Structure and Composition of Viruses

Question 1

What is the smallest virus at 17nm?

Answer 1

Porcine circovirus type 1

Question 2

What is the largest virus of animals at 200nm x 300nm?

Answer 2

Poxvirus

Question 3

Viruses can have what shapes?

Answer 3

Filament (Ebola)
Bullet (Rabies)
Tadpole (bacteriophages)
Rod (Tobacco Mosaic)
Brick (Poxvirus)
Spherical (Rotavirus)

Question 4

What is it called when a virus can change its shape or size?

Answer 4

Pleomorphism

Question 5

What are the 4 common ways to determine the morphology of a virus?

Answer 5

Electron microscopy
Cryo-electron microscopy
X-ray crystallography
NMR

Question 6

The protein shell that encases the viral nucleic acid:

Answer 6

Capsid

Question 7

Building blocks of the capsid:

Answer 7

Capsomeres held together by non-covalent bonds

Question 8

Which type of viruses have a double-layered capsid?

Answer 8

Reoviruses

Question 9

What makes up the nucleocapsid?

Answer 9

Capsid + viral nucleic acid

Question 10

Types of viral morphology/shapes:

Answer 10

Helical: in animal viruses are enveloped, but can be naked in plant viruses ie tobacco mosaic.

Cubic/Icosahedral: seen in spherical viruses, can be naked or enveloped.

Complex: composed of several parts with separate shapes/symmetries. (Poxvirus and bacteriophages)

Question 11

What is the triangulation number for icosahedral viruses?

Answer 11

T = h^2 + (h x k) +k^2

Question 12

What does the triangulation number determine?

Answer 12

Relation between the number of pentagons and hexagons of the icosahedron.

Question 13

In an icosahedral virus, which capsomeres makes up the vertices and which make up the facets?

Answer 13

Pentons make up vertices

Hexons make up facets

Question 14

What is the simplest icosahedron, with a triangulation number of 1 and a capsid containing 60 copies of CP protein?

Answer 14

Parvovirus

Question 15

What are the triangulation numbers for the inner and outer capsids of Reoviridae?

Answer 15

Inner: T=2

Outer T=13

Question 16

What are the functions of the capsid?

Answer 16

Structural symmetry

Protection of viral nucleic acid from enzymes, chemicals, and pH/Temp

Attachment to host cells

Interaction with host cell membrane to form envelope

Uncoating of the viral genome in host cell

Transporting viral genome to correct site

Packaging of nucleic acid genome

Determines antigenicity of virus (contains antigenic sites)

Question 17

The ______ is a lipid bilayer with embedded proteins.

Answer 17

Envelope

Question 18

How is the envelope formed?

Answer 18

Budding of the nucleocapsid through a cellular membrane (cytoplasmic, golgi, or nuclear).

Question 19

What are the 2 types of proteins found in the viral envelope?

Answer 19

Glycoproteins (spikes) and matrix proteins

Question 20

What are the 2 types of glycoproteins in the viral envelope?

Answer 20

External: major antigens

Channel: hydrophobic, form a channel through the envelope.

Question 21

Major functions of external glycoproteins in the viral envelope.

Answer 21

Antigenicity, hemagglutination, receptor binding, membrane fusion

Question 22

Major functions of channel glycoproteins in the viral envelope.

Answer 22

Alters permeability of the membrane (ion channels). Modify internal environment of the virus.

Question 23

Functions of matrix proteins in the viral envelope.

Answer 23

Link nucleocapsid to envelope
Virus assembly
Stabilize envelope

*recognition site of the nucleocapsid at the plasma membrane and mediates encapsidation of nucleocapsid into the membrane envelope

Question 24

Limiting environments for the viral envelope:

Answer 24

Dry, hot, change in pH

*maintained only in aqueous or moist env

Question 25

Products that can inactivate enveloped viruses by dissolving the lipid membrane:

Answer 25

Ether
Chloroform
Sodium deoxycholate, detergents

Question 26

Which are easier to sterilize and survive shorter periods in the environment, naked or enveloped viruses?

Answer 26

enveloped

Question 27

T/F: the viral nucleic acid can be double- or single-stranded DNA, or double- or single-stranded RNA?

Answer 27

TRUE

Question 28

Mechanisms of genetic diversity in viruses:

Answer 28

Antigenic drift

Antigenic shift

Question 29

_______ _____ leads to point mutations (silent, missense, nonsense) that normally cause minor changes, but may induce resistance to antiviral drugs and vaccines.

Answer 29

Antigenic drift

Question 30

_______ _____ is the recombination, or exchange of nucleotide sequences between related viruses during replication.

Answer 30

Antigenic shift

Question 31

What is the most important mechanism for high genetic diversity in viruses with segmented genomes?

Answer 31

Reassortment

Question 32

What type of antigenic shift occurs in viruses with a single gene segment?

Answer 32

Recombination

Question 33

Retroviral integrase is a viral enzyme responsible for:

Answer 33

enabling viral genetic material to be integrated into the DNA of the infected cell. (HIV)

Question 34

Reverse transcriptase is a viral enzyme responsible for:

Answer 34

generating complementary DNA from an RNA template.

Question 35

Nucleic acid polymerases are responsible for:

Answer 35

viral genome replication

Question 36

What type of viral proteins play a role WITHIN the infected cell during virus replication, or regulate virus replication/assembly.

Answer 36

Nonstructural proteins

Question 37

An incomplete virion is missing:

Answer 37

Nucleic acid. (empty capsid)

Question 38

A defective virion cannot replicate because it lacks:

Answer 38

A full complement/copy of viral genes.

*can result from mutations or errors in production or assembly of virions

Question 39

A ________ contains nonviral genome within the capsid.

Answer 39

Pseudovirion

Question 40

Virus pseudotypes occur when:

Answer 40

related viruses infect the same cell and the genome of one virus is enclosed in the capsid of another virus.