LUMINESCENS.

PlantibodiesTM A trademark owned by EPIcyte Pharmaceutical, Inc. It refers to antibodies (akin to mammalian ones) produced in plants that are genetically engineered to produce those (specific) antibodies. That

© 2002 by CRC Press LLC

PHOTORHABDUS

AGROBACTERIUM TUMEFACIENS,

GENETIC ENGINEERING,

plants. It influences and regulates plant physiological processes. Also called a phytochrome. The four general types of hormones that together influence cell division, enlargement, and differentiation are the auxins, gibberellins, kinins, and abscisic acid. See also

HORMONE, GIBBERELLINS, PHYTOCHROME, GPA1,

ETHYLENE, LYSOPHOSPHATIDYLETHANOLAMINE.

Plant Protection Act A law passed by the U.S. Congress in 1930 that enabled intellectual property protection via patents for new plants (developed by scientists) which are propagated asexually (e.g., via grafting). See

also U.S. PATENT AND TRADEMARK OFFICE

(USPTO), EUROPEAN PATENT CONVENTION, EURO-

PEAN PATENT OFFICE (EPO), PLANT’S NOVEL TRAIT

(PNT), PLANT BREEDER’S RIGHTS (PBR), COMMU-

NITY PLANT VARIETY OFFICE, PLANT VARIETY

PROTECTION ACT (PVP).

Plant Sterols See PHYTOSTEROLS.

Plant Variety Protection Act (PVP) A l a w passed by the U.S. Congress in 1970 that enables intellectual property protection (analogous to copyright protection) for new seed plants and seeds in America. See also

U.S. PATENT AND TRADEMARK OFFICE (USPTO),

EUROPEAN PATENT CONVENTION, EUROPEAN

PATENT OFFICE (EPO), PLANT’S NOVEL TRAIT

(PNT), PLANT BREEDER’S RIGHTS (PBR), PLANT

PROTECTION ACT, UNION FOR PROTECTION OF NEW

PVARIETIES OF PLANTS (UPOV), COMMUNITY PLANT VARIETY OFFICE.

Plant’s Novel Trait (PNT) The new (novel) trait added to a plant (e.g., crop plant such as cotton, corn/maize, soybean, etc.). Examples of novel traits are herbicide-tolerance (via inserted CP4 EPSPS gene, PAT gene, etc.), insect resistance (via inserted B.t. gene,

Photorhabdus luminescens gene, etc.), and resistance to aluminum toxicity (via inserted CSb gene, etc.). See also TRAIT, CORN, SOY-

BEAN PLANT, CP4 EPSPS, GENE, PAT GENE, B.t.,

BACILLUS THURINGIENSIS (B.t.), EVENT, CITRATE SYNTHASE (CSb) GENE,

process (genetically engineering plants to cause them to produce plantibodies) was invented during the 1990s by Andrew Hiatt and Mich Hein. Although plants do not always glycosylate (i.e., attach oligosaccharide units to protein molecules such as these antibodies) in the same manner as animal cells, an antibody against HSV-2 pathogen expressed in genetically engineered soybean plants has proven comparable to that same antibody expressed in genetically engineered animal cells. See also ANTIBODY,

GENETIC ENGINEERING, GLYCOSYLATION, OLI-

GOSACCHARIDES, EXPRESS, SOYBEAN PLANT,

PATHOGEN, MOLECULAR PHARMING™.

Plantigens Antigens (e.g., of pathogenic bacteria) produced in plants which are genetically engineered to produce those (specific) antigens. That process (i.e., genetically engineering plants to cause them to produce specific antigens) can be utilized to produce edible vaccines for the pathogenic bacteria possessing those antigens. Then people could be “vaccinated” against disease merely by eating the genetically engineered plant (e.g., banana). See also ANTIGEN, PATHO-

GENIC, BACTERIA, VACCINE, GENETIC ENGINEER-

ING, EDIBLE VACCINES.

Plaque Refers to deposits of (oxidized) cholesterol intermixed with smooth-muscle cells, lining the inside of certain blood vessels. These deposits can result in the disease atherosclerosis, and/or adversely increasing blood platelet aggregation (e.g., clotting).

See also VITAMIN E, ATHEROSCLEROSIS, CHOLESTEROL, EPITHELIUM.

Plasma A pale, amber-colored fluid constituting the fluid portion of the blood in which are suspended the cellular elements. Plasma contains 8–9% solids. Of these, 85% are proteins consisting of three major groups, which are: fibrinogen, albumin, and globulin. The other components are the lipids, which include the neutral fats, fatty acids, lecithin, and cholesterol. Also present are sodium, chloride and bicarbonate, potassium, calcium, lycopene, and magnesium. A most essential function of plasma is the maintenance of blood pressure and the exchange (with tissues) of nutrients for waste. See also

ABSORPTION, HOMEOSTASIS, LYCOPENE.

