11.4 DNA as Construction Material 221 If more energy than z opt is used, then decreases because of the energy cost of information; if less, then decreases because of the irreversibility (dissipation, etc.). For a macroscopic system these quantities are insignificant. But consider the myosin motor (Figure 11.2): taking F j 2 pN, the displacement x 10 nm and Q 0.067 aJ (the energy released by hydrolyzing a single ATP molecule), then the energy cost of optimum control, Qz opt , is equivalent to hydrolyzing almost 150 ATP molecules and . = rev / opt D 0.0033. Reversible operation is evidently far from opti- mal; chemical to mechanical conversion occurs at a finite rate that may essentially be uncontrolled, i.e., determined intrinsically. This analysis and conclusion allows the loose coupling model for muscle (Section 11.3.1) to be rationalized. 11.4 DNA AS CONSTRUCTION MATERIAL The specific base-pairing of DNA, together with the ease of nucleotide polymeriza- tion (it can be accomplished artificially using automated equipment) and the relative robustness of the molecule, has engendered interest in the design and construction of artificial nanoscale artifacts of arbitrary shape made from DNA, as Nadrian Seeman