(DNA),

afflicted with hemorrhagic lesions in the brain (cause of abnormal serotonin activation/production) often became “passionate culinary afficionados.” See also TRYPTOPHAN

(trp), ESSENTIAL AMINO ACIDS, BLOOD-BRAIN

BARRIER (BBB), NEUROTRANSMITTER.

Serotypes A variety (sub-strain) of a microorganism that is distinguished from others (in the strain) via its serological effects (within immune system of the host organism it inhabits). See also BACTERIA, STRAIN, E. COLI

0157:H7, SEROLOGY, HUMAN IMMUNODEFICIENCY

VIRUS TYPE 1 (HIV- 1), HUMAN IMMUNODEFICIENCY

VIRUS TYPE 2 (HIV- 2).

Serum Blood plasma that has had its clotting factor removed. See also FACTOR VIII, FACTOR

IX, PLASMA.

Serum Half Life See SERUM LIFETIME.

Serum Immune Response See HUMORAL IMMU-

NITY.

Serum Lifetime The average length of time that a molecule circulates in an organism’s bloodstream before it is cleared from the bloodstream. See also IMMUNE RESPONSE,

ANTIGEN.

Sessile (Micro)organisms that are attached to a (support) substrate directly by their base; not attached via an intervening peduncle (i.e., stalk). Can also refer to fruit or leaves that are attached directly to the main stem or branch of a plant. See also VAGILE.

Sex Chromosomes T h o s e c h r o m o s o m e s whose content is different in the two sexes of a given species. They are usually labeled X and Y (or W and Z); one sex has XX (or WW), the other sex has XY (or WZ). XX

S (WW) is female and XY (WZ) is male. Sexual Conjugation An infrequent occurrence

in which two adjacent bacteria stretch out portions of their (cell) membranes to touch one another, fuse, and then pass transposons, jumping genes, or plasmids to each other. See

also ASEXUAL, BACTERIA, CELL, CONJUGATION,

PLASMID, TRANSPOSON, JUMPING GENES.

Shotgun Cloning Method A technique for obtaining the desired gene that involves “chopping up” the entire genetic complement of a cell using restriction enzymes, then attaching each (resultant) DNA fragment to a vector and transferring it into a bacterium, and

finally screening those (engineered) bacteria to locate the bacteria that are producing the desired product (e.g., a protein). See also

GENETIC ENGINEERING, GENOME, RESTRICTION

ENDONUCLEASES, VECTOR.

Shotgun Sequencing Sometimes called Wholegenome Shotgun Sequencing. A technology for rapid sequencing of DNA, in which an organism’s genome (DNA) is first fragmented (“broken up”), and then randomly selected pieces of the DNA are individually sequenced. Those individual pieces’ sequences must subsequently be “bridged” (i.e., “assembled” in an overlapping end-by- end pattern) in order to assemble a complete map (e.g., of an organism’s chromosome or

genome). See also SEQUENCING (OF DNA MOLECULES), DEOXYRIBONUCLEIC ACID

SEQUENCE (OF A DNA MOLECULE), GENOME, DNA

“BRIDGES”, CHROMOSOME, GENETIC MAP.

Shuttle Vector A vector capable of replicating in two unrelated species. See also VECTOR,

REPLICATION (OF VIRUS).

Signal Transducers and Activators of Transcription (STATs) Molecules that cause signal transduction to occur (i.e., when a hormone or other chemical “binds” to it), or molecules that cause transcription to occur (i.e., when transcription factor(s) “bind” to it). STATs can be attached to solid surfaces (e.g., in a bioassay or biosensor) for use in such research applications as high-through- put screening. See also SIGNAL TRANSDUCTION,

HORMONE, TRANSCRIPTION FACTORS, BIOCHIPS,

BIOSENSORS (ELECTRONIC), BIOASSAY, HIGH-

THROUGHPUT SCREENING (HTS), MICROARRAY

(TESTING), TARGET (OF A HERBICIDE OR INSECTI-

CIDE), CASCADE.

Signal Transduction The “reception” and “conversion” of a “chemical message” (e.g., hormone) by a cell. For example, G-proteins (which are embedded in the surface membrane of certain cells, but extend through to outside and inside of the membrane) accomplish signal transduction. When a hormone, drug, neurotransmitter, or other signal chemical binds (i.e., “docks”) to the receptor (on the exterior of the cell’s plasma membrane), the receptor activates the G-protein, causing an effector inside cell to produce a “signal”

© 2002 by CRC Press LLC

chemical inside the cell, which then reacts to the original external chemical signal received. See also CELL, PLASMA MEMBRANE,

TRANSMEMBRANE PROTEINS, RECEPTORS, EGF

RECEPTOR, RAS GENE, NUCLEAR RECEPTORS, SIG-

NALING, G-PROTEINS, MAST CELLS, CD95 PROTEIN,

HORMONE, SUBSTANCE P, LECITHIN, CASCADE.

