Heterotrophic plate counts (HPC).

A plating method for enumerating the number of viable organic carbon-using (heterotrophic) bacteria m a water sample.

Heterozygosity.

The genetic state in which the two genes specifying a particular enzyme or protein, from both parents contain DNA sequence inferences.

Homeostasis.

The stable expression of total cellular metabolism.

Homologous recombination.

A mechanism of DNA repair and genetic exchange between two DNA homologs.

Hormesis.

The concept that very low doses of ionizing radiation may be beneficial to the irradiated cells or organisms.

I

ICRP.

International Commission on Radiological Protection and Measurements, founded in 1928 and since 1950 has been providing general guidance on radiation protection.

Immunoglobulin.

The protein consisting of pairs of heavy and light chains that make the circulating antibodies which exhibit great diversity in recognition and binding target molecules known as antigens.

Interphase.

The period of the cell cycle during which chromosomes are not visible as discrete structures. At this time the nucleus of the cell is somewhat like a spherical zone surrounded by a nuclear membrane that contains the encapsulated DNA and also regulates the traffic of molecules between the inner volume of the nucleus and the outer volume of the cytoplasm. Interphase can be subdivided into Gl, S, and G2 phases according to the state of duplication of the DNA.

Ion exchange treatment.

A method used to remove anionic or cationic contamination from water. The contaminants adhere to locations containing anions or cations normally associated with the resin. When the resin becomes saturated with the contaminant, it is regenerated with a brine containing a high concentration of the originally-sorbed anion or cation.

Ionization.

A process by which a neutral atom or molecule loses or gains electrons, thereby acquiring a net electric charge. Ionization can be produced by the interaction of ionizing radiation with matter.

K

Karstic.

A type of topography characterized by sink-holes, caves, and underground drainage, usually formed in limestone or salt deposits.

Karyotype.

The full set of chromosomes in the nucleus of a cell that is characteristic of a particular individual or species.

L

Lacustrine.

Pertaining to, produced by, or formed in a lake.

Linear no-threshold (LNT) model.

A risk-projection model that expresses the effect (e.g., mutation or cancer) as a proportional (linear) function of the dose and assumes that no minimum ( threshold) dose exists below which radiation injury does not occur.

Loss of heterozygosity (LOH).

A process occurring during tumor progression by which one chromosome of a pair is lost and the partner is duplicated.

Lumen.

The interior open space of an organ such as a blood vessel or intestine.

M

Maximum contaminant level (MCL).

The highest concentration of a contaminant permitted by regulations in public drinking water supplies.

Meiotic.

The process by which a germ cell in the testis or ovary divides into two cells with a reduction in chromosome number such that each cell has one copy of each chromosome, and ultimately develops into either sperm or egg cells.

Meta-analysis.

An analysis of epidemiological data based on grouping or pooling information obtained from several studies.

Microsatellite repeats.

Regions of DNA in which the same short sequence is repeated numerous times to create characteristic sequence motifs useful for individual identification and which slow expansion and reduction in size in some tumors.

Mitochondria.

Organelles in the cytoplasm of cells that contain a small circular DNA molecule which encodes many of the genes required for oxidative phosphorylation and provides most of the energy for the cell through ATP production.



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