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Virology > Virus Structure (Lecture 8) > Flashcards

Virus Structure (Lecture 8) Flashcards

1
Q

What are the basic principles of viral capsids?

A

they are durable and inexpensive (very simple)

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2
Q

What leads to the diversity we see in viral capsids?

A

the structure of the viral capsid

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3
Q

What are capsid proteins?

A

asymmetrical proteins that will come together to form symmetrical units

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4
Q

What is the benefit of symmetry?

A

ensures for enough and maximal contact

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5
Q

Define the viral capsid structure

A

created by symmetrical arrangement of many identical proteins to provide maximal contact and non-covalent bonding

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6
Q

What are the 2 functions of the capsid?

A

protect and deliver genome

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7
Q

What is a virion?

A

extracellular phase of infectious viral life cycle

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8
Q

What is a nucleocapsid?

A

protein interacting with nucleic acid genome

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9
Q

What is an envelope?

A

host-cell derived lipid-bilayer membrane (can be from any organelle)

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10
Q

What is a subunit of the viral structure?

A

a single folded polypeptide (viral protein)

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11
Q

What is a structural unit of a viral structure?

A

one or more subunits that came together

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12
Q

What is viral tegument?

A

proteins that interact with envelope

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13
Q

What are the 3 different types of viral structures

A

icosahedral (naked/envelope), helical (naked/envelope), complex (bacteriophages)

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14
Q

What are 3 necessary things if we want a stable protein coat?

A

stable structure (need to be asymmetrical to form a symmetrical unit) | need to interact with host cell viral receptor (need to be resistant to external/environmental factors but be vulnerable to host cell) | recognize and be specific for the viral genome

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15
Q

What are the 4 requirements that viral structure proteins need to meet in order to successfully deliver the genome?

A

need to interact with host lipid bilayer (for enveloped viruses) | be able to easily uncoat/fall apart inside host cell (non-covalent bonds) | deliver it to proper location in the cell | fuse with host cell membrane

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16
Q

What does it mean that virion capsids are metastable?

A

virion capsids need to be stable enough to protect the genome but still be unstable in order to quickly fall apart inside the host cell

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17
Q

At what state of the viral capsid has it not attained “minimum free energy”? What does it mean by “minimum free energy”?

A

When the viral capsid is assembled, it is loaded with potential energy which keeps it stable and it minimum free energy is met, the viral capsid would easily disassemble. “Minimum free energy” refers to the energy barrier that needs to be met to cause the capsid to open.

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18
Q

What term do we use to describe the potential energy that is loaded within the viral capsid?

A

“spring-loaded”

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19
Q

What causes the viral capsid to pop open? Or how is this “minimum free energy” (energy barrier) met?

A

host cell will provide a signaling event to drop the energy barrier to open the virus (varies depending on virus)

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20
Q

How is metastability attained?

A

asymmetrical viral capsid proteins symmetrically arrange to provide maximal contact with each other

21
Q

What provides the assurance that you need a specific event to disrupt the bonds within the subunits of the capsid proteins?

A

the maximal contact between viral capsid protein structural units

22
Q

Why is it better to use non-covalent bonds within a viral capsid than covalent bonds?

A

using covalent bonds will increase the energy barrier causing it more difficult to open the capsid

23
Q

What are the 4 principles of building virions?

A

virions are either spherical or rod-shaped, made with many copies of few proteins (genetic economy/polycistronic), viral proteins need to allow regular and repetitive interactions, capsids are constructed from single/multi asymmetrical proteins that form symmetrical units

24
Q

What type of symmetry do rod-shaped viruses have? How many subunits?

A

helical, 1 subunit

25
Q

What type of symmetry do round-shaped viruses have? How many subunits?

A

icosahedral, 3 subunits

26
Q

What are the 2 rules of symmetry and self-assembly?

A

each subunit has identical bonding contacts with neighboring proteins (symmetry) and bonding contacts are composed of non-covalent bonds and therefore are error-free (self-assembly)

27
Q

Why are non-covalent bonds considered “error-free”?

A

nothing is permanent

28
Q

What are VLPs?

A

virus-like particles = capsid proteins without the viral genome in them (only protein coat)

29
Q

How can VLPs help induce an immune response against the actual virions that have this capsid?

A

injections with these VLPs that are specific to a certain virion will train up your immune system to recognize these foreign particles so when you come into contact with these proteins = your immune system will be ready to defend

30
Q

What type do symmetry do many ssRNA viruses have?

A

helical

31
Q

How many genes do helical-symmetry virions encode for their capsid protein?

A

one (because of 1 subunit)

32
Q

What does the flexibility of the rods depend on?

A

the strength of the non-covalent bonds

33
Q

What are the 2 properties of virion proteins and their genomes?

A

genomes non-covalently bind to proteins in packaged virions – due to the interactions between the (-)charged side of amino acids and the (+)charged side of the nucelic acids

34
Q

How do we get a round capsid from asymmetrically shaped proteins?

A

all round capsids have the exact/precise number of proteins in multiples of 60 & capsid proteins are uniform in size

35
Q

What is an icosahedron?

A

sphere-shape made up of 20 identical faces of an equilateral triangle

36
Q

What does the icosahedral symmetry allow for?

A

allows the formation of a closed shell with the smallest number (60) identical subunits with identical bonding contacts

37
Q

What are the 3 different folds of symmetry of an icosahedron?

A

5-fold, 3-fold, 2-fold

38
Q

How is the lipid bilayer envelope virus-specific?

A

viral proteins will interact with the lipid bilayer and the genome of the virus will be targeted to that area of the host-membrane and will become enveloped

39
Q

What are integral proteins on the viral envelope? What is it’s role?

A

viral glycoproteins that will be integrated into the envelope where the virus will bud off from; these proteins help recognize viral receptors on host cells

40
Q

What is the ectodomain on the viral envelope? What is it’s role?

A

these are the viral-receptor binding proteins that will be used to attach to the viral receptor on host cell surfaces; has a role in fusing; also serves as an antigenic site (what the immune system recognizes)

41
Q

What is the internal domain of the viral envelope? What is it’s role?

A

proteins responsible for recruiting the viral genome and viral capsid proteins to the envelope

42
Q

What are oligomeric spikes? What is it’s role?

A

proteins that have a role in fusion and can puncture the lipid bilayer (role/function depends on virus)

43
Q

What is one benefit to getting an envelope?

A

can exit cell without killing it (naked virions are more likely to to lyse cells)

44
Q

How would the removal of the envelope on a generally-enveloped virus affect its pathogenesis?

A

virion would be less infectious

45
Q

What are some enzymes that virions may carry with them? (name 6)

A

polymerases, integrases, proteases, poly(A) polymerases, capping enzymes, topoisomerases

46
Q

What are 2 reasons why a virion may carry activators with them?

A

for mRNA degradation or/and efficient infection

47
Q

Which type of virus may carry histones with them?

A

dsDNA viruses

48
Q

Which type of virus is known to carry tRNA molecules with them?

A

retroviruses (HIV)

Virology (23 decks)

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