POLYPEPTIDE

INFORMATIONAL

SPECIES,

dish environment which contains the nutrients necessary for cell growth. One use of tissue culture is to produce disease free offspring from certain (valuable, high quality) crop plants. Another use of tissue culture methods is for “embryo rescue” to enable “wide crosses” between two different species of plants. In that procedure, pollen from one plant species (e.g., a wild plant possessing disease resistance) is induced to fertilize a plant from another species (e.g., a domesticated crop). The resultant fertilized plant embryo, which would not grow on its own, is “rescued” via tissue culture methods. Following maturation, that wide cross (i.e., a hybrid plant from two species that normally would not cross) produces fertile seeds on its own without any need for further intervention by man. See also CELL, ORGANISM,

CULTURE MEDIUM, HYBRIDIZATION

(PLANT GENETICS).

Tissue Plasminogen Activator (tPA) A glycoprotein that possesses thrombolytic (i.e., blood clot-dissolving) activity. It is used as a drug to dissolve clots and acts by first binding to fibrin (clots). It then activates (i.e., proteolytically cleaves) plasminogen (molecules) to yield plasmin, a bloodborne enzyme that itself cleaves molecular bonds in the fibrin clot. The plasmin molecules diffuse through the fibrin clot and cause the clot to dissolve rapidly. With the dissolution of the clot, blood flow to the formerly blocked blood vessel (e.g., the heart) is restored. See

also THROMBUS, THROMBIN, THROMBOLYTIC

AGENTS, GLYCOPROTEIN, FIBRIN, FIBRINOLYTIC

AGENTS.

TKI See TYROSINE KINASE INHIBITORS.

TTME (N) Abbreviation for “true metaboliz-

able energy (corrected for nitrogen)”; a measure of the amount of energy that a given animal (e.g., chicken) can extract from a given feed ration. See also METABOLISM,

CHEMOMETRICS, CALORIE.

TMEn See TME (N).

Tobacco Budworm See HELIOTHIS VIRESCENS

(H. VIRESCENS).

Tobacco Hornworm Caterpillars (pupae) of the Lepidopteran insect Manduca sexta. Tobacco Hornworm is susceptible to Cry1A(b) protein (e.g., they are killed if they

eat plants genetically engineered to contain Cry1A(b) protein). See also CRY1A(b) PROTEIN.

Tobacco Mosaic Virus (TMV) O n e t h e o f smallest viruses, consisting of some 2,200 chains of identical polypeptides and a molecule of RNA. All of the genetic/heredity information of the Tobacco Mosaic Virus is contained in its RNA. The first discovery of a self-assembling, active biological structure occurred in 1955, when Heinz Frankel-Con- rat and Robley Williams showed that TMV will reassemble into functioning, infectious virus particles (after the TMV has been dissociated into its components via immersion in concentrated acetic acid). The TMV virus infects the leaves of tomato and tobacco plants, causing disease. Tobacco plants can be genetically engineered to resist TMV infection. A tomato plant, genetically engineered to resist TMV infection, has been commercially available since 1992. See also

GENETIC ENGINEERING, CAPSID, VIRUS, RNA,

(PROTEIN), GENE,

MOLECULES, HEREDITY, SELF-ASSEMBLY (OF A

LARGE MOLECULAR STRUCTURE).

Tocopherols A “family” of different molecular forms of vitamin E; each of which has a saturated phytyl “tail” attached (to the “backbone” of the molecule). Commercial tocopherols are extracted from soybeans, although some are also naturally present in canola and sunflower. See also VITAMIN, SOY-

BEAN PLANT, VITAMIN E.

Tocotrienols A “family” of different molecular forms of vitamin E; each of which has an unsaturated isoprenoid “side chain” attached (to the “backbone” of the molecule). Tocotrienols are naturally present in cereal grains (e.g., oats, barley, rye, and rice

bran). See also VITAMIN, ISOPRENE, VITAMIN E.

Tomato A green bushy plant, botanical name

Lycopersicon esculentum. The wild type is native to South America, but the (domesticated) tomato is grown worldwide today. Its fruit, known as tomatoes, are a natural source of the antioxidant carotenoid lycopene, a phytochemical whose consumption has been linked to a reduction in coronary heart disease and some cancers (e.g., prostate

cancer). See also LYCOPENE, PHYTOCHEMICALS,

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ANTIOXIDANTS, CANCER, CAROTENOIDS, CORONARY

HEART DISEASE (CHD), WILD TYPE.

