Figure 50.

(a) Transcription process: Simulation of a long DNA (10,000 units) in a cubic lattice of linear size 100 lattice units, using the reptation method. The red circles represent the transcription targets. A single transcriptor executes a 3D random walk inside the free lattice space and can perform a 1D random walk along the blue path. Once moving along the DNA chain, the transcriptor can leave its 1D walk and move to the 3D free lattice if the target has not been found. Its remains along the DNA for a finite number of steps only, in keeping with the faster diffusion in the free space that accelerates the target-finding process. (b) Simulation of 20 SAW chains with $N=20$ monomers each, using the reptation method, within a cubic lattice of linear size $L=10$ lattice units with PBC, yielding a total chain occupation of 40% inside the confining cube. Courtesy of Francesco Marini.