2-1 Virus Structure and Classification

Question 1

What is a:

a) virus?
b) virion?

Answer 1

a) A virus is an obligate intracellular parasite that encodes a capsid (protein shell that encapsulates the nucleic acid genome)

B) A virion is the particle encoded by a virus genome

Question 2

Describe a virus genome.

Answer 2

Virus genomes are modular and have 3 basic gene modules:

1. Capsid proteins: “structural” because they form the virion
2. The “replicon,” which encodes the nucleic acid polymerase and accessory proteins to copy the genome
3. Multifunctional proteins that interact with the host. Usually “non-structural” because they are left behind in the infected cell and not packaged into the virion

Question 3

What is capsid structure?

Answer 3

Helical or icosahedral symmetry

Independent of genome type

Question 4

What is external virion structure?

Answer 4

Enveloped virions obtain a lipid bilayer from the host cell; naked virions lack an envelope

Question 5

How are viruses classified?

Answer 5

Host cell (Kingdom)

• Eukaryotic or prokaryotic
• Plant, insect, animal

Genome type

• RNA or DNA
• Single- or double-stranded

Virion structure

• Enveloped or naked
• Helical, icosahedral, or complex

Question 6

What are the components of a virus?

Answer 6

• Genome segment(s)
• Nucleocapsid
• Capsid or core
• Tegument
• Matrix
• Envelope
• Glycoprotein
• Spike or fiber

Question 7

What is the 3-part general strategy viruses use to survive?

Answer 7

1. Protect: capsid
2. Carry information: to infect a cell, replicate genome, survive intracellularly, and assembly virions
3. Transmit to a new host