Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 32

Competition and gravity preclude the emergence of unicellular organisms over a certain size. Moreover, gradient-based biochemical signaling and interactions would be inefficient on long distances inside large unicellular organisms. Multicellular organisms seem to have found a balance between the speed of response and the size of the cells. Small cells have a larger surface area relative to their volume. Each unit of volume can exchange gases and nutrients at a higher rate compared to larger cells. Note that the principle is equivalent to smaller salt granules that dissolve faster in water than large ones. Cooperation for development of cell specialization in the direction of a circulatory system formation ensured an optimal exchange with the outside environment and a fast response for the entire organism. In the case of very large unicellular organisms, the response time for any stimulus may be dictated by distances inside the cell and the metabolic rate. For instance, a biochemical interaction between two points in the cytoplasm of such an organism would require time and high amounts of messenger molecules to diffuse in a large volume until the target is stochastically encountered. In other words, “time contracts” for giant unicellular organisms. It is likely that giant single-celled organisms have existed in the distant past. However, competition with smaller unicellular organisms with higher response times may have eliminated them from the evolutionary chain.