12 Desaturase One of the desaturases (enzymes). See also DELTA 12 DESATURASE,

COSUPPRESSION, ENZYME, DESATURASE.Endotoxins See DELTA ENDOTOXINS.

∆ 15 Desaturase One of the desaturases (enzymes). See also ENZYME, DESATURASE,

DELTA 12 DESATURASE.

D Loop A region within mitochondrial DNA in which a short stretch of RNA is paired with one strand of DNA, displacing the original partner DNA strand in this region. The same term is used to describe the displacement of a region of one strand of duplex DNA by a single-stranded invader in the reaction catalyzed by RecA protein.

Daffodil Rice See GOLDEN RICE.

Daffodils Refers to the approximately 80 species of flowering plants within the genus Narcissus. Native to southern Europe and northern Africa, they are the source of “golden rice” and the Alzheimer’s disease treatment compound galantamine hydrobromide. See also

GOLDEN RICE, ALZHEIMER’S DISEASE. Daidzein See ISOFLAVONES. Daidzen See ISOFLAVONES.

Daidzin The β-glycoside form (isomer in which glucose is attached to the molecule at the seven position of the A ring) of the isoflavone known as daidzein (aglycone form).

See also ISOFLAVONES, ISOMER, DAIDZEIN.

Dalton A unit of mass very nearly equal to that of a hydrogen atom (precisely equal to 1.0000 on the atomic mass scale). Named after John Dalton (1766–1844), who developed the atomic theory of matter. It is 1.660 × 10–24 gram. See also KILODALTON (Kd).

DBT An acronym used by some to designate the Indian Department of Biotechnology.

See also INDIAN DEPARTMENT OF BIOTECHNOLOGY.

0-8493-XXXX-X/01/$0.00+$1.50 © 2001 by CRC Press LLC

D

Deamination The removal of amino groups from molecules (e.g., in an animal’s food) via the energy-consuming metabolism of excess amino acids eaten by that animal. For example, when livestock are fed more lysine (amino acid) than their body needs in a given day (animals’ bodies can only utilize the e s s e n t i a l a m i n o a c i d s i n p r e c i s e amounts/ratios of their daily diet), the excess lysine is metabolized to urea and then

excreted. See also METABOLISM, AMINO ACID,

ESSENTIAL AMINO ACIDS, LYSINE (lys), IDEAL PRO-

TEIN, “IDEAL PROTEIN” CONCEPT, PDCAAS, ACC

SYNTHASE.

Defective Virus A virus that, by itself, is unable to reproduce when infecting its host (cell), but that can grow in the presence of another virus. The other virus provides the necessary molecular machinery that the first virus lacks.

Defensins A class of peptides that inhibits certain fungal diseases. These are produced as a natural defense by some plants. For example, the alfalfa plant produces a defensin known as alfAFP (alfalfa antifungal peptide). In addition to protecting the plant from certain diseases, the alfAFP also inhibits a fungal disease known as potato early dying complex (also called Verticillium wilt), which is caused by the fungus Verticillium

dahliae. See also PEPTIDE, FUNGUS.

Degenerate Codons Two or more codons that code for the same amino acid. For example, isoleucine is specified by the AUU, AUC, and AUA triplets. Since in this case more than one triplet codes for isoleucine, the codons are called degenerate. See also

GENETIC CODE, CODON.

Dehydrogenases Enzymes that catalyze the removal of pairs of hydrogen atoms from

their substrates. See also SUBSTRATE (CHEMI-

CAL), GLUTAMATE DEHYDROGENASE, ENZYME,

DEHYDROGENATION.

Dehydrogenation The removal of hydrogen atoms from molecules. When those molecules are the components of vegetable

Durated fats results. See also FATS, MONOUN-oils/fats, a lower content percentage of sat-

SATURATED FATS, SATURATED FATTY ACIDS

(SAFA), FATTY ACID.

Deinococcus radiodurans A species of bacteria capable of surviving 1.5 million rads of gamma radiation (3000 times the lethal radiation dose for humans), surviving long periods of dehydration, and surviving high doses of ultraviolet radiation. Deinococcus radiodurans was discovered in 1956 in some canned meat. See also BACTERIA, EXTREMO-

PHILIC BACTERIA.

Delaney Clause Formerly part of American federal law (1959 Delaney amendment to the Food, Drug and Cosmetic Act), it was eliminated in 1996. The Delaney Clause had set a zero-risk tolerance level for carcinogenic pesticide residues in processed foods. See

also CARCINOGEN.

Deletions Loss of a section of the genetic material from a chromosome. The size of a deleted material can vary from a single nucleotide to sections containing a number of genes. See also GENE, CHROMOSOMES.

