Cells with a true nucleus are called eukaryotes. Eukaryotes also have structures called organelles that are bound by membranes; prokaryotes have neither a true nucleus nor organelles. The term "eukaryote" literally means "true nucleus."
The nuclei of eukaryotic cells house the genetic information called DNA. The genetic information is the set of instructions that cells use to make all proteins. By keeping the DNA isolated from the rest of the cell, eukaryotic cells have better control over the creation of proteins. Because prokaryotes do not have nuclei, their genetic material is scattered around the cell.
The nuclear envelope is the membrane that surrounds the nucleus. The nuclear envelope contains pores that allow certain substances to enter and exit the nucleus. This membrane is also continuous with the transport system of the cell, which is known as the endoplasmic reticulum. This close association allows proteins to be transported to the nucleus efficiently.