8. Lecture

Question 1

the cause and frequency of mutations in cells, DNA virus and in RNA virus

Answer 1

failures in the NA replication
•Cell: 10⁻⁹
•DNA virus: 10⁻⁵
•RNA virus: 10⁻³
→effective polymerase, but no proofreading activity

Question 2

mutations can be spontanious and induced, what can they be induced by?

Answer 2

• irradiation – UV, X-ray, atomic radiation

* mutagenic drugs – halogenated uridine

Question 3

silent mutation

Answer 3

no phenotypic change
•untranslated region
•redundant translation code
•not important amino acid

Question 4

lethal mutation

Answer 4

nonsense (stop) or missense (aa. change)

Question 5

•Conditionally lethal mutation:

Answer 5

• changes in the multiplication activity

* i.e.: thermo-sensitive mutants

Question 6

•Beneficial mutation:

Answer 6

• rare

* accidental!

Question 7

evolution of virus compaired to the host’s evolution

Answer 7

the virus evolution is a million times quicker than the host’s evolution - no proof reading

Question 8

how to stabilize virus strains

Answer 8

• protect from mutations – low passages
• seed virus, virus banks
• freeze drying, 4°C, (-20°C), -80°C, -196°C

Question 9

antigenic change

Answer 9

antigen structure change, cannot neutralize the virus

Question 10

Antigenic change causing viral phenotype change due to

8

Answer 10

• escape mutants
• antigenic drift
• Changes in host species specificity:
• Changes in organ specificity
• different tissue tropism
• virulence variants
• Cytopathic effect, plaque formation
• Temperature optimum

Question 11

antigenic shift

Answer 11

antigenic structure changes

Question 12

escape mutants

Answer 12

defend itself from host immune responses by making mutations in its genotype and phenotype

Question 13

tissue tropism

Answer 13

(cell cultures, the tissue that support viral growth

Question 14

Virulence variants

Answer 14

( ability to infect or damage a host.)