DNA supercoiling A conformation with loops or coils that DNA adopts in response to superhelical tension; conversely, creating various loops or coils in the helix can create such tension.
DNA topoisomerase (topoisomerase) Enzyme that binds to DNA and reversibly breaks a phosphodiester bond in one or both strands. Topoisomerase I creates transient single-strand breaks, allowing the double helix to swivel and relieving superhelical tension. Topoisomerase II creates transient double-strand breaks, allowing one double helix to pass through another and thus resolving tangles. (Figures 5–21 and 5–22)
DNA tumor virus   General term for a variety of different DNA viruses that can cause tumors.
DNA-only transposon   Transposable element that exists as DNA throughout its life cycle. Many move by cut-and-paste transposition. See also transposon.
dolichol   Isoprenoid lipid molecule that anchors the precursor oligosaccharide in the endoplasmic reticulum membrane during protein glycosylation.
domain (protein domain) Portion of a protein that has a tertiary structure of its own. Larger proteins are generally composed of several domains, each connected to the next by short flexible regions of polypeptide chain. Homologous domains are recognized in many different proteins.
Dorsal protein   Transcription regulator of the NFκB family regulating gene expression and involved in establishing the dorsoventral axis in the embryo.
double helix   The three-dimensional structure of DNA, in which two antiparallel DNA chains, held together by hydrogen-bonding between the bases, are wound into a helix.  (Figure 4–5) drivers   Mutations that are causal factors in the development of cancer.
dynamic instability   Sudden conversion from growth to shrinkage, and vice versa, in a protein filament such as a microtubule or actin filament. (Panel 16–2, pp. 902–903) 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   Large motor protein that undergoes ATP-dependent movement along microtubules.
E2F protein   Transcription regulatory protein that switches on many genes that encode proteins required for entry into the  S phase of the cell cycle.
early endosome   Common receiving compartment with which most endocytic vesicles fuse and where internalized cargo is sorted either for return to the plasma membrane or for degradation by inclusion in a late endosome.
ectoderm   Embryonic epithelial tissue that is the precursor of the epidermis and nervous system.
edema factor One of the two A subunits of anthrax toxin; an adenylyl cyclase that catalyzes production of cAMP, leading to ion imbalance and consequent edema in the skin or lung.
effector Bcl2 family proteins   Pro-apoptotic proteins of the intrinsic pathway of apoptosis that in response to an apoptotic stimulus become activated and aggregate to form oligomers in the mitochondrial outer membrane, inducing the release of cytochrome c and other intermembrane proteins. Bax and Bak are the main effector Bcl2 family proteins in mammalian cells.
effector cell   Cell that carries out the final response or function in a particular process. The main effector cells of the immune system, for example, are activated lymphocytes and phagocytes that help eliminate pathogens.
egg-polarity genes Genes in the Drosophila egg that define the anteroposterior and dorsoventral axes of the future embryo through the creation of landmarks (mRNA or protein) in the egg that provide signals organizing the developmental process.
elastic fiber   Extensible fiber formed by the protein elastin in many animal connective tissues, such as in skin, blood vessels, and lungs, which gives them their stretchability and resilience.
elastin   Extracellular protein that forms extensible fibers (elastic fibers) in connective tissues.