DNA is a linear polymer made up of four different monomers. It has a fixed backbone from which protrude variable
substituents (Figure 1.1). The backbone is built of repeating sugar-phosphate units. The sugars are molecules of
deoxyribose from which DNA receives its name. Joined to each deoxyribose is one of four possible bases: adenine (A),
cytosine (C), guanine (G), and thymine (T).
All four bases are planar but differ significantly in other respects. Thus, the monomers of DNA consist of a sugarphosphate
unit, with one of four bases attached to the sugar. These bases can be arranged in any order along a strand of
DNA. The order of these bases is what is displayed in the sequence that begins this chapter. For example, the first base in
the sequence shown is G (guanine), the second is A (adenine), and so on. The sequence of bases along a DNA strand
constitutes the genetic information the instructions for assembling proteins, which themselves orchestrate the
synthesis of a host of other biomolecules that form cells and ultimately organisms.
DNA Is Constructed from Four Building Blocks
Bacterial Metabolism in Wastewater Treatment Systems
Water that has been used by people and is disposed into a receiving water body with
altered physical and/or chemical parameters is defined as wastewater. If only the
physical parameters of the water were changed, e.g., resulting in an elevated temperature
after use as a coolant, treatment before final disposal into a surface water
may require only cooling close to its initial temperature. If the water, however, has
been contaminated with soluble or insoluble organic or inorganic material, a combination
of mechanical, chemical, and/or biological purification procedures may be
required to protect the environment from periodic or permanent pollution or damage.
For this reason, legislation in industrialized and in many developing countries
has reinforced environmental laws that regulate the maximum allowed residual
concentrations of carbon, nitrogen, and phosphorous compounds in purified wastewater,
before it is disposed into a river or into any other receiving water body However,
enforcement of these laws is not always very strict. Enforcement seems to be
related to the economy of the country and thus differs significantly between wealthy
industrialized and poor developing countries. In this chapter basic processes for biological
treatment of waste or wastewater to eliminate organic and inorganic pollutants
are summarized.
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