(A) Scanning electron micrograph showing the irregular shape of this small bacterium, reflecting the lack of any rigid wall. (B) Cross section (transmission electron micrograph) of a Mycoplasma cell. Of the 477 genes of Mycoplasma genitalium, 37 code for transfer, ribosomal, and other nonmessenger RNAs. Functions are known, or can be guessed, for 297 of the genes coding for protein: of these, 153 are involved in DNA replication, transcription, and translation and related processes involving DNA, RNA, and protein; 29 in the membrane and surface structures of the cell; 33 in the transport of nutrients and other molecules across the membrane; 71 in energy conversion and the synthesis and degradation of small molecules; and 11 in the regulation of cell division and other processes. (A, from S. Razin, M. Banai, H. Gamliel, A. Pollack, W. Bredt, and I. Kahane, Infect. Immun. 30:538–546, 1980; B, courtesy of Roger Cole, in Medical Microbiology, 4th edn., [S. Baron ed.]. Galveston: University of Texas Medical Branch, 1996.)