Immuno - Anti-viral agents

Question 1

Definition of viruses

Answer 1

Obligate infectious intracellular parasites

Question 2

What is a tegument and give an example of a virus with such structure?

Answer 2

Proteins in coat encapsulated with an envelope which surround the capsid of the virus
Herpes virus

Question 3

Why do RNA and retroviruses have a higher mutation rate?

Answer 3

Lack of proof-reading capacity

They use own polymerase to replicate (reverse transcriptase)

Question 4

Why are RNA viruses smaller than DNA viruses?

Answer 4

Inherent instability of RNA limits size

Question 5

How do smaller viruses utilize their genetic material more efficiently?

Answer 5

Overlapping reading frames

Question 6

What do DNA viruses have that RNA viruses can’t have due to size?

Answer 6

Accessory genes

Question 7

What are accessory genes?

Answer 7

Genes that modify the immune response of the host cell and are often lost in passage in cultures because are not utilized

Question 8

What is a rapid form of evolution for viruses and what is required for them to do that?

Answer 8

Recombination when two different viruses infect the same cell

Need to have segmented genome like the human one
E.g. - influenza has 8 segments and rotavirus - 2

Question 9

Describe the replication of HIV

Answer 9

HIV spike protein Gp120 binds to cell surface CD4 receptor => T helper cell specific

Virus further interacts with second co-receptor CCR5 or CXCR4 depending on whether it’s a macrophage or a T-cell

integrase splices the reverse transcribed viral DNA into host

Question 10

Genome of influenza virus

Answer 10

8 segment or negative sense RNA

Question 11

How does influenza replicate?

Answer 11

RNA dependent RNA polymerase in nucleus replicates them into mRNAs and new genomes

exponential viral culture

Question 12

What is the cytopathic effect?

Answer 12

Virus lysing the cell due to shut down of host protein synthesis or due to accumulation of viral proteins

Question 13

How can you detect a viral infection using monolayers?

Answer 13

Plaques are formed and you can use a plaque assay to determine how many virions are in a particular preparation

Question 14

What is a syncitium

Answer 14

Viruses with surface proteins that can fuse at neutral pH often fuse cells together

Question 15

What does electron microscopy or haemagglutination assay detect?

Answer 15

Presence of viral particles

Question 16

When can you look at the serum (serology) for the presence of virus?

Answer 16

2-3 weeks later when the person has seroconverted (made an immune response to the virus)

Question 17

What is serology useful for?

Answer 17

Counting how many people have been infected during an outbreak and how many people have some level of immunity

Question 18

What does aetiology mean?

Answer 18

Cause or origin of the disease

Question 19

What is a therapeutic index?

Answer 19

How much drug you have to use to control virus and how much drug makes a person feel ill from side effects because it affects the host function

Question 20

What is key to improving the therapeutic index?

Answer 20

Selectivity and specificity => find things that the virus does that the host cell doesn’t

Question 21

Why do we strive to an acceptable therapeutic index?

Answer 21

Difficult to distinguish between virus replicative mechanisms and host

Question 22

What does understanding the structure of viral components and enzymes lead to?

Answer 22

Rational drug design

Question 23

What is important to consider in nucleoside analogues?

Answer 23

They need a certain level of specificity to viral polymerase so they don’t interfere with human cell replication

Question 24

When are DAAs used?

Answer 24

Usually possible to act on one virus because they target specific viral factors => need for accurate diagnosis

Question 25

Explain the function of acyclovir

Answer 25

• nucleoside analogue - chain terminator
• looks like guanosine but the bottom half of ring is gone so misses the 3’ hydroxyl group
• the lack of 3’ OH- means no phoshphodiester bond can form

Question 26

Difference between nucleotide and nucleoside

Answer 26

nucleotide - nucleobase, 5C sugar and one or more phosphate groups

nucleoside - only N-base and 5C sugar