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Infection Biology and Microbiology > Lecture 16: Virus structure > Flashcards

Lecture 16: Virus structure Flashcards

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1
Q

What structures do all viruses contain on their surfaces?

A

VAPs (Viral attachment proteins)

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2
Q

What is the key function of VAPs?

A

To help the virus recognise, bind and enter the host cell.

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3
Q

What is a virus that doesn’t have an envelope called?

A

A naked virus

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4
Q

What is a spike protein?

A

a surface protein found on many viruses that helps the virus to bind to and enter host cells by attaching to specific receptors on the cell surface.

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5
Q

What 2 types of gene does the poliovirus genome have?

A

Structural genes and non-structural genes

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6
Q

Give some examples of structural poliovirus proteins

A
  • Capsid proteins
  • VAPs
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7
Q

Give some examples of non-structural poliovirus proteins

A
  • DNA polymerase, RNA polymerase
  • Pathogenesis
  • Transformation (HPV and cervical cancer)
  • Proteins involved in the modulation of host defences
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8
Q

What is not coded in viral genomes?

A
  • Genes encoding the complete protein synthesis machinery(eIFs, tRNAs..)
  • Genes encoding proteins involved in cell wall production or membrane biosynthesis
  • Centromeres or telomers found in standard host chromosomes
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9
Q

What is the viral envelope derived from ?

A

The host cell

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10
Q

Describe capsids

A
  • Protein shell that surrounds the viral genome
  • Protects the nucleic acid
  • Facilitates the delivery of the nucleic acid into host cells
  • Made up of protein molecules called caspemeres
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11
Q

What is a nucleoplasmid?

A

the combination of the capsid and the viral nucleic acid. This term is mostly used for enveloped viruses, where the nucleocapsid is wrapped by the envelope.

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12
Q

How big is a typical viral genome?

A

The viral genome is typically very small, usually encoding a limited number of proteins.

So viral particles are usually built with multiple copies of these few proteins

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13
Q

How many genes does poliovirus have?

A

10/11

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14
Q

Why can’t viruses synthesize their own proteins?

A

Because they’re obligate intracellular parasites. So they don’t encode proteins for protein synthesis or buliding cell walls

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15
Q

How many different capsid structures are there?

A

3

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16
Q

What are the 3 types of caspid?

A

Helical

Icosahedral

Complex

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17
Q

do caspids protect the viral genome?

A

Yes

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18
Q

How many protein subunits is an icosahedron made up of?

A

60 identical subunits

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19
Q

Describe an icosahedral caspid

A
  • Symmetrical
  • Has a stable and efficient structure which allows for the packing of proteins in a way that minimises energy use and maximises stability
20
Q

Describe capsid assembly in a simple virus

A

In a simple virus, 60 subunits assemble into the icosahedral capsid.

21
Q

Describe capsid assembly in larger vrisues

A

Larger viruses use more than 60 subunits and can have hundreds of protein copies.

22
Q

Give some examples of icosahedral viruses

A

Adeno-associated virus, Poliovirus, Herpes Simplex Virus

23
Q

Describe the Adeno-associated virus

A

Small virus with a genome encoding just one protein that forms a stable capsid using 60 copies of that protein.

24
Q

Describe a poliovirus

A

A larger virus that uses three different proteins (VP1, VP2, and VP3), with 180 subunits forming a stable capsid.

25
Q

Describe the ‘metastability’ property of viruses

A

A larger virus that uses three different proteins (VP1, VP2, and VP3), with 180 subunits forming a stable capsid.

26
Q

How does the fact that capsids are symmetrical help them?

A

The capsid’s symmetry (2-fold, 3-fold, or 5-fold) helps in organizing the proteins and contributes to the structural strength of the virus.

27
Q

desrcibe Helical Capsids

A

In some viruses, the capsid proteins arrange in a spiral (helical) shape around the genome.

28
Q

Describe Herpes Simplex Virus

A

This virus has a special structure where, in addition to its icosahedral capsid, one of the vertices has a hole or portal that allows the viral genome to be injected into the host cell.

29
Q

What is an example of a virus that has a helical caspid?

A

Tobacco Mosaic Virus

30
Q

What is the length of helical virsues based on?

A

the length of the nucleic acid

31
Q

What is the width of helical viruses based on?

A

the size and packaging of protein subunits

32
Q

Is it true that the capsid dissociates from the virus upon infection of a host cell?

A

Yes, otherwise the viral genome would not be able to be released into the host cell and begin the replication process.

33
Q

Under an electron microscope, what will helical viruses look like?

A

Rods

34
Q

Are viral caspids metastable?

A

Yes

35
Q

Is it true that Capsid proteins recognize each other and self-assemble into a stable structure without the need for the viral genome?

A

Yes, this ability is exploited in vaccine development, where empty virus-like particles (VLPs) can be used to stimulate the immune system without being infectious (since they lack nucleic acid).

36
Q

What are VLPs?

A

Virus-like particles

37
Q

Which viruses are usually more stable, enveloped viruses or naked viruses?

A

Non-enveloped viruses

38
Q

When do enveloped virueses acquire their envelopes?

A

From the host cell during replication

39
Q

WHy are enveloped virueses usually less stable than non-enveloped viruses?

A

Because the lipid envelope is sensitive to detergents, solvents, and environmental conditions like stomach acid. This makes enveloped viruses easier to deactivate (e.g., using soap or disinfectants).

40
Q

Give some examples of enveloped RNA virueses with helical capsids

A

paramyxoviridae (measles and mumps virus)

rhabdoviridae (rabies virus)

orthomyxoviridae (influenza virus)

filoviridae (ebola virus)

41
Q

What are some examples of viruses that have a complex structure?

A

Poxviruses(smallpox) and bacteriophages

42
Q

What are some examples of viruses with helical capsids?

A

Measles, mumps, rabies, influenza, and Ebola

43
Q

What are some examples of viruses with icosahedral capsids?

A

These include many common viruses with symmetrical capsids, such as polio and adenoviruses.

44
Q

Vaccines and antivral treatmeants…

A

…The design of vaccines and antiviral treatments often leverages the unique properties of viral capsids, including their ability to self-assemble and the fact that their capsid proteins can be used to create non-infectious virus-like particles for immunization.

45
Q

Are viral proteins, including attachment proteins, synthesised by the host cell?

A

Yes

46
Q
A

Infection Biology and Microbiology (23 decks)

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