Viral structures

Question 1

Size

Answer 1

20 – 300 nm

Question 2

What encases and stabilizes the nucleic acid?

Answer 2

Capsid, a protein shell, which may be surrounded by a lipid-containing membrane

• Memory aid:*
• Capsid encapsulates the nucleic acid

Question 3

Capsid composition

Answer 3

Capsomeres

Question 4

Entire infectious unit

Answer 4

Virion

Question 5

Nucleic acid (DNA or RNA) + capsid

Answer 5

Nucleocapsid

Question 6

Interstitial space between the nucleocapsid and envelope

Answer 6

Matrix or tegument

Question 7

Only virus with fiber (penton fiber)

Answer 7

Adenovirus

Question 8

1. What are the two components of the naked icosahedral virus structure?
2. What are the four components of an enveloped icosahedral virus structure?
3. What are the four components of the enveloped helical virus structure?

Answer 8

1. Nucleocapsid and nucleic acid
2. Surface protein, lipid bilayer, capsid, and nucleic acid
3. Surface protein; matrix or core protein; lipid bilayer; and nucleic acid and nucleocapsid protein

Question 9

Structurally, what are the three main classes of viruses?

Answer 9

Naked icosahedral, enveloped icosahedreal, enveloped helical

Question 10

General rule on shape and presence of envelop

Answer 10

• All helical viruses are enveloped
• Icosahedral viruses can be enveloped or naked

Question 11

Examples of nonenveloped viruses

Answer 11

• DNA viruses
  
  • Papillomavirus
  • Adenovirus
  • Polyomavirus
  • Parvovirus
• RNA viruses
  
  • Calicivirus
  • Picornavirus
  • Reovirus
  • Hepevirus

Memory aid:

• Give PAPP smears and CPR to a naked hippie (hepevirus)
• DNA = PAPP; RNA = CPR and hepevirus
• Alternate: Naked Pop star Adele and Polyoma partied while Calici picked reo as hepe!

Question 12

Source of envelope is the ____ except ____, which acquire envelopes from ____

Answer 12

• Plasma membrane when they exit from cell (budding)
• Herpesviruses
• Nuclear membrane

Question 13

Proteins and actions

Answer 13

• Surface protein
  
  • Attachment to host cell receptor
• Matrix protein
  
  • Interaction between nucleocapsid and envelope
• Antigenic (serotypic) variants
  
  • Evasion of host defense

Question 14

Purified nucleic acids from which viruses are considered infectious?

Answer 14

Most double-stranded DNA viruses and positive-strand single-stranded RNA viruses

Question 15

Why are negative-strand single-stranded RNA and double-stranded RNA viruses not infectious?

Answer 15

They require enzymes found in the complete virion to become infectious

Question 16

The purified nucleic acids of what two double-stranded DNA viruses are not considered infectious?

Answer 16

Poxviruses and hepatitis B virus; both require enzymes not found in human cells for replication