This means that the energy is dispersed throughout the cylinder, as seen in Figure 2. When the polymers separate from one another, they are not crowded together and can take up more space. This means the polymers’ energy is not dispersed throughout the cylinder, a state that is analogous to Figure 1. When the polymers are overlapping, they are close together and compacted. Polymer physics is a wide and varied field that has applications outside of biophysics, but the study of chromosomes is a major focus of research for polymer physicists.
This is a polymer: a series of connected identical molecules called monomers. We can model the chromosomes as simple, hard spheres connected in a ring – like a string of pearls. It is not feasible to model every detail of a chromosome, but even when we greatly simplify it we can still gain information relevant to the physics of the cell. Then we can examine what happens to the orientation of the chromosomes as the system is left to evolve. To understand how entropy plays a part in chromosome segregation, we first need a model of chromosomes inside the cell. Chromosomes that exist in a neat, ordered state inside a cell will inevitably become disordered as time progresses and the system’s energy is dispersed. These concepts can be applied to chromosomes, too. Because of this dispersal of energy, we say that the entropy of the system is high. The particles are spread out evenly, which means that the energy is also dispersed evenly inside the system. High entropy means that the energy of a system is very spread out among its components.įigure 2: Final configuration of the system. It can be described as a measure of the dispersal of energy. This simplicity raises the question: What could possibly drive the chromosomes apart after replication? Statistical physicists have an idea: entropy.Įntropy is a notoriously difficult concept to explain, even in classes focused on statistical mechanics. There are no spindle fibres, no centrioles, or anything else – nothing that aids in moving each chromosome to the corresponding daughter cell.
Bacterial cells lack the structures that facilitate chromosome segregation. Anaphase in bacteria is another story.īacteria are simple structures, much less complicated than eukaryotic cells. Anaphase in eukaryotes is well understood among biologists. These include plant, animal, and fungus cells. This process occurs in eukaryotes, which are organisms whose cells contain a nucleus and other organelles enclosed within membranes. (Roy van Heesbeen of Delta Vision Roy van Heesbeen, Public Domain)