Final answer:
A retrovirus infectious particle contains RNA as its genomic component, which is reverse transcribed into DNA by the viral enzyme reverse transcriptase after infecting a host cell.
Step-by-step explanation:
A retrovirus infectious particle contains RNA as its genomic component. This RNA is used as a template by the virally encoded enzyme reverse transcriptase to synthesize DNA once it infects a host cell.
The process begins when a retrovirus, like HIV, attaches to a host cell. Upon entry, the viral RNA is reverse transcribed into complementary DNA (cDNA). This cDNA can then integrate into the host genome as a provirus, leading to potential chronic infection. During the replication cycle, the provirus DNA is transcribed into mRNA, which gets translated into viral proteins, resulting in the assembly of new viral particles that can go on to infect other cells.
Unlike other mobile genetic elements like retrotransposons, retroviruses have an ENV gene-encoded protein envelope that surrounds the viral RNA. Infection leads to the shedding of this envelope, allowing the reverse transcription process to occur, ultimately producing viral particles capable of leaving the host cell to infect new cells.