The strength of the response is fixed and not
dependent on the strength of the stimulus. (5.2)
allosteric regulation regulation of enzyme activity
by inhibitors and activators. (2.2)
allosteric site location on an enzyme at which an
inhibitor molecule binds. (2.2)
Ames test simple test that measures the potential
for a chemical to be mutagenic. (9.1)
amino acid attachment site site at the 3 ′end of the
tRNA strand across from the anticodon loop that
binds a particular amino acid, specified by the
mRNA codon, to a tRNA molecule. (8.3)
amino-acetyl tRNA (aa-tRNA) tRNA molecule
bound to a specific amino acid by an amino acid
attachment site. (8.3)
anaerobic describes an organism, environment, or
cellular process that does not require oxygen.
(3.1)
anaerobic cellular respiration the breakdown of
glucose and formation of ATP molecules in the
absence of oxygen (e.g., during fermentation).
(3.2)
analogous structures body parts in different species
that have a similar function, but evolved
separately (e.g., insect and bird wings). (10.3)
anion negatively charged ion (has more electrons
than protons). (1.2)
antagonistic hormones hormones that have
opposing physiological properties, but that work
together. (4.3, 6.1)
antenna pigments chlorophyll molecules in a
photosystem that collect and channel light
energy. (3.3)
anthropogenic of human origin. (15.3)
antibody immunity defence against previously
encountered diseases that is performed by
B cells. (4.4)
anticodon specialized base triplet located on one
lobe of a tRNA molecule that recognizes its
complementary codon on an mRNA molecule.
(8.3)
anti-diuretic hormone (ADH) hormone that
regulates sodium levels in the bloodstream. The
hormone is produced in the hypothalamus. (6.1)
antigen protein or other large molecule on the
surface of a non-self cell (attacking or unfamiliar
cell) that helps the body recognize the cell as
non-self. (4.4)
antiparallel describes the property by which the 5 ′
to 3 ′phosphate bridges run in opposite
directions on each DNA strand. (7.2)
anti-sense strand strand of nucleotides that is
complementary to a sense strand. (8.2)apoptosis during an immune response, programmed
cell death of plasma cells after the danger has
passed. (4.4)
aqueous humour the liquid filling the area between
the cornea and the lens of the eye. (5.3)
aquifer natural reservoir of groundwater held
beneath the surface of Earth. (15.3)
artificial selection human selection of particular
traits (e.g., faster horses, disease-resistant plants)
by breeding. (10.1)
assortative mating type of non-random mating in
which individuals choose partners that have
similar phenotypes (e.g., size). (11.3)
astigmatism abnormality in the shape of the cornea
or lens that results in uneven focus. (5.3)
atom the smallest unit of matter involved in
chemical reactions. (1.1)
atomic mass the average mass of all the naturally
occurring isotopes of an element (1.2)
atomic number the number of protons in the
nucleus of one atom of an element. Atomic
number is different for every element. (1.2)
AT P adenosine triphosphate. It is the universal
energy unit in cells, and contains adenine (an
amino acid) bound to ribose, which is bound to
three phosphate groups. (2.3)
ATP synthase complex the multienzyme complex
that forms ATP molecules through the movement
of hydrogen ions across a membrane. (3.2)
autonomic nervous system the part of the nervous
system that relays information to internal organs
that are not under the conscious control of the
individual. The system is made up of the
sympathetic and parasympathetic nervous
systems. (5.1)
autotroph a primary producer that gets energy from
the Sun and builds organic molecules from water,
carbon dioxide, and nutrients from soil. (13.2)
axon a long, cylindrical extension of a neuron’s cell
body that can range from 1 mm to 1 m in length.
It transmits impulses along its length to the next
neuron. (5.1)BAC-to-BAC sequencing sequencing step in which
the bacterial artificial chromosomes (BACs) are
broken into smaller fragments that can then be
sequenced using the chain termination reaction.
(9.2)
bacterial artificial chromosome (BAC) bacterial
vector used for DNA cloning. (9.2)
base compound that decreases the concentration of
H+ions in solution, usually by either attracting
H+ions or by releasing OH−ions. (1.3)B
570 MHR • Glossary