Chapter 2 The structure of cells
All eukaryotic cells share the same basic layout, in that they are surrounded by a membrane, and filled with cytoplasm within which there is a variety of membrane-bound organelles that perform specialized tasks. One major organelle is the nucleus which contains DNA. At roughly one-thousandth the volume of the eukaryote cell volume, the organization of a prokaryote is relatively straightforward by comparison, although bacteria possess very similar structural aspects and machinery to eukaryotic cells. Their cell membrane is based on the same lipid bilayer (which we will discuss next) and their molecular machinery such as ribosomes for protein assembly functions in much the same way as eukaryotes. Bacteria do have specialized cell structures for motility such as flagella, and may possess internal membranes as in the case of a gas vacuole that serves as a buoyancy aid. However, the DNA in a bacterial cell is a single circular molecule and there is no separate nuclear compartment.