Why Cells Grow and Divide? General Growth Mechanism and How it Defines Cells’ Growth, Reproduction and Metabolic Properties

Abstract

We consider a general growth mechanism, which acts at cellular level and above (organs, systems and whole organisms). Using its mathematical representation, the growth equation, we study the growth and division mechanisms of amoeba and fission yeast Schizosaccharomyces pombe. We show how this mechanism, together with biomolecular machinery, governs growth and reproduction of cells, and these organisms in particular. This mechanism provides revealing answers to fundamental questions of biology, like why cells grow and divide, why and when cells' growth stops. It also sheds light on questions like why and how life originated and developed. Solving the growth equation, we obtain analytical expression for the growth curve of fission yeast as a function of geometrical characteristics and nutrient influxes for RNA and protein synthesis, and compare the computed growth curves with 85 experiments. Statistical evaluation shows that these growth curves correspond to experimental data significantly better than all previous approximations. Also, using the general growth mechanism, we show how metabolic characteristics of cells, their size and evolutionary traits relate, considering fission yeast. In particular, we found that fission yeast S. pombe consumes about 16-18 times more nutrients for maintenance needs than for biomass synthesis.

Metabolic allometric scaling model. Combining cellular transportation and heat dissipation constraints

“…It is interesting to note that the amoeba, when it grows, also increases its nutrient consumption in a manner similar to that expressed in Eqn 8 (Shestopaloff, 2012a(Shestopaloff, , 2015. The obtained result is valid for other forms increasing proportionally in two dimensions, such as squares, rectangles and stars, whose height remains constant.…”

“…Also, it was found (Shestopaloff, 2014b(Shestopaloff, , 2015 that during normal growth in a stable nutrient environment, the amoeba increases nutrient consumption per unit of surface by approximately 68%, while fission yeast increases consumption by 340%. In other words, the cell membrane capacity of these organisms has several-folds reserve to accommodate the sharp increase of nutrient and waste fluxes when in need.…”

“…For example, the average growth time of fission yeast S. pombe at 25°C is 269 min, while at 28°C it is 167 min (Shestopaloff, 2015). In Glazier (2010), the author summarizes results obtained in Ivleva (1980) for crustaceans as follows: 'the scaling exponent … decreases significantly with habitat temperature (b=0.781±0.016, 0.725±0.086, 0.664±0.026 at temperatures of 20, 25 and 29°C)'.…”

Cell Growth Measurement

“…The cell is the smallest unit of living organisms [1] and grows both in population and size. Cellular growth [2] is tightly regulated and usually shows three sequential steps, including incubation, exponential hyperplasia, and stagnation/ death phases [3]. Unrestricted cell growth causes cancer, and drugs cure the disease by regulating the cell growth back to normal.…”