See also GENE, TRANSCRIPT, MESSENGER RNA

(mRNA), CODING SEQUENCE, TRANSLATION, CODON,

PROTEIN, GENOME, GENETIC CODE, CENTRAL

DOGMA (NEW), ORGANISM, CONFORMATION,

METABOLISM, TERTIARY STRUCTURE, INTRON,

BASE.

Transduction (gene) The transfer of bacterial genes (DNA) from one bacterium to another by means of a (temperature or defective) bacterial virus (bacteriophage). There exist two kinds of transduction: specialized and general. In the case of specialized transduction, a restricted group of host genes becomes integrated into the virus genome. These “guest” genes usually replace some of the virus genes and are subsequently transferred to a second bacterium. In the case of generalized transduction, host genes become part of the mature virus particle in place of, or in addition to, the virus DNA. However, in this case the genes can come from virtually any portion of the host genome and this material does not become directly integrated into the virus genome. In the case of plants, the vector can be Agrobacterium tumefaciens. See

also BACTERIOPHAGE, VECTOR, GENETIC CODE,

AGROBACTERIUM TUMEFACIENS, RETROVIRAL VEC-

TORS, GENE DELIVERY, TRANSFECTION.

Transduction (signal) See SIGNAL TRANSDUCTION.

Transfection This term has several different meanings, depending on the context in which it is used: A word utilized generally to refer to insertion of DNA segments (genes) into cells (via electroporation, endocytosis, etc.); a special case of transformation in which an appropriate recipient strain of bacteria is exposed to (free) DNA isolated from a transducing phage with the

T“take up” of that DNA by some of the bacteria and consequent production and release of complete virus particles. The process involves the direct transfer of genetic material from donor to recipient. See also MARKER

(GENETIC MARKER), TRANSFORMATION, ELEC-

TROPORATION, GENE, VIRUS, CELL, BACTERIA,

DEOXYRIBONUCLEIC ACID (DNA), TRANSDUCTION

(gene).

Transfer RNA (tRNA) A class of relatively small RNA (ribonucleic acid) molecules of molecular weight 23,000 to about 30,000. tRNA molecules act as carriers of specific

amino acids during the process of protein synthesis. Each of the 20 amino acids found in proteins has at least one specific corresponding tRNA. The tRNA binds covalently with its specific amino acid and “leads” it to the ribosome for incorporation into the growing peptide chain. See also RIBONUCLEIC

ACID (RNA), MOLECULAR WEIGHT, AMINO ACID,

MESSENGER RNA (mRNA).

Transferases Enzymes that catalyze the transfer of functional groups to molecules (from other molecules). See also TRANSAMINASE, ENZYME,

HEDGEHOG PROTEINS, GLYCOSYLTRANSFERASES.

Transferred DNA See Ti PLASMID.

Transferrin The protein molecule responsible for transporting iron (molecules) to tissues throughout the body, via the circulatory sys-

tem. See also PROTEIN, TRANSFERRIN RECEPTOR,

HEME, BLOOD-BRAIN BARRIER (BBB).

Transferrin Receptor The receptor molecule (located on the surface of cells throughout the body) responsible for binding to transferrin molecules, then bringing those ironrich transferrin molecules into the cell where the iron is released to be used by the cell.

See also TRANSFERRIN, RECEPTORS, HEME,

BLOOD-BRAIN BARRIER (BBB).

Transformation The process in which free DNA is transferred directly into a competent recipient cell. The direct transfer of genetic material from donor to recipient. The acquisition (e.g., by bacteria cells) of new genetic markers (new traits coded for by the new DNA) via the process of transformation. See

also DEOXYRIBONUCLEIC ACID (DNA), TRANSFEC-

TION, MARKER (GENETIC MARKER).

Transforming Growth Factor-Alpha (TGFalpha) An angiogenic growth factor produced by tumor cells. It is able to induce specific malignant characteristics in normal cells (such as fibroblasts), thereby “transforming” those cells. TGF-alpha appears to possess a variety of potentially useful pharmaceutical properties, such as powerful stimulation of scar tissue formation following wounding of a tissue, as indicated by preliminary research. See also TRANSFORMING

GROWTH FACTOR-BETA (TGF-BETA), GROWTH

FACTOR, NERVE GROWTH FACTOR (NGF), TUMOR,

FIBROBLASTS, ANGIOGENIC GROWTH FACTORS.

