Glossary M-O

Metabolism: A general term applied to the chemical process taking place in living tissues, necessary for the maintenance of the living organism.

Micron: A unit of length in the metric system equal to one-thousandth of a millimeter.

Mitochondria: Compartmentalized, double membrane, self-reproducing organelles present in the cytoplasm of almost all living cells.

Molecule: The smallest fundamental unit of a substance which can exist in a free state and still retain the chemical properties of the substance. A molecule consists of a combination of atoms.

mRNA (messenger RNA): All cells store their permanent genetic information in DNA, due to the inherent stability of the DNA molecule. RNA is used to transmit this information to the rest of the cell - DNA information is copied into RNA, which can be read out by the cell's ribsomes. This RNA is then dissoved into its component molecules and reused in the creation of new RNA. These temporary RNA copies of DNA information are known

as "messenger RNA" (mRNA).

Multicelluar: Composed of numerous cells.

Mutagenic: Any agent that causes a permanent change in genetic material.

Mutation: The process in which a gene undergoes a permanent, heritable structural change.

Nanometer: One billionth of a meter, or approximately 250 millionths of an inch.

Nitrogen: A colorless, odorless, gaseous element forming about 47 percent of the earth's atmosphere. In the combined form the element is a constituent of all proteins.

Nitrogen Excretion: The removal of excess nitrogen from the cell.

Nucleocapsids: The core of a virus, including the protein coat and the genetic material contained inside.

Nucleotide: One of the compounds into which nucleic acid splits on hydrolysis, consisting of a nitrogenous base, a sugar, and a phosphate group.

Nuclear Membrane: an ordered membrane interface regulating the exchange of material between the nucleus and cytoplasm of the cell.

Nucleic acid: Chemical compounds at the utmost biologic importance, contained in all living organisms in the form of DNA and RNA; they consist mainly of sugar moiety, nitrogenous bases, and phosphoric acids.

Nucleus: The generally oval protoplasmic body in the center of the cell which contains the genetic material and is surrounded by a nuclear membrane; an essential organelle that controls metabolism, growth, and reproduction.

Organism: Any living entity.

Organelles: A specialized cytoplasmic structure of a cell performing a specific function.

Oxidation: A chemical reaction in which electrons from one reactant (the reducing agent) are transferred to the other reactant (the oxidizing agent); the atoms in the element in the losing electrons increase their valence correspondingly.