Scaling of Cell Growth and Macromolecules

Biological systems span a wide spectrum of scales; size scales ranging from atomic to planetary and time scales from femtoseconds to billions of years. Scaling analysis has been a powerful tool to relate size scales and time scales and has revealed allometric relations between dynamics and sizes across diverse biological organisms, providing a potentially unifying framework. J. T. Bonner has demonstrated a natural scaling of size-scales with time-scales across organisms and showed that they are directly related in his now classic work Why Size Matters . In this article, we focus on cells, the fundamental unit of life that can be unambiguously identified as being ‘alive’. We highlight the size scales of cells from submicron prokaryotes to single cells visible to the naked eye and compare these scales to those of the molecular building blocks of biology, namely, the macromolecules of DNA, RNA, lipids, and proteins. We then examine the scaling of these sizes with the reported times of cell growth, along with molecular replication and turnover. We find that the scaling over such a wide range of molecular and cellular processes matches the classical scaling seen by Bonner across organisms. In conclusion, this scaling relationship points to the need for a more detailed biophysical understanding of how molecular networks govern cellular processes.