2. Virus Structure

Define virus.

A small infectious agent containing a DNA or RNA genome enclosed within a protein coat, which can replicate only within a living host cell

Which of the following best describes a virus?

Obligate intracellular parasite

What makes up a virus?

Viral nucleic acid, capsid, envelope, and viral enzymes

Which of the following classifies the genome of MOST veterinary DNA viruses?

dsDNA

What is the viral genome enclosed within?

Protein capsid

What are capsids constructed from?

Repeating viral protein subunits

What is something that some viruses have surrounding the nucleocapsid that other viruses do not?

Lipid envelope

What projects from the envelope and form surface spikes?

Glycoproteins

What are the types of capsid symmetry?

Icosahedral, helical, and complex

Which of the following best describes a capsid symmetry that is approximately spherical?

Icosahedral

Which of the following describes a capsid symmetry that is rod-like?

Helical

Which of the following describes a capsid symmetry that does not conform?

Complex

How does an icosahedral capsid build itself?

Using multiple copies of relatively few proteins

All animal viruses with helical symmetry are enveloped.

True

What are some traits that a complex capsid can have?

Large and complex virions, multiple membranes, central core containing genome, and additional lateral structures

Virion shape and capsid/nucleocapsid symmetry are the same thing.

False, not necessarily

What are the functions of the capsid proteins?

Form the structural components, package and protect the genome, help determine virion structure and stability, (non-enveloped) participate directly in attachment and entry to host cell, contain antigenic determinants recognized by the immune system

What do the capsid proteins of non-enveloped viruses do?

Protect the genome outside of host cell, bind to host-cell receptors, deliver the genome into the host cell, frequently contain the major antigenic determinants recognized by neutralizing antibodies

What is a viral envelope?

A lipid bilayer acquired from the host-cell membrane that contains viral encoded proteins and may contain some host-cell components

The viral envelope contains virus-encoded glycoproteins that mediate the attachment to host-cell receptors and host cell entry.

True

A virus that is enveloped is more environmentally stable than a non-enveloped one.

False

What are enveloped viruses generally sensitive to?

Detergents and lipid solvents, disinfectants, drying, heat, and acidic conditions

Transmission of enveloped viruses requires relatively close or rapid contact between hosts.

True

Enveloped viruses bud from the cell membrane while non-enveloped are released by cell lysis.

True

All icosahedral capsids that infect vertebrates are enveloped but only some helical viruses that infect vertebrates are enveloped.

False, all helical but only some icosahedral that infect vertebrates are enveloped

What is another term for a non-enveloped virus?

Naked capsid

What are the components of non-enveloped viruses?

Proteins only

What are the components of enveloped viruses?

Proteins, lipids, and glycoproteins

Non-enveloped viruses are environmentally stable to temperature, pH, proteases, detergents, and drying allowing them to survive for long periods at the environment.

True

Which type of virus is more likely to be the cause of acute infection? Why?

Non-enveloped; they are released by cell lysis

Which type of virus is more likely to be the cause of persistent infections?

Enveloped; they are released by budding

When they are mentioned together, what are the genome and the capsid called?

Nucleocapsid

What are the morphological units visible on the surface of icosahedral capsids?

Capsomers

What are the virus-encoded glycoproteins projecting from the envelope as spikes sometimes called?

Peplomers

What is a virion?

A complete extracellular virus particle