Cell Geometry: How Cells Count and Measure Size

The cell represents a highly organized state of living matter in which numerous geometrical parameters are under dynamic regulation in order to match the form of a cell with its function. Cells appear capable of regulating not only the total quantity of their internal organelles, but also the size and number of those organelles. The regulation of three parameters, size, number, and total quantity, can in principle be accomplished by regulating the production or growth of organelles, their degradation or disassembly, and their partitioning among daughter cells during division. Any or all of these steps could in principle be under regulation. But if organelle assembly or disassembly is regulated by number or size, how would the cell know how many copies of an organelle it has, or how big they are?