The secret life of knots

Timing and properties of spontaneous knotting in the macromolecular world

2013-06-10

(Press-News.org) Nanotechnologies require a detailed knowledge of the molecular state. For instance, it is useful to know when and how a generic polymer, a long chain of polymers (chain of beads), knots. The study of molecular entanglement is an important field of study as the presence of knots affects its physical properties, for instance the resistence to traction. Previous studies had mainly obtained "static" data on the knotting probability of such molecules. In other words, they focused on the likelihood that a polymer may knot. The novelty of the study carried out by Micheletti and colleagues lies in the fact that this time the dynamic aspect of the phenomenon has been simulated.

"It's a little like the difference that lies between a disorganized collection of photographs and a video. With the former we obtain statistical information (for instance, how many times a knot will appear), but we don't know how that situation occurred and how it will evolve", explained Micheletti. "Thanks to dynamic simulation we have found, for instance, that knots tend to form at the ends, where they are very frequent yet ephemeral, that is, they are short-lived."

According to the team's observations, in fact, once formed the knot moves along the chain in an apparently casual manner, it may take a step to the left, then two to the right and so on, so that at the end of the chain it generally tends to disappear, "falling" outside the filament. Micheletti also explains that, although more infrequently, it has been observed that the knot moves towards the centre of the polymer: "When this occurs, the knots average lifetime is higher than when they remain trapped at the ends."

At the center of the polymer also slip-knots or pseudo-knots, may form. "At first a loop is formed and this blocks another part of the filament. If thermal fluctuations pull to the correct side the knot disappears, while if they pull to the loop side, a proper knot may be created. These knots are very long-lived," explains Rosa.

"This research is useful since the data on simple knotting probability reveal nothing about knotting timing", underlines Tubiana. "If knots form and disappear very quickly, after a certain amount of time we may observe a given percentage of average knotting, yet we do not know whether the knots have remained the same or if they have changed through time. Researchers who carry out experiments of this kind need, instead, more detailed information."

INFORMATION:

Cristian Micheletti will present these data on 10 June at Harvard University, in the United States, as one of the four speakers selected for the Engineering and Physical Biology Symposium 2013.

"Spontaneous Knotting and Unknotting of Flexible Linear Polymers: Equilibrium and Kinetic Aspects", L. Tubiana, A. Rosa, F. Fragiacomo, and C. Micheletti; Macromolecules, 2013, 46 (9), pp 3669 DOI: 10.1021/ma4002963

ELSE PRESS RELEASES FROM THIS DATE:

Uni Basel researchers discover master regulator in cancer metastasis

2013-06-10

The predominant cause of death in cancer patients is metastasis, the formation of secondary tumors in other organs like the brain, liver, and lungs. Cancer cells detach from the original primary tumor and reach a single cell or group of cells in another organ. The cells of the body normally remain in place through adhering to an extracellular substance. However, cancer cells learn how to release themselves from these bonds and invade surrounding tissues, blood, and the lymphatic system. The transformation of sedentary, specialized cells into wandering, invasive, and ...

Do antidepressants impair the ability to extinguish fear?

2013-06-10

An interesting new report of animal research published in Biological Psychiatry suggests that common antidepressant medications may impair a form of learning that is important clinically. Selective serotonin reuptake inhibitors, commonly called SSRIs, are a class of antidepressant widely used to treat depression, as well as a range of anxiety disorders, but the effects of these drugs on learning and memory are poorly understood. In a previous study, Nesha Burghardt, then a graduate student at New York University, and her colleagues demonstrated that long-term SSRI treatment ...

Treatment of mental illness lowers arrest rates, saves money

2013-06-10

Research from North Carolina State University, the Research Triangle Institute (RTI) and the University of South Florida shows that outpatient treatment of mental illness significantly reduces arrest rates for people with mental health problems and saves taxpayers money. "This study shows that providing mental health care is not only in the best interest of people with mental illness, but in the best interests of society," says Dr. Sarah Desmarais, an assistant professor of psychology at NC State and co-author of a paper describing the research. The researchers wanted ...

