Which structure acts as a barrier and facilitates communication between the nucleus and the cell?

The nuclear envelope is a double-membrane structure that surrounds the nucleus of a cell, effectively acting as a barrier that separates the contents of the nucleus from the cytoplasm. This separation is crucial for maintaining an organized environment within the nucleus, where processes such as DNA replication and transcription occur. The nuclear envelope contains pores that allow for the regulated exchange of materials, such as RNA and proteins, between the nucleus and the cytoplasm. This selective transport is vital for cellular functions, as it ensures that genetic information and other necessary molecules can move in and out of the nucleus, facilitating communication and coordination between the nucleus and the rest of the cell. The other structures listed do not play a role in separating the nucleus from the cell or communicating between them in the same direct manner as the nuclear envelope.