Plasma Membrane A thin structure that completely surrounds the cell as a “skin.” It may be seen with the aid of an electron microscope. The entire membrane appears to be about 100 Angstroms (Å; 0.1 mm) thick and is composed of two dark lines, each about 30 Å thick which are, however, separated by a lighter area. This trilaminar “sandwich” structure is referred to as the unit membrane. The plasma membrane is composed of lipoidal (fat-like) material in which proteins and protein complexes and whole functional systems are embedded. In the plasma membrane are incorporated such energy-dependent transport systems as Na+ and K+ transporting ATPase and amino acid transport systems. Besides the cell, membranes surround such systems as the endoplasmic reticulum, vacuoles, lysosomes, Golgi bodies, mitochondria, chloroplasts, and the nucleus, to mention just a few. The plasma membrane and membranes in general function in part as a permeability barrier to the free movement of substances between the inside and exterior of the cell or organelles that they surround.

See also CELL, PROTEIN, CECROPHINS (LYTIC PROTEINS), MAGAININS, MEMBRANES (OF A CELL),

TRANSMEMBRANE PROTEINS, RECEPTORS, LIPIDS,

MEMBRANE TRANSPORT.

Plasmid An independent, stable, self-replicat- ing piece of DNA in bacterial cells that is not part of the normal cell genome and that never becomes integrated into the host chromosome. This is in contrast to a similar genetic element known as an episome plasmid that may exist independently of the chromosome or may become integrated into the host chromosome. Plasmids are known to confer resistance to antibiotics and may be transferred by cell-to-cell contact (by conjugation via the sex pilus) or by viralmediated transduction. Plasmids are commonly used in recombinant DNA experiments as acceptors of foreign DNA. Known forms of plasmids include both linear and circular molecules. See also EPISOME, VECTOR,

COPY NUMBER, MULTI-COPY PLASMIDS, DEOXY-

RIBONUCLEIC ACID (DNA), CELL, GENOME,

CHROMOSOME, ANTIBIOTIC, Ti PLASMID.

Plasmocyte Another name for a blast cell. See

also BLAST CELL.

	Plastid An independent, stable, self-replicat-
	ing piece of DNA inside a plant cell that is
	not part of the reproduction cell genome
	(i.e., in nucleus). Because there can exist up
	to 10,000 plastids in a given plant cell, the
	insertion of a gene (e.g., via genetic engi-
	neering) into plastids can result in a higher
	yield (of the specific protein coded for by
	that gene) than is achieved via insertion of
	the gene into the cell’s nuclear DNA. See
	also DEOXYRIBONUCLEIC ACID (DNA), CELL,
	NUCLEAR DNA, COPY NUMBER, GENOME, PRO-
	MOTER, GENE, GENETIC ENGINEERING, FATS,
	CHLOROPLASTS.
	Platelet Activating Factor (PAF) See CHOLINE.
	Platelet-Derived Growth Factor (PDGF)
	An angiogenic growth factor produced by
	the blood’s platelet cells which attracts the
	growth of capillaries into the vicinity of a
	fresh wound. This action releases still other
	growth factors, and starts the process of
	building a fibrin network to support the sub-
	sequent (blood) clot. PDGF is a competence
	factor (i.e., a growth factor that is required
	to make a cell able or competent to react to
	other growth factors). PDGF is normally
	contained within the platelet cells, so does
	not circulate in the blood in a form enabling
	it to be freely available to its “target cells.”
	This “containment” of PDGF in platelets
		P
	ensures site-specific delivery of the PDGF
	directly to a wound site so stimulus (i.e., of
	capillary growth) is localized to the actual
	wound site. After PDGF has caused the for-
	mation of the initial clot at a wound site,
	PDGF attracts connective tissue cells into
	the vicinity of the wound (to start the tissue-
	repair process). PDGF also acts as a mitogen
	(substance causing cell to divide and thus
	multiply) for connective tissue cells, granu-
	locytes, and monocytes (each of which is
	involved in the wound’s healing process).
	See also ANGIOGENIC GROWTH FACTORS, FIBRIN,
	FIBRONECTIN, PLATELETS, MITOGEN, GRANULO-
	CYTES, MONOCYTES, CYCLOOXYGENASE.
	Platelet-Derived Wound Growth Factor
	(PDWGF) See PLATELET-DERIVED GROWTH
	FACTOR (PDGF).
	Platelet-Derived Wound Healing Factor
	(PDWHF) See PLATELET-DERIVED GROWTH
	FACTOR (PDGF).

