Materials can enter and leave the nucleus through nuclear pores, which are large protein complexes that span the nuclear envelope. These pores allow for the transport of molecules such as proteins, RNA, and DNA between the nucleus and the cytoplasm.

The nuclear pore complex (NPC) is a highly organized structure that consists of multiple proteins called nucleoporins. These proteins form a channel through the nuclear envelope that allows for the passage of molecules. The NPC is also responsible for regulating the transport of molecules into and out of the nucleus.

Molecules that need to enter or leave the nucleus are transported through the NPC by carrier proteins. These proteins bind to the molecules and carry them through the channel. The transport of molecules through the NPC is an active process that requires energy.

The NPC is also responsible for preventing the entry of harmful substances into the nucleus. It does this by selectively allowing certain molecules to pass through while blocking others. This process is important for maintaining the integrity of the cell.