ATOMfrom each other (not generally recommended for
precise nomenclature purposes of complicated systems).
In organic systems, the prefix designates groups on
opposite sides of a double bond.
See alsoCIS.
transcription The process by which the GENETIC
information encoded in a linear SEQUENCE of
NUCLEOTIDEs in one strand of DNA is copied into an
exactly complementary sequence of RNA.
transduction (1) The transfer of GENETICinformation
from one bacterium to another by means of a transduc-
ing bacteriophage. When the phage is grown on the first
host, a fragment of the host DNA can be incorporated
into the phage particles. This foreign DNA can be trans-
ferred to the second host upon infection with progeny
phage from the first experiment.
(2) In cell biology, the transduction of a signal
(mechanical signal, hormone, etc.) to cells or tissues
summarizes the chain of events between the primary
reception of the signal and the final response (change
in growth and/or METABOLISM) of the target cells or
tissues. Inorganic substances (e.g., calcium ions) are
frequently involved in the transduction of signals.
transferability Transferability assumes invariance of
properties that are associated conceptually with an
atom or a fragment present in a variety of molecules.
The property, such as ELECTRONEGATIVITY, nucle-
ophilicity, NMR CHEMICAL SHIFT, etc., is held as retain-
ing a similar value in all these occurrences.
transferase An ENZYMEof EC class 2 that catalyzes
the transfer of a group from one SUBSTRATEto another.
See alsoECNOMENCLATURE FOR ENZYMES.
transferrin An iron-transport protein of blood PLASMA
that comprises two similar iron-binding DOMAINs with
high affinity for Fe(III). Similar proteins are found in
milk (lactoferrin) and eggs (ovotransferrin).
transformation The conversion of a SUBSTRATE
into a particular product, irrespective of reagents or
MECHANISMs involved. For example, the transforma-
tion of aniline (C 6 H 5 NH 2 ) into N-phenylacetamide
(C 6 H 5 NHCOCH 3 ) can be effected by the use of
acetyl chloride or acetic anhydride or ketene. A trans-
formation is distinct from a reaction, the full descrip-
tion of which would state or imply all the reactants
and all the products.
See alsoCHEMICAL REACTION.transient (chemical) species Relating to a short-
lived reaction INTERMEDIATE. It can be defined only in
relation to a time scale fixed by the experimental condi-
tions and the limitations of the technique employed in
the detection of the intermediate. The term is a relative
one. Transient species are sometimes also said to be
“metastable.” However, this latter term should be
avoided because it relates a thermodynamic term to a
kinetic property, although most transients are also ther-
modynamically UNSTABLEwith respect to reactants and
products.transition coordinate The reaction coordinate at the
transition state corresponding to a vibration with an
imaginary frequency. Motion along it in the two oppo-
site senses leads toward the reactants or toward the
products.
See also REACTION COORDINATE; TRANSITION
STATE.transition element A transition element is an ele-
ment whose atom has an incomplete d-subshell, or
which gives rise to a cation or cations with an incom-
plete d-subshell. The first transition series of elements
in which the 3d subshell is incomplete is Sc, Ti, V, Cr,
Mn, Fe, Co, Ni, and Cu. The second and third transi-
tion series are similarly derived from the 4d and 5d
subshells.transition state In theories describing ELEMENTARY
REACTIONs, it is usually assumed that there is a transi-
tion state of more positive molar Gibbs energy between
the reactants and the products through which an
assembly of atoms (initially composing the MOLECULAR
ENTITIESof the reactants) must pass upon going from
reactants to products in either direction. In the formal-268 transcription