22.1. INTRODUCTION

Biomolecular motor are proteins that, central to their natural function, produce or consume mechanical energy. Working in concert, motor proteins can exert forces exceeding kilonewtons, enabling massive animals such as whales and elephants to move in their native habitats. They can also act individually; piconewton forces from single molecules ferry cargo between different points in a cell, transport ions across membranes, or generate biochemical fuel necessary for other cellular activities. Molecular motors are necessary and vital for cell functions and life processes, transporting essential solutes and organelles when diffusion is insufficient. The ability of biological systems to structure and organize materials hierarchically enables forces ranging over orders of magnitude to arise from the same components.

Although motor proteins have existed in nature for millions of years, much of what we know about them has only been learned in the last decade. Various motor proteins can act as rotary motors, linear steppers, and screws. Individual motors range in size from five to hundreds of nm and can operate over a large range of speeds: different subtypes of Myosin move from 0.06 to 60 ?m/sec!1 Nature has indeed created some highly efficient (some close to 100% efficient)2 compact, and often non-intuitive designs for her molecular motors. Due to their unique sizes, speeds, and functions, the function and mechanisms of motor proteins at the single molecule level have been the subject of much recent scientific...