Delta 12 Desaturase A n e n z y m e p r e s e n t within the soybean plant and in other oilseed crops (canola, maize/corn, etc.). Delta 12 desaturase (∆12) is involved in the synthesis “pathway” utilized by oilseed crops to synthesize (manufacture) polyunsaturated fatty acids (e.g., linoleic acid) from monounsaturated fatty acids (e.g., oleic acid) in seeds (while those seeds are developing). See also

ENZYME, DESATURASE, FATTY ACID, UNSATUR-

ATED FATTY ACID, MONOUNSATURATED FATTY

ACIDS (MUFA), POLYUNSATURATED FATTY ACIDS

(PUFA), PATHWAY, OLEIC ACID, LINOLEIC ACID,

SOYBEAN PLANT, CORN, CANOLA.

Delta Endotoxins See CRY PROTEINS, PROTEIN.

Denaturation The loss of the native conformation of a macromolecule resulting, for instance, from heat, extreme pH (i.e., by acidity or basicity) changes, chemical treatment, etc. It is accompanied by loss of biological

activity. See also CONFORMATION, CONFIGURA-

TION, MACROMOLECULES.

Denatured DNA DNA converted from dou- ble-stranded to single-stranded form by a denaturation process such as heating the DNA solution. In the case of heat denaturation, the solution becomes very gelatinous and viscous. See also DENATURATION, DEOXY-

RIBONUCLEIC ACID (DNA), DUPLEX.

Denaturing Gradient Gel Electrophoresis

See D E N A T U R I N G P O L Y A C R Y L A M I D E G E L

ELECTROPHORESIS.

Denaturing Polyacrylamide Gel Electrophoresis The use of PAGE (polyacrylamide gel electrophoresis) in order to separate and analyze DNA fragments (sequences) after that DNA is first denatured. This methodology can be employed to scan DNA in order to detect point mutations. See also

POLYACRYLAMIDE GEL ELECTROPHORESIS (PAGE),

POINT MUTATION, DENATURING GRADIENT GEL

ELECTROPHORESIS, DEOXYRIBONUCLEIC ACID

(D N A ), D E N A T U R E D D N A , B A S E E X C I S I O N

SEQUENCE SCANNING (BESS).

Dendrimers Polymers (i.e., molecules composed of repeating atomic units within the molecule) that repeatedly branch (while “growing” due to addition of more atoms in a repeating pattern) until that branching is stopped by the physical constraint of contacting itself (i.e., having formed a complete, hollow sphere). Discovered during the 1970s by Donald Tomalia, dendrimers possess sites on their exterior surface to which genetic material (e.g., genes or other portions of DNA) can be “attached.” Dendrimers bearing such genetic material have shown the capacity to successfully transfer that genetic material into more than thirty types of living animal cells. See also POLYMER, DENDRITIC

POLYMERS, GENE, GENETIC ENGINEERING, GENE

DELIVERY, INFORMATIONAL MOLECULES, CODING

SEQUENCE, TUMOR-SUPPRESSOR GENES, DEOXY-

RIBONUCLEIC ACID (DNA), GENETIC TARGETING,

GENETICS.

Dendrites Highly branched structures that extend from the (nucleus of) neurons to (synapse junctions with) other neurons (e.g., in human brain tissue). The primary purpose of dendrites is to process signals that are generated/received at the synapses (e.g., from

the dendrites of adjoining neurons). Neuron ribosomes are located in the dendritic spines, the dendrite projections that form synapses (the junctions between dendrites where “signal transfer” between neurons takes place). Thus, those ribosomes make the proteins that are crucial to learning and memory (e.g., accomplished via growth/changes of dendrites). Messenger RNAs are synthesized (manufactured) in the nucleus of the neuron, then transported on microtubules (filaments within the neuron cell) to the ribosomes in the dendrites, where they cause manufacture of proteins (e.g., enzymes) in response to synapse activity (i.e., signals). See also NEU-

RON, CELL, NEUROTRANSMITTER, RIBOSOMES,

PROTEIN, ENZYME, MESSENGER RNA (mRNA),

MICROTUBULES.

Dendritic Cells These are rare white blood cells, which act to stimulate the human immune system (T cells) to combat certain types of cancer. See also CELL, IMMUNE

RESPONSE, CANCER, LEUKOCYTES.

Dendritic Langerhans Cells A type of cell, located in the mucous membranes of the mouth and genital areas, that permits the human immunodeficiency virus (the virus that causes AIDS) to enter and infect the body, even when there are no cuts or abrasions through those mucous membranes. See

also HUMAN IMMUNODEFICIENCY VIRUS TYPE 1

(HIV- 1), HUMAN IMMUNODEFICIENCY VIRUS

TYPE 2 (HIV- 2), ACQUIRED IMMUNE DEFICIENCY

SYNDROME (AIDS), ADHESION MOLECULE, DEN-

DRITIC POLYMERS.

Dendritic Polymers Polymers (i.e., molecules composed of repeating atomic units within the molecule) that repeatedly branch (while “growing” due to the addition of more atoms in a repeating pattern) until that branching is stopped (e.g., by physical constraints, for those polymers within living tissues). In the absence of physical constraints, dendritic polymers can continue branching (and growing) until they form a complete (hollow) sphere. Such spheres are potentially useful for protecting and “delivering” a fragile pharmaceutical molecule to specific tissue(s) within the body. See also POLYMER, DENDRIMERS.

