FIGURE 6.

Energetics of packaging. (a) Force versus distance curve for the packaging of DNA into φ29, as determined in single-molecule pulling experiments (red line) (8), and as measured in a simulation (points) (33). Error bars are ±1 SD. (b) About 39% of the free-energy cost of packaging DNA into the viral capsid is due to the entropic penalty of confinement. The remainder of the cost is due to the change in internal energy, including electrostatic repulsions (51%) and elastic bending deformations (10%). The contributions from DNA stretching, DNA-DNA hard-core repulsions (volume exclusion), and DNA-capsid volume exclusion repulsions are all negligible.