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IDIT Test 3 > Virsuses > Flashcards

Virsuses Flashcards

1
Q

Define virion:

Define nucleocapsin;

A

virion - mature virus particle

proteins attached to genome

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2
Q

How does +ssRNA make proteins?

How does -SSRNA make proteins?

What do RNA viruses use to make proteins/ own genome?

A

+ssRNA is same polarity as mRNA, translate direclty to protein, also make - strand to replicate genome into virion.

-ssRNA is complementary to mRNA, makes mRNA 1st, then protein, can also use + synthesized to make genomes for virions.

+/-ssRNA viruses use RNA dependent RNA polymerase (have to bring with them on genome/ not in host)

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3
Q

Why doe RNA viruses mutate rapidly?

A

RNA viruses have lack of proofreading mechanism to assure fidelity of other processes (i.e. DNA rep)

Retroviruses are the most error prone - due to RNA dep. DNA polymerase

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4
Q

What is transfection?

A

infection of mammalian cell by bare viral nucleic acid

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5
Q

Transformation

A

heritable change in genes/phenotype of cell from a viral infection, resulting in neoplasm (cancer).

Can be used to increase machinery for virus

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6
Q

Permissive cells

A

cells that support the complete viral life cycle, producing viral particles

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7
Q

Non permissive cells

A

don’t permit life cycle, or only permit part of it. Transformed by virus (esp DNA virus)

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8
Q

Defective virus

What is an example of defective virus?

A

virus not capable of going through entire replication unelss cell is infected w/ helper particle (complete virus)

Ex: Hepititis D virus- need B to replicate

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9
Q

Cytopathic effect (CPE)

A

observable damage to cell from infection

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10
Q

Describe animal viruses by:

  • size
  • nucleic acid
A

size - visible under light microscope
NA - length can vary from a few proteins to 100s
- genomes can be segemented (cause shift), or a single pieces (can be cut)
- only DNA or RNA / virus, not both

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11
Q

Explain the capsid

A

structural units (capsomers) that surround and protect viral nucleic acid

Complex - poxviruses
Icoshohedral - 2/3/5 symmetry, 20 faces/ 12 vertices
Helical

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12
Q

Envelope

A

Membrane of phospholipid bilayer taken by host cell to surround nucleocapsid
- contains virus derived glycoproteins/ proteins for attachment/fusion
Ex: Herpes Simplex
-M proteins - inner layer, help w/ viral structure

-F proteins - envelope surface, catalyze fusion w/ host cell

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13
Q

Which viruses are easier to inactivate: naked or enveloped?

A

Enveloped viruses are easier to inactivate. Lipids can be stripped away by soaps/dettergents, prevent particle from attaching to host cells. (Lose F protein)

Naked capsids are harder to kill, survive disinfection

GI viruses are naked–> hard to remove

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14
Q

How many classes of viruses are there? What are the classes of virus based on? (5 aspects)

A 
DNa - 6 families
RNA - 13 families based on:
1)Nucleic Acid structure
2) Symmetry of nucleocapsid
3)Envelope?
4)Capsid/virion dimension
5) NA sequence similarities
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15
Q

What are the steps to host cell infection?

A

1) Attachment
2) entry into host cell
3) viral protein/genome synthesis
4) Assembly/ release of virion

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16
Q

Explain attachement

A

Most important for specificity: viral receptors on cell surface

can also lead to tissue specificity

17
Q

How does HIV enter cell?

A
  1. SU exposes Cxcr4 and Ccr5 (chemokine receptors) on CD4 cells.
  2. Cxcr4 = Tcell tropic strain receptor.
  3. Ccr5 = macrophage- tropic strain receptor. (ccr5 deletion mutation = HIV-1 immune)
  4. binding to receptors causes confirmational change–> fusion peptide inserts into membrane
18
Q

How to enveloped viruses enter host cell?

A

1.F proteins catalyze fusion of viral membrane with host cell membrane
OR
2. F protein mediates phagocytosis and fusion of viral membrane and phagosome

19
Q

How do naked viruses enter host cell?

A
  1. Bind to host cell at surface and capsid reearranges to allow genome out
    OR
  2. Viruses can be engulfed by receptor mediated endocytotis, causes partial breakup of capsid in vacuole–>cytoplasm for more uncoating
20
Q

How does poliovirus enter cells

A

Naked: viroid is endocytosis, binds to receptor resulting in VP1 change, genetic material leaves into cytoplasm

21
Q

How do adenovirus enter cells:

A

Penton base reacts w/ integrin receptor–> endocytosis, penton disassembled, capside release into cytoplasm
Capsid attaches to nuclear pore–> release of genome

22
Q

How does the F protein work?

A

Has hydrophobic domain that grativates towards and inserts into host membrane.

This lowers activation energy of fusion

23
Q

What is a syncytium?

A

A giant cell formed by the attachment of smaller cells to infected cell, catalyzed by F protein

24
Q

What is the eclipse period of infection?

What is the latenet period of intection?

A

Eclipse - post entry, no formed virus particles inside or outside cell. Includes genomse synthesis.

Latent - mature particles formed inside cell, but not-outside

25
Q

Do +ssRNA carry RNA pol?

A

No, +ssRNA don’t carry polymerase, host machinery

this makes +ssRNA infectious

26
Q

How are -ssRNA/ dsRNA viral dna non infectious?

A

-ssRNA and dsDNA can’t immediately produce mRNA, need to by translate by cellular machinery into mRNA 1st.

27
Q

What makes retrovirus (and hepadna DNA viruses) special?

A

Retroviruses convert RNA dsDNA, then into mRNA.

need reverse transcriptase (*RNA dependent DNA pol), and have 50-100 molecules of it in their capsule

28
Q

What is “shuffling”?

A

If multiple viruses w/ segmented genomes infect the same cell, they can switch out segments between each other, adding genetic diversity

29
Q

How are viral particles released from a cell?

A
  1. Naked virus/ some enveloped - viroids burst/ lyse cell, don’t need to use membranes
  2. Enveloped viruses - acquisition of the envelope of host cell as particle escapes cell (does not necesarilly kill host cell)

Hepititis B - slow release (acquisition of membrane), doesn’t kill host cell

HIV - slow release that ultimately results in cell death

30
Q

Lecture 2-3

What is a localized infection?

A

Virus has multiplied and caused damage near the site that it entered host.

31
Q

What is a disseminated infection?

A
  1. Virus enters host at specific location, multiplies locally
  2. Primary viremia - New virus particles spread via lymphatics to blood
  3. Virus multiplies in blood–> secondary viremia
  4. Infection of target organ.

From initial infection to blood stream, known as “incubation period”

32
Q

What is an inapparent infection?

A

Inapparent infection = asympomatic infection resulting from attenuated virus or effective host defense

Represent unrecognized source for viral dissemination, confer host immunity.

IDIT Test 3 (2 decks)

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