Models of the pericentric chromatin spring. (A–C) The pericentric chromatin (40–50 kb) is modeled as a linear loop (A), a 30-nm chromatin fiber (B), or a network of thermally fluctuating loops, denoted as thermal loops (C). The inset details three spring models: (i) the protein spring, in which cohesin and/or condensin (gray) linked via DNA are the elastic elements; (ii) the DNA spring, in which the DNA WLC adopts a random coil that expands and contracts in response to force; and (iii) the axial DNA/protein spring, in which protein springs limit the amount of DNA under tension, which in turn increases the spring constant. Elastic proteins and the DNA WLC expand and contract in response to force.