ABSTRACT
Eukaryotic cells are generally much larger than prokaryotic cells. To avoid havoc, eukaryotic cells are subdivided into functionally distinct membrane-enclosed compartments or organelles. Most of the genetic material of eukaryotes is stored in a single organelle, the nucleus. The nucleus is suspended in the cytosol, together with all other organelles such as the endoplasmic reticulum, the Golgi apparatus, lysosomes, mitochondria, and (in plants) chloroplasts. This compartmentation brings about the problem of how molecules are exchanged between organelles. For example, most nucleic acids are synthesized in the nucleus, but proteins are synthesized (using RNA templates) in the cytoplasm. Several fundamentally different mechanisms allow the exchange of molecules between compartments.
