant cells

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6
Q

Capsid structure is made of individual units called_______

A

-Capsomeres

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7
Q

What are the characteristics of a Capsomere?

A

-arranged in repetitive pattern around nucleic acid
-each capsomere can be made of single or multiple proteins
-self assembly – when 1° sequence of protein directs folding of viral proteins and spontaneous assembly into capsid
-sometimes assembly requires help from chaperone proteins

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8
Q

Every protein needs what to be active?

A

Needs to be at least in tertiary structure

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9
Q

What is a domain?

A

An independent folding unit, a domain by itself isn’t functional

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10
Q

What is a chaperone?

A

A helper protein

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11
Q

What are envelope proteins used for?

A

-Attachment and penetration of animal host cells.

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12
Q

What are the 2 types of Viral symmetry?

A

-Rod-shaped, and spherical

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13
Q

Rod-shaped symmetry?

A

-helical symmetry
-example – tobacco mosaic virus

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14
Q

Spherical symmetry?

A

-icosahedral symmetry meaning 20 triangular faces and 12 vertices (minimum of 60 capsomeres)
-to have sufficient size to package nucleic acid, most spherical viruses have some multiple of 60 capsomere units

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15
Q

What is the typical symmetry of Phage and Human Papilloma virus?

A

-phages – icosahedral symmetry in head and helical symmetry in tail.
-Human papilloma virus is icosahedral

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16
Q

What is plus sense as it relates to ssRNA?

A

– exact same sequence as viral mRNA

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17
Q

What is minus sense as it relates to ssRNA?

A

-complementary to mRNA sequence.

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18
Q

What is the range of genome in viruses?

A

139 kb (smallest known) – 1.25 Mb (marine Megavirus).

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19
Q

What is the gene range in viruses?

A

-From a few to approximately 350

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20
Q

What does metagenomics suggest concerning function of viral genes?

A

Metagenomics
suggest function of 75% of viral gene sequences are novel/new!

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21
Q

Classification of viruses

A

can be on basis of type of
genome (Baltimore classification), host range, morphology, type of replication; Multiple ways.

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22
Q

Class I & VII viruses

A
  • dsDNA (+/-) virus Include phage T4 (I), and Hepatitis B (VII)

-Class VII are dsDNA viruses that
use reverse transcription as part of their reproduction cycle.

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23
Q

Class II viruses

A

-ssDNA(+) virus include *X174 and Parvovirus

24
Q

Class III viruses

A

-dsRNA(+/-) virus include Phage phu6, and Rotavirus

25
Q

Class IV viruses

A

-ssRNA(+) virus includes Phage MS2, and poliovirus

26
Q

Class V viruses

A

-ssRNA(-) virus includes rabies virus and influenza virus

27
Q

Class VI viruses

A

-ssRNA(+) retrovirus
-Includes HIV, and mouse leukemia virus

28
Q

What does Rotavirus affect?

A

Stomach

29
Q

Viruses can infect host cells from which domains of life?

A

-Eukarya, Bacteria, Archaea
-viruses aren’t cells because they cannot reproduce independently, they need a host and they cannot make their own organelles

30
Q

The vast majority of RNA viruses only infect_______

A

Eukarya

31
Q

Retroviruses only known to infect_____

A

Animals

32
Q

What is the Overview of the Viral life cycle?

A

-Attachment(adsorption) of the virion to a susceptible host cell
-Entry (penetration) of the virus or its nucleic acid
-Synthesis of virus nucleic acid and protein by cell metabolism as redirected by virus
-Assembly of capsids and packaging of viral genomes into new virions (maturation)
-Release of mature virions from host cell

33
Q

Does the nucleic acid and capsid enter prokaryotic host cells being infected by viruses?

A

When prokaryotic cells (bacteria & Archaea)
infected by viruses, only nucleic acid enters host.

34
Q

Does the nucleic acid and capsid enter eukaryotic (plant and animal) host cells being infected by viruses?

A

-When plant and animal cells infected, entire virion (including capsid) is taken up by host cell.

35
Q

What is the length of viral replication cycle for bacteriophages and animal viruses?

A

-~20 – 60 min for bacteriophages
-~8 - 40 hr for animal viruses

36
Q

What is a Permissive (host)?

A

-When host cell supports complete replication cycle of virus

37
Q

What is the Burst size?

