A quantitative comparison of cellular motile systems

Abstract

Cellular motile systems as diverse as muscle and the mitotic spindle have been compared by their specific power output: the maximum power they develop per unit of engine volume. Striated muscles and flagella have high specific output; their performance is comparable to that of typical automobile engines. The cytokinetic furrow and the mitotic spindle have very much lower specific power output. The furrow's output is 7,000 times lower than muscle and the spindle's is 300,000 times lower. Different macromolecules have been used to generate power in systems with similar output (muscles and flagella) and, conversely, the same macromolecular motor has been used in systems with very different output (muscles and cytokinetic furrows). The common feature amid this diversity is adaptation to a particular biological role, which specific power output reflects very well. High values are found where a powerful, compact engine should be advantageous, while low values are found where precision, not power, matters most.

Beyond the code: the mechanical properties of DNA as they relate to mitosis

“…How powerful is this machine and how does it compare to other nanomachines? The performance of a machine over a range of sizes can be compared by power output or volume (Nicklas 1984(Nicklas , 1988 (Table 1). This measure includes force and velocity and, by including volume, reveals how concentrated the force generators are.…”

Design Features of a Mitotic Spindle: Balancing Tension and Compression at a Single Microtubule Kinetochore Interface in Budding Yeast

“…The performance of a machine over a range of sizes can be compared by power output/volume (88,89). This measure relates force and velocity to volume to reveal how concentrated force generators are.…”

“…Motor proteins such as kinesin or dynein translocate microtubules on the order of microns/sec. The spindle sacrifices speed to prevent shear force that might damage DNA as well as for accuracy of segregation (88,89). These early mechanical manipulations revealed that velocity was independent of chromosome size, or load-independent, and led to influential models that invoked a "velocity-governor" regulating chromosome movement.…”

“…However, the forces that move chromosomes are also very small (87,88). In proposing new perspectives from a composite mitotic segregation apparatus of DNA and microtubules, one lesson from the physical properties of these polymers is the role of entropic forces.…”

Flagellar apparatus of south‐seeking many‐celled magnetotactic prokaryotes

“…For a spherical assembly with an averaged diameter of 7 lm (Keim et al, 2004b), traveling at 100 lm/s, the power consumed is *6.6 3 10 À16 J/s, which corresponds to *660 ATP molecules/s (Bray, 1992). This figure is relatively low if the typical cell metabolic rate, which is 10 7 ATP molecules/s (Nicklas, 1984), is considered. However, hydrodynamic interactions among the flagella may reduce the nominal efficiency to some extent.…”