Researchers took wet-spun samples ofÂ DNA,Â which they wound onto a bobbin. These were then placed into a neutron scattering spectrometer. The team measured how the frequency of sound waves running along the double helix structure changed with their wavelength. Professor Mark Johnson, an ILL physicist, explained: "We are essentially measuring the speed of sound in DNA, which gives you a direct measurement of its structural flexibility."
By using computer simulations of the DNA stretching, they could then account for the whole range of previously reported values. They noticed that the solution used to suspend the DNA -- composed of charged ions like lithium and sodium in water to mimic cell conditions -- can influence the stiffness of the DNA. If DNAÂ is pulled sharply, it tends to block -- much like a seatbelt -- because the ions in the solution get between DNA atoms. However if it is pulled slowly it stretches.
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What is DNA?
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms (with the exception of RNA viruses). The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for all known forms of life.
DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called nucleobases (informally, bases). It is the sequence of these four nucleobases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA in a process called transcription.
Within cells DNA is organized into long structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. Wikipedia