Signaling The “communication” that occurs between and within cells of an organism, e.g., via hormones, nitric acid, etc. Such signaling “tells” certain cells to grow, change, or produce specific proteins at specific times. See

also RECEPTORS, PROTEIN, NUCLEAR RECEPTORS,

G-PROTEINS, SIGNAL TRANSDUCTION (SIGNAL),

TRANSDUCTION (GENE), CD95 PROTEIN, HORMONE,

PARKINSON’S DISEASE, HARPIN, SUBSTANCE P,

LECITHIN, NITRIC OXIDE, SIGNAL TRANSDUCERS

AND ACTIVATORS OF TRANSCRIPTION (STATs),

PROTEIN SIGNALING, CASCADE, CHOLINE.

Signaling Molecule A molecule utilized to “signal” (communicate) with cells, or to deliver a signal to other organisms (e.g., a signal by the soybean plant to attract beneficial Rhizobium bacteria to colonize the roots of that soybean plant).

For example, the young offspring of fleas can remain immature (larvae) for up to 2 years in the absence of a food source, until carbon dioxide molecules and heat from a nearby mammal (potential host/food source) signal them to mature into adults in order to prey on the mammal. Another example: the larvae of North American tree frogs are signaled by chemicals released into a pond’s water when the first such frog larva is killed by a (predatory) dragonfly nymph (i.e., when those dragonflies first arrive each year at a given pond, to prey on the frog larvae). That chemical “signal” causes all of the North American tree frog larvae in that pond to subsequently grow tails that are twice as large as were grown by them prior to that chemical signal, to facilitate their escape from the dragonfly nymphs. See

also SIGNALING, NITRIC OXIDE, G-PROTEINS , HOR-

MONE, SUBSTANCE P, LEUKOTRIENES, ISOFLA-

VONES, SOYBEAN PLANT, RHIZOBIUM (BACTERIA),

HARPIN, OCTADECANOID/JASMONATE SIGNAL COM-

PLEX, SALICYCLIC ACID (SA).

Signaling Protein See SIGNALING MOLECULE.

Silencing See GENE SILENCING.

	Silent Mutation A mutation in a gene that
	causes no detectable change in the biological
	characteristics of that gene’s product (e.g., a
	protein). See also EXPRESS, GENE, PROTEIN.
	Silk A natural, protein polymer with a predom-
	inance of alanine and glycine amino acids.
	Silk is produced by silkworms that have fed
	on mulberry tree leaves. The body of a silk-
	worm can retain proteins (i.e., raw material
	for silk) amounting to as much as 20% of its
	body weight. It is thought that silk may be
	altered, via genetic engineering of silk-
	worms, to produce fibers of very high
	strength. See also GENETIC ENGINEERING, PRO-
	TEIN ENGINEERING, AMINO ACID.
	Simple Protein A protein that yields only
	amino acids on hydrolysis (i.e., cleavage of
	the protein molecule into fragments), and
	does not have other molecular constituents
	such as lipids or polysaccharide attachments.
	See also PROTEIN, AMINO ACID, GLYCOPROTEIN,
	LIPIDS, POLYSACCHARIDES.
	Simple Sequence Repeat (SSR) DNA Marker
	Technique A “genetic mapping” technique
	which utilizes the fact that microsatellite
	sequences “repeat” (appear repeatedly in
	sequence within the DNA molecule) in a
	manner enabling them to be used as “mark-
	ers.” See also GENETIC MAP, SEQUENCE (OF A
	DNA MOLECULE), RANDOM AMPLIFIED POLYMOR-
	PHIC DNA (RAPD) TECHNIQUE, RESTRICTION FRAG-
	MENT LENGTH POLYMORPHISM (RFLP) TECHNIQUE,
	DEOXYRIBONUCLEIC ACID (DNA), PHYSICAL MAP
	(OF GENOME), LINKAGE, LINKAGE GROUP, MARKER
	(GENETIC MARKER), LINKAGE MAP, TRAIT, MICRO-
	SATELLITE DNA, QUANTITATIVE TRAIT LOCI (QTL).
		S
	Single-Cell Protein (SCP) Protein derived
	from single-celled organisms with a high
	protein content. Yeast is an example. Gener-
	ally used in regard to those organisms that
	are edible by domesticated animals or
	humans. Single-Domain Antibodies (dAbs)
	VH “heavy chains” (portion of antibody
	molecules) produced by genetically engi-
	neered Escherichia coli cells that act to bind
	antigens in a manner similar to antibodies or
	monoclonal antibodies (MAbs). Similar to
	MAbs, dAbs can be produced in large quan-
	tities, to be used as human or animal thera-
	peutics (e.g., to combat diseases). See also

© 2002 by CRC Press LLC

ANTIBODY, MONOCLONAL ANTIBODIES (MAb),

ANTIGEN, ESCHERICHIA COLI.

