transcription factor The regulatory protein that
binds to DNA and stimulates the transcription of genes.
transduction (1) The transfer of genetic information
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 incorpo-
rated into the phage particles. This foreign DNA can be
transferred 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.
See alsoGENETIC CODE.
transferase An ENZYME ofEC class 2, which cat-
alyzes the transfer of a group from one SUBSTRATEto
another.
See alsoEC NOMENCLATURE FOR ENZYMES.
transferrin An iron-transport protein of blood PLAS-
MA, that comprises two similar iron-binding DOMAINs
with high affinity for Fe(III). Similar proteins are found
in milk (lactoferrin) and eggs (ovotransferrin).
transfer RNA (tRNA) RNA that translates the
nucleotide language of codons into the amino acid lan-
guage of proteins. The tRNAs bond with amino acids
and transfer them to the ribosomes, where the new pro-
teins are assembled based on the genetic code carried
by mRNA.
transformation The assimilation of external genetic
material into a cell.
transition element A transition element is an element
whose atom has an incomplete d-subshell, or that
gives rise to a cation or cations with an incomplete
d-subshell. The first transition series of elements is Sc,
Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The second and third
transition series are similarly derived: these include the
lanthanoids (lanthanides) and actinoids (actinides),
respectively, which are designated inner (or f) transition
elements of their respective periods in the periodic table.transition-state analog A compound that mimics
the transition state of a substrate bound to an ENZYME.translation The unidirectional process that takes
place on the RIBOSOMEs whereby the genetic informa-
tion present in an mRNA is converted into a corre-
sponding SEQUENCEof amino acids in a protein.
See alsoGENETIC CODE.translocation A mutation that occurs and that
moves a piece of chromosome to a different chromo-
some. A balanced translocation happens when two
chromosomes break and exchange places, leaving no
net loss of genetic material. While an individual with a
balanced translocation will be unaffected, future chil-
dren may be. A Robertsonian translocation occurs
when the translocations of chromosomes involve an
end-to-end fusion with the resulting loss of the short
arms. While the carrier has 45 chromosomes and is
normal, resulting children may be affected. A reciprocal
translocation happens when single breaks in two non-
homologous chromosomes produce an exchange of
chromosome sections between them. An insertion is a
form of translocation where an interstitial segment
from one chromosome that resulted from two breaks is
inserted within a nonhomologous chromosome at a
third break point.
Translocation is also the term used for the trans-
port of food by way of the phloem.transpiration The loss of water from a plant or tree
by way of the stomata.transposon(transposable element) A mobile piece
of DNA that can move and be inserted into a new loca-
tion (transposition). Formerly called jumping genes.328 transcription factor