differentiate stearate (on food product labels) from the other saturated long-chain fatty acids used as food ingredients.

In order to make milk, dairy cows require more stearic acid than a conventional digestive system alone could provide from the cow’s (mainly carbohydrate) diet. Therefore, cows utilize microorganisms living in their rumen (a special sort of pre-stomach) to convert carbohydrate (grass) to stearic acid. Thus, high-performance dairy cows might benefit from a diet that contains high-stear- ate soybeans, if their milk output is limited by dietary stearate availability. See also

FATTY ACID, LOW-DENSITY LIPOPROTEINS (LDLP),

SATURATED FATTY ACIDS, FOOD AND DRUG

ADMINISTRATION (FDA), HIGH-STEARATE SOY-

BEANS, FATS, ENOYL-ACYL PROTEIN REDUCTASE,

HIGH-STEARATE CANOLA.

Stearic Acid See STEARATE.

Stearoyl-ACP Desaturase A “ f a m i l y ” o f enzymes that is naturally produced in oilseed plants. They play the central role in determining the ratio of saturated to unsaturated fatty acids (in the vegetable oils produced from such plants). See also FATS, FATTY ACID,

ENZYME, GENETIC ENGINEERING, GENETIC CODE,

LAURATE, HIGH-STEARATE SOYBEANS, HIGH-

STEARATE CANOLA.

Stem Cell Growth Factor (SCF) A growth factor (glycoprotein hormone) that acts upon stem cells in a wide variety of ways to increase growth, proliferation, and maturity (into red blood cells or white blood cells).

See also STEM CELLS, GROWTH FACTOR, HORMONE, GLYCOPROTEIN, DIFFERENTIATION, TOTI-

SPOTENT STEM CELLS, COLONY STIMULATING FACTORS (CSFs).

Stem Cell One The single stem cell in the bone marrow of a fetus from which every immune system cell in the adult is subsequently derived. The primordial stem cell is stimulated to develop into the mature immune system’s differentiated, specialized cells by interleukin-7. See also STEM CELLS,

TOTIPOTENT STEM CELLS, INTERLEUKIN- 7 (IL- 7),

EMBRYONIC STEM CELLS, DIFFERENTIATION.

Stem Cells Certain cells — present in the bodies of mammals even prior to birth, although also present in adult mammals — that can grow/differentiate into different cells/tissues

© 2002 by CRC Press LLC

of the (adult organism) body. For example, bone marrow (stem) cells, some of which eventually mature into red blood cells or white blood cells. The stem cells that remain in the bone marrow maintain their own numbers by self-renewal divisions, yielding more cells to start the maturation process. This maturation process is stimulated and controlled by stem cell growth factor (SCF), granulocyte colony stimulating factor (G-CSF), and by granulocyte-macrophage colony stimulating factor (GM-CSF).

During 2000, research by Richard Childs showed that stem cells (i.e., collected from a sibling’s bloodsteam) transplanted into a patient suffering from kidney cancer could induce generation of a “new” immune system which could help stop/reverse the kid-

ney cancer. See also CELL, MULTIPOTENT ADULT STEM CELLS, ECTODERMAL ADULT STEM CELLS,

ENDODERMAL ADULT STEM CELLS, MESODERMAL ADULT STEM CELLS, HEMATOPOIETIC STEM CELLS,

RED BLOOD CELLS, WHITE BLOOD CELLS, BASOPHILS, STEM CELL ONE, STEM CELL GROWTH FACTOR

(SCF), TOTIPOTENT STEM CELLS, TOTIPOTENCY,

EMBRYONIC STEM CELLS, DIFFERENTIATION,

IMMUNE RESPONSE, CANCER.

Stereoisomers Molecules that have the same structural formula but different spatial arrangements of dissimilar groups (of atoms) bonded to a common atom (in the molecule). Many of the physical and chemical properties of stereoisomers are the same, but there are differences in the crystal structures, in the direction in which they rotate polarized light (which has been passed through a solution of the stereoisomer), and in their use in an enzyme-catalyzed (biological) reaction. See also RACEMATE, POLARIME-

TER, DEXTROROTARY (D) ISOMER, EPIMERS,

ISOMER, LEVOROTARY (L) ISOMER, ISOMERASE,

DIASTEREOISOMERS.

Steric Hindrance Refers to the compression that a group (chemical entity) suffers by being too close to its nonbonded neighbors. If an enzyme and a substrate try to come together in order to react, but the substrate has on it a bulky group that disallows close contact between the two (because the group bumps into the enzyme), then the reaction will not occur because of steric hindrance.

