German States (Länder), that regulate all recombinant DNA (i.e., gene-splicing) activities in Germany. See also GENETIC MANIPU-

LATION ADVISORY COMMITTEE (GMAC), CTNBio,

KENYA BIOSAFETY COUNCIL, GENE TECHNOLOGY

OFFICE, RECOMBINANT DNA ADVISORY COMMIT-

TEE (RAC), GENETIC ENGINEERING, RECOMBINANT

DNA (rDNA), RECOMBINATION, BIOTECHNOLOGY,

INDIAN DEPARTMENT OF BIOTECHNOLOGY, COM-

MISSION OF BIOMOLECULAR ENGINEERING.

Zoonoses Diseases that are communicable from animals to humans.

Zoonotic See ZOONOSES.

Zygote A fertilized egg formed as a result of the union of the male (sperm) and female (egg) sex cells. The zygote gives rise to the placenta (lining of the uterus) in addition to growing into the adult (organism) body. See also

X CHROMOSOME , Y CHROMOSOME, TELOMERES,

GAMETE, ORGANISM, CELL, CELL DIFFERENTIATION.

Zyme Systems Chemical reactions characterized by the presence of an inactive precursor

of an enzyme. The enzyme is activated via another enzyme that normally removes an extra piece of peptide chain at a physiologically appropriate time and place. See also ZYMOGENS,

FIBRIN, DIGESTION (WITHIN ORGANISMS).

Zymogens The enzymatically inactive precursors of certain proteolytic enzymes. The enzymes are inactive because they contain an extra piece of peptide chain. When this peptide is hydrolyzed (clipped away) by another proteolytic enzyme, the zymogen is converted into the normal, active enzyme. The reason for the existence of zymogens may be to protect the cell, its machinery, and/or the place of manufacture within the cell from the potentially harmful or lethal effects of an active, proteolytic enzyme. In other words, the strategy is to activate the enzyme only when, and especially where, it

is needed. See also PROTEOLYTIC ENZYMES,

FIBRIN, ZYME SYSTEMS, LIPOPROTEIN-ASSOCIATED

COAGULATION (CLOT) INHIBITOR (LACI).

Z

© 2002 by CRC Press LLC