FIGURE 1-11 Prokaryotic cells are have a relatively simple structure. (Left) Electron micrograph of a thin section of Escherichia coli, a common intestinal bacterium. The nucleoid, consisting of the bacterial DNA, is not enclosed within a membrane. E. coli and other gram-negative bacteria are surrounded by two membranes separated by the periplasmic space. The thin cell wall is adjacent to the inner membrane. (Right) This artist’s drawing shows the nucleoid (blue) and a magnification of the layers that surround the cytoplasm. Most of the cell is composed of water, proteins, ions, and other molecules that are too small to be depicted at the scale of this drawing.

[Electron micrograph courtesy of I. D. J. Burdett and R. G. E. Murray.]