A 3D dislocation dynamics (DD) model for plastic deformation, which connects the macroscopic mechanical properties to the basic physical laws that govern dislocation mobility and related interaction mechanisms, has been under development. In this model there is a set of critical reactions that, basically, determine the overall results of the simulations. These reactions are annihilation, formation of jogs, junctions, dipoles, and cross-slip. In this paper we discuss these reactions and the manner in which they influence the predicted stress-strain behavior in bcc metals. In particular, the formation (zipping) and strength of dipoles and junctions, and effect of jogs, using the dislocation dynamics model are examined. The strengths (unzipping) of these reactions for various configurations are determined by direct evaluation of the elastic interaction forces.