Seen another way, two chemical groups bump into each other and cannot get by each other because they are held in place by the bonds binding them to other atoms. Hindrance of movement or activity occurs because chemical groups bump into each other and cannot occupy the same space. See

also REPRESSION (OF AN ENZYME), INHIBITION,

COREPRESSOR.

Sterile (environment) One that is free of any living organisms or spores. For example, a hypodermic needle that has been sterilized (e.g., by heating it) and is free of living microorganisms is said to be sterile.

Sterile (organism) One that is unable to reproduce. For example, a bull that has been castrated is rendered sterile. See also TRIPLOID,

BARNASE.

Sterilization See STERILE (ENVIRONMENT), STER-

ILE (ORGANISM).

Steroid A chemical compound composed of a series of four carbon rings joined together to form a (molecular) structural unit called cyclopentanoperhydrophenanthrene. Any of a group of naturally occurring, fat-soluble substances essential to life, usually classed as lipids.

Steroids of importance to the body are the sterols, which are bile acids (produced by the liver, characterized by the presence of a carboxyl group in the molecule’s side chain), and the hormones of the sex glands and the adrenal cortex. In addition, the plant kingdom possesses a wide variety of steroid gly-

cosides. See also GLYCOSIDE, LIPIDS, HORMONE,

CHOLESTEROL, STEROLS, SAPONINS.

Sterols Solid alcohols consisting of ring-struc- tured molecules (i.e., a ‘ring’ made of atoms). Evidence suggests that human consumption of certain phytosterols (i.e., sterols produced in plant seeds) can help to prevent certain types of cancers, and can help lower levels of total blood serum cholesterol and low-density lipoproteins (LDLP); thereby reducing risk of coronary heart disease (CHD). Evidence indicates that those phytosterols interfere with absorption of cholesterol by the intestines, and they decrease the body’s recovery and reuse of cholesterolcontaining bile salts, which causes more cholesterol to be excreted from the body.

	During 2000, researcher Joseph Judd fed
	phytosterols extracted from soybeans (Gly-
	cine max L.) to human volunteers who were
	already consuming a “low fat” diet. Their
	total blood serum cholesterol and low-den-
	sity lipoprotein (LDLP) levels decreased by
	more than 10%, in a short time. During 2001,
	the U.S. FDA approved a (label) health claim
	that associates the consumption of plant ste-
	rols with reduced blood cholesterol content,
	and with reduced coronary heart disease
	(CHD). Some of the sterols known to impart
	health benefits when consumed by humans
	include β-sitosterol (beta-sitosterol) and
	squalene. See also PHYTOSTEROLS, STEROID,
	CHOLESTEROL, BILE, SITOSTANOL, SOYBEAN PLANT,
	CAMPESTEROL, STIGMASTEROL, BETA-SITOSTEROL,
	CORONARY HEART DISEASE (CHD), LOW-DENSITY
	LIPOPROTEINS (LDLP), FOOD AND DRUG ADMINIS-
	TRATION (FDA).
	Sticky Ends Complementary single strands of
	DNA (deoxyribonucleic acid) that protrude
	from opposite ends of a DNA duplex or from
	ends of different DNA duplex molecules.
	They can be generated by staggered cuts in
	DNA. They are called “sticky” because the
	exposed single strands can bind (stick) to
	complementary single strands on another
	DNA molecule. A hybrid piece of DNA is
	hence produced (by that binding). See also
	STAGGERED CUTS, HYBRIDIZATION (MOLECULAR
	GENETICS), DUPLEX, ANNEAL, DEOXYRIBONUCLEIC
	ACID (DNA), BLUNT-END LIGATION, RESTRICTION
	ENDONUCLEASES.
	Stigmasterol A phytosterol produced within
	the seeds of the soybean plant (Glycine
		S
	max L.), among others. Evidence indicates
	that human consumption of stigmasterol
	helps reduce levels of total serum cholesterol
	and low-density lipoproteins (LDLP); thereby
	lowering risk of coronary heart disease
	(CHD). Evidence indicates that certain phy-
	tosterols (including stigmasterol) interfere
	with absorption of cholesterol by the intes-
	tines, and decrease the body’s recovery and
	reuse of cholesterol-containing bile salts;
	which causes more cholesterol to be excreted
	from the body. See also PHYTOSTEROLS, PHYTO-
	CHEMICALS, STEROLS, SOYBEAN PLANT, CHOLES-
	T E R O L , C A M P E S T E R O L , B E T A -S I T O S T E R O L ,
	CORONARY HEART DISEASE (CHD).

© 2002 by CRC Press LLC

Stomatal Pores See GPA1, ABSCISIC ACID.