Single-nucleotide Polymorphisms (SNPs)

Variations (in individual nucleotides) that occur within DNA at the rate of approximately one in every 1,300 base pairs in most organisms (approximately one in every 100 base pairs in humans’ DNA). SNPs usually occur in the same genomic location (e.g., on the organism’s DNA) in different individuals. These variations account for:

•Diversity within a given species (e.g., black cattle and white cattle, different strains/serotypes within a given bacteria species, etc.)

•Some genetic diseases [e.g., the disease cystic fibrosis is due to one SNP, the disease known as familial dysautonomia is due to one SNP, the disease known as (Duchenne) muscular dystrophy is due to one SNP, etc.]

•The body’s response to certain pharmaceuticals and food ingredients (e.g., the diuretic drug thiazide works to control hypertension in 60% of U.S. African Americans, but only 8% of U.S. Caucasian people, due to one SNP)

Certain pharmaceuticals do not have the desired effect in some groups of humans possessing certain specific “grouped SNPs” known as haplotypes. Because those “groupings of SNPs” are linked (i.e., tend to “travel together” as a group within the genetics of a given population), they can collectively

S confer a given “multiple-SNP-trait” to an identifiable subpopulation of individuals. For example, the pharmaceuticals acetaminophen, aspirin, and Valium remain in the bodies of women (who constitute a haplotype for that pharmacogenomic trait) longer than in men.

Methods utilized to identify SNPs include examination of the DNA of populations of individuals with and without a given (genetically related) disease and with and without a given trait. “SNP mapping” is a “genetic mapping” technique that utilizes the fact that individual nucleotides (within a DNA molecule) can exist in different forms (for a

particular “site”/location on that DNA molecule), which enables such SNPs to be utilized as “markers.” One example would be to track a given SNP vs. occurrence of genetically related disease in a given human pop- u l a t i o n . S e e a l s o P O I N T M U T A T I O N ,

DEOXYRIBONUCLEIC ACID (DNA), SEQUENCE (OF

A DNA MOLECULE), NUCLEOTIDE, POLYMORPHISM

(GENETIC), GENETICS, GENETIC MAP, PHYSICAL MAP (OF GENOME), GENOME, TRAIT, MARKER

(GENETIC MARKER), QUANTITATIVE TRAIT LOCI

(QTL), DIVERSITY (WITHIN A SPECIES), BASE PAIR

(bp), TRANSVERSION, CYSTIC FIBROSIS TRANS-

MEMBRANE REGULATOR PROTEIN (CFTR), MUSCU-

LAR DYSTROPHY (MD), PHARMACOGENETICS,

PHARMACOGENOMICS, HAPLOTYPE, SNP MAP,

TOXICOGENETICS, ORGANISM.

Site-Directed Mutagenesis (SDM) A t e c h - nique that can be used to make a protein that differs slightly in its structure from the protein normally produced (by an organism or cell). A single mutation (in the cell’s DNA) is caused by hybridizing the region in a codon to be mutated with a short, synthetic oligonucleotide. This causes the codon to code for a different specific amino acid in the protein gene product. Site-directed mutagenesis holds the potential to enable man to create modified (engineered) proteins that have desirable properties not currently available in the proteins produced by existing organisms. See also MUTANT, MUTATION,

POINT MUTATION, PROTEIN, GENE, INFORMATIONAL MOLECULES, HEREDITY, GENETIC CODE,

GENETIC MAP, AMINO ACID, DEOXYRIBONUCLEIC ACID (DNA), CODON, OLIGONUCLEOTIDE, PROTEIN ENGINEERING.

Sitostanol A chemical (ester) derived from sitosterol (a sterol present in pine trees), and fibers (e.g., the hull or seed coat) of corn/maize (Zea mays) or soybeans (Glycine max L.). When sitostanol is consumed by humans in sufficient quantities, it causes their total serum cholesterol and their lowdensity lipoprotein (LDLP) levels to be lowered by approximately 10%, via inhibition (i.e., the sitostanol is preferentially absorbed by the gastrointestinal system instead of cholesterol). During 2000, the U.S. Food and Drug Administration approved a (label) health claim that associates consumption of

© 2002 by CRC Press LLC

sitostanols with reduced blood cholesterol content and with reduced coronary heart dis-

ease (CHD). See also ABSORPTION, DIGESTION

(WITHIN ORGANISMS), SOYBEAN PLANT, LOW-

DENSITY LIPOPROTEINS (LDLP), SERUM LIFETIME,

CHOLESTEROL, STEROLS, PHYTOSTEROLS, SITO-

STEROL, CORONARY HEART DISEASE (CHD).

