Force extension of a titin molecule

Force extension profile of titin unfolding, with worm-like chain fits to the unfolding events.

The unfolded part of the molecule behaves like an entropic spring with a persistence length of 0.4 nm. The repeated I27 domains have a contour length of 28.5 nm, so the total length of the polypeptide increases by this step for each unfolding event.