© 2002 by CRC Press LLC

(SNPs),

POINTS

(BESS),

MUTATION,

Platelets Disk-shaped blood cells that stick to the (microscopically “jagged”) edges of wounds. The aggregation of platelets at the wound site leads to blood clotting, forming a temporary wound covering. During this blood clotting process, the platelets release platelet-derived growth factor (PDGF) which attracts fibroblasts to the wound area (for subsequent healing process). See also

FIBRIN, FIBRONECTIN, PLATELET-DERIVED GROWTH

FACTOR (PDGF), FIBROBLASTS, CYCLOOXYGENASE,

CHOLINE, OXIDATIVE STRESS.

Pleiotropic Adjective used to describe a gene that affects more than one trait (apparently unrelated) characteristic of the phenotype (appearance of an organism). For example, biologist David Ho in 1993 discovered a single gene in the barley (Hordeum vulgare) plant that controls the traits of the plant’s height, drought resistance, strength, and time to maturity. See also GENE, GENETIC CODE,

DEOXYRIBONUCLEIC ACID (DNA), INFORMATIONAL

MOLECULES, PHENOTYPE.

Pluripotent Stem Cells Refers to those stem cells from which each of the human body’s 210 different types of tissues could arise. See

also STEM CELLS, STEM CELL GROWTH FACTOR

(SCF), DIFFERENTIATION, HUMAN EMBRYONIC

STEM CELLS.

PPNT See PLANT’S NOVEL TRAIT (PNT).

Point Mutation A mutation consisting of a change of only one nucleotide in a DNA molecule. At “hot spots” (i.e., certain locations on the DNA within some organisms), numerous point mutations can occur. In the case of single-nucleotide polymorphisms (SNPs), the same point mutation occurs at the same location (on the DNA within some organisms) across a population of individu-

als of that organism. See also

HEREDITY, MUTANT, MUTAGEN, DEOXYRIBO-

NUCLEIC ACID (DNA), NUCLEOTIDE, HOT SPOTS,

BASE EXCISION SEQUENCE SCANNING

ORGANISM, SITE-DIRECTED MUTAGENESIS (SDM),

SINGLE-NUCLEOTIDE POLYMORPHISMS

TRADITIONAL BREEDING METHODS.

“Points to Consider” Document See

TO CONSIDER IN THE MANUFACTURE AND TESTING

OF MONOCLONAL ANTIBODY PRODUCTS FOR

HUMAN USE.

Points to Consider in the Manufacture and Testing of Monoclonal Antibody Products for Human Use The U.S. Food and Drug Administration’s (FDA’s) governing rules for IND (investigational new drug) submission for monoclonal antibody (MAb)-based pharmaceuticals. See also IND.

Polar Group A hydrophilic (“water loving”) portion of a molecule; it may carry an electrical charge. A group that “likes” to be in the presence of water molecules or other polar compounds. See also NONPOLAR GROUP,

P O L A R I T Y (C H E M I C A L ), P O L A R M O L E C U L E

(DIPOLE), AMPHIPATHIC MOLECULES, AMPHOTERIC

COMPOUND, LIPID BILAYER.

Polar Molecule (dipole) A molecule in which the centers of positive and negative (electrical) charge do not coincide, so that one end of the molecule carries a positive (or partial positive) charge and the other end a negative (or partial negative) charge. See also POLAR-

ITY (CHEMICAL), POLAR GROUP, ION-EXCHANGE

CHROMATOGRAPHY, NONPOLAR GROUP.

Polar Mutation A mutation in one gene which, because transcription occurs only in one direction, reduces the expression of subsequent genes in the same transcription unit further down the line. See also TRANSCRIP-

TION, TRANSLATION, EXPRESS, NUCLEIC ACIDS.

Polarimeter An instrument used for measuring the degree of rotation of plane-polarized light by an optically active compound/solu-

tion. See also STEREOISOMERS, OPTICAL ACTIVITY, LEVOROTARY (L) ISOMER, DEXTROROTARY

(D) ISOMER.

Polarity (chemical) The degree to which an atom or molecule bears an electrical charge or a partial electrical charge. In general, the more polar (i.e., separation or partial separation of charge) a molecule is, the more hydrophilic (“water loving”) it is. Polarity results from an uneven distribution of electrons between the atoms comprising a mol-

ecule. See also POLAR GROUP, HYDROPHILIC,

POLAR MOLECULE (DIPOLE).

