Nuclear pore complexes. Diagram of a nucleus showing the area represented by a coloured atomic force micrograph (AFM, right) of the nuclear surface. The surface is covered in nuclear pore complexes (NPCs), which are complexes of proteins that are embedded in the nuclear envelope. All material moving between the nucleus and the cell cytoplasm passes through these channels. They allow passive transport (diffusion) of ions and small molecules and active transport (energy dependent) of proteins and RNAs (ribonucleic acids). Magnification of AFM: x14,500 when whole image printed at 10 centimetres wide.