MAS See MARKER ASSISTED SELECTION.

Mass Applied Genomics See GENOMICS, BIO-

CHIPS, MICROARRAYS (TESTING), BIOINFORMATICS.

Mass Spectrometer An analytical device that can be used to determine the molecular weights (mass) of proteins and nucleic acids, the sequence of (composition and order of amino acids comprising) protein molecules, the chemical composition of virtually any material, and the rapid identification of intact gram-negative and gram-positive microorganisms (the latter, using matrixassisted laser desorption ionization time of flight mass spectrometry). See also GRAM-

NEGATIVE, GRAM-POSITIVE, MOLECULAR WEIGHT,

SEQUENCING (OF DNA MOLECULES), PROTEIN,

AMINO ACID, NUCLEIC ACIDS, GENE MACHINE,

MALDI-TOF-MS.

Mast Cells Fixed (noncirculating) cells that are present in many different kinds of body tissues. When two IgE molecules of the same antibody “dock” at adjacent receptor sites on a mast cell, then (the two IgE molecules) capture an allergen (e.g., a particle of pollen)

Mbetween them, a chemical-energetic signal is sent to the interior (inside mast cell) portion of receptor molecules, which causes that interior portion of molecule to change (i.e., transduction). That signal transduction causes a protein named “syk” to set off a chemical chain reaction inside the mast cell; thereby causing that mast cell to release leukotrienes, histamine, serotonin, bradykinin, and “slow reacting substance.” Release of these chemicals into the body causes the blood vessels to become more permeable (leaky) and causes the nose to run, and itchy and watery eyes. These chemicals also cause smooth muscle contraction, causing sneezing, breath constriction, coughing, wheezing, etc. See

also BASOPHILS, ANTIGEN, ANTIBODY, RECEPTORS,

SIGNAL TRANSDUCTION, HISTAMINE, ALLERGIES

(FOODBORNE), SIGNALING, LEUKOTRIENES.

Matrix Metalloproteinases (MMP) A family of enzymes that contain the zinc metal ion (Zn2+) at their active sites. Among this family are the collagenases. See also ENZYME, ION,

ACTIVE SITE, CATALYTIC SITE, STROMELYSIN

(MMP- 3), COLLAGENASE.

Maximum Residue Level (MRL) Term used for an officially established upper allowable

limit of a given compound (e.g., a synthetic hormone) in a particular product, such as meat. For example, in 1994, the Codex Alimentarius Commission in Rome, Italy, decided to establish maximum residue levels for each of five growth promotants commonly utilized by the U.S. beef industry. Because the World Trade Organization (WTO) subsequently stated that it would respect MRLs, a WTO member nation cannot legally refuse to allow import of meat products on growth promotant-content basis if the content of the promotant contained in the meat is less than its maximum residue

level. See also GROWTH HORMONE, GROWTH FACTOR, CODEX ALIMENTARIUS COMMISSION,

WORLD TRADE ORGANIZATION (WTO).

MCA See MEDICINES CONTROL AGENCY (MCA).

MEA Acronym for Multilateral Environmental Agreement; an agreement (treaty) between a number of nations intended to protect/benefit the environment. See also CONVENTION ON

BIOLOGICAL DIVERSITY (CBD).

Medicines Control Agency (MCA) The British Government agency that, in concert with the Committee on Safety in Medicines, regulates the approval and sale of pharmaceutical products in the United Kingdom. See

also COMMITTEE ON SAFETY IN MEDICINES, FOOD

AND DRUG ADMINISTRATION (FDA), COMMITTEE

FOR PROPRIETARY MEDICINAL PRODUCTS (CPMP),

KOSEISHO, NDA (TO KOSEISHO), IND, BUNDESGE-

SUNDHEITSAMT (BGA).

Medifoods See NUTRACEUTICALS, PHYTOCHEMI-

CALS.

Medium A substance used to provide nutrients for cell growth. It may be liquid (e.g., broth) or solid (e.g., agar). See also CULTURE

MEDIUM, AGAR, MAMMALIAN CELL CULTURE.

Mega-Yeast Artificial Chromosomes (mega YAC) A large (greater than 500 base pairs in length) piece of DNA that has been cloned (made) inside a living yeast cell. While most bacterial vectors cannot carry DNA pieces that are larger than 50 base pairs, and “standard” YACs typically cannot carry DNA pieces that are larger than 500 base pairs, mega YACs can carry DNA pieces (chromosomes) as large as one million base pairs in

length. See also YEAST, CHROMOSOMES, HUMAN

ARTIFICIAL CHROMOSOMES (HAC), ARABIDOPSIS

© 2002 by CRC Press LLC

THALIANA, DEOXYRIBONUCLEIC ACID (DNA),

CLONE (A MOLECULE), VECTOR, BASE PAIR (bp),

YEAST ARTIFICIAL CHROMOSOMES (YAC).

