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^[1]. 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. A motor is a device that converts energy into mechanical power, and is often synonymous with engine. ... Thermal bath has different meanings in various contexts. ... Johnson-Nyquist noise (sometimes thermal noise, Johnson noise or Nyquist noise) is the noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor, which happens without any applied voltage, due to the random thermal motion of the charge carriers (the electrons). ...

Examples

Some examples of biologically important molecular motors are:

• 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^[2]
• RNA polymerase transcribes RNA from a DNA template^[3]
• 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

Myosin is a motor protein filament found in muscle tissue. ... Kinesins typically consist of two large globular heads that allow attachment to microtubules, a central coiled region, and a region termed light-chain, which connects the kinesin to the intracellular component to be moved. ... Microtubules are protein structures found within cells. ... Dynein is a class of protein found in biological cells and is involved in their reproduction. ... An ATP synthase (EC 3. ... The enzyme RNA polymerase or RNAP is a nucleotidyltransferase that polymerises ribonucleotides in accordance with the information present in DNA. RNA polymerase enzymes are essential and are found in all nucleated cells of all organisms. ... Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ... Actin (red) profilin (blue) complex Actin is a globular protein that polymerizes helically forming actin filaments (or microfilaments), which like the other two components of the cellular cytoskeleton form a three-dimensional network inside an eukaryotic cell. ... Propulsion method may refer to a number of different articles: For a list of space transport methods, see spacecraft propulsion. ... Topoisomerases (type I: EC 5. ... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Binomial name Escherichia coli T. Escherich, 1885 E. coli at 10,000x magnification Escherichia coli (usually abbreviated to E. coli) is one of the main species of bacteria that live in the lower intestines of warm-blooded animals (including birds and mammals) and are necessary for the proper digestion of...

Theoretical Considerations

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. Stochastic, from the Greek stochos or goal, means of, relating to, or characterized by conjecture; conjectural; random. ... The Fokker-Planck equation (also known as the Kolmogorov Forward equation) describes the time evolution of the probability density function of position and velocity of a particle. ... Monte Carlo methods are a class of computational algorithms for simulating the behavior of various physical and mathematical systems. ... Brownian motors are nano-scale or molecular devices by which thermally activated processes (chemical reactions) are controlled and used to generate directed motion in space and to do mechanical or electrical work. ...

Experimental Observation

In experimental biophysics, the activity of molecular motors is observed with many different experimental approaches, among them: Biophysics (also biological physics) is an interdisciplinary science that applies theories and methods of the physical sciences to questions of biology. ...

• 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 ocurring molecular motors will be helpful in constructing synthetic nano-scale motors. Fluorescence resonance energy transfer (or Förster resonance energy transfer) describes an energy transfer mechanism between two fluorescent molecules. ... Also known as FCS Categories: Science stubs | Spectroscopy | Biochemistry | Cell biology | Biotechnology | Microscopes | Biophysics ... This article needs to be cleaned up to conform to a higher standard of quality. ... Optical tweezers are the application of a laser beam to physically move very small translucent objects. ...

References

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. Full text at PMC: 14681
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. Full text at PMC: 137841

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See also

• Nanotechnology
• Stochastic processes
• Cytoskeleton