Figure 8. Simulation of pulling of the model chromatids.

A. Model chromatids at different pulling forces. For small elongations the chromatid is stretched but the total number of cross-links does not change. For higher elongation the number of cross-links decreases rapidly and the chromatid becomes inhomogeneous. B. Detailed look at the force elongation curve for the configuration . In the range of extensions up to two times of the native length, a linear dependency can be observed, where the total number of cross-links remains nearly constant. For higher extensions a force plateau is reached. Here the number of cross-links decreases and the chromatid is unfolded rapidly. This region corresponds to a decondensation region. C. The slope of the force elongation curve in the linear part depends strongly on the mean loop concentration. Here we show results for and three different values for . The force modulus for configurations with mean loop concentration is more than double than the modulus for configurations with . Hence we conclude that different elastic responses can be explained by altered loop structures. The inset shows the relative change in chromatid thickness against the relative extension. Similar Poisson's ratios are obtained for the different configurations. The values are in the range and and therefore close to experimental findings. D. Although the total number of loops is constant in the linear region, there are changes in the loop structure. Shown are results for . The loop domains are reorganized due to the pulling force, with the proportion of small loops (size) increasing at the expense of the number of large loops (size). As the thickness is essentially determined by the size of the loops this finding indicates that chromosome width decreases in this area which is consistent with experimental results.