rectly to an atom other than oxygen.
Examples are hydrogen chloride
(HCl) and hydrogen sulphide (H 2 S).
Such compounds are sometimes
called hydracids. Compare oxoacid.
binding site An area on the surface of a molecule that combines
with another molecule. Binding sites
on enzymes can be *active sites or
*allosteric sites.
bioaccumulation An increase in
the concentration of chemicals, such
as pesticides, in organisms that live
in environments contaminated by a
wide variety of organic compounds.
These compounds are not usually decomposed in the environment (i.e.
they are not biodegradable) or metabolized by the organisms, so that their
rate of absorption and storage is
greater than their rate of excretion.
The chemicals are normally stored in
fatty tissues. *DDT is known as a persistent pesticide, as it is not easily
broken down and bioaccumulates
along food chains, so that increasing
concentrations occur in individual organisms at each trophic level.
bioactivation A metabolic process
in which a product that is chemically
reactive is produced from a relatively
inactive precursor.
biochemical fuel cell A system
that exploits biological reactions for
the conversion of biomass (chemical
energy) to electricity (electrical energy). One potential application is the
generation of electricity from industrial waste and sewage. Methyltrophic organisms (i.e. organisms that
use methane or methanol as their
sole carbon sources) are being investigated for their potential use in biochemical fuel cells.
biochemical oxygen demand
(BOD) The amount of oxygen taken
up by microorganisms that decompose organic waste matter in water.
It is therefore used as a measure of
the amount of certain types of organic pollutant in water. BOD is calculated by keeping a sample of water
containing a known amount of oxygen for Üve days at 20°C. The oxygen
content is measured again after this
time. A high BOD indicates the presence of a large number of microorganisms, which suggests a high level
of pollution.
biochemistry The study of the
chemistry of living organisms, especially the structure and function of
their chemical components (principally proteins, carbohydrates, lipids,
and nucleic acids). Biochemistry has
advanced rapidly with the development, from the mid-20th century, of
such techniques as chromatography,
X-ray diffraction, radioisotopic labelling, and electron microscopy.
Using these techniques to separate
and analyse biologically important
molecules, the steps of the metabolic
pathways in which they are involved
(e.g. glycolysis) have been determined. This has provided some
knowledge of how organisms obtain
and store energy, how they manufacture and degrade their biomolecules,
and how they sense and respond to
their environment. See Chronology.
biodiesel See biofuel.
bioelement Any chemical element
that is found in the molecules and
compounds that make up a living organism. In the human body the most
common bioelements (in decreasing
order of occurrence) are oxygen, carbon, hydrogen, nitrogen, calcium,
and phosphorus. Other bioelements
include sodium, potassium, magnesium, and copper. See essential element.
bioenergetics The study of the
Ûow and the transformations of enbinding site
68
b
www.AzShimi.ir www.AzShimi.com
Examples are hydrogen chloride
(HCl) and hydrogen sulphide (H 2 S).
Such compounds are sometimes
called hydracids. Compare oxoacid.
binding site An area on the surface of a molecule that combines
with another molecule. Binding sites
on enzymes can be *active sites or
*allosteric sites.
bioaccumulation An increase in
the concentration of chemicals, such
as pesticides, in organisms that live
in environments contaminated by a
wide variety of organic compounds.
These compounds are not usually decomposed in the environment (i.e.
they are not biodegradable) or metabolized by the organisms, so that their
rate of absorption and storage is
greater than their rate of excretion.
The chemicals are normally stored in
fatty tissues. *DDT is known as a persistent pesticide, as it is not easily
broken down and bioaccumulates
along food chains, so that increasing
concentrations occur in individual organisms at each trophic level.
bioactivation A metabolic process
in which a product that is chemically
reactive is produced from a relatively
inactive precursor.
biochemical fuel cell A system
that exploits biological reactions for
the conversion of biomass (chemical
energy) to electricity (electrical energy). One potential application is the
generation of electricity from industrial waste and sewage. Methyltrophic organisms (i.e. organisms that
use methane or methanol as their
sole carbon sources) are being investigated for their potential use in biochemical fuel cells.
biochemical oxygen demand
(BOD) The amount of oxygen taken
up by microorganisms that decompose organic waste matter in water.
It is therefore used as a measure of
the amount of certain types of organic pollutant in water. BOD is calculated by keeping a sample of water
containing a known amount of oxygen for Üve days at 20°C. The oxygen
content is measured again after this
time. A high BOD indicates the presence of a large number of microorganisms, which suggests a high level
of pollution.
biochemistry The study of the
chemistry of living organisms, especially the structure and function of
their chemical components (principally proteins, carbohydrates, lipids,
and nucleic acids). Biochemistry has
advanced rapidly with the development, from the mid-20th century, of
such techniques as chromatography,
X-ray diffraction, radioisotopic labelling, and electron microscopy.
Using these techniques to separate
and analyse biologically important
molecules, the steps of the metabolic
pathways in which they are involved
(e.g. glycolysis) have been determined. This has provided some
knowledge of how organisms obtain
and store energy, how they manufacture and degrade their biomolecules,
and how they sense and respond to
their environment. See Chronology.
biodiesel See biofuel.
bioelement Any chemical element
that is found in the molecules and
compounds that make up a living organism. In the human body the most
common bioelements (in decreasing
order of occurrence) are oxygen, carbon, hydrogen, nitrogen, calcium,
and phosphorus. Other bioelements
include sodium, potassium, magnesium, and copper. See essential element.
bioenergetics The study of the
Ûow and the transformations of enbinding site
68
b
www.AzShimi.ir www.AzShimi.com