Molecular motors are biological molecular machines that are the essential agents of movement in living organisms. Generally speaking, a motor may be defined as a device that consumes energy in one form and converts it into motion or mechanical work; for example, many protein-based molecular motors harness the chemical free energy released by the hydrolysis of ATP in order to perform mechanical work [1]. In terms of energetic efficiency, these types of motors can be 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 the fluctuations due to thermal noise are significant.
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Examples
Some examples of biologically important molecular motors[2]:
- Cytoskeletal motors
- Polymerisation motors
- Rotary motors:
- FoF1-ATP synthase generates ATP using the transmembrane electrochemical proton gradient inside mitochondria [3]
- The bacterial flagellum responsible for the swimming and tumbling of E. coli and other bacteria acts as a rigid propeller that is powered by a rotary motor. This motor is driven by the flow of protons across a membrane, possibly using a similar mechanism to that found in the Fo motor in ATP synthase.
- Nucleic acid motors:
- RNA polymerase transcribes RNA from a DNA template [4]
- DNA polymerase turns single-stranded DNA into double-stranded DNA. [5][6]
- Nucleic acid double strand separation prior to transcription or replication (helicase)
- Topoisomerases reduce supercoiling of DNA in the cell
- chromatin remodeling (RSC complex)
- chromosome condensation (SMC protein)[7]
- Viral DNA packaging motors inject viral genomic DNA into capsids as part of their replication cycle, packing it very tightly. [8]
- Synthetic molecular motors have been created by chemists that yield rotation, possibly generating torque
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.
Experimental Observation
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)
- Magnetic tweezers can also be useful for analysis of motors that operate on long pieces of DNA
- Neutron spin echo spectroscopy can be used to observe motion on nanosecond timescales
- Optical tweezers are well-suited for studying molecular motors because of their low spring constants
- Single-molecule electrophysiology can be used to measure the dynamics of individual ion channels
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 nanoscale motors.
Non-biological
Recently, chemists and those involved in nanotechnology have begun to explore the possibility of creating molecular motors de novo. These synthetic molecular motors currently suffer many limitations that confine their use to the research laboratory. However, many of these limitations may be overcome as our understanding of chemistry and physics at the nanoscale increases. Systems like the nanocars, while not technically motors, are illustrative of recent efforts towards synthetic nanoscale motors.
See also
- Brownian motor
- Brownian ratchet
- Cytoskeleton
- Molecular machines
- Molecular mechanics
- Molecular propeller
- Motor proteins
- Nanomotor
- Protein dynamics
- Synthetic molecular motors
References
- ^ C. Bustamante, Y. R. Chemla, N. R. Forde, D. Izhaky (2004). "Mechanical processes in biology," Annual Review of Biochemistry, 73: 705-748. PMID 15189157
- ^ Nelson, P.; M. Radosavljevic, S. Bromberg (2004). Biological physics. Freeman.
- ^ "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
- ^ "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
- ^ I. Hubscher, U.; Maga, G.; Spadari, S. (2002). "Eukaryotic DNA polymerases". Annual Review of Biochemistry 71: 133. doi:. PMID 12045093.
- ^ Nature 413, 748-752 (18 October 2001) | doi:10.1038/35099581;
- ^ Peterson C (1994). "The SMC family: novel motor proteins for chromosome condensation?". Cell 79 (3): 389–92. doi:. PMID 7954805.
External links
- Cymobase - A database for cytoskeletal and motor protein sequence information
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