Viruses

Question 1

Definition?

Answer 1

Viruses are not living organisms because they are unable to carry out all life-processes

• Is not a cell or made of cells
• Cannot reproduce on their own
• Do not grow or undergo cell-division
• Has no metabolism, do not transform energy
• Lack machinery for protein synthesis

Question 2

What are they?

Answer 2

Obligate intracellular parasites
Viruses are one of the smallest infectious agents that we know of
• 20-300 nm large
The genome only encodes components the virus
cannot “steal” from its host!

Question 3

The structure of virions?

Answer 3

DNA (DNA-viruses) or RNA (RNA-viruses)
• A primary way of classifying viruses

Genome
• Can be linear, circular or consist of several segments

Capsid
• A protective protein shell

Glycoprotein
• Helps the virion to attach the host-cell

Question 4

The viral envelope?

Answer 4

• A membrane that originates from the host-cell

* Consists of phospholipids

Question 5

Spikes?

Answer 5

• Viral-encoded glycoproteins

* Are often crucial for the virion to recognize its host-cell

Question 6

APSAR?

Answer 6

Attachment 
Penetration
Synthesis
Assemble
Release

Question 7

To infect animal cells?

Answer 7

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 8

To exit animal cells?

Answer 8

Naked viruses
• via exocytosis

Enveloped viruses
• via budding
• The virus keeps some of the
host-cell’s membrane as envelope

Question 9

Persisterant infection?

Answer 9

• The virus lives
• Continuous release
• The cell is not lysed

Question 10

Latent infection?

Answer 10

• Virus inactive
• Stays latent
• Reactivation?

Question 11

Effects of viruses on host cells?

Answer 11

Cancer-cell
Lytic infection
Persistant infection
Latent infection