Molecular Motor - Wik

Molecular motorFrom Wikipedia, the free encyclopedia

Molecular motors are biological molecular machines that are the essential agents of movement in livingorganisms. In general terms, a motor may be defined as a device that consumes energy in one form and convertsit into motion or mechanical work; for example, many protein-based molecular motors harness the chemicalfree energy released by the hydrolysis of ATP in order to perform mechanical work.[1] In terms of energeticefficiency, this type of motor can be superior to currently available man-made motors. One important differencebetween molecular motors and macroscopic motors is that molecular motors operate in the thermal bath, anenvironment in which the fluctuations due to thermal noise are significant.

Contents

1 Examples2 Theoretical Considerations3 Experimental Observation4 Non-biological5 See also6 References7 External links

Examples

Some examples of biologically important molecular motors:[2]

Cytoskeletal motorsMyosins are responsible for muscle contraction, intracellular cargo transport, and producingcellular tension.Kinesin moves cargo inside cells away from the nucleus along microtubulesDynein produces the axonemal beating of cilia and flagella and also transports cargo alongmicrotubules towards the cell nucleus

Polymerisation motorsActin polymerization generates forces and can be used for propulsion. ATP is used.Microtubule polymerization using GTP.Dynamin is responsible for the separation of clathrin buds from the plasma membrane. GTP isused.

Rotary motors:FoF1-ATP synthase family of proteins convert the chemical energy in ATP to the electrochemicalpotential energy of a proton gradient across a membrane or the other way around. The catalysis ofthe chemical reaction and the movement of protons are coupled to each other via the mechanicalrotation of parts of the complex. This is involved in ATP synthesis in the mitochondria andchloroplasts as well as in pumping of protons across the vacuolar membrane[3]

The bacterial flagellum responsible for the swimming and tumbling of E. coli and other bacteriaacts as a rigid propeller that is powered by a rotary motor. This motor is driven by the flow of

Molecular motor - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Molecular_motor

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protons across a membrane, possibly using a similar mechanism to that found in the Fo motor inATP 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]

Helicases separate double strands of nucleic acids prior to transcription or replication. ATP is used.Topoisomerases reduce supercoiling of DNA in the cell. ATP is used.RSC and SWI/SNF complexes remodel chromatin in eukaryotic cells. ATP is used.SMC protein responsible for chromosome condensation in eukaryotic cells.[7]

Viral DNA packaging motors inject viral genomic DNA into capsids as part of their replicationcycle, 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 equationor with Monte Carlo methods. These theoretical models are especially useful when treating the molecular motoras a Brownian motor.

Experimental Observation

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

Fluorescent methods: fluorescence resonance energy transfer (FRET), fluorescence correlationspectroscopy (FCS), total internal reflection fluorescence (TIRF)Magnetic tweezers can also be useful for analysis of motors that operate on long pieces of DNANeutron spin echo spectroscopy can be used to observe motion on nanosecond timescalesOptical tweezers are well-suited for studying molecular motors because of their low spring constantsSingle-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 thatknowledge of naturally occurring molecular motors will be helpful in constructing synthetic nanoscale motors.

Non-biological

Main article: Synthetic molecular motor

Recently, chemists and those involved in nanotechnology have begun to explore the possibility of creatingmolecular motors de novo. These synthetic molecular motors currently suffer many limitations that confine theiruse to the research laboratory. However, many of these limitations may be overcome as our understanding ofchemistry and physics at the nanoscale increases. Systems like the nanocars, while not technically motors, areillustrative of recent efforts towards synthetic nanoscale motors.

See also


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Brownian motorBrownian ratchetCytoskeletonMolecular machinesMolecular mechanicsMolecular propellerMotor proteinsNanomotorProtein dynamicsSynthetic molecular motors

References^ Bustamante C, Chemla YR, Forde NR, Izhaky D(2004). "Mechanical processes in biochemistry".Annu. Rev. Biochem. 73: 705–48.doi:10.1146/annurev.biochem.72.121801.161542(http://dx.doi.org/10.1146%2Fannurev.biochem.72.121801.161542).PMID 15189157 (//www.ncbi.nlm.nih.gov/pubmed/15189157).

1.

^ Nelson, P.; M. Radosavljevic, S. Bromberg (2004).Biological physics. Freeman.

2.

^ Tsunoda SP, Aggeler R, Yoshida M, Capaldi RA(January 2001). "Rotation of the c subunit oligomer infully functional F1Fo ATP synthase". Proc. Natl.Acad. Sci. U.S.A. 98 (3): 898–902.Bibcode:2001PNAS...98..898T(http://adsabs.harvard.edu/abs/2001PNAS...98..898T).doi:10.1073/pnas.031564198 (http://dx.doi.org/10.1073%2Fpnas.031564198). PMC 14681(//www.ncbi.nlm.nih.gov/pmc/articles/PMC14681).PMID 11158567 (//www.ncbi.nlm.nih.gov/pubmed/11158567).

3.

^ Dworkin J, Losick R (October 2002). "Does RNApolymerase help drive chromosome segregation inbacteria?". Proc. Natl. Acad. Sci. U.S.A. 99 (22):14089–94. Bibcode:2002PNAS...9914089D(http://adsabs.harvard.edu/abs/2002PNAS...9914089D).doi:10.1073/pnas.182539899 (http://dx.doi.org/10.1073%2Fpnas.182539899). PMC 137841(//www.ncbi.nlm.nih.gov/pmc/articles/PMC137841).PMID 12384568 (//www.ncbi.nlm.nih.gov/pubmed

4.

/12384568).^ I. Hubscher, U.; Maga, G.; Spadari, S. (2002)."Eukaryotic DNA polymerases". Annual Review ofBiochemistry 71: 133–63.doi:10.1146/annurev.biochem.71.090501.150041(http://dx.doi.org/10.1146%2Fannurev.biochem.71.090501.150041).PMID 12045093 (//www.ncbi.nlm.nih.gov/pubmed/12045093).

5.

^ Smith DE, Tans SJ, Smith SB, Grimes S, AndersonDL, Bustamante C (October 2001). "Thebacteriophage straight phi29 portal motor canpackage DNA against a large internal force". Nature413 (6857): 748–52. Bibcode:2001Natur.413..748S(http://adsabs.harvard.edu/abs/2001Natur.413..748S).doi:10.1038/35099581 (http://dx.doi.org/10.1038%2F35099581). PMID 11607035(//www.ncbi.nlm.nih.gov/pubmed/11607035).

6.

^ Peterson C (1994). "The SMC family: novel motorproteins for chromosome condensation?". Cell 79 (3):389–92. doi:10.1016/0092-8674(94)90247-X(http://dx.doi.org/10.1016%2F0092-8674%2894%2990247-X).PMID 7954805 (//www.ncbi.nlm.nih.gov/pubmed/7954805).

7.

^ Robert Sanders, Molecular motor powerful enoughto pack DNA into viruses at greater than champagnepressures, researchers report(http://www.berkeley.edu/news/media/releases/2001/10/18_motor.html), Press release, University ofCalifornia

8.

External links

Cymobase (http://www.cymobase.org/cymobase) - A database for cytoskeletal and motor proteinsequence informationJonathan Howard (2001), Mechanics of motor proteins and the cytoskeleton. ISBN 9780878933334


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