The inside of the nucleus is shown in the lower section and the cytoplasm in the upper section of the image. The nuclear double membrane stretches from upper left to middle right. The nuclear pore complex (NPC) – the gatekeeper that connects these two cellular compartments – is located in the nuclear double bilayer. Transport through the NPC includes nuclear RNA and ribosomes funneled into the cytoplasm and cytoplasmic proteins, signaling molecules, and lipids moving into the nucleus. Under the nuclear membrane is the nuclear lamina – composed of intermediate filaments called lamins. In the nucleus, chromatin is depicted in various levels of compactness, from euchromatin, where the DNA and nucleosomes are more openly beaded, to the 30 nm fiber, a more compact structure shown in the background. Overlaid onto this nuclear landscape is a mist of nucleotides (the building blocks for transcription and replication) as well as key nuclear proteins.