3. Structure and Composition

Lecture 2

Pleomorphism

A virus’ ability to alter its shape or size

400nm

Diameter of the largest viruses

17nm

Diameter of the smallest viruses

Capsid

Protein shell of a virus. Encases viral nucleic acid/genome. Composed of basic subunit proteins called capsomeres.

Capsomeres

Capsids are composed of _________ held together by non-covalent bonds.

Non-covalent

Capsids are composed of capsomeres held together by ___________ bonds.

nucleocapsid

Capsid + Viral Nucleic Acid/Genome =

Helical

Type of symmetry in which capsomeres and nucleic acid are wound together to form a spiral tube.

True

TRUE/FALSE: In all animal viruses, the helical nucleocapsid is enclosed within a lipoprotein envelope.

False

TRUE/FALSE: In all plant viruses, the helical nucleocapsid is enclosed within a lipoprotein envelope.

Cannot

Due to interactions between nucleic acid and capsid proteins, incomplete virions - empty helical particles - (CAN/CANNOT) form.

Icosahedral

Type of symmetry present in spherical viruses.

Cubic

Icosahedral symmetry is also called __________ symmetry.

Pentons, vertices

Icosahedral capsids are composed of ________ (pentagonal capsomeres) at the ___________, and hexons (hexagonal capsomeres) for the facets.

Hexons, facets

Icosahedral capsids are composed of pentons (pentagonal capsomeres) at the vertices, and ________ (hexagonal capsomeres) for the _______.

12, 20, 30

An icosahedron has (*#)* corners/vertices, (#) facets (triangular faces), and (#) edges.

12

There are always (#) pentons in a spherical virus.

True

(TRUE/FALSE): The number of hexons varies between spherical viruses.

False

(TRUE/FALSE): The number of pentons varies between spherical viruses.

pentagons

The T-number describes the relation between the number of __________________ and hexagons of the icosahedron.

hexagons

The T-number describes the relation between the number of pentagons and _____________ of the icosahedron.

triangulation

The “T” in “T-number” stands for

H

The formula for the triangulation (T) -number is

T = __^(2) + h \* k + k^(2)

h

The formula for the triangulation (T) -number is

T = h^(2) + __ \* k + k^(2)

k

The formula for the triangulation (T) -number is

T = h^(2) + h \* __ + k^(2)

k

The formula for the triangulation (T) -number is

T = h^(2) + h \* k + __^(2)

distances

In the formula for T-number, h and k are the _____________ between successive pentagons on the virus surface per axis.

simple

Parvovirus has a T value of 1. It is the most (SIMPLE/COMPLEX) icosahedron.

reoviridae

______________ has two capsids with different T-numbers.

family

\*REVIEW: The name “Reoviridae” describes a(n): (ORDER/FAMILY/SUBFAMILY/GENUS/SPECIES).

genus

\*REVIEW: The name “Parvovirus” describes a(n): (ORDER/FAMILY/SUBFAMILY/GENUS/SPECIES).

1

The parvovirus T-number is =

2

The outer capsid of Reoviridae has a T=13 icosahedral symmetry, while the inner has a T=___.

13

The outer capsid of Reoviridae has a T=____ icosahedral symmetry, while the inner has a T=2.

reoviridae

The outer capsid of ______________ has a T=13 icosahedral symmetry, while the inner has a T=2.

complex

Virions are composed of several parts with separate shapes and symmetries. This includes Pox viruses and bacteriophages. They have _____________ symmetry.

symmetry

The viral capsid is responsible for the structural ___________ of the virus particle.

nucleic acid

The viral capsid encases and protects the viral _________ ________ from enzymes, chemicals, and physical conditions.

attachment

The receptor attachment proteins on a viral capsid facilitate the ______________ of the virus to specific receptors on susceptible host cells.

receptors

The receptor attachment proteins on a viral capsid facilitate the attachment of the virus to specific _________ on susceptible host cells.

host cells

The receptor attachment proteins on a viral capsid facilitate the attachment of the virus to specific receptors on susceptible __________ ___________.

cell membranes

The viral capsid aids in interaction with the host ___________ ___________ to form the envelope.

uncoating

The viral capsid aids in _______________ of the genome in the host cell.

viral genome

The viral capsid aids in transport of the __________ __________ to the appropriate site.

packaging

The viral capsid facilitates specific recognition and ____________ of the nucleic acid genome.

antigenicity

The viral capsid can contribute to the ____________ of the virus, being targeted by and binding to antibodies.

lipid bilayer

Virus envelopes are usually a _____________ _____________ with embedded proteins.

proteins

Virus envelopes are usually a lipid bilayer with embedded ________________.

budding

The process by which a virus acquires an envelope.