Transforming Growth Factor-Beta (TGFbeta) An angiogenic growth factor produced by tumor cells, it is able to induce specific malignant characteristics in normal cells (such as fibroblasts), thereby “transforming” those cells. TGF-beta stimulates blood vessel growth, even though it inhibits the division of endothelial cells. TGF-beta is a strong “attracting agent” for macrophages (i.e., TGF-beta is chemotactic), and appears to be responsible for the high concentrations of macrophages often found in tumors. TGFbeta has shown immunosuppressive activity (i.e., it suppresses the immune system). For example, transforming growth factor-beta works together with osteoinductive factor (OIF) to promote bone-formation by first causing connective tissue cells to grow together to form a matrix of cartilage (e.g., across a bone break); bone cells slowly replace that cartilage. See also TRANSFORMING

GROWTH FACTOR-ALPHA (TGF-ALPHA), GROWTH

FACTOR, OSTEOINDUCTIVE FACTOR (OIF), IMMUN-

OSUPPRESSIVE, NERVE GROWTH FACTOR (NGF),

TUMOR, FIBROBLASTS, ANGIOGENIC GROWTH FACTORS, MITOGEN, ENDOTHELIAL CELLS, CHEMOTAXIS, MACROPHAGE.

Transgalacto-oligosaccharides A “family” of oligosaccharides (produced via enzymatic conversion of lactose, using β-glucosidase enzyme); some of which help to foster the growth of beneficial bifidobacteria in the lower colon of monogastric animals (humans, swine, etc.). See also OLIGOSACCHA-

RIDES, PREBIOTICS, BACTERIA, BIFIDOBACTERIA,

BIFIDUS, ENZYME.

Transgene A “package” of genetic material (i.e., DNA) that is inserted into the genome of a cell via gene splicing techniques. May include promoter(s), leader sequence, termination codon, etc. See also

NUCLEIC ACID (DNA), GENE SPLICING, GENOME,

LEADER SEQUENCE, PROMOTER, GENETIC CODE,

TERMINATION CODON (SEQUENCE), GENETIC ENGI-

NEERING, CASSETTE.

Transgenic An organism whose gamete cells (sperm/egg) contain genetic material originally derived from an organism other than the parents, or in addition to the parental genetic material. See also GENETIC ENGINEER-

ING, GAMETE, NUCLEAR TRANSFER.

Transgressive Segregation A plant breeding (propagation) technique, in which genetically very different members of the same species are mated with each other. The offspring of that mating can be more healthy, productive (e.g., fast growing), and uniform than their parents, a phenomenon known as “hybrid vigor.” See also GENETICS, SPECIES, F1

HYBRIDS, HYBRIDIZATION (PLANT GENETICS).

Transit Peptide A peptide that, when fused to a protein, acts to transport that protein between compartments within eucaryotic cells. Once inside the “destination compartment,” the transit peptide is cleaved off the protein and that protein is then free (to do its designed task). See also PEPTIDE, PROTEIN,

EUCARYOTE, CELL, FUSION PROTEIN, GATED

TRANSPORT, VESICULAR TRANSPORT, CHLOROPLAST

TRANSIT PEPTIDE (CTP).

Transition Refers to the replacement (i.e., in DNA or RNA molecule) of one purine by another purine; or one pyrimidine by another pyrimidine. See also PURINE, PYRIMIDINE,

DEOXYRIBONUNCLEIC ACID (DNA), RIBONUCLEIC

ACID (RNA), BASE SUBSTITUTION.

Transition State (in a chemical reaction) That point in the chemical reaction at which the reactants (i.e., chemical entities about to react with each other) have been “brought to the brink.” It is a point in the chemical reaction process in which an “activated condition” is reached. From this point the probability of the reaction going to completion and producing a product is very high. The transition state separates (energetically) products from reactants. It is viewed as being at the top of the energy barrier separating reactants and products. The reacting species

in the transition state can, because of their T location at the “top” of the energy barrier,

“fall” to either products or reactants. See also

CATALYST, ENDERGONIC REACTION, ACTIVATION

ENERGY, FREE ENERGY, CATALYTIC ANTIBODY,

SEMISYNTHETIC CATALYTIC ANTIBODY, EXERGONIC

REACTION.

Translation The process whereby the genetic information present in an mRNA molecule directs the order of incorporation of specific amino acids, and hence the growth of the polypeptide chain during protein synthesis. One can think of translation as the process

of translating one language into another. In this particular case the nucleic acid-based language represented by mRNA is translated into the amino acid-based language of pro-

teins. See also CODING SEQUENCE, CODON, RIBOSOMES, MESSENGER RNA (mRNA), PROTEIN, GENE,

GENETIC CODE.

Translocation Genetic mutation in which a section of a chromosome “breaks off” and moves to a new (abnormal) position in that (or a different) chromosome. See also GENE,

C H R O M O S O M E S , G E N E T I C C O D E , C O D I N G SEQUENCE, TRANSPOSITION, DEOXYRIBONUCLEIC

ACID (DNA), MUTATION, INTROGRESSION, JUMPING

GENES, HOT SPOTS.

Transmembrane Proteins Refers to those protein molecules that extend from one side of a cell membrane to the other side of that membrane. For example, G-proteins are transmembrane proteins that act to accomplish signal transduction (i.e., convey “signal” from outside the cell to one or more internal cell parts). EGF receptors bind to EGF molecules (e.g., passing-by in the blood), then both enter the cell (through the cell membrane) together, where the EGF stimulates growth/division of that cell. See

also PROTEIN, CELL, PLASMA MEMBRANE, RECEP-

TORS, MEMBRANE (OF A CELL), MEMBRANE

TRANSPORT, ABC TRANSPORTERS, EGF RECEPTOR,

G-PROTEINS, CECROPHINS (LYTIC PROTEINS),

MAGAININS, SIGNAL TRANSDUCTION, SIGNALING,

EPIDERMAL GROWTH FACTOR (EGF).

Transposable Element See TRANSPOSON.

Transposase An enzyme required for transposition to occur. It is coded for by the transposon known as the P element. See also

TRANSPOSITION, TRANSPOSON, ENZYME, GENETIC

TCODE, CODING SEQUENCE.

Transposition Movement of a gene or set of genes from one site in the genome to another without a reciprocal exchange (of DNA).

See also GENE, JUMPING GENES, GENOME,

TRANSPOSON, TRANSPOSASE, HOT SPOTS, DEOXY-

RIBONUCLEIC ACID (DNA).

Transposon A DNA (deoxyribonucleic acid) sequence (segment of molecule) able to replicate and insert one copy (of itself ) at a new location in the genome (i.e., a transposition of location). Discovered in 1950 by geneticist Barbara McClintock in corn (maize)

plants (Zea mays L.); and in bacteria a decade later by Joshua Lederberg.

Transposons can either carry genes along one organism’s genome, or even into another organism’s genome (e.g., via sexual conjugation, in bacteria). By such sexual conjugation, transposons can carry genes that confer new phenotypic properties (e.g., resistance to certain antibiotics, for a given bacterial cell). See also DEOXYRIBONUCLEIC

ACID (DNA), REPLICATION (OF VIRUS), GENOME,

TRANSPOSITION, TRANSPOSASE, SEQUENCE (OF A

DNA MOLECULE), CORN, JUMPING GENES, GENE,

SEXUAL CONJUGATION, PHENOTYPE, CONJUGATION.

Transversion The substitution of a purine for a pyramidine, or of a pyramidine for a purine (at a specific site, within a given nucleotide in a molecule of DNA). See also NUCLEOTIDE,

DEOXYRIBONUCLEIC ACID (DNA), SINGLE-NUCLEO-

TIDE POLYMORPHISMS (SNPs), MUTATION, BASE

SUBSTITUTION.

TRANSWITCH® A “sense” technology used to “turn off “ (suppress) a gene (e.g., the one that causes tomato to ripen) that causes an unwanted effect (e.g., premature softening of tomato). TRANSWITCH® and its registered trademark are owned by DNA Plant Technology Corp. See also GENE SILENCING,

SUPPRESSOR GENE, SENSE.

“Treatment” IND Regulations Food and Drug Administration (FDA) regulations promulgated in 1987, to provide a more rapid formal pharmaceutical approval mechanism than the usual IND (Investigational New Drug) regulatory approval process. Its purpose is to enable drug developers to provide promising experimental drugs to patients suffering from immediately life-threatening diseases or certain serious conditions (e.g., acquired immune deficiency syndrome, or AIDS) before complete data on that drug’s efficacy or toxicity are available. See also

IND, FOOD AND DRUG ADMINISTRATION (FDA),

DELANEY CLAUSE, KOSEISHO, COMMITTEE FOR

PROPRIETARY MEDICINAL PRODUCTS (CPMP).

Treatment Investigational New Drug See

“TREATMENT” IND REGULATIONS.

