During mitosis in eukaryotic cells, mechanical forces generated by the mitotic spindle pull the sister chromatids into the nascent daughter cells. How do mitotic chromosomes achieve the necessary mechanical stiffness and stability to maintain their integrity under these forces? Here we use optical tweezers to show that ions involved in physiological chromosome condensation are crucial for chromosomal stability, stiffness and viscous dissipation. We combine these experiments with high-salt histone depletion and theory to show that chromosomal elasticity originates from the chromatin fibre behaving as a flexible polymer, whereas energy dissipation can be explained by modelling chromatin loops as an entangled polymer solution. Taken together, we show how collective properties of mitotic chromosomes, a biomaterial of incredible complexity, emerge from molecular properties, and how they are controlled by the physico-chemical environment.

在真核细胞的有丝分裂过程中，有丝分裂纺锤体产生的机械力将姐妹染色单体拉入新生的子细胞中。有丝分裂染色体如何获得必要的机械刚度和稳定性，以在这些力下保持其完整性？在这里，我们使用光镊来表明参与生理染色体凝聚的离子对于染色体稳定性、刚度和粘性耗散至关重要。我们将这些实验与高盐组蛋白耗竭和理论相结合，表明染色体弹性源于表现为柔性聚合物的染色质纤维，而能量耗散可以通过将染色质环建模为缠结聚合物溶液来解释。综上所述，我们展示了有丝分裂染色体（一种极其复杂的生物材料）的集体特性如何从分子特性中出现，以及它们如何受到物理化学环境的控制。