structural formula The structural formula of a com-
pound shows how the atoms and bonds are arranged in
the molecule; indicates the arrangement of the atoms in
space.
structure-activity relationship (SAR) The relation-
ship between chemical structure and pharmacological
activity for a series of compounds.
structure-based design A DRUG design strategy
based on the three-dimensional structure of the target
obtained by X ray or NMR.
structure-property correlations(SPC) All statisti-
cal mathematical methods used to correlate any struc-
tural property to any other property (intrinsic,
chemical, or biological); based on statistical regression
and PATTERN RECOGNITIONtechniques.subspecies Ageographical isolate of a species. The
federally listed endangered Karner blue butterfly
(Lycaeides melissa samuelis) is a subspecies of the
Melissa blue butterfly (Lycaeides melissa).
See alsoSPECIES.substrate Asubstrate can be a chemical species of
particular interest, the reaction of which with some
other chemical reagent is under observation (e.g., a
compound that is transformed under the influence of
a catalyst). It can also be the chemical entity whose
conversion to a product or products is catalyzed by an
ENZYME. Also a solution or dry mixture containing all
ingredients that are necessary for the growth of a
microbial culture or for product formation. Finally, it
can be a component in the nutrient medium, supply-
ing the organisms with carbon (C-substrate), nitrogen
(N-substrate), etc.substrate-level phosphorylation The formation or
synthesis of the energy source ATP (adenosine triphos-
phate) by transferring an inorganic phosphate group to
ADP (adenosine diphosphate).HHHHCC OHHThe structural formula of ethanol.316 structural formula
This view of a stromatolite field ground by glaciers shows
the concentric ring formation created over millions of years of
deposition by blue-green alga.(Courtesy of Joseph Deuel,
Petrified Sea Gardens, Inc.)