Trehalose A disaccharide (simple sugar) that is naturally synthesized (manufactured) by many plants and animals in response to the stresses of freezing, heating, or drying. That

is because trehalose protects certain proteins (needed for life) and prevents loss of crucial volatile (i.e., easily evaporated) compounds from organisms during those stressful (dry, frozen, or hot) conditions. Trehalose also provides a source of quick energy after the stressful conditions have passed. That is why dried baker’s yeast (which contains up to 20% trehalose by weight) can be stored in its dry state for many years, yet quickly leavens bread dough within minutes of being rehydrated (i.e., rewetted).

Trehalose accomplishes this protection by forming a nonhygroscopic “glass” on the surfaces of cells and large molecules. It immobilizes and stabilizes large molecules (e.g., proteins), but still allows water to diffuse out so complete drying can occur. Thus, trehalose holds potential as a food additive to keep proteins (e.g., eggs) fresh in the dried form. In 1991, the U.K. approved trehalose for use in food, and the U.S. approved its use in 2001. Trehalose hydrolyzes (e.g., during digestion) into two molecules of glucose.

See also DISACCHARIDES, PROTEIN, GLUCOSE

(GLc), HYDROLYSIS, CONFORMATION, “SWITCH”

PROTEINS, TERTIARY STRUCTURE, PROTEIN FOLD-

ING.

Tremorgenic Indole Alkaloids A “family” of toxic alkaloids (chemical compounds) that are naturally produced (within some plants) by certain fungi (which sometimes grow in those plants). For example, the alkaloid known as Penitrem D is produced by certain fungi which grow in some grass species. It causes tremors, weakness, lack of coordination, and convulsions in animals that consume those fungus-infested grasses. See also

ALKALOIDS, TOXIN, FUNGUS, ENDOPHYTE.

Triacylglycerols See TRIGLYCERIDES.

Trichoderma harzianum A microorganism that possesses (natural) fungicide activity.

See also BACILLUS THURINGIENSIS (B.t.), WHEAT

TAKE-ALL DISEASE, FUNGUS, FUNGICIDE.

Trichosanthin An enzyme extracted from a specific Chinese plant. It has been discovered to “cut apart” the ribosomes in some cells infected with the HIV (i.e., AIDS) virus, thus potentially stopping the virus and preventing infection of additional cells. See

also RIBOSOMES, ACQUIRED IMMUNE DEFICIENCY

SYNDROME (AIDS), ENZYME, PROTEIN, HUMAN

IMMUNODEFICIENCY VIRUS TYPE 1 (HIV- 1), HUMAN

IMMUNODEFICIENCY VIRUS TYPE 2 (HIV- 2).

Triglycerides The primary constituent of fats or oils; triglycerides are molecules that consist of three fatty acids attached to a glycerol “molecular backbone.” More accurately called triacylglycerols, although long-term historical usage of “triglycerides” has made the latter term more common. Similarly, the term “diglyceride” is often used to refer to those molecules which consist of two fatty acids attached to a glycerol “molecular backbone.” “Diglycerides” (more accurately called diacylglycerols) can result from the splitting-off (i.e., hydrolysis) of one fatty acid from a triacylglycerol (“triglyceride”) molecule (e.g., during fat breakdown/oxidation); or from the combination of two fatty acids with glycerol (e.g., during synthesis of fats). The “triglyceride level” in human bloodstream refers to the blood’s content of noncholesterol total fats. Research during the 1990s provided evidence that high blood levels of triglycerides in humans (e.g., immediately after meals) contribute to thrombosis.

See also FATS, THROMBOSIS, FATTY ACID, SATURATED FATTY ACIDS (SAFA), LPAAT PROTEIN,

UNSATURATED FATTY ACID, HYDROLYSIS, OXIDA-

TION (of fats/oils/lipids), ADIPOCYTES, FRUCTOSE

OLIGOSACCHARIDES, BIFIDUS, POLYUNSATURATED

FATTY ACIDS (PUFA), DIACYLGLYCEROLS.

Triploid Refers to organisms that possess three sets of chromosomes, instead of the normal two sets. Conversion of a diploid (i.e., two sets of chromosomes) organism to triploid can be done by man (certain fish, “seedless” grapes, etc.). For example, fish are ordinarily

diploid. By exposing fish eggs to certain spe- T cific combinations of temperature and pres-

sure, immediately after fertilization of those eggs, scientists can cause the resultant fish to become triploid. Triploid fish are unable to reproduce. This sterility is desired by man, in order to prevent certain fish (e.g., those that have been genetically engineered) from mating with wild fish. Such induced (triploid) sterility also prevents the (genetically engineered) fish from wasting energy on the act of reproduction, so they grow faster and larger. That transfer (of energy use from