Sitosterol A phytosterol that is naturally produced in fibers within soybean (Glycine max L.) hulls, pumpkin seeds, pine trees, fibers of corn/maize (Zea mays) seed coats, etc. Sitosterol can exist in several different molecular forms (known as alpha a, beta b, etc.). A human diet containing large amounts of sitosterol and/or certain other phytosterols (campesterol, stigmasterol, etc.) has been shown to lower total serum (blood) cholesterol and low-density lipoprotein (LDLP) levels; and thereby lower the risk of coronary heart disease (CHD).

Evidence indicates that certain phytosterols (including sitosterol) interfere with absorption of cholesterol by the intestines, and decrease the body’s recovery and reuse of cholesterol-containing bile salts, which causes more cholesterol to be excreted from the body than previously. During 2000, the U.S. Food and Drug Administration approved a (label) health claim that associates consumption of sitosterols with reduced blood cholesterol content and with reduced coronary heart disease (CHD). See also PHY-

TOSTEROLS, SOYBEAN PLANT, CORN, STEROLS,

SITOSTANOL, CAMPESTEROL, STIGMASTEROL, COR-

ONARY HEART DISEASE (CHD), BETA-SITOSTEROL,

CHOLESTEROL.

SK See SUBSTANCE K.

Slime An extracellular (i.e., outside of the cell) material produced by some (micro)organisms and characterized by a slimy consistency. The slime is of varied chemical composition. However, usual components are polysaccharides (polysugars) and specific protein molecules.

Smut See TELETHIA CONTROVERSIA KOON SMUT.

SNP See SINGLE-NUCLEOTIDE POLYMORPHISMS

(SNPs).

SNP MAP A group of known/detailed SNPs (single-nucleotide polymorphisms), superimposed onto the genome map of an organism

(e.g., to facilitate genetic/population studies, such as of genetically related disease suscep-

tibility). See also SINGLE-NUCLEOTIDE POLY- M O R P H I S M S (S N P s ), O R G A N I S M , G E N O M E ,

GENOMIC SCIENCES, MAPPING (OF GENOME), MAP

DISTANCE, MARKER (DNA SEQUENCE).

SNP MARKERS See S I N G L E - N U C L E O T I D E

POLYMORPHISMS (SNPs).

Sodium Dodecyl Sulfate See SDS.

Sodium Lauryl Sulfate See SDS.

Solanine A glycoside neurotoxin naturally present at low levels within potatoes. As a result, solanine is present at detectable levels in the bloodstream of humans who consume potatoes. The U.S. Food and Drug Administration (FDA) prohibits the sale in the U.S. of potatoes which contain more (than a very low level of solanine); e.g., the naturally present level in potatoes can unfortunately increase in potatoes that are exposed to direct sunlight. See also TOXIN, PHYTOTOXIN,

CHACONINE, GLYCOSIDE, WILD TYPE, FOOD AND

DRUG ADMINISTRATION (FDA), TRADITIONAL

BREEDING METHODS.

	Solid-Phase Synthesis See SYNTHESIZING (OF
	PROTEINS), SYNTHESIZING (OF DNA MOLECULES).
	Soluble CD4 A synthetic version of the CD4
	protein that may interfere with the ability of
	HIV (i.e., AIDS) viruses to infect human
	immune system cells with the acquired
	immune deficiency syndrome (AIDS) virus.
	See also CD4 PROTEIN, ADHESION MOLECULE,
	SELECTINS, LECTINS, PROTEIN.
	Soluble Fiber See WATER SOLUBLE FIBER.
	Somaclonal Variation The genetic variation
		S
	(i.e., new traits) that results from the growing
	of entire new plants from plant cells or tis-
	sues (e.g., maintained in culture). Frequently
	encountered when plants are regenerated
	(grown) from plant cells that have been
	altered via genetic engineering. However,
	somaclonal variation (i.e., new genetic traits)
	can occur even when plants are regenerated
	from cells that were part of the same original
	plant. See also CELL CULTURE, SOMATIC VARI-
	ANTS, CLONE (AN ORGANISM), AGROBACTERIUM
	TUMEFACIENS, BIOLISTIC® GENE GUN, “EXPLOSION”
	METHOD, SHOTGUN METHOD.
	Somatacrin See also G R O W T H H O R M O N E -
	RELEASING FACTOR (GRF or GHRF).

© 2002 by CRC Press LLC