Viral Genetics

Question 1

types of virus genomes

Answer 1

• DNA or RNA
• RNA pos or neg sense
• ss or ds
• segmented or non-segmented (RNA)
• linear or circular
• from 2-200 genes
• depend on cellular genes

Question 2

parvo

Answer 2

-2 genes

Question 3

retro

Answer 3

3 genes

Question 4

papillomaviruses

Answer 4

8 genes

Question 5

adeno

Answer 5

10 genes

Question 6

herpes

Answer 6

70 genes

Question 7

prokaryotic vs eukaryotic

Answer 7

• enhancer/promotor and operator and multiple open reading frames vs
• enhancer/promotor and cellular TFs, only one open reading frame
• viruses are eukaryotic

Question 8

virus genomes are efficient

Answer 8

1. no space wasted
2. reading frames can overlap
3. ribosomal frame shifting-gets caught in loop and moves over one and starts again
4. alternative splicing of RNA
5. cleaving of polyproteins by viral proteases

Question 9

polyproteins

Answer 9

-targets for drugs

Question 10

virus mutations

Answer 10

• mutant frequency is high because of high error rate of pol
• lack of proofreading and error correction
• lack of second strand in some viruses
• point, deletions, insertions, recombinations/rearrangements, insertion into host cell genome
• DNA more stable, RNA 1 mutation per generation

Question 11

virus mutations 2

Answer 11

• allow epidemiological studies
• can allow live vaccines to be made
• can produce new antigens which avoid immunity
• can lead to drug resistance
• integration of viral genome can cause disease

Question 12

conditional lethal mutations

Answer 12

• only allow a virus to grow under certain conditions
• temp sensitive mutants of flu
• host range mutants of polio, measles

Question 13

antigenic variants

Answer 13

• produce new strains spontaneously over time

- antigenic drift

Question 14

drug resistant mutants

Answer 14

• appear in response to some antiviral drugs
• acyclovir resistant herpes
• protease inhibitor resistant HIV
• amantidine resistance of flu

Question 15

complementation

Answer 15

• one gene works in one virus and the other in the other
• when together, can use genes to make new viruses
• progeny are same as parents and will need complement to grow in new cell

Question 16

phenotypic mixing of similar viruses

Answer 16

• exchange of capsid proteins
• make pseudotypes-genetic material of one virus with the capsid of another
• progeny still the same as parents

Question 17

recombination of homologous viruses

Answer 17

• the exchange of genes by crossing over at regions of homology
• progeny are different from parents
• hybrid virus reproduces

Question 18

reassortment

Answer 18

• rearrangement of parts or a segmented genome to form a new set of segments
• antigenic shift-makes new subtype-flu

Question 19

interference

Answer 19

• infection of one virus tends to prevent infection by another by:
• blocking receptors
• competition for resources
• production of interferon or other antiviral agents

Question 20

insertion mutations

Answer 20

-RT viruses insert into genome and cause mutation

Question 21

gene therapy

Answer 21

• deletion of essential gene and insert that gene into packaging cell
• grow virus in presence of packaging cell-virus isn’t virulent but can still grow
• clone the therapeutic gene into the virus
• test in cells, then animals, then humans

Question 22

monogenic disorders that may be treated

Answer 22

• hemophiia
• immune deficiencies
• retinal disorders
• liver enzyme deficiencies
• CF

Question 23

approaches to cancer

Answer 23

tumor suppressor, 
silence oncogenes, 
immune response genes, 
toxic or suicide genes, 
replicating cytotoxic viruses

Question 24

problem with replicating in human

Answer 24

-doesn’t spread beyond needle track because its made to grow with essential gene in cell culture doesn’t have essential gene

Question 25

gene therapy vectors

Answer 25

• retroviruses
• adenoviruses
• herpes
• adeno associated

Question 26

problems with gene therapy

Answer 26

• short duration of expression
• low efficiency of gene transfer
• inflammation in response to virus
• potential for chromosomal disturbances by virus-leukemia

Question 27

future research will yield

Answer 27

• mutated viruses that cause less inflammation
• viruses that target a specific tissue
• conditionally replicating viruses
• non-viral methods of transfer of genes