The cell envelope encases the cytoplasm and all its components. The chromosome, a single, continuous strand of DNA, is localized, but not contained, in a region of the cell called the nucleoid. All the other cellular components are scattered throughout the cytoplasm. Cytoplasmic Membrane - A layer of phospholipids and proteins, called the cytoplasmic membrane, encloses the interior of the bacterium, regulating the flow of materials in and out of the cell. Membranes are highly organized and asymmetric having two sides, each side with a different surface and different functions.
Membranes are also dynamic, constantly adapting to different conditions.
One of those components, plasmids, are small, extrachromosomal genetic structures carried by many strains of bacteria. Unlike the chromosome, they are not involved in reproduction. Only the chromosome has the genetic instructions for initiating and carrying out cell division, or binary fission, the primary means of reproduction in bacteria. Plasmids replicate independently of the chromosome and, while not essential for survival, appear to give bacteria a selective advantage. Plasmids are passed on to other bacteria through two means.