Question

why is reverse transcriptase essential for a retrovirus to successfully infect a host? it creates the mrna necessary for expression of viral genes. it creates a complementary cdna copy of host genes to block their translation. it creates a complementary cdna copy of the viral rna genome. it is responsible for integrating the viral genome into the host genome. it is responsible for the evasion of host defense mechanisms.

Explanation:

Retroviruses have an RNA - based genome. Reverse transcriptase is an enzyme that catalyzes the synthesis of a complementary DNA (cDNA) copy from the viral RNA genome. This cDNA can then integrate into the host genome. The other options are incorrect as reverse - transcriptase doesn't create mRNA for viral gene expression, doesn't create cDNA of host genes to block translation, isn't responsible for integrating the viral genome (integrase does that), and isn't responsible for evasion of host defenses.

Answer:

It creates a complementary cDNA copy of the viral RNA genome.