Strain A group or organisms of the same species that possess(es) distinctive genetic characteristics that set it apart from others within the same species, but whose differences are not “severe” enough for it to be considered a different breed or variety (of that species). The basic taxonomic unit of microbiology. Can also be used to designate a population of cells derived from a single cell. See also

SPECIES, CELL, CLONE (AN ORGANISM).

Streptococcus Refers to bacteria of the genus

Streptococcus. See also BACTERIA, GENUS,

STREPTOCOCCUS MUTANS.

Streptococcus mutans The strain of Streptococcus bacteria that grows on the surface of teeth and can contribute to causing tooth “decay.” See also STRAIN, BACTERIA, STREPTO-

COCCUS.

Stress Proteins Discovered by Italian biologist Ferruchio Ritossa in the 1960s, these molecules are also called heat-shock proteins. Proteins made by many organisms’ (plant, bacteria, and mammal) cells when those cells are stressed by environmental conditions such as certain chemicals, pathogens, or heat.

When corn/maize (Zea mays L.) is stressed during its growing season by high nighttime temperatures, that plant switches from its normal production of (“immune system” defense) chitinase to production of heat-shock (i.e., stress) proteins, instead.

Stress proteins are also produced by tuberculosis and leprosy bacteria after these bacteria have invaded (infected) cells in the

Shuman body, in an attempt by those bacteria to mimic the stress proteins that (mammal) cells would normally manufacture to repair damage done to the (mammal) cells. This mimicry makes it more difficult for the immune system to recognize and attack those pathogenic bacteria (and/or repair misshaped protein molecules in the body’s cells). Similarly, production of stress proteins helps some types of cancer cells to avoid being attacked by the immune system. Because consumption of genistein by humans causes a reduction in the production of stress proteins, genistein may thereby help the human immune system destroy

cancerous cells. In 1996, Richard I. Morimoto discovered that two stress proteins known as HSP 90 and HSP 70 help ensure that certain crucial proteins in cells are folded into the configuration/conformation needed by that cell. See also ANTIGEN, IMMUNE

RESPONSE, PATHOGEN, PROTEIN, PROTEIN FOLDING, CONFORMATION, CHAPERONES, PROTEIN

STRUCTURE, ABSOLUTE CONFIGURATION, PRION,

CHITINASE, AFLATOXIN, GENISTEIN, CANCER,

LIPOXYGENASE (LOX), PHYTOALEXINS.

Stromelysin (MMP-3) A collagenase (enzyme) that “clears a path” through living tissue, ahead of tumor cells, thereby enabling a cancer to spread within the body. See also

COLLAGENASE, ENZYME, CANCER, TUMOR.

Structural Biology See STRUCTURAL GENE.

Structural Gene A gene that codes for any RNA (ribonucleic acid) or protein product other than a regulator molecule. It determines the primary sequences (i.e., the amino acid sequences) of a polypeptide (protein).

See also GENE, EXPRESS, POLYPEPTIDE (PROTEIN),

AMINO ACID, PRIMARY STRUCTURE, RIBONUCLEIC

ACID (RNA).

Structural Genomics Study of, or discovery of, where (gene) sequences are located within the genome, and what (DNA) subunits comprise those sequences. See also

GENE, SEQUENCE (OF A DNA MOLECULE), DEOXY-

RIBONUCLEIC ACID (DNA), SEQUENCING (OF DNA

MOLECULES), GENOME, GENOMICS, PRIMARY

STRUCTURE.

STS Sulfonylurea (Herbicide)-Tolerant Soybeans These are soybeans that have been bred (via insertion of ALS gene by traditional breeding methods) to resist the (weed killing) effects of sulfonylurea-based herbicides. The ALS gene was discovered by Scott Sebastian in 1986. See also GENE,

GENETIC ENGINEERING, HTC, ALS, ALS GENE, BAR

GENE, PAT GENE, EPSP SYNTHASE, GLYPHOSATE

OXIDASE, HERBICIDE-TOLERANT CROP.

Stx Shiga-like toxins. See also TOXIN, TOXI-

GENIC E. COLI, ENTEROHEMORRHAGIC E. COLI,

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

Substance K See TACHYKININS.

