Final answer:
Viruses can enter host cells through injection or endocytosis/fusion. The viral capsid is degraded, releasing the nucleic acid for replication. Retroviruses use reverse transcriptase to convert RNA into DNA and integrate it into the host genome.
Step-by-step explanation:
Viruses have different ways of entering host cells and overcoming host defenses. Viruses can enter host cells through injection or endocytosis/fusion. The viral capsid is degraded, releasing the nucleic acid for replication. Retroviruses use reverse transcriptase to convert RNA into DNA and integrate it into the host genome.
Bacteriophages inject their nucleic acid into the host cell, leaving the capsid outside. Plant and animal viruses can enter cells through endocytosis or fusion with the cell membrane. Once inside, the viral capsid is degraded, releasing the nucleic acid for replication and transcription.
Some viruses, like retroviruses, have special enzymes, such as reverse transcriptase, that allow them to convert RNA into DNA and integrate it into the host cell genome.