Those Amazing Molecular Motors

In my undergraduate course in biology at Caltech in the late 1950s, a cell was understood simply as a variety of chemical reactions going on inside a tiny test tube.1 Now, 50 years later, scientists know that the structure inside a cell is far more complex and exhibits elegant organization suggestive of a Designer.

Among other things, the cell includes an astonishing array of molecular motors, some of which travel along thin filaments just a few molecules in diameter. The cargoes needed for the various cell processes are hauled around the cell on these microfilaments, in a manner resembling the huge transportation systems found in a modern city.

Biologists have identified multiple categories of motor-proteins in the cell. Three that have been studied extensively are myosins, kinesins, and dyneins.2 The first two contain as many as 20 different classes, and in time it is likely many more will be discovered. The different categories reflect properties such as (a) the motors’ exact shapes dictated by the proteins from which they are made; (b) the types of tracks the motors travel on, whether actin or microtubule microfilaments; and (c) the direction the motors travel along these microfilaments. Stunning illustrations of these motors (and other features and processes within the cell) can be seen in the 8-minute animated video The Inner Life of a Cell, available on Studio Daily.3

Researchers take special interest in comparing these biological motors with those designed by humans. Two key characteristics for comparison are efficiency (where 100% is maximum) and size. For man-made macroscopic devices, electric motors are the most efficient, operating at as much as 64% efficiency. For internal combustion engines, the efficiency rarely gets above 30%. No naturally occurring motors exist at this size.

However, when considering microscopic devices, scientists find many naturally occurring molecular motors that are incredibly small and highly efficient. Over the last few years, the emerging field of nanotechnology, which includes the study, design, and implementation of molecular-scale motors, has mimicked nature’s elegance. While researchers can’t yet build proteins with specific physical shapes, they have constructed motors relying on existing biological systems for components.

Research on the efficiency of nature’s tiny motors is dazzling. The rotary motors of the bacterial cilia and flagellum demonstrate an efficiency near the perfect 100%.4 As a physicist familiar with the difficulty of designing and constructing small, efficient devices, I find this phenomenon absolutely remarkable.

Personal observations notwithstanding, scientists acknowledge that the motors found in biological systems are vastly superior to anything man-made. Nature’s amazing molecular motors also show the characteristics that people usually associate with exquisite design and a Designer.