Megakaryocyte Stimulating Factor (MSF)

A colony stimulating factor (protein) involved in the regulation of platelet production, white blood cell production, and red blood cell production from stem cells in bone marrow. See also COLONY STIMULATING

FACTORS (CSFs), PLATELETS, STEM CELLS.

Meiosis Discovered by Edouard Van Beneden in the 1870s, meiosis is the sequence of complex cell nucleus changes resulting in the production of cells (as gametes) with half the number of chromosomes present in the original cell. It typically involves an actual reduction division in which the chromosomes without undergoing prior splitting join in pairs with homologous chromosomes (of maternal and paternal origin) and then separate (i.e., pulled apart by microtubules within the cell), so that one member of each pair enters each product cell nucleus and undergoes a second division not involving reduction. Occurs by two successive divisions (meiosis I and II) that reduce the starting number of 4n chromosomes to 1n in each of four product cells. Product cells may mature to germ cells (sperm or eggs). See

also OOCYTES, CELL, CHROMOSOME, NUCLEUS,

MICROTUBULES.

Melting (of DNA) Melting DNA means to heat-denature it. When this happens, the hydrogen bonds holding the DNA molecule together in the normal way are disrupted, allowing a more random polymer structure to exist. See also DENATURED DNA.

Melting (of substance other than DNA) To change from a solid to a nonsolid (e.g., liquid) state by the addition of heat (to the solid substance).

Melting Temperature (of DNA) (Tm) T h e midpoint of the temperature range over which DNA is denatured. See also MELTING

(OF DNA).

Membrane Transport The facilitated transport of a solute across a membrane, usually by a specific membrane protein (e.g., adhesion

molecule). See also ENDOCYTOSIS, EXOCYTOSIS,

SIGNAL TRANSDUCTION, G-PROTEINS , VAGINOSIS,

RECEPTORS, ADHESION MOLECULE, VESICULAR

TRANSPORT, GATED TRANSPORT, CALCIUM CHAN-

NEL-BLOCKERS.

Membrane Transporter Protein A class of transmembrane proteins (i.e., protein molecules embedded in a cell’s membrane, extending through both sides of the membrane) that function to transport certain molecules through the cell’s membrane. Such molecules which are thus “transported” include: sugar molecules (utilized by the cell as “fuel”); inorganic ions (which catalyze certain cellular processes); polypeptides [e.g., “manufactured” in the cell’s ribosome(s) and then secreted from the cell to perform some function elsewhere in the body of the organism]; anticancer drugs; antibiotics. See also PROTEIN, CELL, PLASMA

MEMBRANE, MEMBRANE TRANSPORT, RIBOSOMES,

POLYPEPTIDE (protein), ABC TRANSPORTERS.

Membranes (of a cell) Refers to the thin “skin-like” structures that surround the exterior of a cell (i.e., plasma membrane), and also surround various specialized bodies (nucleus, mitochondria, etc.) within the cell

itself (e.g., the membrane that surrounds the M cell’s nucleus is called the “nuclear enve-

lope”). Membranes are lipoidal, i.e., made of fat-like material, in which proteins and protein complexes are embedded. For example, protein molecules known as receptors are embedded in the plasma membrane (i.e., the outermost membrane of the cell) and in the nuclear envelope. See also C E L L ,

CECROPHINS (LYTIC PROTEINS), MAGAININS,

PLASMA MEMBRANE, TRANSMEMBRANE PROTEINS,

ION CHANNELS, RECEPTORS, NUCLEAR RECEPTORS.

MEMS (nanotechnology) Acronym utilized by Americans to refer to “micro-electrome- chanical systems” (which Europeans tend to refer to as “microsystems technology” —

MST). See also NANOTECHNOLOGY, BIOCHIP,

GENOSENSORS, BIOSENSORS (ELECTRONIC), BIO-

SENSORS (CHEMICAL), NANOCRYSTAL MOLECULES

MICROFLUIDICS, QUANTUM WIRE, QUANTUM DOT,

MOLECULAR MACHINES, BIOMOTORS, BIOMEMS.

mEPSPS The “m” variant (of the many forms of) the enzyme 5-enolpyruvyl-shikimate-3- phosphate synthase. mEPSPS is unaffected by glyphosateor sulfosate-containing herbicides, so introduction of the gene (coding for mEPSPS) into crop plants (e.g.,

© 2002 by CRC Press LLC

corn/maize) makes those crop plants essentially impervious to glyphosateor sulfosatecontaining herbicides. See also ENZYME,

GENE, GENETIC ENGINEERING, EPSP SYNTHASE,

GLYPHOSATE, SULFOSATE, CORN, HERBICIDE-TOL-

ERANT CROP, ARO A.