How Archaea might find their food

2013-06-10

The microorganism Methanosarcina acetivorans lives off everything it can metabolize into methane. How it finds its sources of energy, is not yet clear. Scientists at the Ruhr-Universität Bochum together with colleagues from Dresden, Frankfurt, Muelheim and the USA have identified a protein that might act as a "food sensor". They characterized the molecule in detail and found both similarities and differences to the system that is responsible for the search for food in bacteria. The team reports in the Journal of Biological Chemistry. MsmS has a different function to that ...

Eww! Only 5 percent of us wash hands correctly

2013-06-10

VIDEO: A study by Michigan State University researchers found that only 5 percent of people who used the bathroom washed their hands long enough to kill the germs that can cause... Click here for more information. EAST LANSING, Mich. — Remember Mom's advice about washing your hands thoroughly after using the restroom? Apparently not. A new study by Michigan State University researchers found that only 5 percent of people who used the bathroom washed their hands long ...

Split liver transplants for young children proven to be as safe as whole organ transplantation

2013-06-10

Boston, Mass.— A new study shows that when a liver from a deceased adult or adolescent donor is split into two separate portions for transplantation—with the smaller portion going to a young child and the larger to an adult—the smaller portion used for the child will last just as long as if the child had received a whole organ from a donor close to his size. The data, collected and analyzed by a team led by Boston Children's Hospital researchers Heung Bae Kim, MD, and Ryan Cauley, MD, MPH, was published online in Liver Transplantation, a journal of the American Association ...

Research shows river dredging reduced fish numbers, diversity

2013-06-10

Comparing dredged and undredged sections of the Allegheny River, reduced populations of fish and less variety of aquatic life occurred in areas where gravel extraction took place, according to researchers in Penn State's College of Agricultural Sciences,. The researchers investigated navigation pools 7 and 8 near Kittanning and Templeton and published their results in the journal Freshwater Biology. "Understanding and untangling the complex effects of human activities on aquatic ecosystems present a challenge to ecologists and resource managers," said lead investigator ...

Mysterious monument found beneath the Sea of Galilee

2013-06-10

The shores of the Sea of Galilee, located in the North of Israel, are home to a number of significant archaeological sites. Now researchers from Tel Aviv University have found an ancient structure deep beneath the waves as well. Researchers stumbled upon a cone-shaped monument, approximately 230 feet in diameter, 39 feet high, and weighing an estimated 60,000 tons, while conducting a geophysical survey on the southern Sea of Galilee, reports Prof. Shmulik Marco of TAU's Department of Geophysics and Planetary Sciences. The team also included TAU Profs. Zvi Ben-Avraham ...

People are overly confident in their own knowledge, despite errors

2013-06-10

Overprecision — excessive confidence in the accuracy of our beliefs — can have profound consequences, inflating investors' valuation of their investments, leading physicians to gravitate too quickly to a diagnosis, even making people intolerant of dissenting views. Now, new research confirms that overprecision is a common and robust form of overconfidence driven, at least in part, by excessive certainty in the accuracy of our judgments. The research, conducted by researchers Albert Mannes of The Wharton School of the University of Pennsylvania and Don Moore of the Haas ...

How cells get a skeleton

2013-06-10

The mechanism responsible for generating part of the skeletal support for the membrane in animal cells is not yet clearly understood. Now, Jean-François Joanny from the Physico Chemistry Curie Unit at the Curie Institute in Paris and colleagues have found that a well-defined layer beneath the cell outer membrane forms beyond a certain critical level of stress generated by motor proteins within the cellular system. These findings, which offer a new understanding of the formation of this so-called cortical layer, have just been published in EPJ E. Active gels are ideal ...

The secret life of knots

ELSE PRESS RELEASES FROM THIS DATE:

LAST 30 PRESS RELEASES: