Final answer:
The nuclear pore complex (NPC) is a protein-lined structure resembling a rosette, essential for the regulated transport of molecules between the nucleus and the cytoplasm, contingent upon ATP hydrolysis.
Step-by-step explanation:
The nuclear pore complex (NPC) resembles a rosette-shaped structure or a protein-lined pore within the nuclear envelope. These nuclear pores are essential for the active transport of molecules, requiring ATP hydrolysis as nuclear proteins enter the nucleus. They are formed by octagonal 'doors' made of protein, which can open up to 26 nanometers in response to specific signals, allowing the regulated passage of ions, RNA, and proteins. These pores are instrumental in maintaining a concentration gradient, and their unique structure facilitates their function as the cellular gateway between the nucleus and the cytoplasm.