Mesenchymal Adult Stem Cells See M E S O -

DERMAL ADULT STEM CELLS.

Mesodermal Adult Stem Cells Certain stem cells present within (adult) bodies of organisms, that can be differentiated (via chemical signals) to give rise to bone, muscle, and/or

fat cells. See also STEM CELLS, MULTIPOTENT ADULT STEM CELLS, CELL, ORGANISM, SIGNALING.

Mesophile An organism that grows best in the temperature range of 25°C (77°F) to 40°C

(104°F). See also THERMOPHILE, PSYCHROPHILE.

“Messenger” Molecule See SIGNALING MOLE-

CULE, HORMONE, NITRIC OXIDE.

Messenger RNA (mRNA) Messenger ribonucleic acid. The intermediary molecule between DNA and ribosomes (in a cell) which synthesize (manufacture) those proteins coded for by the cell’s DNA. Upon

Mreceiving the “message” encoded in the DNA, the messenger RNA passes through the ribosomes like a reel of punched paper passes through an old player piano (pianola), giving the ribosomes the specifications for making the coded-for proteins. This process is aided by transfer RNA (tRNA) molecules, which forage for amino acids that float around in the cell (outside of the cell’s nucleus and ribosomes). The transfer RNA (tRNA) molecules attach to, and escort, individual amino acids to the ribosome, as and when the messenger RNA (mRNA) directs. Each of the 20 different amino acids has at least one of its own purpose-built tRNA molecules, which possess a three-letter code of nucleotides at the stem of the cloverleafshaped rRNA molecule.

The ribosome has room for only two tRNA molecules at a time. The messenger RNA (mRNA) molecule (which itself is passing through the ribosome) calls over the first tRNA molecule, which brings with it the specified amino acid. Short sections of the messenger RNA (mRNA) and transfer RNA (tRNA) molecules lock together inside

the ribosome (because where these two molecules meet, their three nucleotides are complementary), the whole (locked together) apparatus shifts along by three notches (i.e., nucleotides), and a second tRNA molecule (bearing another amino acid) slips in next to the first tRNA molecule.

Next, the first amino acid (brought in by the first tRNA molecule) jumps over to the second tRNA molecule, joining to the amino acid that was brought in by the second tRNA molecule, thus making the start of a protein (i.e., a poly-amino acid molecule, also known as polypeptide or protein molecule). The empty (first) tRNA molecule falls out of the ribosome, and the whole (locked together) apparatus (i.e., mRNA plus second tRNA molecule) moves three more notches (i.e., nucleotides) along the mRNA molecule to make room for a third tRNA molecule bearing another amino acid, and so on.

This process of creating ever-longer chains of amino acids continues to repeat itself inside the ribosome until the protein (coded for by the DNA, which code was transferred to mRNA, which transferred it to the ribosome) is completed. See also TRAN-

SCRIPTION, COMPLEMENTARY DNA (c-DNA), CEN-

TRAL DOGMA, DEOXYRIBONUCLEIC ACID (DNA),

RIBONUCLEIC ACID (RNA), NUCLEIC ACIDS, COD-

ING SEQUENCE, GENETIC CODE, CELL, INFORMA-

T I O N A L M O L E C U L E S , C O D O N , R I B O S O M E S ,

POLYRIBOSOME (POLYSOME), rRNA (RIBOSOMAL

RNA), NUCLEOTIDE, POLYMER, TRANSFER RNA

(tRNA), PROTEIN, AMINO ACID, POLYPEPTIDE

(PROTEIN), ANTISENSE (DNA SEQUENCE).

MessengerTM See HARPIN.

Metabolic Engineering The selective, deliberate alteration of an organism’s metabolic pathway(s) via genetic engineering of the genes that define/control the organism’s metabolism. Some reasons to do metabolic engineering of an organism include:

•Altering cell “behavior” and organism metabolic patterns to induce production of proteins/polypeptides and/or metabolites that are desired by mankind (e.g., “golden rice”).

© 2002 by CRC Press LLC

•Altering cell “behavior” and organism metabolic patterns to induce a given organism to consume or accumulate toxic wastes or valuable materials (e.g., gold) that are present at a site in low concentration or highly dispersed.

