(6.4) Molecular motors and free energies. 51 Biology 2 Figure 6.11 shows the set-up of an experiment on the molecular motor RNA polymerase that transcribes DNA into RNA Choosing a good ensemble for this system is a bit involved. It is under two constant forces (F and pressure), and involves complicated chemistry and biology Nonetheless, you know some things based on fun damental principles. Let us consider the optical trap and the distant fluid as being part of the external environment, and define the system’ as the local region of DNA, the RNA, motor, and the fluid and local molecules in a region immedi- ately enclosing the region, as shown in Fig. 6.11. Focused laser Bead RNA DNA