Skip to main content
. 2007 Jun 8;93(7):2400–2409. doi: 10.1529/biophysj.107.106112

FIGURE 2.

FIGURE 2

Measurements with 1000-basepair-long double-stranded DNA (DNA1000s). (a) Example of a typical force-extension curve. The inset shows the experimental setup. Complementary single strands are attached to the tip of a cantilever and the surface. By lowering the cantilever, the two single strands hybridize and form a duplex. By retracting the cantilever from the surface the DNA duplex is loaded with force until it finally ruptures. The force-extension curve (recorded at a velocity of 632 nm/s) exhibits a B-S transition between 65 and 75 pN. Due to incomplete hybridization the B-S transition only shows a lengthening of 25 nm, which corresponds to a DNA duplex with 105 basepairs. After the B-S transition the force increases to a value of ∼130 pN where the DNA finally ruptures. (b) Histogram of the rupture forces of DNA1000s. The histogram (FWHM = 37.8 pN) clearly shows that the DNA duplex ruptures at forces higher than the B-S transition force.