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WHY IS THE HELIX SUCH A POPULAR SHAPE? PERHAPS BECAUSE THEY ARE NATURE'S SPACE SAVERS
17 February 2005 - Pennsylvania State University
| Something about nature loves a helix, the ubiquitous spiral shape taken on by DNA and many other molecules found in the cells of living creatures. The shape is so useful that, while researching the means of creating self-assembling artificial helices, physicists at the University of Pennsylvania believe that they have come across a plausible mathematical reason for why the helical shape is so common. Their findings appear in the Feb. 18 issue of the journal Science. |
Something about nature loves a helix, the ubiquitous spiral shape taken on by DNA and many other molecules found in the cells of living creatures. The shape is so useful that, while researching the means of creating self-assembling artificial helices, physicists at the University of Pennsylvania believe that they have come across a plausible mathematical reason for why the helical shape is so common. Their findings appear in the Feb. 18 issue of the journal Science. 'The classic answer is that helices are helical because the shape is dictated by bonds between molecules. But that only answers how a helix is formed and not why they are that shape,' said Randall Kamien, a professor in Penn's Department of Astronomy and Physics. 'It turns out that a helix, essentially, is a great way to bunch up a very long molecule, such as DNA, in a crowded place, such as a cell.' In the dense environment of the cell, long molecular chains frequently adopt ordered helical conformations. Not only does this enable information to be tightly packed, as in DNA, but it also forms a surface that allows molecules, such as the machines that enable DNA transcription and repair, to grapple on to it at regular intervals. To picture how space matters to the formation of helices, Kamien and graduate student Yehuda Snir envisioned the system as a flexible, unbreakable tube immersed in a mixture of hard spheres, analogous to a molecule in a very crowded cell. As they saw it, the space occupied by the tube is space that could be otherwise occupied by the spheres. They find that the best shape for the short flexible tube – the conformation that takes the least amount of energy and takes up the least space – is that of a helix with a geometry close to that found in natural helices. 'It would seem that the success of the helix as a shape in biological molecules is a case of nature working the best it can with the constraints at hand,' Kamien said. 'The spiral shape of DNA is dictated by the space available in a cell much like the way the shape of a spiral staircase is dictated by the size of an apartment.'
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About: Pennsylvania State University
From agricultural college to world-class learning community - the story of the Pennsylvania State University is one of an expanding mission of teaching, research, and public service. But that mission was not so grandly conceived in 1855, when the Commonwealth chartered the school at the request of the Pennsylvania State Agricultural Society. The goal was to apply scientific principles to farming, a radical departure from the traditional curriculum grounded in mathematics, rhetoric, and classical languages. Penn State has continued to respond to Pennsylvania’s changing economic and social needs. In 1989 the Pennsylvania College of Technology in Williamsport became an affiliate of the University. In 1997, Penn State and the Dickinson School of Law joined ranks. And Penn State’s new World Campus, which "graduated" its first students in 2000, uses the Internet and other new technologies to offer instruction on an "anywhere, anytime" basis. To help meet the increasing demands placed on it, Penn State has looked to philanthropy for additional resources. President Bryce Jordan in 1984 launched a six-year effort that raised $352 million in private gifts to the University. This initiative enabled Penn State to attract world-class teachers and researchers, and assist thousands of financially needy and academically talented students. The Grand Destiny campaign (1996-2003) raised $1.37 billion, further strengthening academic programs and broadening the University's service to the Commonwealth and beyond. The Materials Research Institute is an administrative unit that coordinates, supports and performs materials research in association with more than 200 faculty in 15 different departments and 4 colleges. The MRI is established under the Office of the Vice President for Research and Dean of the Graduate School to promote integration of research, teaching and outreach in materials research, science and engineering with a University-wide, interdisciplinary perspective. The MRI has several sister organizations with similar missions including the Institute for Life Science and the Penn State Institutes of the Environment (PSIE). The mission of the MRI is to strategically position Penn State University - its students, research associates, faculty and corporate partners - to make important and significant advances in materials science, materials engineering, and their technological applications for communication, computers, energy, manufacturing, medicine and transportation. |
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