high cost of developing and shepherding the drug through the FDA would be such that the company would not be able to regain its development costs and make a profit. Hence, orphan drug status was designed to encourage drug development efforts for otherwise noneconomic pharmaceuticals with less than 200,000 patients a year.

Orphan Genes Genes within an organism’s genome/DNA, that have no apparent func-

tion. See also GENE, ORGANISM, GENOME,

DEOXYRIBONUCLEIC ACID (DNA), FUNCTIONAL

GENOMICS.

Orphan Receptors Refers to cellular receptors (i.e., embedded in surface of cell membrane) that are not coupled to G-protein (cell) system complexes. See also BIORECEP-

TORS, RECEPTORS, CELL, PLASMA MEMBRANE,

G-PROTEINS , ADHESION MOLECULE, MICROARRAY

(TESTING), BIOCHIPS, HIGH-THROUGHPUT SCREEN-

ING (HTS), TARGET-LIGAND INTERACTION SCREEN-

ING, LIGAND (IN BIOCHEMISTRY), BIOASSAY, GENE

EXPRESSION ANALYSIS, TARGET (OF A THERAPEUTIC

AGENT).

Orthophosphate Cleavage Enzymatic cleavage of one of the phosphate ester bonds of ATP to yield ADP and a single phosphate molecule known as orthophosphate (designated as Pi). The cleavage of the phosphate bond is energy-yielding and is (except in the case of a futile cycle) coupled enzymatically to reactions that utilize the energy to run the cell. An orthophosphate cleavage reaction releases relatively less energy than does a corresponding pyrophosphate cleavage reac-

tion. See also ADENOSINE DIPHOSPHATE (ADP),

ADENOSINE TRIPHOSPHATE (ATP), FUTILE CYCLE,

PYROPHOSPHATE CLEAVAGE.

Osmosis Bulk flow of water through a semipermeable (or more accurately, differentially permeable) membrane into another (aqueous) phase containing more of a solute (dissolved compound). As an example, let us set up an osmotically active system. There are two solutions, A and B. Solution A has less salt dissolved in it than solution B and, furthermore, the two solutions are separated by a differentially permeable membrane (this looks like a plastic film). Water molecules (and only water molecules) will flow from solution A through the membrane and into

solution B. The reason for this is that the membrane allows free passage only to water molecules. The bulk flow of water has the effect of diluting solution B, while concentrating solution A. Water will flow from region A to region B until the salt concentrations of both solutions are equal. Osmosis is therefore a process in which water passes from regions of low salt concentration to regions of high salt concentration. The process can be viewed as equalizing the number of water and solute molecules on both sides of the membrane. See also OSMOTIC PRESSURE.

Osmotic Pressure May be defined as the hydrostatic pressure which must be applied to a solution on one side of a semipermeable membrane (solution B in the example for osmosis) in order to offset the flow of solvent (water) from the other side (solution A in the example for osmosis). It is a measure of the tendency or “strength” of water to flow from a region of low salt concentration (and conversely high water concentration) to regions of high salt concentration (and conversely low water concentration). See also OSMOSIS.

Osmotins A category of proteins, which are produced by some organisms as a natural defense against pathogenic fungi. See also

CECROPHINS, MAGAININS, ORGANISM, FUNGUS, O

PATHOGENIC.

Osteoarthritis A disease that affects primarily women older than 45, in which cartilage within the body’s joint breaks down. Osteoarthritis encompasses approximately half of all cases of arthritis.

Osteoinductive Factor (OIF) A protein that induces the growth of both cartilage-forming cells and bone-forming cells (e.g., after a bone has been broken). When applied in the presence of transforming growth factor-beta, type 2 (another protein), osteoinductive factor first causes connective tissue cells to grow together to form a matrix of cartilage (e.g., across the bone break), then bone cells slowly replace that cartilage. Osteoinductive factor also seems to thwart a type of cell that tears down bone formation, so OIF may someday be used to combat osteoporosis. See also

GROWTH FACTOR, TRANSFORMING GROWTH FAC-

TOR-BETA (TGF-BETA), FIBROBLASTS, FIBROBLAST

GROWTH FACTOR (FGF), OSTEOPOROSIS.

