Biological Oxidation in Bacteria
The nutrients, acquisited by microbial cells, contain low amounts of energy in each of chemical bonds within their molecules. The total energy is distributed throughout the molecule and it is not readily available for direct assimilation.
The pathways of energy metabolism comprise the sets of versatile enzymatic reactions resulting in slow stepwise concentration of diffuse energy of many low-energy chemical bonds of various nature into a few high-energy equivalents (such as macroergic phosphate-containing substances or proton-motive force). The latter forms can be easuly utilized by the cell.
The energy is eventually transferred to adenosine diphosphate (ADP) to form adenosine triphosphate, abbreviated ATP, which is used like universal energy storage in the cells. The same function is maintained by guanosine triphosphate, or GTP.
Within ATP molecule the energy is concentrated by two high-energy bonds (tagged by the symbol ~). After ATP or GTP enzymatic cleavage these bonds break down, and large amounts of energy are liberated.
ATP-derived release of energy can be outlined according to the following general scheme of the reaction:
ATP = ADP + (inorganic phosphate P) + Energy
Accumulation of energy in bacteria is predominantly realized via the process of biological oxidation.
Chemoheterotrophic bacteria, because of their dependency on some organic source for energy, exploit two basic pathways of biological oxidation that collect the diffuse energy of “fuel” nutrient molecules within the high-energy of ATP bonds.
One pathway is termed fermentation, the second one is respiration (aerobic or anaerobic).
Together with energy gain, all the pathways create a number of valuable precursor metabolites – intermediate organic substances that should be further transformed into the structural subunits of biopolymers (e.g., amino acids) after a set of specific biochemical reactions.