A

-Number of virions released per host cell
-Growth curve for viruses is one-step growth curve.
-when monitoring in lab, medium basically shows no increase in viral number until the cell bursts. Then there is a sharp increase.

38
Q

What is the Eclipse phase?

A

– first few min after infection when genome replication and some translation occurs
-virion can no longer infect another cell

39
Q

What is the Maturation phase?

A

-at start new viral particles assembled but can’t be detected in medium yet
-at end, new virions released through lysis or budding

40
Q

What is the Latent Period?

A

-Eclipse+ part of maturation period; when no new virions released into media

41
Q

What is Attachment in viral life cycle?

A

-major determinant of host specificity for virus

-virion (enveloped or naked) has protein on surface that interacts
with receptor on host. (Receptor evolution could make host
resistant to that virus.)

-receptors have ‘normal’ metabolic function in host cell but have
been exploited by virus for infection

42
Q

What are some examples of host cell receptors?

A

-Phage T4 – uses carbohydrates in LPS layer of E. coli
-Phage T1 – uses iron uptake protein
-Chi bacteriophage – uses flagellum
-M13 phage –uses pilus

43
Q

What happens during Penetration of Phage into Bacterial Host Cell?

A

-genome of phage enters bacterial host cell
-special proteins (e.g. enzyme for replication of viral
RNA genome that host cell doesn’t have) may enter too

Example: Phage T4 entering E. coli
-tail fibers attached to E. coli polysaccharides in outer membrane
of LPS layer
-fibers retract and tail pins directly contacts cell wall
-T4 lysozyme makes hole in peptidoglycan layer and tail sheath
contracts (becomes more compact)
-linear dsDNA of phage enters cell through tail tube

44
Q

Why do viruses bring in enzymes in to copy RNA genomes?

A

-Bacteria don’t have the ability to copy RNA genomes so the virus brings in those enzymes that help

45
Q

What happens during Penetration of viruses into animal and plant host cells?

A

Two key differences between bacterial and animal/plant viruses:
i) animal and plant cells are eukaryotic; have nuclei where viral
genome will be replicated
ii) entire virion needs to enter host cell
-for animal cells, virus receptors are often surface proteins that
mediate cell-cell contact, or intercellular communication
-in multicellular organisms (e.g. humans) receptors can be found
in only in some tissues e.g. respiratory tract for rhinovirus
(common cold)

-penetration of animal virus can occur through endocytosis or
fusion with cytoplasmic membrane
-uncoating – release of viral genome from capsid – must occur
so genome can be replicated in nucleus of host cell
-can occur at membrane and or in cytoplasm

46
Q

What happens when Rotavirus enters animal cells?

A

-rotaviruses are naked
-spike proteins responsible for attachment

-then certain rotaviruses (bovine, porcine) taken up through
receptor-mediated endocytosis
-endocytosed virus transported to host lysosome
-lysosomal enzymes uncoat viral genome

47
Q

Nonenveloped DNA viruses include?

A

-Parvovirus, papovavirus, adenovirus, iridovirus

48
Q

Enveloped DNA viruses include?

A

-Hepadnavirus, pox virus, herpes virus

49
Q

Nonenveloped RNA viruses include?

A

-Picornavirus, reovirus

50
Q

Enveloped RNA viruses include?

A

-Rhabdovirus, togavirus, orthomyxovirus, bunyavirus, coronavirus, arenavirus, retrovirus, paramyxovirus

51
Q

What are Temperate viruses?

A

-Some dsDNA viruses are temperate (latent) – do not immediately cause host cell lysis; Most commonly
bacteriophages.

-Instead, virus remains ‘quiescent’ (most genes not
expressed) and genome is replicated along with host cell genome and passed to daughter cells.

52
Q

What is a Lysogen?

A

-host cells that contains temperate virus.

● Viral genome can be integrated into host cell genome
(e.g. prophage) OR be maintained as plasmid

53
Q

What is Lytic life cycle?

A

Cell death

54
Q

What is a Lysogenic life cycle

A

-Lysogenic life cycle is when viral DNA is integrated into host cell and doesn’t kill cell immediately and forms a prophage (be quiet for a while and when other cells are healthy again attacks them and goes back to lytic life cycle)

55
Q

What does the Lysogenic state depend on?

A

-Lysogenic state depends on expression of a repressor
protein; If repressor inactivated or not expressed then lytic cycle will resume

56
Q

Phage Lambda and

A

Immunology & Virology (6 decks)

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