matrix protein

There are two kinds of viral proteins typically found in an envelope: glycoprotein and __________ _____________.

glycoprotein

There are two kinds of viral proteins typically found in an envelope: ____________ and matrix protein

external glycoproteins

Virus envelope glycoproteins may be either ____________ ______________, anchored into the envelope, or channel proteins, hydrophobic proteins altering the permeability of the membrane.

channel proteins

Virus envelope glycoproteins may be either external glycoproteins (anchored into the envelope) or ___________ ____________ (hydrophobic proteins altering the permeability of the membrane).

antigens

External glycoproteins are typically major _____________ of the virus. They also contribute to hemagglutination, receptor binding, and membrane fusion.

internal environment

Channel proteins alter the permeability of the viral membrane, helping to modify the ___________ ____________ of the virus.

virus envelope matrix

__________ _________ _______ Proteins link the internal nucleocapsid to the lipid membrane envelope.

assembly

Virus envelope matrix proteins play a crucial role in virus ____________

nucleocapsid

The virus envelope matrix protein serves as the recognition site of ________________ at the plasma membrane.

encapsidation

The virus envelope matrix protein mediates the ___________________ of the RNA-nucleoprotein cores into the membrane envelope.

cytoplasmic membrane

The virus matrix protein coats the inside of the host cell’s ____________ ______________.

host

The viral envelope is acquired from a cellular membrane of a ___________ cell.

lipid envelope

The viral _________ ________ is maintained only in aqueous or moist environments.

less

Enveloped viruses are (MORE/LESS) hardy than non-enveloped viruses.

more

Enveloped viruses are (MORE/LESS) susceptible to sterilization than non-enveloped viruses.

inactivated

Enveloped viruses can be ___________ by the dissolution of the lipid membrane with lipid solvents such as ether, chloroform, and detergents.

cannot

Enveloped viruses (CAN/CANNOT) survive long periods in the environment.

capsule

Which of the following is NOT a component of a virus

• nucleic acid

• capsid

• envelope

• capsule

false

(TRUE/FALSE) The viral matrix protein is located between the viral nucleic acid and the capsid.

true

(TRUE/FALSE): The viral matrix protein is located along the inside of the host cytoplasmic membrane

DNA

Virus Nucleic Acids are typically either _____ or RNA.

RNA

Virus nucleic acids are typically either DNA or ______.

single

Viral nucleic acids - DNA/RNA - can be either double or ______ stranded.

double

Viral nucleic acids - DNA/RNA - can be either single or __________ stranded.

circular

Viral DNA can be linear or

linear

Viral DNA can be either circular or

sense

Viral RNA can be either (+) or (-)-_______________

infectious

A (+)-sense RNA virus is a/n (INFECTIOUS/NONINFECTIOUS) genome.

noninfectious

A (-)-sense RNA virus is a/n (INFECTIOUS/NONINFECTIOUS) genome.

translated

The positive-sense RNA virus is similar to mRNA and can be immediately ___________ by the cell.

converted

Negative-sense viral RNA is complementary to mRNA and must be ____________

drift

Viruses can undergo antigenic _______ or antigenic shift

shift

Viruses can undergo antigenic drift or antigenic _______

antigenic drift

Mechanism of viral genetic diversity resulting in mutations.

antigenic shift

Mechanism of viral genetic diversity resulting in recombination and reassortment

Missense

Point mutations can be

• silent

• nonsense

• __________

nonsense

Point mutations can be

• silent

• ___________

• missense

silent

Point mutations can be

• ____________

• nonsense

• missense

recombination

The exchange of nucleotide sequences between different, but usually closely related, viruses during replication.

reassortment

The most important mechanism for genetic diversity in viruses with segmented genomes

true

(TRUE/FALSE) Recombination can occur with a virus that has a non-segmented genome.

false

(TRUE/FALSE) Reassortment can occur with a virus that has a non-segmented genome.

larger

DNA viruses are generally (LARGER/SMALLER) than RNA viruses.

gene segment

Recombination occurs in a single ________ ________

proteins

Enzymes and inhibitors are examples of viral ____________.

enzymes

Retroviral integrase, reverse transcriptase, and nucleic acid polymerases are important viral _____________

retroviral integrase

Enzyme produced by a retrovirus that enables it to integrate its genetic material into the DNA of the infected cell.

reverse transcriptase

Enzyme used to generate complementary DNA from an RNA template.

nucleic acid polymerase

Enzyme required for viral genome replication.

viral nonstructural proteins

Proteins that play roles within the infected cell during virus replication or act in the regulation of virus replication or assembly. They are encoded by a viral genome and produced in the infected cell, but not packaged into the virus particles.

false

(TRUE/VALSE) Nonstructural proteins are seen in extracellular virions.