1. Which is a stage in the growth cycle of a lysogenic virus? A. Synthesis of vi
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Question
1. Which is a stage in the growth cycle of a lysogenic virus?
A. Synthesis of viral structural proteins.
B. Integration of viral genome into host cell DNA.
C. Transport of viral DNA or RNA across the host cell plasma membrane.
D. All are correct.
2. Retrovirus genomes encode the enzyme reverse transcriptase (RT). Why is it necessary that functional RT enzyme be packaged into the assembled virion?
A. Functional RT cannot be produced due to mutations in the viral gene that encodes RT.
B. The host cell RT gene is not transcribed during viral infection.
C. RT is not a normal constituent of the host cell cytoplasm.
D. All are correct.
3. Crossing of a diploid mutant that is homozygous for a recessive mutation (aa) with a heterozygous wild type (Aa) will result in what proportion of F1 progeny that are heterozygous?
A. 50%
B. 25%
C. 100%
D. 75%.
4. In the preceding question, what proportion of the F1 progeny will have the mutant phenotype for gene A?
A. 50%
B. 25%
C. 75%
D. 100%
5. Which of the following enzymes will produce a 3' protruding single strand overhang after cleavage of double stranded DNA? (The cut site is indicated by the * in the recognition sequence.):
A. EcoRI G*AATTC
B. EcoRV GAT*ATC
C. SacI GAGCT*C
D. PstI CTGCA*G
Explanation / Answer
1 the first step is Synthesis of viral structural proteins.Integration of viral genome into host cell DNA and Transport of viral DNA or RNA across the host cell plasma membrane.
2) The first strand of complementary DNA (cDNA) is extended and the majority of viral RNA is degraded by RNAse H. Once the strand is completed, second strand synthesis is initiated from the viral RNA. There is then another ‘jump’ where the PBS from the second strand hybridizes with the complementary PBS on the first strand Both strands are extended further and can be incorporated into the hosts genome by the enzyme integrase
3) 50%
4) 25%
5) EcoRI G*AATTC
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