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D
Deoxyribonucleic acid (DNA) The molecule that carries
the genetic information for most living systems.
The DNA molecule consists of four bases (adenine,
cytosine, guanine and thymine) and a sugar-phosphate
backbone, arranged in two connected strands to form
a double helix. See also Complementary DNA; Double
helix; Recombinant DNA.
Differentiation The process of biochemical and structural
changes by which cells become specialized in form and
function.
Diploid A cell with two complete sets of chromosomes.
Compare Haploid.
DNA See Deoxyribonucleic acid.
DNA chip A small piece of glass or silicon that has small
pieces of DNA arrayed on its surface.
DNA fingerprinting The use of restriction enzymes to
measure the genetic variation of individuals. This
technology is often used as a forensic tool to detect
differences or similarities in blood and tissue samples
at crime scenes.
DNA hybridization The formation of a double-stranded
nucleic acid molecule from two separate strands. The
term also applies to a molecular technique that uses
one nucleic acid strand to locate another.
DNA library A collection of cloned DNA fragments that
collectively represent the genome of an organism.
DNA polymerase An enzyme that replicates DNA. DNA
polymerase is the basis of PCR-the polymerase chain
reaction.
DNA probe A small piece of nucleic acid that has been
labeled with a radioactive isotope, dye or enzyme and
is used to locate a particular nucleotide sequence or
gene on a DNA molecule.
DNA repair enzymes Proteins that recognize and repair
certain abnormalities in DNA.
DNA sequence The order of nucleotide bases in the DNA
molecule.
DNA vaccines Pieces of foreign DNA that are injected
into an organism to trigger an immune response.
Double helix A term often used to describe the
configuration of the DNA molecule. The helix consists of
two spiraling strands of nucleotides (a sugar, phosphate
and base) joined crosswise by specific pairing of the
bases. See also Deoxyribonucleic acid; Base; Base pair.
Diagnostic A product used for the diagnosis of disease or
medical condition. Both monoclonal antibodies and
DNA probes are useful diagnostic products.
Drug delivery The process by which a formulated drug
is administered to the patient. Traditional routes have
been oral or intravenous perfusion. New methods
deliver through the skin with a transdermal patch or
across the nasal membrane with an aerosol spray.
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