Molecular motor - Citizendia

Molecular motors are biological molecular machines that are the essential agents of movement in living organisms. A molecular machine has been defined as a discrete number of molecular components that have been designed to perform mechanical-like movements (output in response to specific stimuli 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 Physics, mechanical work is the amount of Energy transferred by a Force. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In Thermodynamics, the Gibbs free energy ( IUPAC recommended name Gibbs energy or Gibbs function) is a Thermodynamic potential which Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy 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. In Thermodynamics and Statistical mechanics, a thermal bath is a reservoir of particles at finite temperature that is in thermal contact and is undergoing Brownian In Statistical physics, the fluctuation dissipation theorem is a powerful tool for predicting the non-equilibrium behavior of a system — such as the irreversible

1 Examples
2 Theoretical Considerations
3 Experimental Observation
4 Non-biological molecular motors
5 References
6 See also

Examples

Some examples of biologically important molecular motors:

Motor proteins
- Myosin is responsible for muscle contraction
- Kinesin moves cargo inside cells away from the nucleus along microtubules
- Dynein produces the axonemal beating of cilia and flagella and also transports cargo along microtubules towards the cell nucleus
- Dynamin is responsible for the separation of clathrin buds from the plasma membrane. Motor proteins are a class of Molecular motors that are able to move along the surface of a suitable substrate Myosins are a large family of Motor proteins found in Eukaryotic tissues. Kinesins are a class of Motor proteins found in Eukaryotic cells Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers Dynein is a Motor protein (also called molecular motor or motor molecule in cells which converts the chemical Energy contained in ATP into the Chlamydomonas TEM 17jpg|thumb|Micrograph of thin x-section cut through Chlamydomonas axoneme]]Numerous Eukaryotic cells carry whip-like appendages ( Cilia A cilium (plural cilia) is an Organelle found in eukaryotic cells Cilia are tail-like projections extending approximately A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Dynamin is a GTPase responsible for Endocytosis in the eukaryotic cell Clathrin is a Protein that is the major constituent of the 'coat' of the clathrin- Coated pits and coated Vesicles formed during Endocytosis
Polymerases
- RNA polymerase transcribes RNA from a DNA template^[2]
- DNA polymerase turns singlestranded DNA into doublestranded DNA. A polymerase (EC 2776/7/19/48/49 is an Enzyme whose central function is associated with Polymers of Nucleic acids such as RNA and DNA RNA polymerase ( RNAP or RNApol) is an Enzyme that produces RNA. Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known A DNA Polymerase is an Enzyme that assists in DNA replication. ^[3]
Actin polymerization generates forces and can be used for propulsion
F_oF₁ ATP synthase generates ATP using the transmembrane electrochemical proton gradient inside mitochondria^[4]
Topoisomerases reduce supercoiling of DNA in the cell
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. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of An ATP synthase ( is a general term for an Enzyme that can synthesize Adenosine triphosphate (ATP from Adenosine diphosphate (ADP and inorganic In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Topoisomerases (type I, type II) are Isomerase Enzymes that act on the topology of DNA. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it This motor is driven by the flow of ions across a membrane, possibly using a similar mechanism to that found in the F_o motor in ATP synthase.
Viral DNA packaging motors inject viral genomic DNA into capsids as part of their replication cycle, packing it very tightly. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known ^[5]
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. Synthetic molecular motors are Molecular machines capable of rotation under energy input Stochastic (from the Greek "Στόχος" for "aim" or "guess" means Random. The Fokker–Planck equation describes the Time evolution of the Probability density function of the position of a particle and can be generalized to other observables Monte Carlo methods are a class of Computational Algorithms that rely on repeated Random sampling to compute their results These theoretical models are especially useful when treating the molecular motor as a Brownian motor. 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

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)
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. Biophysics (also biological physics) is an Interdisciplinary Science that employs and develops theories and methods of the Physical sciences for Förster resonance energy transfer (abbreviated FRET) also known as Fluoresence resonance energy transfer or resonance energy transfer ( RET Fluorescence correlation spectroscopy ( FCS) is a common technique used by physicists chemists and biologists to experimentally characterize the dynamics of fluorescent species Electrophysiology (from Greek grc ἥλεκτρον ēlektron, "amber" the [[Electron#Etymology|etymology of "electron"]] grc φύσις An optical tweezer is a scientific instrument that uses a focused Laser beam to provide an attractive or repulsive force (typically on the order of pico Newtons) depending 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 molecular motors

Recently, chemists and those involved in nanotechnology have begun to explore the possibility of creating molecular motors de novo. A chemist is a Scientist trained in the Science of Chemistry. Nanotechnology, sometimes shortened to nanotech, refers to a field of Applied science whose theme is the control of matter on an Atomic and Molecular These synthetic molecular motors currently suffer many limitations that confine their use to the research laboratory. Synthetic molecular motors are Molecular machines capable of rotation under energy input 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. The nanocar is a molecule designed in 2005 at Rice University in the group of Professor James Tour.

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
^ "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. PubMed Central is a free digital database of full-text Scientific literature in biomedical and life sciences Full text at PMC: 137841
^ Robert Sanders, Molecular motor powerful enough to pack DNA into viruses at greater than champagne pressures, researchers report, Press release, University of California

Contents

Examples

Theoretical Considerations

Experimental Observation

Non-biological molecular motors

References

See also