Slow Diffusion Underlies Alternation of Fast and Slow Growth Periods of Microtubule Assembly

Ming Yang

doi:10.1155/2014/601898

Abstract

In vitro microtubule assembly exhibits a rhythmic phenomenon, that is, fast growth periods alternating with slow growth periods. Mechanism underlying this phenomenon is unknown. Here a simple diffusion mechanism coupled with small diffusion coefficients is proposed to underlie this phenomenon. Calculations based on previously published results demonstrate that such a mechanism can explain the differences in the average duration of the interval encompassing a fast growth period and a slow growth period in in vitro microtubule assembly experiments in different conditions. Because no parameter unique to the microtubule assembly process is involved in the analysis, the proposed mechanism is expected to be generally applicable to heterogeneous chemical reactions. Also because biological systems are characterized by heterogeneous chemical reactions, the diffusion-based rhythmic characteristic of heterogeneous reactions is postulated to be a fundamental element in generating rhythmic behaviors in biological systems.

Highlights

A living system such as a cell consists of multiple heterogeneous catalytic reactions that occur at the solid-liquid interphase
From the small values of Ds of large molecules in cellular compartments one may speculate that slow diffusion rates in heterogeneous catalytic reactions in living systems may generate characteristics that are typically associated with living systems
In [10], the ts without XMAP215 is longer than the ts with XMAP215 (t-test, P = 0.03). These results indicate that the assembly reactions in all conditions occurred at a similar rate, and the variation in total diffusion time primarily derives from the variation in the duration of the slow growth period

Summary

Introduction

A living system such as a cell consists of multiple heterogeneous catalytic reactions that occur at the solid-liquid interphase. How diffusion affects a heterogeneous reaction involving a cellular structure has not been described with the support of experimental data. Diffusion coefficients of small and large molecules in cellular compartments have been experimentally determined, with the Ds of proteins in the cytoplasm of various cells ranging from 0.15 to 40 μm2/s [4,5,6,7]. From the small values of Ds of large molecules in cellular compartments one may speculate that slow diffusion rates in heterogeneous catalytic reactions in living systems may generate characteristics that are typically associated with living systems. The significance of slow diffusion rates to living systems has not been demonstrated with an actual biological process

Methods

Results

Conclusion