Tomato Fruitworm See the link. See also

HELICOVERPA ZEA (H. ZEA).

Topotaxis See TROPISM.

TOS See TRANSGALACTO-OLIGOSACCHARIDES.

Totipotency The ability to grow/differentiate into all of the types of cells/tissues constituting an (adult) organism’s body. See also STEM

CELL ONE, CELL, ZYGOTE, CELL-DIFFERENTIATION,

CELL-DIFFERENTIATION PROTEINS, TOTIPOTENT

STEM CELLS.

Totipotent Stem Cells Bone marrow cells that (when signaled) mature into both red blood cells and white blood cells. Receptors on the surface of totipotent stem cells “grasp” passing blood cell growth factors (e.g., Interleu- kin-7, Stem Cell Growth Factor, etc.), bringing them inside these stem cells and thus causing the maturation and differentiation into red and white blood cells. These receptors are called FLK-Z receptors. See

also STEM CELL ONE, STEM CELLS, WHITE BLOOD

CELLS, GROWTH FACTOR, RECEPTORS, CELL-DIF-

FERENTIATION PROTEINS, CELL DIFFERENTIATION,

CELL.

Toxic Substances Control Act (TSCA) A 1976 American federal law under which the U.S. Environmental Protection Agency (EPA) has regulated the release of genetically engineered organisms (e.g., bacteria or plants) that produce natural insecticides. This is based on legal analogy to synthetic chemical insecticides, which are clearly regulated under TSCA. See also OAB (OFFICE OF

AGRICULTURAL BIOTECHNOLOGY), FEDERAL

INSECTICIDE FUNGICIDE AND RODENTICIDE ACT

(FIFRA), GENETICALLY ENGINEERED MICROBIAL

PESTICIDES (GEMP), WHEAT TAKE-ALL DISEASE,

BACILLUS THURINGIENSIS (B.t.).

Toxicogenomics A branch of toxicology that deals with the reactions between toxins and the specific differences in response of different organisms due to their different genomes/DNA (of the different individuals that consume the same toxin). For example, some rare humans can tolerate eating certain poisonous mushrooms (which sicken or kill all other humans that consume those particular mushroom species).

During 2001, Fred Gould, David Heckel, and Linda Gahan showed that a rare, recessive gene (allele) known as BtR-4 could confer (to tobacco budworms possessing two copies of that particular gene) resistance to at least some of the “cry” proteins (which kill all other tobacco budworms that consume those “cry proteins”). The subgroup of all those individuals whose DNA (genome) causes their bodies to resist the effects of a given toxin, is known as a haplotype. A haplotype could (theoretically) be as small as one individual, because the particular resis- tance-to-toxin could result from one singlenucleotide polymorphism (SNP). See also

GENE, GENOMICS, PHARMACOGENOMICS, TOXIN,

GENOME, DEOXYRIBONUCLEIC ACID (DNA), HAP-

LOTYPE, SINGLE-NUCLEOTIDE POLYMORPHISMS

(SNPs), RECESSIVE ALLELE, CRY PROTEINS,

TOBACCO BUDWORM.

Toxigenic E. coli See E N T E R O H E M O R R H A G I C

E. COLI, ESCHERICHIA COLIFORM 0157:H7 (E. COLI

0157:H7).

Toxin A substance (e.g., produced in some cases by fungi, weeds, ants, or disease-caus- ing microorganisms) which is poisonous to certain other living organisms. See also ANTI-

TOXIN, ABRIN, RICIN, COLICINS, BACTERIOCINS,

ESCHERICHIA COLIFORM 0157:H7 (E. COLI 0157:H7),

ENTEROHEMORRHAGIC E. COLI, PFIESTERIA PISCI-

CIDA, PHYTOTOXIN, PHOTORHABDUS LUMINESCENS,

ENTEROTOXIN, GLUCOSINOLATES, ALKALOIDS,

AFLATOXIN, MYCOTOXINS, FUNGUS,.

TPS See TECHNOLOGY PROTECTION SYSTEM.

