DNA VIRUSES Clinical features and replicatio

Question 1

Why are the life cycles of DNA viruses interesting?

Answer 1

• cause life-threatening human disease (oncogenic) e.g HBV and liver cancer and papilloma and cervical cancer)
• therapeutic agents (anti-cancer) e.g adenovirus to treat head and neck cancer. Herpes simplex to treat solid tumours

Question 2

When do viruses cause cancer?

Answer 2

-when their life cycle goes wrong (not a usual part of life cycle as it is a dead end for the virus)

Question 3

What is the role of immunosurvellience?

Answer 3

important in recognition and destruction of transformed cells before they grow into tumours and important in controlling DNA virus infections

Question 4

How long does it usually take after a virus for a cancer to develop?

Answer 4

10 years

Question 5

Where do DNA viruses replicate?

Answer 5

in the nucleus (except pox)

Question 6

What are the requirements for DNA viral replication?

Answer 6

virus encoded immediate early and early protein can induce:
-polymerase plus other factors (thymidine kinase)
-access to nucleotides
OR induce the host cell to express the polymerase

Question 7

Where do the replication proteins come from?

Answer 7

For small DNA viruses:
-do not encode a whole genome replication system
-encode proteins that orchestrate the host
Large DNA viruses
-encode proteins in their genome

Question 8

What are the roles of the viral early proteins?

Answer 8

Affect host functions that regulate growth:

• stimulate cell proliferation
• block cell death
• orchestrate host cell so it supports virus genome replication

Question 9

What is the role of early proteins E6 and E7?

Answer 9

• deregulate cell growth control

- deregulate host tumour suppressor (Rb and p53) pathways

Question 10

What is the role of E7?

Answer 10

host cell cycle regulators (suppresses Rb and pushed cells through S phase)

Question 11

What us the role of E6?

Answer 11

cell regulators of apoptosis (prevent apoptosis even when cells have been programmed for cell death)

Question 12

How could HPV case cancer?

Answer 12

• E7 and E6 constantly targeting tumour suppressor genes so there is no way of monitoring genomic stability and preventing replication of cells with damaged DNA
• higher risk of acquiring mutations

Question 13

What makes up the HPV vaccine?

Answer 13

HPV16 L1 protein expressed in insect cells

-assembled into empty particles to form virus like particles

Question 14

Why does the HPV vaccine not cure women with cervical cancer?

Answer 14

-prophylactic and not therapeutic vaccines

Question 15

What does the HPV vaccine do?

Answer 15

blocks infection with HPV16 and HPV18 neutralising antibiotics