Basic Virology

Question 1

What is the difference between a virus and a virion?

Answer 1

Viruses are intracellular, replicate and are in a sense metabolically active
Virions are extracellular, do not replicate and metabolically inactive

Question 2

Why do we say that a virus is an obligate intracellular parasite?

Answer 2

Because it depends on the host cell to carry out vital functions like protein synthesis & energy generation.

Question 3

What is a capsid? Describe its structure

Answer 3

A capsid is a protective protein shell that encloses the viral genome and is made up of several oligomeric subunits made up of promoters.

Question 4

What is a viral envelope? When during the viral replication does the virus get its envelope?

Answer 4

A membrane that originates from the host-cell & consists of phospholipids & spikes which are viral-encoded glycoproteins are often crucial for the virion to recognize its host-cell, during budding

Question 5

Animal viruses can infect cells by direct penetration, membrane fusion or endocytosis. What are the differences between these?

Answer 5

Direct penetration
• Only naked viruses and the viral genome enters the cell, while the capsid remains on cell’s
surface
Membrane-fusion
• Only enveloped viruses and the capsid is removed when the virion has entered the host cell
Endocytosis
• The capsid is removed when the virion has entered the host cell

Question 6

How do bacteriophages replicate?

Answer 6

Attachment/Adsorption 
• The virion attaches its host-cell 
2. Penetration/Injection 
• Since it is a phage only the nucleic acid is  
injected into the host-cell 
3. Synthesis of nucleic acid and protein 
• Taken care of by the host-cell machinery 
4. Assembly and packaging 
• The viral genomes are packed and the  
capsid is assembled 
5. Release 
• Since it is a phage release from the  
host-cell occurs through cell-lysis 
6. Spread

Question 7

How do non-enveloped and enveloped viruses exit the cell?

Answer 7

Exocytosis 
• Only naked viruses  
• Escape the cell by using the  
endoplasmic reticulum (ER) 
o ER is an organelle that can attach  
o proteins to transport vesicles 
Budding 
• Only enveloped viruses  
• The virus keeps some of the host-cell’s  
membrane as envelope 
• During the viral replication the host cell is forced  
to produce membrane-associated proteins 
o After the budding these will be part  
of the viral envelope

Question 8

What are the differences between persistent and latent infections?

Answer 8

Persistent: stays alive, cell is not lysed, continues release

Latent: the virus is alive but inactive, and stays latent

Question 9

What effects can a virus have on its host-cell?

Answer 9

Cancer-cell
Lytic infection
Persistant infection
Latent infection

Question 10

What is a prion?

Answer 10

misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein.

Question 11

How do prions cause diseases?

Answer 11

Prion diseases occur when normal prion protein, found on the surface of many cells, becomes abnormal and clump in the brain, causing brain damage