Featured Research

from universities, journals, and other organizations

How DNA Molecules Move Through Small Spaces:

Date:
October 19, 1999
Source:
Cornell University
Summary:
On a steeplechase track about half the width of a human hair, Cornell University researchers are racing individual DNA molecules to learn how they move through tiny spaces. One of the surprising results: Large DNA molecules squeeze through certain small spaces faster than small ones.

Sometimes the bigger you are, the easier it is to squeeze through

Related Articles


ITHACA, N.Y. -- On a steeplechase track about half the width of a human hair, Cornell University researchers are racing individual DNA molecules to learn how they move through tiny spaces. One of the surprising results: Large DNA molecules squeeze through certain small spaces faster than small ones.

The research is aimed at better understanding the methods biologists use to decipher genetic information contained in a sample of DNA. The findings could help in the development of new DNA chips to speed and simplify such processes as DNA fingerprinting or the sequencing of bases in DNA samples.

In sequencing, for example, a sample of DNA is chopped into many small fragments that are forced through an organic gel that separates them by length as they move through the gel's maze of microscopic pores. Exactly what happens as the fragments move through the maze is difficult to measure because the pores vary randomly in size and shape.

In order to do controlled studies, Harold Craighead, Cornell professor of applied and engineering physics, and graduate students Jongyoon Han and Stephen Turner have used the Cornell Nanofabrication Facility to make microscopically small sieves with openings of controlled sizes. In an experiment reported in the Aug. 23, 1999, issue of Physical Review Letters, they describe the movement of DNA through a microscopic channel with a series of narrow constrictions.

Using the photolithography techniques originally created to make electronic devices on silicon chips, the researchers carved channels 30 microns wide with alternating deep and shallow sections. The deep sections are about 1 micron high. The shallow sections are about 90 nanometers high, small enough to form "traps" that slow the progress of DNA fragments. (A micron, or micrometer, is one-millionth of a meter; a nanometer is one-billionth of a meter, or about three times the diameter of an atom.) DNA molecules in a water solution were introduced at one end of the channel, and an electric field was applied to pull them toward the other end. Even a large molecule like DNA is too small to see under a light microscope; to observe the behavior of individual molecules, the samples were tagged with fluorescent dyes, and researchers observed their movement through a glass plate covering the device. In video, individual molecules traveling through the channel appear as wiggling blobs of light moving across the screen.

Floating freely in water, a DNA chain contracts into a roughly spherical blob. In order to pass through the shallow traps, the molecules have to stretch out into a flatter shape. The time to pass through the channel varies with the time it takes individual molecules to deform and slip through the traps.

The researchers worked with two kinds of DNA. One, called T2 chains, are 4.3 times as long as the other, called T7 chains, and, consequently, contract into a much larger blob. Surprisingly, the larger molecules move through the channel faster. While both molecules move through the deep portions of the channel at the same speed, the smaller molecules wait longer at the beginning of each trap before squeezing through.

The reason, Craighead says, is that after a molecule presses against the start of a trap, a portion of the chain extends into the narrow space, and the rest of the molecule then stretches out to follow. The larger molecule, he explains, presses against the opening over a wider area, offering more places where a bit of itself can pull out to form such a "beachhead."

The researchers made channels with various spacings and found that the time taken by a molecule moving through the entire course also varies with the length of the deep sections of the channel. If the deep section is long enough, a molecule can return fully to its spherical shape before reaching the next trap. Otherwise the molecule might still be partly stretched when it reaches the next trap and can move into it more quickly.

"It was generally believed that it would be more difficult for longer DNA molecules to pass through the small constrictions," Craighead says, pointing out that in gel electrophoresis, longer molecules generally move slower than shorter ones. The opposite occurs in this device, he says, because of the deformability of the DNA polymers and the shape of the constriction. "It is important to recognize that a DNA molecule is not a solid particle and can deform to pass through the constriction," he says.

The paper, titled "Entropic Trapping and Escape of Long DNA molecules at Submicron Size Constriction," appears in the Aug. 23 issue of Physical Review Letters. The research was funded by the National Institutes of Health.

-30-

Related World Wide Web sites -- The Craighead Research Group: http://www.hgc.cornell.edu/frindex.htm


Story Source:

The above story is based on materials provided by Cornell University. Note: Materials may be edited for content and length.


Cite This Page:

Cornell University. "How DNA Molecules Move Through Small Spaces:." ScienceDaily. ScienceDaily, 19 October 1999. <www.sciencedaily.com/releases/1999/10/991019075025.htm>.
Cornell University. (1999, October 19). How DNA Molecules Move Through Small Spaces:. ScienceDaily. Retrieved April 24, 2015 from www.sciencedaily.com/releases/1999/10/991019075025.htm
Cornell University. "How DNA Molecules Move Through Small Spaces:." ScienceDaily. www.sciencedaily.com/releases/1999/10/991019075025.htm (accessed April 24, 2015).

Share This


More From ScienceDaily



More Matter & Energy News

Friday, April 24, 2015

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

3D Food Printing: The Meal of the Future?

3D Food Printing: The Meal of the Future?

AP (Apr. 23, 2015) — Developers of 3D food printing hope the culinary technology will revolutionize the way we cook and eat. (April 23) Video provided by AP
Powered by NewsLook.com
'Safest Bike Ever' Devised by British Entrepreneur

'Safest Bike Ever' Devised by British Entrepreneur

Reuters - Innovations Video Online (Apr. 23, 2015) — A British inventor says his Babel bike is the safest bicycle ever produced. Crispin Sinclair - son of famous British inventor Sir Clive Sinclair - hopes the bike&apos;s safety cage, double seatbelt, and host of other measures will inspire non-cyclists to get in the saddle. Jim Drury went to see it in action. Video provided by Reuters
Powered by NewsLook.com
First Successful Aerial Refueling of a Drone

First Successful Aerial Refueling of a Drone

Reuters - Innovations Video Online (Apr. 23, 2015) — The bat-wing U.S. Navy drone that became the first autonomous airplane to take off and land on an aircraft carrier accomplished yet another milestone on Wednesday, becoming the first unmanned aircraft to undergo aerial refueling. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
Human or Robot You Decide

Human or Robot You Decide

Reuters - Business Video Online (Apr. 23, 2015) — An ultra-realistic humanoid robot called &apos;Han&apos; recognises and interprets people&apos;s facial expressions and can even hold simple conversations. Developers Hanson Robotics hope androids like Han could have uses in hospitality and health care industries where face-to-face communication is vital. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins