Standing guard between a cell’s nucleus and its main chamber, called the cytoplasm, are thousands of behemoth protein structures called nuclear pore complexes, or NPCs. NPCs are like the bouncers of a cell’s nucleus, tightly guarding exactly what goes in and out. Each structure contains about 1,000 protein molecules, making NPCs some of the biggest protein complexes in our bodies. One of the most notable clients of NPCs is a class of molecules known as messenger RNAs, or mRNAs. These are the messengers that carry genetic instructions from the nucleus to the cytoplasm, where they are then translated into proteins.