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Within the cells of the body, intracellular microtubule-based movement is directed by the proteins kinesin anddynein. The long-accepted explanation for this transport action is that the kinesins, fueled by energy provided by ATP, use their twoappendage-like globular heads to “walk” deliberately along the lengths of the microtubule paths to which they are attached.Kinesin, as a motor protein, has conventionally been understood to allow for the movement of objects within cells by harnessing theenergy released from either the breaking of chemical bonds or the energy released across a membrane in an electrochemical gradient.The kinesin proteins thus were believed to function as cellular “tow trucks” that pull chemicals or enzymes along these microtubulepathways.

New research, however, posits that what appeared to be a deliberate towing action along the microtubules isactually a result of random motion controlled by ATP-directed chemical switching commands. It is now argued that kinesins utilizerectified Brownian motion (converting this random motion into a purposeful unidirectional one).

We begin with a kinesin protein with both of its globular heads chemically bound to a microtubule path.According to the traditional power stroke model for motor proteins, the energy from ATP hydrolysis provides the impetus to trigger achemo-mechanical energy conversion, but according to the rectified Brownian motion model, the energy released by ATP hydrolysis causesan irreversible conformational switch in the ATP binding protein, which in turn results in the release of one of the motor proteinheads from its microtubule track. Microtubules are composed of fibrous proteins and include sites approximately 8 nm apart wherekinesin heads can bind chemically. This new model suggests that the unbound kinesin head, which is usually 5-7 nm in diameter, is movedabout randomly because of Brownian motion in the cellular fluid until it by chance encounters a new site to which it can bind.Because of the structural limits in the kinesin and because of the spacing of the binding sites on the microtubules, the moving headcan only reach one possible binding site – that which is located 8 nm beyond the bound head that is still attached to the microtubule.Thus, rectified Brownian motion can only result in moving the kinesin and its cargo 8 nm in one direction along the length of themicrotubule. Once the floating head binds to the new site, the process begins again with the original two heads in interchangedpositions. The mechanism by which random Brownian motion results in movement in only one pre-determined direction is commonly referredto a Brownian ratchet.

Ordinarily, Brownian motion is not considered to be purposeful or directional on account of its sheer randomness.Randomness is generally inefficient, and though in this case only one binding site is possible, the kinesin head can be likened toencounter that binding site by “trial and error.” For this reason, Brownian motion is normally thought of as a fairly slow process;however, on the nanometer scale, Brownian motion appears to be carried out at a very rapid rate. In spite of its randomness,Brownian motion at the nanometer scale allows for rapid exploration of all possible outcomes.

Brownian motion and nanotechnology

An artist’s rendition of a tourist submarine, shrunk to cellular size, in Asimov’s Fantastic Voyage.
If one were to assume that Brownian motion does not exercise asignificant effect on his or her day-to-day existence, he or she, for all practical purposes, would be correct. After all, Brownianmotion is much too weak and much too slow to have major (if any) consequences in the macro world. Unlike the fundamental forces of,for instance, gravity or electromagnetism, the properties of Brownian motion govern the interactions of particles on a minutelevel and are therefore virtually undetectable to humans without the aid of a microscope. How, then, can Brownian motion be of suchimportance?

As things turn out, Brownian motion is one of the main controlling factors in the realm of nanotechnology. When one hears about the concept ofnanotechnology, tiny robots resembling scaled down R2D2-style miniatures of the larger ones most likely come to mind.Unfortunately, creating nano-scale machines will not be this easy. The nano-ships that are shrunk down to carry passengers through thehuman bloodstream in Asimov’s Fantastic Voyage, for example, would due to Brownian motion be tumultuously bumped around and flexed bythe molecules in the liquid component of blood. If, miraculously, the forces of Brownian motion did not break the Van der Waals bondsmaintaining the structure of the vessel to begin with, they would certainly make for a bumpy voyage, at the least.

Eric Drexler’s vision of rigid nano-factories creating nano-scale machines atom by atom seems amazing. While itmay eventually be possible, these rigid, scaled-down versions of macro factories are currently up against two problems: surfaceforces, which cause the individual parts to bind up and stick together, and Brownian motion, which causes the machines to bejostled randomly and uncontrollably like the nano-ships of science fiction.

As a consequence, it would seem that a basic scaling down of the machines and robots of the macro world will notsuffice in the nano world. Does this spell the end for nanotechnology? Of course not. Nature has already proven that thisrealm can be conquered. Many organisms rely on some of the properties of the nano world to perform necessary tasks, as manyscientists now believe that motor proteins such as kinesins in cells rely on rectified Brownian motion for propulsion by means ofa Brownian ratchet. The Brownian ratchet model proves that there are ways of using Brownian motion to our advantage.

Brownian motion is not only be used for productive motion; it can also be harnessed to aid biomolecularself-assembly, also referred to as Brownian assembly. The fundamental advantage of Brownian assembly is that motion isprovided in essence for free. No motors or external conveyance are required to move parts because they are moved spontaneously bythermal agitation. Ribosomes are an example of a self-assembling entity in the natural biological world. Another example of Brownianassembly occurs when two single strands of DNA self-assemble into their characteristic double helix. Provided simply that therequired molecular building blocks such as nucleic acids, proteins, and phospholipids are present in a given environment, Brownianassembly will eventually take care of the rest. All of the components fit together like a lock and key, so with Brownianmotion, each piece will randomly but predictably match up with another until self-assembly is complete.

Brownian assembly is already being used to create nano-particles, such as buckyballs. Most scientists viewthis type of assembly to be the most promising for future nano-scale creations.

Questions & Answers

An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
Akash
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
Carole
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
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salma
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salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
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Tamia
hii
Uday
hi
salma
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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Source:  OpenStax, Nanotechnology: content and context. OpenStax CNX. May 09, 2007 Download for free at http://cnx.org/content/col10418/1.1
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