© 2002 by CRC Press LLC

Osteoporosis A disease of humans in which the bones gradually weaken and become brittle. A diet containing a large amount of soy isoflavones (i.e., genistein) has been shown to increase bone density; thereby lowering the risk of osteoporosis. Groups that are especially at risk for osteoporosis include postmenopausal women (particularly of Caucasian or Asian ethnicity), those who have undergone early menopause (i.e., prior to age 45), those who smoked, those who consumed excessive amounts of alcohol, and those who consumed excessive amounts of certain pharmaceuticals (e.g., steroids such as prednisone, thyroid hor-

mone, etc.). See also OSTEOINDUCTIVE FACTOR

(OIF), GENISTEIN (Gen), SOY PROTEIN, ISOFLAVONES, STEROID, SOYBEAN PLANT, HIGH-ISOFLA-

VONE SOYBEANS, HAPLOTYPE.

Outcrossing The transfer of a given gene or genes (e.g., one synthesized by man and inserted into a plant via genetic engineering) from a domesticated organism (e.g., crop plant) to a wild type (relative of plant). See

also GENE, INTROGRESSION, SYNTHESIZING (OF DNA

MOLECULES), GENETIC ENGINEERING, WILD TYPE.

Overwinding Positive supercoiling. Winding which applies further tension in the direction of the winding of the two strands about each

Oother in the duplex. See also DEOXYRIBO-

NUCLEIC ACID (DNA), SUPERCOILING, DOUBLE

HELIX, DUPLEX.

Oxalate A salt or ester of oxalic acid. See also

CALCIUM OXALATE.

Oxidant See OXIDIZING AGENT.

Oxidation (chemical reaction) Loss of electrons from a compound (or element) in a chemical reaction. When one compound is oxidized, another compound is reduced. That is, the other compound must “pick up” the electrons which the first has lost. See also

OXIDATION-REDUCTION REACTION, HYDROGENATION, OXIDATION (of fats/oils/lipids).

Oxidation (of fats/oils/lipids) A c h e m i c a l transformation of fat/lipid molecules, in which oxygen (e.g., from air) is combined with those molecules. As a result of that (oxidation chemical reaction), various chemical entities are created (peroxides, aldehydes, etc.) which possess objectionable flavors/odors, and are harmful to animals that consume such (rancid) fats/oils. See also

© 2002 by CRC Press LLC

FATS, FATTY ACID, LIPIDS, PLASMA MEMBRANE,

OXIDATION (chemical reaction), OXIDATIVE STRESS,

HYDROLYSIS.

Oxidation (of fatty acids) See CARNITINE. Oxidation-Reduction Reaction A chemical

reaction in which electrons are transferred from a donor to an acceptor molecule or

atom. See also OXIDATION (chemical reaction), OXIDIZING AGENT, REDUCTION (IN A CHEMICAL REACTION).

Oxidative Phosphorylation The enzymatic phosphorylation of ADP to ATP coupled to electron transport from a substrate to molecular oxygen. The synthesis (production) of ATP from the starting materials of ADP and inorganic phosphate (orthophosphate). See

also ADENOSINE DIPHOSPHATE (ADP), ADENOSINE

TRIPHOSPHATE (ATP), ORTHOPHOSPHATE CLEAVAGE.

Oxidative Stress The physiological stress/damage that results from the (chemical reaction) breakdown of all or part of an organism, via oxidation reaction(s). For example, oxidative stress appears to be present in the brains of all victims of neurodegenerative diseases (Alzheimer’s disease, Parkinson’s disease, etc.). One common result of such oxidation reactions is the generation (within organism’s body) of reactive oxygen species (“free radicals”) that can adversely affect:

•Endothelial function (i.e., the inner lining of blood vessels)

•Platelet aggregation (e.g., inappropriate blood clotting/clumping)

•Atherosclerosis (i.e., buildup of oxidized fatty deposits known as plaque on internal walls of arteries)

•Myocardial function (e.g., heart failure)

•Eye and kidney tissue (especially in diabetics)

A key indicator of oxidative stress is the peroxidation of membrane lipids to form monoand bifunctional aldehydes (e.g., 4-hydroxy- 2-nonenal, also known as HNE). See also ORGANISM, OXIDATION (chemical reaction),

ALZHEIMER’S DISEASE, PARKINSON’S DISEASE,

CELL, ANTIOXIDANTS, PLASMA MEMBRANE, LIPIDS,

GLUTATHIONE, CAROTENOIDS, ENDOTHELIAL CELLS,

PLATELETS, ATHEROSCLEROSIS, INSULIN, CORO-

NARY HEART DISEASE (CHD), HAPTOGLOBIN.