Tracer (radioactive isotopic method) A metabolite that is labeled by incorporation of an isotopic atom into its structure. The metabolic fate of the labeled metabolite can then

be traced in intact organisms. That is, one is T able to ascertain where (in what kind of struc-

ture) the metabolite ends up as well as the transformation products (intermediate molecules) that were involved in its formation.

Certain atoms of a given metabolite are labeled. This is done by substituting radioactive isotopes for the atom in question. Because an atom is replaced by an isotope, the metabolite as a whole is chemically and biologically indistinguishable from its normal analog. The presence of the isotope allows the metabolite and its transformation products to

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be detected and measured. Without this technique, many aspects of metabolism could not have been studied. These include: the process of photosynthesis, metabolic turnover rates, and the biosynthesis of proteins and nucleic

acids. See also REASSOCIATION (OF DNA), RADIOACTIVE ISOTOPE, RADIOIMMUNOASSAY.

Traditional Breeding Methods A phrase utilized by some people to refer to some or most techniques/technologies utilzed by crop plant breeders prior to some arbitrarily chosen date (after which some people feel that “genetic engineering” arrived abruptly). For example, in 1992 Tim Croughan discovered a single rice (Oryza sativa) plant that had survived (what should have been a lethal dose of) an imidazolinone-based herbicide, due to a (mutated) gene in its DNA that made it resistant to imidazolinones. That plant was then propagated via straightforward breeding to yield seeds still sown today. Many years ago, some other crops similarly were given new traits (e.g., herbicide tolerance, compositional improvements, etc.) via mutation breeding (i.e., soaking seeds or pollen in mutation-causing chemicals, or bombarding seeds with ionizing radiation to cause random genetic mutations, followed by grow-out and selection of the particular mutation desired such as herbicide tolerance, as described above).

Other crops were given new traits via crossing them with related wild plants, which occasionally resulted in extremely high levels of natural toxicants in those plants/seeds (solanine, psoralene, etc.). Still others were given new traits via wide-cross- ing them with other domesticated species

T(e.g., the tangelo is a hybrid of the grapefruit and the tangerine). The U.S. Food and Drug Administration (FDA) regulates all new crop plants similarly (e.g., also requires testing of plants produced via “traditional breeding methods” for the potential presence of introduced or increased natural toxicants). See

also GENETIC ENGINEERING, HERBICIDE-TOLERANT CROP, GENETICS, MUTATION, MUTATION BREEDING,

TRAIT, CANOLA, SOYBEAN PLANT, CORN, SOLANINE,

PSORALENE, FOOD AND DRUG ADMINISTRATION

(FDA), BARLEY, HYBRIDIZATION (PLANT GENETICS),

MARKER (DNA SEQUENCE), MARKER ASSISTED

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SELECTION, POINT MUTATION, SOMACLONAL

VARIATION, SOMATIC VARIANTS, WIDE CROSS,

EMBRYO RESCUE, TISSUE CULTURE.

Traditional Breeding Techniques See TRADI-

TIONAL BREEDING METHODS.

Trait A characteristic of an organism, which manifests itself in the phenotype (physically). Many traits are the result of the expression of a single gene, but some are polygenic (result from simultaneous expression of more than one gene). For example, the level of protein content in soybeans is controlled by five genes. See also PHENOTYPE,

GENOTYPE, EXPRESS, GENE, POLYGENIC, PROTEIN,

CALLIPYGE.

trans Fatty Acids One of the two isomeric forms that fatty acids can exist in. Trans fatty acids are naturally present in some meat and dairy products (which constitute approximately 5% of the average American diet).

See also FATTY ACID, ISOMER, STEREOISOMERS,

HYDROGENATION.

trans-Acting Protein A trans-acting protein has the exceptional property of acting (having an effect) only on the molecule of DNA (deoxyribonucleic acid) from which it was expressed. See also EXPRESS, cis-ACTING

PROTEIN.

Transactivating Protein See VIRAL TRANSACTI-

VATING PROTEIN.

Transaminase A large group of enzymes that catalyze the transfer of the amino group from any one of at least 12 amino acids to a keto acid to form another amino acid. Also known as aminotransferases. See also ENZYME,

AMINO ACID.

Transamination The reaction of the enzymatic removal and transfer of an amino group from one specific compound to

another. See also TRANSAMINASE, AMINO ACID.