Substance P A neuropeptide (i.e., peptide produced by cells of the nervous system) which is involved in activation of the immune system, pain sensation, and (when in excess)

© 2002 by CRC Press LLC

some psychiatric disorders. In the case of chronic, intractable pain (hypersensitivity), approximately 1% of the nerve cells in the human spine processes substance P (thereby “transmitting” its pain message via signal transduction). In 1997, Patrick Mantyh showed that killing those (1%) cells relieved chronic pain hypersensitivity without impairing sense of touch or normal (beneficial) pain sensation, in humans. See also

TACHYKININS, PROTEIN, POLYPEPTIDE (PROTEIN),

SIGNAL TRANSDUCTION, SIGNALING, PEPTIDE,

NEUROTRANSMITTER.

Substantial Equivalence See CANOLA, ORGANI-

ZATION FOR ECONOMIC COOPERATION AND

DEVELOPMENT (OECD).

Substantially Equivalent See S U B S T A N T I A L

EQUIVALENCE.

Substrate (chemical) The substance acted upon by an enzyme. For example, the enzyme amylase catalyzes the breakdown of starch molecules into glucose polysaccharide molecules; starch is the substrate (of the enzyme amylase). See also ENZYME, AMYLASE,

CATALYST, SUBSTRATE (STRUCTURAL).

Substrate (in chromatography) The (usually solid or gel) substance that attracts and noncovalently binds (interacts) with one or more of the molecules in a solution that is passed over that substrate (e.g., in a chromatography column). This preferential binding (interaction with the substrate) enables one or more of the solution’s molecular ingredients to be separated from the other(s). See

also CHROMATOGRAPHY.

Substrate (structural) The substance (support) to which the agent of interest (a molecule) is attached. For example, some catalyst molecules are chemically attached to nonreactive solids to preserve the catalyst from being flushed away when the chemical substrate (the molecule to be converted by the catalyst) is washed by the catalyst immobilized on the structural substrate. See also

SUBSTRATE (CHEMICAL), CATALYST, HYBRIDIZA-

TION SURFACES.

Sudden Death Syndrome A plant disease caused by the Fusarium solani fungus, that sometimes afflicts soybean plants. See also

SOYBEAN PLANT, SOYBEAN CYST NEMATODES

(SCN).

Sugar Molecules S e e O L I G O S A C C H A R I D E S ,

POLYSACCHARIDES, MONOSACCHARIDES, CARBO-

HYDRATES, ALDOSE, GLYCOBIOLOGY, PYRANOSE,

GLUCOSE (GLc), FURANOSE, GLYCOPROTEIN.

Suicide Genes See GENE, p53 GENE, APOPTOSIS.

Sulfate Reducing Bacterium See SRB (SULFATE

REDUCING BACTERIUM).

	Sulforaphane A compound naturally pro-
	duced within cruciferous plants such as
	broccoli and cabbage. Research indicates
	that human consumption of significant
	amounts of sulforaphane helps lower the risk
	of several cancers. See also NUTRACEUTICALS,
	PHYTOCHEMICALS, CANCER.
	Sulfosate An active ingredient in some herbi-
	cides, it kills plants (e.g., weeds) by inhibit-
	ing the crucial plant enzyme EPSP Synthase.
	Chemically, sulfosate is a trimethylsulfo-
	nium salt of the same organic acid as gly-
	phosate, so sulfoste can be applied over
	crops (e.g., soybeans) that have been genet-
	ically engineered to be tolerant to glypho-
	sate-based herbicides. See also ENZYME, EPSP
	SYNTHASE, CP4 EPSPS, GLYPHOSATE, ACID, SOY-
	BEAN PLANT, HERBICIDE-TOLERANT CROP,
	GENETIC ENGINEERING.
	Superantigens Certain types of antigens that
	activate a large proportion of an organism’s
	immune system T cells. These superanti-
	gens, which thus overactivate the organism’s
	immune system, are thought to be responsi-
	ble for some autoimmune diseases (in which
	T cells attack and destroy the organism’s
	own, healthy tissues). See also ANTIGEN,
	T CELLS , AUTOIMMUNE DISEASE.
	Supercoiling Also known as superhelicity. The
		S
	coiling of a closed duplex DNA (deoxyribo-
	nucleic acid molecule) in space so that it
	crosses over its own axis. See also DEOXY-
	RIBONUCLEIC ACID (DNA), HELIX, DUPLEX, DOUBLE
	HELIX, POSITIVE SUPERCOILING.
	Supercritical Carbon Dioxide A solvent that,
	when combined with water and an appropri-
	ate surfactant (e.g., fluoroethers), forms a
	solvent system that can effectively dissolve
	large biological molecules without causing
	those molecules to lose biological activity.
	Carbon dioxide is a gas at normal (atmo-
	spheric) pressure and ambient temperature,
	but in its supercritical state — temperature
	above 31.3°C (88°F) and pressure greater

© 2002 by CRC Press LLC