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Home >> Biotechnology Dictionary >> Dabs - Density gradient centrifugation
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Dab - antibodies with only one (instead of two) protein chain derived from only one of the domains of the antibody structureDabs exploit the finding that, for some antibodies, half of the antibody molecule binds to its target antigen almost as well as the whole moleculeThe potential advantages of dabs are that they can be made easily by bacteria or yeasts, and offer a way to clone antibodylike molecules into bacteria, and hence to be able to easily screen millions of antibodiesRelated ideas are single-chain antigen binding technology (SCA), biosynthetic antibody binding sites (BABS), minimum recognition units (MRUs), and complementary determining regions (CDRs).
Degeneration - 1.changes in cells, tissues or organs due to disease.
2.the reduction in size or complete loss of organs during evolution.
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Dalton - a unit of atomic mass roughly equivalent to the mass of a hydrogen atom1.67 X 10 to 24 g Named after the famous nineteenth-century chemist, John Dalton (1766-1844)) Used in shorthand expressions of molecular weight, especially as kilo (kDa) or megadaltons (MDa), which are equal to respectively to 1 x 103 and X 106 daltons.
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Darwinian cloning - selection of a clone from a large number of essentially random starting points, rather than isolacing a natural gene or making a carefully designed artificial oneMolecules which are more similar to those needed are selected, mutated to generate new variants, and reselected The cycle proceeds until the required molecule is found. The advantage of the system is that the selection is from a vast number of possibilities.
Degeneracy -
the specification of one amino acid by more than one codon It arises from the inevitable redundancy resulting from 64 triplets in a triplet code (4 x 4 x 4 = 64) encoding only 20 amino acids.
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De novo - arising, anew, afresh, once moreAlso ex novo.
Death phase - the fInal growth phase, during which nutrients have been depleted and cell number decreases.
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Deceleration phase - the phase of declining growth rate, following the linear phase and preceding the stationary phase in most batchsuspension cultures.
De differentiation - the process by which cells lose their specialization and proliferate by cell division to form a mass of cells which, in response to appropriate stimuli, may later differentiate again to form either the same cell type or a different one Dedifferentiation occurs in response to wounding and in tissue cultures.
Deficiency - insufficiency or absence of one or more usable forms of enzymatic, nutritional or environmental requirements, so that development, growth or physiological functions are affected.
Defined - 1.fixed conditions of medium, environment and protocol for growth.
2.precisely known and stated dements of a tissue culture mediumif undefined.
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Dehalogenation - the removal of halogen atoms(chlorine, iodine, brominefluorine) from molecules, usually during biodegradation.
Dehiscence - the spontaneous and often violent opening of a fruit, seed pod or anther to release and disperse the seeds or pollen
Dehydrogenase - an enzyme that catalyses the remove of hydrogen atoms in biological reactions.
Dehydrogenation - a chemical reaction in which hydrogen is removed from a compound.
De ionised water - water which is free of most inorganic (not completely free, since Na is present in ample quantities) and most organic compounds.
Deletion - a mutation involving the removal of one or more base pairs in DNA sequence Large deletions are visible as the lack of chromosomal segments.
Deliberate release - putting something into the outside world; in biotechnology it means putting a genetically modified organism (GMO) into field trials.
Deme - a group of organisms in the same taxon.
Demineralise -
to remove the mineral content (salts, ions) from a substance, especially waterRemoval methods include distillation and electrodialysisThe process is de-mineralisation denaturated DNA duplex DNA that has been converted to single strands by breaking the hydrogen bonds of complementary nucleotide pairsUsually achieved by heating.
Denaturation - loss of native configuration' of a macro-molecule (protein or nucleic acid) by physical or chemical means, usually accompanied by loss of biological activityDenatured proteins often unfold their polypeptide chains and express changed properties of solubilityThe separation of duplex nucleic acid molecules into single strandsMost commonly used by genetic engineers to describe the destruction of hydrogen bonds maintaining the double-stranded nature of all or part of a DNA molecule.
Denature -
to induce structural alterations that disrupt the biological activity of a molecule. Often refers to breaking hydrogen bonds between base pairs in double-stranded nucleic acid molecules to produce single-stranded polyuncleotides, or altering the secondary and tertiary structure of a protein, destroying its activity.
Denitrification - a chemical process in which nitrates in the soil are reduced to molecular nitrogen, which is released to the atmosphere.
Density gradient centrifugation - high-speed centrifugation in which molecules float at a point where their density equals that in a gradient of caesium chloride or sucroseThe density gradient may either be formed before centrifugation by mixing two solutions of different density (as in sucrose density gradients) or it can be formed by the process of centrifugation itself (as in CsCl and CS2SO 4 density gradients).
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