•Altering cell “behavior” and organism metabolic patterns to cure disease.

See also METABOLISM, INTERMEDIARY METABOLISM, CELL, PATHWAY, METABOLIC PATHWAY,

GENETIC ENGINEERING, ORGANISM, GENE, GENE

SPLICING, PROTEIN, PHYTO-MANUFACTURING,

POLYPEPTIDES, BIOLEACHING, BIODESULFURIZATION, BIORECOVERY, BIOREMEDIATION, GOLDEN

RICE, PHYTOREMEDIATION.

Metabolic Pathway Refers to a particular pathway [i.e., series of chemical reactions, each of which is dependent on previous one(s)] within the overall process of metabolism in an organism. For example, when humans consume the herb known as Saint John’s Wort (Hypericum perforatum), certain components in that herb induce a (new) metabolic pathway — catalyzed by cytochrome P450 enzymes — that (more) rapidly metabolizes (i.e., breaks down) a number of commercial pharmaceuticals (thereby lowering the effectiveness of a given dose of that particular pharmaceutical). See

also METABOLISM, PATHWAY, ORGANISM, INTER-

MEDIARY METABOLISM, CYTOCHROME p450, CYTO-

CHROME P4503A4, CATALYST, GOLDEN RICE.

Metabolism The entire set of enzyme-catalyzed transformations of organic nutrient molecules (to sustain life) in living cells. Conversion of food and water into nutrients that can be used by the body’s cells, and the use of those nutrients by those cells (to sustain life, grow, etc.).

See also ENZYME, CELL, INTERMEDIARY METABOLISM, METABOLITE, COMBINATORIAL BIOLOGY, CIT-

RIC ACID, AFLATOXIN, FUSARIUM, CYTOCHROME

P4503A4, PATHWAY, METABOLIC PATHWAY.

Metabolite A chemical intermediate in the enzyme-catalyzed chemical reactions of metabolism. See also METABOLISM, ENZYME,

CELL, INTERMEDIARY METABOLISM, AFLATOXIN,

FUSARIUM.

Metalloenzyme An enzyme having a metal ion as its prosthetic group. See also ENZYME,

PROSTHETIC GROUP, METALLOPROTEINS.

Metalloproteins A term that is utilized to refer to any protein molecule that contains within it (i.e., in “peptide chain”) a metal atom (zinc, iron, copper, etc.). Approximately one third of all proteins are metalloproteins. Those that contain a zinc atom (Zn2+) are generally enzymes (thus called metalloenzymes), because that metal acts as a catalyst.

See also PROTEIN, PEPTIDE, ENZYME, CATALYST,

METALLOENZYME.

	Metamodel	Methods (of Bioinformatics)
	These refer to methods utilized to integrate
	data that has been independently gener-
	ated/created (and generally stored in separate
	database models) via independent genomics
	research projects, combinatorial chemistry
	projects, high-throughput screening projects
	(e.g., via biochip use), etc. Metamodel meth-
	ods sometimes reveal important interrelation-
	ships that were not apparent in the individual
	models (i.e., created solely for the genomics
	project data, or created solely for the combi-
	natorial chemistry project data, or created
	solely for the high-throughput screening
			M
	project data, etc.). See also BIOINFORMATICS,
	GENOMICS,	FUNCTIONAL GENOMICS, STRUCTURAL
	GENOMICS,	COMBINATORIAL CHEMISTRY, HIGH-

THROUGHPUT SCREENING, BIOCHIP.

Metastasis The process via which a given cancer (e.g., initial tumor) spreads from the site of its initial formation (in body) to other parts of the body. See also CANCER, OLIGOSAC-

CHARIDES, LECTINS, ANGIOGENESIS, GENISTEIN

(Gen), ISOFLAVONES.

Meter A unit of measurement that was contrived by French scientists during the 1670s. It was initially defined to be one ten-mil- lionth of the distance from the earth’s equator to its poles. See also NANOMETERS (NM).

Methionine (met) An essential amino acid; furnishes (to organism) both labile methyl groups and sulfur necessary for normal metabolism. See also ESSENTIAL AMINO ACIDS,

METABOLISM, CYSTINE, HIGH-METHIONINE CORN.

Methyl Jasmonate The volatile chemical compound that results when methyl groups (CH3) are chemically added to a molecule of jasmonic acid. See also JASMONIC ACID.

Methyl Salicylate The volatile chemical compound that results when methyl groups

© 2002 by CRC Press LLC