Viruses

Question 1

How are viruses classified?

Answer 1

• specificity of infection
• genome
• structures

Question 2

Outline the innate immune response

Answer 2

• non-specific
• Produces soluble factors
• Phagocytic cells
• Immediate and early

Question 3

Outline adaptive immunity

Answer 3

• Takes 1-2 weeks
• highly antigen specific
• memory based
• Activation of B+T cells

Question 4

Outline the features of influenza type A virus

Answer 4

• SSRNA virus
• Envelope virus carrying glycoproteins
• Infects birds and mammals

Question 5

What are the 2 main vaccine targets on influenza type A virus?

Answer 5

• Hemagglutinin
• Neuraminidase

Question 6

What is antigenic drift?

Answer 6

Minor antigenic changes in glycoproteins on the surface of a virus

Question 7

What is antigenic shift?

Answer 7

The abrupt and major changes in glycoprotein

Question 8

What causes antigenic drift in influenza A?

Answer 8

• Has an RNA genome
• Replication of RNA has high mutation rate
• No proofreading

Question 9

Why does the flu vaccine not work every year?

Answer 9

• The annual flu vaccine is based on predicting the HA and NA antigens
• Mutations in HA and NA surface proteins which occur may be different to the ones predicted

Question 10

How does Antigenic shift occur?

Answer 10

• Genetic reassortment of HA and NA genes occurs in an intermediate host
• This leads to recomination or reassortment of viral strains
• This often occurs when a flu strain jumps species

Question 11

Outline the features of HIV-1 retrovirus

Answer 11

• RNA envelope virus
• Replication requires reverse transcriptase
• Infects immune cells

Question 12

What type of cells does HIV infect?

Answer 12

CD4+ helper T cells

Question 13

What are the features of Reverse transcriptase?

Answer 13

• Replicates the viral RNA genome into DNA
• Not normally expressed in human cells
• Lacks 3’-5’ proofreading so high error rate

Question 14

What are impacts of reverse transcriptase not having prrofreading?

Answer 14

• Mutations accumulate
• Mutations which affect reverse transcriptase itself occur
• Affects the therapeutic outcome

Question 15

How can viral replication be inhibited with nucleoside analogues?

Answer 15

• DNA synthesis joins 3’OH of growing DNA chain to 5’ phosphate group of the incoming dNTP
• If the 3’OH is blocked (by analogues) then DNA chain growth will terminate

Question 16

Give the name of a treatment for HIV?

Answer 16

AZT

Question 17

How does AZT work to treat HIV?

Answer 17

• Acts as a nucleoside analogue
• Lacks 3’ OH so causes chain termination

Question 18

How can AZT target HIV infected cells specifically?

Answer 18

Reverse transcriptase is 100x better at incorporating AZT into DNA than DNA polymerase

Question 19

What sort of virus is herpes simplex?

Answer 19

Double stranded DNA virus

Question 20

Give the name of a treatment for herpes simplex virus

Answer 20

Acyclovir

Question 21

How does acyclovir have specificity?

Answer 21

• For the drug to be activated it must have a phosphate group attached within the cell by thymidine kinase
• The viral thymidine kinase is much better than host TK at phosphorylating

Question 22

Which enzyme is used to phosphorylating acyclovir?

Answer 22

Thymidine kinase

Question 23

How does acyclovir treat herpes?

Answer 23

Causes replication chain termination due to a lack of 3’OH

Question 24

What is an oncogenic virus?

Answer 24

A gene suspected of causing cancer in organisms

Question 25

What is a long terminal repeat?

Answer 25

A sequence present at the ends of viral genome which provides promoter activity and drives gene expression

Question 26

What are the 3 ways viruses can cause cancer?

Answer 26

1. Virus inserts oncogene into host genome 2. Insertion of virus brings a strong promoter to activate a cellular proto-oncogene 3. Insertion of a virus (which lacks an oncogene) distrupts and inactivates a tumour suppressor gene

Question 27

What is a proto-oncogene?

Answer 27

A normal cellular gene capable of causing cancer when dysregulated