Guide to BioTerminology 2nd edition - - BioPharm International


Guide to BioTerminology 2nd edition

BioPharm International

detergents Cleaning agents: chemicals with both hydrophobic (averse to water) and hydrophilic (water-attracted) properties that can dissolve fats and oils.

dextran A polysaccharide of bacterial origin.

dialysis/diafiltration Membrane ultrafiltration in which a large solute (such as a protein) is washed or dialyzed with another solution; for example, changing buffer conditions without affecting protein concentration.

diastereomer A stereoisomer (one of two or more molecules with the same atoms in the same order but different three-dimensional shapes) having two or more chiral centers that is not a mirror image of another stereoisomer of the same compound; glucose, galactose, and mannose are all diastereomers.

differential scanning calorimetry Analytical method that independently measures the rate of heat flow to a sample against a reference standard of the same temperature. Data are obtained by monitoring the differential heat flow as a function of temperature. DSC can measure heat capacities, phase transitions, dehydration, and heats of reaction.

diluent A chemically inert substance added to a solution to increase the volume and reduce the concentration; a diluting agent.

dimer A polymer made up of two identical molecules. When three monomers link up, the resultant polymer is called a trimer. Larger polymers are usually referred to by placing a number before the "-mer" suffix: 4-mer, 5-mer, 6-mer, and so on.

dissociation constant A specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions. The dissociation constant is usually denoted K d and is the inverse of the affinity constant. Dissociation constants are commonly used to describe how tightly a ligand (such as a drug) binds to a protein. Such binding is usually non-covalent, i.e., no chemical bonds are made or broken. Since the binding is usually described by a two-state process P + L = C the corresponding dissociation constant is defined K d = [P][L]/[C] where [P], [L] and [C] represent the concentrations of the protein, ligand and bound complex, respectively. The dissociation constant has the units of molar (M), and corresponds to the concentration of ligand [L] at which the binding site on the protein is half occupied, i.e., when the concentration of protein with ligand bound [C] equals the concentration of protein with no ligand bound [P]. The smaller the dissociation constant, the more tightly bound the ligand is; for example, a ligand with a nanomolar (nM) dissociation constant binds more tightly than a ligand with a micromolar (μM) dissociation constant.

disulfide bond A covalent bond formed between sulfur atoms of different cysteines in a protein; such bonds (links, bridges) help hold proteins together

divalent cations Cations with a net positive charge of +2.

DIW Deionized water, very pure water in which contaminants have been ionized and removed by special filtration.

DMSO Dimethysulfoxide; a common cryoprotectant used to cryopreserve cells and tissues.

Using the scanning electron microscope.
DNA Deoxyribonucleic acid, the nucleic acid based on deoxyribose (a sugar) and the nucleotides G, A, T, and C. Double-stranded DNA has a corkscrew-ladder shape (the "double helix") and is the primary component of chromosomes, which thus carry inheritable characteristics of life. (See nucleotides, nucleic acids.)

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