Viral Structure?

Question 1

What is a virus?

Answer 1

a virus is a simple, acellular organism. It is an obligate intracellular parasite and an infectious agent

Question 2

what are the two forms of living behavior of a virus?

Answer 2

• extracellular, referred to as virions. They are unable to reproduce. They are metabolically inactive when not present in a host cell.
• intracellular, referred to as viruses

Question 3

What is the submicroscopic size of a virus?

Answer 3

20-300 nanometers

Question 4

what are the components of the virion?

Answer 4

• a protein coat or capsid
• nucleic acid
• envelope (only present in some viruses)

Question 5

what are the types of nucleic acid?

Answer 5

• ssDNA: single stranded DNA
• dsDNA: double stranded DNA
• ssRNA: single stranded RNA. There are two types: positive (+) and negative (-)
• dsRNA: double stranded RNA

Question 6

what are the types of viruses?

Answer 6

• naked/ non-enveloped: nucleic acid and capsid

- enveloped: nucleic acid, capsid and cellular membrane

Question 7

what is the structure and function of the capsid?

Answer 7

the capsid is viral nucleic acid packed in a protein coat.

It has multiple functions:

• protects viral nucleic acid
• interacts with the viral nucleic acid for packaging/ assembling the virus
• interacts with vector for specific transmission
• interacts with host receptors to facilitate the host cell entry
• assists in viral and/or host gene regulation

Question 8

what are the principles of basic virus structure?

Answer 8

capsid = protein coat
structural unit = protein subunit
nucleocapsid = nucleic acid + protein
virion = virus particle

Question 9

what are the different types of capsid symmetry?

Answer 9

• icosahedral: 20 equilateral triangles as faces
• helical: rod-shaped
• complex: combination of icosahedral and helical

Question 10

what is the envelope, its function and the types?

Answer 10

the envelope helps with the attachment to host cells

• lipoprotein: derived from the host cell’s membrane
• glycoproteins: spike-like formations with viral origin
• matrix protein: regulate gene expression

Question 11

what are the differences between enveloped viruses and non-enveloped viruses?

Answer 11

non-enveloped viruses have increased stability and are transferred by fecal-oral path

enveloped viruses have decreased stability and are transferred by direct person to person

Question 12

what are the atypical virus-like agents?

Answer 12

• defective viruses: cannot replicate without a helper virus
• pseudovirions: contain DNA from the host cells/other viruses. Can infect but cannot replicate
• viriods: contain a single circular RNA molecule with double stranded regions. Does not contain any protein or envelope structure but can infect and replicate inside a host (plants)
• prions: no nucleic acid containing infectious proteins

Question 13

what are the routes of entry for viruses?

Answer 13

inhalation
ingestion
inoculation
blood/organ transplant
sexual 
congenital