naturally, such as a *polysaccharide,
*protein, or *nucleic acid.bioreactor (industrial fermenter)A
large stainless steel tank used to
grow producer microorganisms in
the industrial production of enzymes
and other chemicals. After the tank
is steam-sterilized, an inoculum of
the producer cells is introduced into
a medium that is maintained by
probes at optimum conditions of
temperature, pressure, pH, and oxy-
gen levels for enzyme production. An
agitator(stirrer) mixes the medium,
which is constantly aerated. It is es-
sential that the culture medium is
sterile and contains the appropriate
nutritional requirements for the
microorganism. When the nutrients
have been utilized the product is sep-
arated; if the product is an extracellu-
lar compound the medium can be
removed during the growth phase of
the microorganisms, but an intracel-
lular product must be harvested
when the batch culture growth stops.
Some bioreactors are designed for
continuous culture.biosensorA device that uses an im-
mobilized agent to detect or measure
a chemical compound. The agents in-
clude enzymes, antibiotics, or-
ganelles, or whole cells. A reaction
between the immobilized agent and
the molecule being analysed is trans-
duced into an electronic signal. This
signal may be produced in response
to the presence of a reaction product,
the movement of electrons, or the
appearance of some other factor (e.g.
light). Biosensors are being used in-
creasingly in diagnostic tests: these
allow quick, sensitive, and speciÜc
analysis of a wide range of biological
products, including antibiotics, vita-
mins, and other important biomole-
cules (such as glucose), as well as the
determination of certain *xenobi-otics, such as synthetic organic com-
pounds.biosynthesisThe production of
molecules by a living cell, which is
the essential feature of *anabolism.
biotechnologyThe development
of techniques for the application of
biological processes to the produc-
tion of materials of use in medicine
and industry. For example, the pro-
duction of antibiotics, cheese, and
wine rely on the activity of various
fungi and bacteria. Genetic engineer-
ing can modify bacterial cells to syn-
thesize completely new substances,
e.g. hormones, vaccines, monoclonal
antibodies, etc., or introduce novel
traits into plants or animals.biotin A vitamin in the *vitamin B
complex. It is the *coenzyme for var-
ious enzymes that catalyse the incor-
poration of carbon dioxide into
various compounds. Adequate
amounts are normally produced by
the intestinal bacteria; other sources
include cereals, vegetables, milk, and
liver.
biotiteAn important rock-forming
silicate mineral, a member of the
*mica group of minerals, in common
with which it has a sheetlike crystal
structure. It is usually black, dark
brown, or green in colour.bipySee dipyridyl.bipyramidSee complex.bipyridylSee dipyridyl.biradical(diradical)A radical that
has two unpaired electrons at differ-
ent points in the molecule, so that
the radical centres are independent
of each other.birefringence See double refrac-
tion.Birge–Sponer extrapolationA
method used to calculate the heat ofbioreactor 72b