dalton Unit of molecular mass. Approximately equal to the mass of a
hydrogen atom (1.66 × 10 24 g). default pathway Constitutive secretory pathway that automatically delivers
material from the Golgi apparatus to the plasma membrane if no other sorting
signals are present. degenerate Not a moral judgment but an adjective that describes multiple
states that amount to the same thing: different triplet combinations of
nucleotide bases (codons) that code for the same amino acid, for example. deletion Type of mutation in which a single nucleotide or sequence of
nucleotides has been removed from the DNA. denaturation Dramatic change in conformation of a protein or nucleic acid
caused by heating or by exposure to chemicals and usually resulting in the loss
of biological function. dendrite Extension of a nerve cell, typically branched and relatively short, that
receives stimuli from other nerve cells. dendritic cell Cell derived from bone marrow and present in lymphoid and
other tissues that is specialized for the uptake of particulate material by
phagocytosis and which acts as a "professional" antigen-presenting cell in
immune responses. desmosome Type of anchoring cell cell junction, usually formed between two
epithelial cells, characterized by dense plaques of protein into which
intermediate filaments in the two adjoining cells insert. detergent Type of small amphipathic molecule that tends to coalesce in water,
with its hydrophobic tails buried and its hydrophilic heads exposed. It is
widely used to solubilize membrane proteins. determined In developmental biology, an embryonic cell is said to be
determined if it has become committed to a particular specialized path of
development. This determination reflects a change in the internal character of
the cell, and it precedes the much more readily detected process of cell
differentiation. development Succession of changes that take place in an organism as a
fertilized egg gives rise to an adult plant or animal. diacylglycerol Lipid produced by the cleavage of inositol phospholipids in
response to extracellular signals. Composed of two fatty acid chains linked to
glycerol, it serves as a signaling molecule to help activate protein kinase C. dideoxy method The standard method of DNA sequencing. differentiation Process by which a cell undergoes a change to an overtly
specialized cell type. diffraction pattern Pattern set up by wave interference between radiation
transmitted or scattered by different parts of an object. diffusion Net drift of molecules in the direction of lower concentration due to
random thermal movement. diploid Containing two sets of homologous chromosomes and hence two
copies of each gene or genetic locus. diplotene Fourth stage of division I of meiosis, in which chiasmata are first
seen. disaccharide Carbohydrate molecule consisting of two covalently joined
monosaccharide units. dissociation constant (Kd) Measure of the tendency of a complex to
dissociate. For components A and B and the binding equilibrium A + B AB,
the dissociation constant is given by [A][B]/[AB], and it is smaller the tighter
the binding between A and B. (See also association constant.) disulfide bond ( S S ) Covalent linkage formed between two sulfhydryl
groups on cysteines. For extracellular proteins, a common way of joining two
proteins together or linking different parts of the same protein. Formed in the
endoplasmic reticulum of eucaryotic cells. division I of meiosis The first cell division of meiosis, in which the members
of each pair of (duplicated) homologous chromosomes are segregated to
opposite poles of the dividing cell. division II of meiosis The second cell division of meiosis, in which the
chromatids of each duplicated chromosome are segregated to opposite poles of
the dividing cell. DNA (deoxyribonucleic acid) Polynucleotide formed from covalently linked
deoxyribonucleotide units. It serves as the store of hereditary information
within a cell and the carrier of this information from generation to generation. DNA affinity chromatography Technique for purifying sequence-specific
DNA-binding proteins by their binding to a matrix to which the appropriate
DNA fragments are attached. DNA footprinting Technique for determining the DNA sequence to which a
DNA-binding protein binds. DNA helicase Enzyme that is involved in opening the DNA helix into its
single strands for DNA replication. DNA library Collection of cloned DNA molecules, representing either an
entire genome (genomic library) or DNA copies of the messenger RNA
produced by a cell (cDNA library).
4..4754 (26
DNA ligase Enzyme that joins the ends of two strands of DNA together with a
covalent bond to make a continuous DNA strand. DNA methylation Addition of a methyl group to DNA. Extensive methylation
of the cytosine base in CG sequences is used in vertebrates to keep genes in an
inactive state. DNA microarray Technique for analyzing the simultaneous expression of
large numbers of genes in cells, in which isolated cellular RNA is hybridized
to a large array of short DNA probes immobilized on glass slides. DNA polymerase Enzyme that synthesizes DNA by joining nucleotides
together using a DNA template as a guide. DNA primase Enzyme that synthesizes a short strand of RNA on a DNA
template, producing a primer for DNA synthesis. DNA repair Collective name for those biochemical processes that correct
accidental changes in the DNA. DNA sequencing Determination of the order of nucleotides in a DNA
molecule. (8 36.) DNA supercoiling Additional twisting of the DNA helix that occurs in
response to the superhelical tension created when, for example, a circular DNA
is partly unwound (6 20.) DNA topoisomerase Enzyme that binds to DNA and reversibly breaks a
phosphodiester bond in one or both strands, allowing the DNA to rotate at that
point. It prevents DNA tangling during replication. DNA transcription see transcription DNA tumor virus A general term for a variety of different DNA viruses that
can cause tumors. DNA-only transposon Type of transposable element that exists as DNA
throughout its life cycle. Many types move by cut-and-paste transposition. domain see protein domain dominant negative mutation Mutation that dominantly affects the phenotype
by means of a defective protein or RNA molecule that interferes with the
function of the normal gene product in the same cell. dominant In genetics, refers to the member of a pair of alleles that is
expressed in the phenotype of the organism while the other allele is not, even
though both alleles are present. Opposite of recessive. dorsal Relating to the back of an animal. Also the upper surface of a leaf,
wing, etc. dorsoventral Describes the axis running from the back to the belly of an
animal or from the upper side to the underside of a structure. double helix The three-dimensional structure of DNA, in which two DNA
chains held together by hydrogen bonding between the bases are wound into a
helix. Drosophila melanogaster Species of small fly, commonly called a fruit fly,
much used in genetic studies of development. dynamic instability The property of sudden conversion from growth to
shrinkage, and vice versa, in a protein filament such as a microtubule or actin
filament. dynamin Cytosolic GTPase that binds to the neck of a clathrin-coated vesicle
in the process of budding from the membrane, and which is involved in
completing vesicle formation. dynein Member of a family of large motor proteins that undergo ATPdependent
movement along microtubules. In cilia, dynein forms the side arms
in the axoneme that cause adjacent microtubule doublets to slide past one
another. dysplasia A change in cell growth and behavior in a tissue in which the
structure becomes disordered.