Denitrification The process (i.e., internal respiration) by which denitrifying bacteria

(e.g., in soil) convert nitrates to gaseous nitrogen/nitrous oxide, which then enters the atmosphere. See also NITRATES, BACTERIA,

RESPIRATION.

information, which is encoded in the sequence of bases; it is present in chromosomes and chromosomal material of cell organelles such as mitochondria and chloroplasts, and also present in some viruses. See

also A-DNA, B-DNA, cDNA, Z-DNA, TRANSCRIP-

DRNA (mRNA), NUCLEOTIDE, PROTEIN, RIBOSOMES,

GENETIC CODE, GENE, CHROMOSOMES, CHROMA-

TIDS, CHROMATIN, MITOCHONDRIAL DNA, CYTO- PLASMIC DNA, NUCLEAR DNA.TION, ANTIPARALLEL, DOUBLE HELIX, MESSENGER

Deprotection (of a peptide) See also HF CLEAV-

AGE.

Desaturase An enzyme (group) family that is present within the soybean plant and other oilseed crops (e.g., canola, corn/maize). One or more desaturases is involved in the synthesis “pathway” through which oilseed crops produce unsaturated fatty acids (e.g., linoleic acid). A desaturase is also involved in production of beta carotene (in some plants). See

also ENZYME, FATS, STEAROYL-ACP DESATURASE,

DELTA 12 DESATURASE, SOYBEAN PLANT, PATH-

WAY, LINOLEIC ACID, FATTY ACID, UNSATURATED

FATTY ACID, GOLDEN RICE, BETA CAROTENE.

Desferroxamine Manganese An iron chelating agent (i.e., it chemically binds to iron atoms in the blood, thus trapping the iron atoms). The molecule also acts as an hSOD mimic by capturing harmful oxygen free radicals in the blood before they damage the walls of blood vessels. Recent research indicates that desferroxamine manganese may be useful in blocking the onset of cataracts.

See also HUMAN SUPEROXIDE DISMUTASE (hSOD),

XANTHINE OXIDASE, LAZAROIDS.

Desulfovibrio A genus of bacteria that reduces sulfate to H2S (hydrogen sulfide). Energy is obtained by oxidation of H2 or organic molecules. Not a strict autotroph because CO2 cannot be used as a sole carbon

source. See also REDUCTION (IN A CHEMICAL REACTION), AUTOTROPH.

Dextran A polysaccharide produced by yeasts and bacteria as an energy storage reservoir (analogous to fat in humans). Consists of glucose residues, joined almost exclusively by alpha-1,6 linkages. Occasional branches (in the molecule) are formed by alpha 1,2, alpha 1,3, or alpha 1,4 linkages. Which linkage is

used depends on the species of yeast or bacteria producing the dextran. See also

POLYSACCHARIDES.

Dextrorotary (D) Isomer A stereoisomer that rotates the plane of plane-polarized light to the right. Dextro means right. See also

ISOMERS, LEVOROTARY (L) ISOMER, POLARIMETER.

DHA See DOCOSAHEXANOIC ACID (DHA).

Diabetes A grouping of diseases in which the body either does not synthesize (manufacture) insulin, or else its tissues are insensitive to the insulin that it does synthesize. Approximately 5–10% of all people with diabetes are unable to synthesize insulin (e.g., because their insulin-making tissue was destroyed by autoimmune disease). Approximately 90–95% of all people with diabetes are insensitive to the insulin their body synthesizes. See also PANCREAS, INSULIN,

INSULIN-DEPENDENT DIABETES MELLITIS (IDDM),

AUTOIMMUNE DISEASE, BETA CELLS, N- 3 FATTY

ACIDS, CALPAIN- 10, TYPE I DIABETES, TYPE II DIA-

BETES, HAPTOGLOBIN.

Diacylglycerols Molecules that consist of two fatty acids attached to a glycerol “backbone.” Research during the 1990s indicated that consumption of vegetable oils (e.g., used in frying foods) containing primarily diacylglycerols (versus typical triacylglycerols), is less likely to result in it being deposited as body fat (adipose tissue). See also FATTY ACID,

SATURATED FATTY ACIDS (SAFA), UNSATURATED

FATTY ACID, ADIPOSE, TRIACYLGLYCEROLS.

Diadzein See DAIDZEIN, ISOFLAVONES.

Dialysis The separation of low molecular weight compounds from high molecular weight components in solution by diffusion through a semipermeable membrane. Frequently utilized to remove salts and biological effectors (such as nicotinamide adenine dinucleotides, nucleotide phosphates, etc.) from polymeric molecules such as protein, DNA, or RNA. Commonly used membranes have a molecular weight cutoff (threshold) of around 10,000 Daltons, but other membrane pore sizes are available. See also HOL-

LOW FIBER SEPARATION, ACTIVE TRANSPORT.

Diamond vs. Chakrabarty See CHAKRABARTY

DECISION.