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Pregnancy Timeline by SemestersFemale Reproductive SystemFertilizationThe Appearance of SomitesFirst TrimesterSecond TrimesterThird TrimesterFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterDevelopmental Timeline
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December 14, 2012--------News Archive Return to: News Alerts


Proteins (in red) are transported along a intracellular highway
(microtubules, in green) to the cell periphery.


Credit: Picture: Sara Wickstroem / Copyright: MPI of Biochemistry







WHO Child Growth Charts

       

New Study Sheds Light on How Cells Transport Materials Along Crowded Intercellular 'Highways'

The study by physicists provides new insights into a cellular system whose failure can lead to neurodegenerative diseases and cancer

The interior of an animal cell is like a small city, with factories—called organelles—dedicated to manufacturing, energy production, waste processing, and other life functions. A network of intercellular "highways," called microtubules, enables bio-molecular complexes, products, and other cargo to move speedily about the cell to keep this vital machinery humming.

A new paper published online in the journal Proceedings of the National Academy of Sciences sheds new light on how cells manage to keep traffic flowing smoothly along this busy transportation network that is vital to the survival of cells and whose failure can lead to a variety of diseases, including Alzheimer's and cancer.

The study, "Motor transport of self-assembled cargos in crowded environments" appeared in Proceedings of the National Academy of Science (PNAS), is co-authored by Jennifer Ross, assistant professor of physics at the University of Massachusetts Amherst, Erkan Tüzel, assistant professor of physics at Worcester Polytechnic Institute (WPI), and Leslie Conway and Derek Wood, graduate students of physics at UMass Amherst. It examines how proteins called motors (the trucks of the intercellular transport network) cooperate to minimize traffic jams and maximize the distance traveled by cargos.

In the study, the researchers used quantum dots (nanometer-sized semiconductors that reflect brightly in microscopy images) as cargo. In the laboratory, they attached these tiny cargos to individual motor proteins and then allowed those proteins to attach to a microtubule.


Motor proteins are able to "walk" along microtubules
by attaching and detaching parts of their structure to
the microtubule, much like the hand-over-hand
motion of a person climbing a rope.

Researchers observed how the quantum dots moved
along the microtubule as they created more and more
traffic by adding more and more motor proteins to
the highways of this simplified transportation system.

They found that the dots moved more slowly as
the traffic increased, but that they were able to travel
farther before becoming detached from the microtubule.

They also observed the pausing of the quantum dots,
with the number of pauses increasing, but the length
of the pauses decreasing, as the concentration
of motor proteins is increased.


The authors hypothesize that as the concentration of motor proteins increased, several of them became bound to each quantum dot. Much like trucks driving side-by-side down a multilane highway, the motor proteins likely became attached to different protofilaments along the microtubule (microtubules are made of 13 parallel protofilaments arranged into a hollow tube).

As an individual protein encountered an obstacle (another motor protein, for example), the motion of the dot would pause until the force exerted by the other proteins attached to the dot caused it to become detached from the blocked protein. The greater the number of proteins pulling the dot along the microtubule, the greater the force acting on it and the more quickly it would become detached from blocked proteins (and thus, the briefer the pauses in its forward motion).

In this way, motor proteins were able to cooperate to move cargo around roadblocks and to keep cargo attached to the microtubules despite heavy traffic, Tüzel says. "This is the first study to really look at the operation of the intracellular transportation system crowded conditions that are typical of living cells," he noted.


"It is important to understand how this system works
and what can keep it from functioning properly
because it is vital to the survival of all animal cells
and motor proteins that make many fundamental
biological processes, such as cell division, possible.

When the transport mechanism fails to work properly,
it can lead to a variety of illnesses, including
neurodegenerative diseases like Huntington's and
Alzheimer's, and to cancer."

Erkan Tüzel
assistant professor, physics
Worcester Polytechnic Institute


Original article: http://www.wpi.edu/news/20123/tuzelpnas.html