Now let's move on to basically the organelle that defines the eukaryotic cell, known as the nucleus. The nucleus is basically an organelle that contains the genetic information and the nucleus contains its own phospholipid bilayer that is called the nuclear envelope or the nuclear membrane to differentiate it from the cell membrane. The nuclear membrane contains nuclear pores, very small openings that allow certain things into and out of that nucleus. Now, at the center, at the heart of our nucleus, is a region of specialized region known as the nucleolus. And the nucleolus is the region where we synthesize incomplete ribosomes, the ribosomes that end up being in this region, the endoplasmic reticulum, or as free ribosomes found inside the cytosol, which we'll talk about in just a moment. So let's move on to this region here.