What's going on in the transition from the prokaryotes, up here, to the eukaryotes, down here, is--one thing that's going on--is that you're going from an organism, like a bacterium, that has a single circular chromosome anchored to a cell wall, to an organism that has a nucleus within which the chromosomes are-- there are then often multiple chromosomes inside the nucleus, plus organelles that are out in the cytoplasm, plus a lot of cell structure that's simply not present in the prokaryotes. 