What will the DNA look like when it is stretched?

DNA is the genetic material found in most living organisms, each of which contains the same amount of DNA. The cell's smoothness is characterized by elasticity, elasticity and zigzag, like chicken intestines.

Each double helix DNA is as flexible as it is, so it can be stretched quite far. The mechanical characteristic behind this process, called "overstretching ", is that each double helix DNA is elastic, less cuts and drier than previously thought by scientists, according to the results of New research shows.

Contrary to popular theory, when we stretch quite a bit the DNA double helix, in DNA molecules there is no breakage of single DNA strands, according to researchers at the Institute of Standards and Technology , in Boulder, Colorado, USA, in the experiment to determine whether or not there is a free fracture when we stretch double strands of DNA. The results of this study, published in the Journal of the American Chemical Society , show that DNA double helix twists almost twice their length and they have the same elastic index when stretched. out.

Thanks to its flexible properties, DNA molecules are easily elastic , responding to small forces, as predicted by molecular theory. But when scientists exert relatively large traction on these DNA molecules, through the use of a device called an optical trap, DNA molecules appear to be more elastic. Acting at a force of 65 piconewtons, each piconewton equals one trillionth of a newton, equal to the force of gravity on a regular apple, at which time the DNA's elasticity is raised to 70%. . " Under the force of traction for a few piconewtons, DNA molecules go from normal elasticity to greater elasticity by being stretched ," says Thomas Perkins, a biophysicist and co-author of new research.

Physiologists notice, the free end of DNA molecules, which may be due to the large stretching force, occurs too suddenly. Recently, when researchers sought to determine the flexibility of DNA molecules, through micro-dragging tests, they removed one of the two strands in the DNA double helix, without securing them. At one end, the purpose is to allow the whole twisted structure of the DNA to twist and turn normally when stretched. But it also makes the remaining fiber stretch freely. The researchers hypothesized that, with sufficiently strong traction, the first single strand of DNA could peel off a second single strand of DNA, such as splitting a fiber, a piece of a piece of cheese, which works to make DNA molecules. much more flexible.

In 2009, an international team of researchers photographed the stretched DNA molecule, in the presence of fluorescent proteins, to bind a single strand of DNA that was stretched freely. The tensile force at 65 piconewtons, the DNA molecule begins to glow, showing the presence of a free stretch of single DNA strands. The observed image helped end the controversial issue among physiologists.

Perkins and his team, however, designed a long-running experiment that both single strands of DNA removed free ends and left the DNA strands intact. They put both DNA strands together, thanks to the trick of using a small additional DNA patch, then identifying molecules by loop. With or without free end, the DNA molecule remains stretched with the force at 65 piconewtons.

" This is a really smart improvement ," said Erwin Peterman, a physiologist, working at VU University Amsterdam, the Netherlands and one of the authors of the study in 2009.

"We should think about this." This study does not make the image of DNA stretching simpler, according to Mark C. Williams, a biophysicist who works at Northeastern University, in Boston, USA, who is not involved in the research. on. " You could peel the second strand of DNA, " he said, " but if you can't peel the second strand of DNA, the DNA molecule is still stretched with the force of 65 piconewtons ."

The double helix DNA can still be slid apart, according to Mark C. Williams, like a bubble being blown up from the middle. However, according to other researchers, when acting a large stretching force on the DNA molecule, it is possible to form a modified DNA structure called S-DNA. S-DNA, like a DNA molecule but has a straight ladder, may have more stairs in the middle than the traditional double-stranded DNA.

The DNA molecule is always stretched with force at 65 piconewtons in experiments, Perkins suggests, these molecules can be used to determine very small forces like piconewton. In other words, the computer, immediately, can select 65 piconewtons, which causes the DNA molecule to stretch too much. But by not knowing exactly how to make this DNA molecule more flexible, this idea is still an uncertain standardization, he said.