Transcript Term used to refer to the various segment(s) of messenger RNA (mRNA) that result from transcription of a gene. See also

GENE, TRANSCRIPTION, MESSENGER RNA (mRNA),

TRANSCRIPTOME, CENTRAL DOGMA (NEW).

Transcription The enzyme-catalyzed process whereby the genetic information contained in one strand of DNA (deoxyribonucleic acid) is used as a template to specify and produce a complementary mRNA strand. Transcription may be thought of as a rewriting

of the information contained in DNA into RNA. The language, however, is the same — both are nucleic acid-based. This is in contrast to translation, in which the information is translated from one language (RNA, nucleic acid-based) into another language (protein, amino acid-based). See also GENE

EXPRESSION, TRANSLATION, MESSENGER RNA

(mRNA), GENETIC CODE, DEOXYRIBONUCLEIC ACID

(DNA), TRANSCRIPTION FACTORS, TRANSCRIPTION

UNIT, ANTICODING STRAND.

Transcription Factors Proteins and/or other chemical compounds that interact with each other, and with regulatory sequences within DNA (when immediately adjacent to the DNA in a cell), to either facilitate (“turn on”) or inhibit (“turn off “) the activity (i.e., coding for proteins) of that DNA’s genes. Transcription factors hold potential to:

•Cure diseases (e.g., by blocking the deleterious effects of certain disease-caus- ing genes).

•To assist farmers in crop protection (e.g., by switching on the genes that cause crop plants to initiate “cold hardening,” or certain types of insect resistance mechanisms).

•To improve human health (e.g., PUFA modulation of genes, modulation of genes by some vitamins, etc.).

Some transcription factors are an integral component in certain gene expression cascades. For example, a gene expression cascade is initiated by the first gene causing expression of a transcription factor, which then itself interacts with the cell’s DNA to either cause or speed-up yet another gene expression. The protein resulting from that second gene expression is yet another transcription factor which triggers another (i.e., third) gene expression, and so on. See also

PROTEIN, GENETIC CODE, CODING SEQUENCE,

DEOXYRIBONUCLEIC ACID (DNA), CELL, INHIBI-

TION, GENE, p53 GENE, TRANSCRIPTION, p53 PRO-

TEIN, CBF1, COLD HARDENING, REGULATORY SEQUENCE, EXPRESS, GENE EXPRESSION, GENE EXPRESSION CASCADE, DOWN REGULATING, VITAMIN, POLYUNSATURATED FATTY ACIDS (PUFA),

RECOMBINASE.

Transcription Unit A group of genes that code for functionally related RNA molecules or protein molecules. This group of genes is expressed (transcribed) together (as a unit, thus the name). See also EXPRESS, GENE, TRAN-

SCRIPTION, TRANSLATION, GENETIC CODE, CODING

SEQUENCE, DEOXYRIBONUCLEIC ACID (DNA),

RIBONUCLEIC ACID (RNA), RIBOSOMES.

Transcriptome Refers to the entire (complete, possible) set of all gene transcripts (i.e., mRNA segments resulting from gene transcription process) in a given organism. Also to knowledge of their roles in that organism’s structure, growth, health, disease (and/or that organism’s resistance to disease), etc. Those roles are predominantly due to the impact of each protein molecule (i.e., resulting from the mRNA segments being translated in cells’ ribosomes); which is itself due to the protein molecule’s composition and its tertiary conformation (which determines the protein’s impact in the organism’s tissues, metabolism, etc.).

More than one protein can result from each gene in an organism’s genome, due to:

•	Interactions between genes.
• Interactions between genes and their
	(protein) products.
•	Interactions between genes and some
	environmental factors.
Mechanistically, this results in different pro-
teins being produced (during translation pro-
cess) via:
•	Alternative splicing of the mRNA tran-
	script. For example, a single intronic
		T
	base substitution that is present within
	the IKAP gene (i.e., the allele respon-
	sible) for the disease known as familial
	dysautonomia affects the splicing of the
	IKAP transcript (i.e., the mRNA seg-
	ment that determines which specific
	protein is subsequently “manufactured”
	by the ribosomes).

• Varying translation start or stop site (on the gene).

• Frameshifting (i.e., different set of triplet codons in the mRNA/transcript is translated by the ribosome).

© 2002 by CRC Press LLC