Final answer:
Enveloped viruses can enter host cells by fusing their envelope with the cell membrane or through receptor-mediated endocytosis. They do not inject their nucleic acids directly like bacteriophages or use competence proteins for entry. The viral genome is released inside the host cell for replication after entry.
Step-by-step explanation:
Enveloped viruses utilize multiple methods to gain entry into host cells. One way is through fusion of their membrane with the host cell membrane. This interaction is facilitated by special fusion proteins that allow the viral envelope to merge with the cell's plasma membrane, subsequently releasing the viral genome and capsid into the cytoplasm. Another common method for entry is receptor-mediated endocytosis, where the virus binds to a specific receptor on the host cell and is then engulfed inside the cell encapsulated in a vesicle.
However, not all viruses inject their nucleic acids into the host cell from the outside; this is a strategy typically seen in bacteriophages. Instead, once inside the animal or plant host cell, either through endocytosis or membrane fusion, the viral capsid disassembles and the nucleic acid becomes available for replication and transcription, leading to the production of new viral particles.
Competence proteins are not typically involved in viral entry; they are more associated with bacterial transformation, a process in which bacteria take up external DNA from their surroundings. Instead, viruses rely on interactions between their proteins and host cell receptors or on the mechanisms of endocytosis and fusion to enter cells.