OXIDATION-REDUCTION

Oxidizing Agent (oxidant) The acceptor of electrons in an oxidation-reduction reaction. The oxidant is reduced by the end of the chemical reaction. That is, the oxidizing agent is the entity that seeks and accepts electrons. Electron acceptance is, by definition,

reduction. See also

REACTION, PEROXIDASE.

Oxygen Free Radical See FREE RADICAL.

Oxygenase An enzyme catalyzing a reaction in which oxygen is introduced into an acceptor molecule.

O

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P

P Element A transposon, whose genes (within this transposon) resist rearrangement during the process (i.e., transposition) of the P element being incorporated into a new location within an organism’s genome (i.e., its deoxyribonucleic acid or DNA). In addition to “carrying” genes to a new location(s) in the genome, the P element itself codes for transposase (an enzyme that makes transposition possible). See also TRANSPOSON, GENE,

ENZYME, TRANSPOSITION, TRANSPOSASE, DEOXY-

RIBONUCLEIC ACID (DNA), GENOME.

P. gossypiella See PECTINOPHORA GOSSYPIELLA.

P-Selectin Formerly known as GMP-140 and PADGEM, it is a selectin molecule that is synthesized by endothelial cells before (adjacent) tissues are infected. Thus “stored in advance,” the endothelial cells can present P-selectin molecules on the internal surface of the endothelium within minutes after an infection (of adjacent tissue) begins. This presentation of P-selectin molecules attracts leukocytes to the site of the infection, and draws them out of the bloodstream (the leukocytes “squeeze” between adjacent endothelial cells). See also SELECTINS, LECTINS,

ELAM-1, ADHESION MOLECULE, LEUKOCYTES,

ENDOTHELIUM.

p53 Gene A tumor-suppressor gene which controls passage (of a given cell) from the “GI” phase to the “s” (i.e., DNA synthesis) phase. The p53 protein that is coded for by the p53 gene is a transcription factor (i.e., it “reads” DNA to determine if damaged, then acts to control cell division, while the p53 gene codes for more production of additional p53 protein).

Discovered in 1993 by Arnold J. Levine and colleagues, it is believed to be responsible for up to 50% of all human cancer

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

tumors (when the p53 gene is damaged or mutated). Normally, the p53 gene codes for (i.e., causes to be manufactured in cell) the p53 protein, which acts to prevent cells from dividing uncontrollably when the cell’s DNA has been damaged (e.g., via exposure to cigarette smoke or ultraviolet light). If, in spite of the presence of p53 protein, a cell begins to divide uncontrollably following damage to its DNA, the p53 gene can cause apoptosis, which is also known as “programmed cell death” (to prevent tumors).

See also GENE, TUMOR-SUPPRESSOR GENES,

	ras GENE, GENETIC CODE, MEIOSIS, DEOXYRIBO-
	NUCLEIC ACID (DNA), CARCINOGEN, RIBOSOMES,
	ONCOGENES, TRANSCRIPTION FACTORS, CANCER,
	TUMOR, p53 PROTEIN, PROTO-ONCOGENES, PROTEIN,
	APOPTOSIS.
	p53 Protein A tumor-suppressor protein,
	sometimes called the master transcription
	factor, or the “guardian of the genome;” but
	whose amino acid sequence alterations
		P
	(resulting from damage or mutation to the
	p53 gene) are believed to be responsible for
	up to 50% of all human cancer tumors. The
	p53 protein has four domains, one of which
	(i.e., the core domain) binds to a specific
	sequence(s) of the cell’s DNA, in order to
	prevent the cell from dividing uncontrollably
	when the cell’s DNA has been damaged
	(e.g., via exposure to cigarette smoke, ultra-
	violet light, or other carcinogen), until the
	damage to that DNA can be repaired. As the
	amount of DNA within a given (damaged)
	cell increases, the concentration of p53 pro-
	tein also increases. Because p53 protein is a
	transcription factor (i.e., “reads” DNA to
	determine if damaged, then acts to control
	cell division, while p53 gene codes for pro-
	duction of more p53), p53 is very efficient

© 2002 by CRC Press LLC