Dabs
(single-domain antibodies) 'Antibodies with only one (instead of two) protein chain derived from only one of the domains of the antibody structure. Dabs exploit the finding that, for some antibodies, half of the antibody molecule binds to its target antigen almost as well as the whole molecule. The potential advantages of dabs are that they can be made easily by bacteria or yeasts, and offer a way to clone antibody-like molecules into bacteria, and hence to be able to easily screen millions of antibodies. Related ideas are single-chain antigen binding technology (SCA), biosynthetic antibody binding sites (BABS), minimum recognition units (MRUs), and complementary determining regions (CDRs).

Darwinian cloning
Selection of a clone from a large number of essentially random starting points, rather than isolating a natural gene or making a carefully designed artificial one. Molecules which are more similar to those needed are selected, mutated to generate new variants, and re-selected. The cycle proceeds until the requiredmolecule is found. The advantage of the system is that the selection is from a vast number of possibilities

Deceleration phase
The phase of declining growth rate, following the linear phase and preceding the stationary phase in most batch-suspension cultures. See growth phases.

Decomposers
Organisms which utilize energy from wastes or dead organism. Decomposers complete the cycle by returning nutrients to the soil or water and carbon dioxide to the air or water.