Molecular motors are biological "nanomachines" and are the essential agents of movement in living organisms. Generally speaking, a motor is defined as a device that consumes energy in one form and converts it into motion or mechanical power; many protein-based molecular motors convert the chemical energy present in ATP into mechanical energy . In terms of energetic efficiency, these types of motors are often superior to currently available man-made motors. One important difference between molecular motors and macroscopic motors is that molecular motors operate in the thermal bath, an environment where thermal noise is significant relative to the motor's energy consumption.

Recently, chemists and those involved in nanotechnology efforts have begun to explore the possibility of creating molecular motors de novo. These synthetic molecular motors currently suffer many limitations that limit their adoption to only experimental use. It should be expected, however, that many of these limitations will soon be overcome, as understanding of chemistry and physics at the nanoscale increases.

Examples

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Some examples of biologically important molecular motors are:

• Moving proteins
  • Myosin is responsible for muscle contraction
  • Kinesin moves cargo within the cell along microtubules
  • Dynein also transports along microtubules
• F₀F₁ ATP synthase generates ATP using the electrochemical proton gradient at the membrane
• RNA polymerase transcribes RNA from a DNA template
• Actin polymerization generates forces and can be used as propulsion
• Topoisomerases reduce supercoiling of DNA in the cell
• The bacterial flagellum is responsible for swimming and tumbling in E. coli and other bacteria
• Synthetic molecular motors have been created by chemists that yield rotation, possibly generating torque

Theoretical Considerations

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Because the motor events are stochastic, molecular motors are often modeled with the Fokker-Planck equation or with Monte Carlo methods. These theoretical models are especially useful when treating the molecular motor as a Brownian motor.

Experimental Observation

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In experimental biophysics, the activity of molecular motors is observed with many different experimental approaches, among them:

• Fluorescent methods: fluorescence resonance energy transfer (FRET), fluorescence correlation spectroscopy (FCS)
• Single-molecule electrophysiology can be used to measure the dynamics of individual ion channels
• Optical tweezers are well-suited for studying molecular motors because of their low spring constants
• Magnetic tweezers can also be useful for analysis of motors that operate on long pieces of DNA

Many more techniques are also used. As new technologies and methods are developed, it is expected that knowledge of naturally occurring molecular motors will be helpful in constructing synthetic nano-scale motors.

References

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1. C. Bustamante, Y. R. Chemla, N. R. Forde, D. Izhaky (2004). "Mechanical processes in biology," Annual Review of Biochemistry, 73: 705-748. PMID 15189157
2. "Rotation of the c subunit oligomer in fully functional F1Fo ATP synthase" by Satoshi P. Tsunoda, Robert Aggeler, Masasuke Yoshida, and Roderick A. Capaldi in Proc Natl Acad Sci U S A (2001) volume 98 pages 898–902.
3. "Does RNA polymerase help drive chromosome segregation in bacteria?" by Jonathan Dworkin and Richard Losick in Proc Natl Acad Sci U S A (2002) volume 99 pages 14089–14094.

See also

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• Cytoskeleton
• Synthetic molecular motors

Biophysics

Motorprotein | Motores moleculares | Moteur protéique | 分子モーター | 分子马达