Viruses and virology

Question 1

Define each of the following:
Nucleocapsid.
Capsid.
Capsomere

Answer 1

Nucleocapsid: Complete complex of nucleic acid and protein packaged in the virion
Capsid: The protein shell surrounding the genome of a virus
Capsomere: Subunit of the capsid, smallest morphological unit

Question 2

List two different symmetries associated with viral nucleocapsids and detail the
shapes that these symmetries result in.

Answer 2

Helical: Rod shaped viruses, length of virus is determined by length of nucleic acid (tobacco mosaic virus)
Icosahedral: spherical shaped, triangular faces give round structure (HPV)

Question 3

List the 5 phases of viral replication

Answer 3

1) Attachment of the virus to a susceptible host cell
2)Entry of the virion or its nucleic acid
3) Synthesis of nucleic acid and protein by cell metabolism
4) Assembly of capsid and packaging of viral genomes
5) Release of virions from host cell

Question 4

What is a permissive cell?
What is restriction modification system?

Answer 4

A cell that allows the complete replication cycle of a virus to occur

A DNA destruction system only effective against double stranded DNA viruses

Question 5

List 3 methods that prokaryotes protect themselves from viral infections?

Answer 5

CRISPR
Restriction modification system
Restriction enzymes

Question 6

Describe three differences between early and late proteins synthesized after a
viral infection of bacterial cells.

Answer 6

Early proteins are synthesised soon after infection
They typically act catalytically
They are synthesised in small amounts
Late proteins are synthesised later
They are typically structural components
They’re synthesised in larger amounts

Question 7

What are virulent and Temperate modes???

Answer 7

Virulent mode is where viruses kill host cells after replication
Temperate mode is where viruses replicate in tandem without killing the hosts

Question 8

Define..
Lysogeny:
Lysogen:
Prophage:

Answer 8

Lysogeny: state where viruses are not expressed
Lysogen: A bacterium containing prophage
Prophage: virus genome

Question 9

What are the consequences of virus infections in animal cells?

Answer 9

Persistent infections: Infected cell stays alive and keeps producing the virus
Latent infection: Delay between infection by the virus and lytic events
Transformation: Conversion of normal cell into tumour cell
Cell fusion: two or more cells become one

Question 10

Define Defective viruses and satellite viruses

Answer 10

Defective viruses are viruses that are parasitic on other viruses and need helper virus to function

Satellite viruses are defective viruses with no intact version they rely on unrelated viruses for help