P R O T O P L A S M
Most of the dry weight of micro-organisms is organic matter comprising the elements: carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur. Inorganic ions, such as sodium, potassium, iron, calcium, magnesium, and chloride, are necessary to facilitate enzymatic catalysis, and to maintain chemical gradients across the cell membrane.
Organic matter is in macromolecules formed by anhydride bonds between building blocks. Synthesis of the anhydride bonds requires chemical energy, which is provided by the 2 phospohodiester bonds in adenosine triphosphate. The proton motive force provides the additional energy required to maintain a relatively constant cytoplasmic composition during growth in a range of extracellular chemical environments. The proton motive force is the potential energy derived when a proton passes across a membrane; in prokayotes, the membrane is the cytoplasmic membrane of the cell; in eukaryotes, the membrane may be part of the mitochondrion or chloroplast. Metabolic processes produce the proton motive force. The free energy may move the cell, maintain ionic or molecular gradients across the membrane, synthesise the anhydride bonds in adenosine triphosphate, or be used for a mix of these processes.