Polarity (genetic) Having to do with the one way or unidirectionality of gene transcription in an operon unit. That is, the region near the operator is always transcribed before the more distant regions. By analogy, transcription begins at the left end of an

© 2002 by CRC Press LLC

(2D)

(MAb),

operon unit and proceeds (reads, transcribes) toward the right end of the operon unit. The distinction between the 5′ and the 3′ ends of nucleic acids. See also POLAR MUTATION,

TRANSCRIPTION.

Polyacrylamide Gel A “sieving” gel, that is used in electrophoresis. See also POLYACRY-

LAMIDE GEL ELECTROPHORESIS (PAGE).

Polyacrylamide Gel Electrophoreis (PAGE)

A form of chromatography in which molecules are separated on the basis of size and charge. The stationary phase (the polyacrylamide gel) is a polymerized version of acrylamide monomers. The gel looks and feels like Jello™. On a molecular basis it consists of an intertwined and cross-linked mesh of polyacrylamide strings. As can be imagined, there are tiny “holes” in the gel (as in a plastic mesh bag) and with enough cross-linking the size of the holes begins to approach the size of the molecules that are to be separated. Since some molecules will be larger and some smaller, some of them will be able to pass through the gel matrix more easily than others. This is part of the basis for separation. It should be noted at this point that if the gel is cross-linked enough, and because of this the holes in that gel are smaller than the molecules to be separated, then the molecules will not be able to penetrate into the gel and no separation can occur. The charge on the molecule also plays a role in the separation. Functionally, the gel serves to hold and separate the molecules. Although details are not presented here, after the gel has been prepared (poured and cross-linked), a small amount of the solution containing the molecules to be separated is placed into wells (grooves to hold the liquid) on the gel and the system is subjected to an electric current. Over the course of minutes to hours, molecules bearing different charge/mass separate.

See also BIOLUMINESCENCE, CHROMATOGRAPHY,

TWO-DIMENSIONAL GEL ELECTROPHORESIS,

FIELD INVERSION GEL ELECTROPHORESIS (FIGE),

ELECTROPHORESIS.

Polyadenylation The addition of a sequence of polyadenylic acid to the 3′ end of a eucaryotic mRNA after its transcription (post-transcriptional). See also MESSENGER

RNA (mRNA), TRANSCRIPTION.

© 2002 by CRC Press LLC

Polycistronic Coding regions representing more than one gene in mRNA (i.e., they code for two or more polypeptide chains). Many mRNA molecules in procaryotes are poly-

cistronic. See also RIBOSOMES, PROCARYOTES.

Polyclonal Antibodies (used in humans) A mixture of antibody molecules (that are specific for a given antigen) that has been purified from an immunized (to that given antigen) animal’s blood. Such antibodies are polyclonal in that they are the products of many different populations of antibody-pro- ducing cells (within the animal’s body). Hence they differ somewhat in their precise specificity and affinity for the antigen.

Years ago, antibodies (then called antitoxin) that were purified from an immunized animal’s blood (e.g., a horse) were injected into humans suffering from certain diseases (e.g., diphtheria). In these cases the pathogen had caused disease by secreting large amounts of toxin into the victim’s bloodstream. The antitoxin combined quantitatively (1:1, 2:1, 1:2, 1:3, 3:1, etc.) with, and neutralized, the toxin (for those few diseases for which it was applicable). Vaccines are now used instead, because of the adverse immune response caused by the horse’s blood (antigens). See also ANTIBODY, PASSIVE

IMMUNITY, MONOCLONAL ANTIBODIES

	ANTIGEN, PATHOGEN, TOXIN.	P
	Polyclonal Response (of immune system to a
	given pathogen) Because a given pathogen
	generally has several antigenic sites on its
	surface, the B lymphocytes (activated by
	helper T cells in response to a pathogen invad-
	ing the body) synthesize several (subtly dif-
	ferent) antibodies against that pathogen. And
	since the antibodies are made by different
	cells, the response is known as poly (many)
	clonal. See also PATHOGEN, ANTIGEN, ANTIBODY,
	HAPTEN, EPITOPE, HELPER T CELLS (T4 CELLS),
	LYMPHOCYTE, B LYMPHOCYTES, LYMPHOKINES.
	Polyethylene-Glycol Superoxide Dismutase
	(PEG-SOD) See PEG-SOD (POLYETHYLENE
	GLYCOL SUPEROXIDE DISMUTASE), HUMAN SUPER-
	OXIDE DISMUTASE (hSOD).

Polygalacturonase (PG) An enzyme (e.g., present in tomatoes) that starts the breakdown (softening) of the fruit tissue. Recent advances make it possible to significantly