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A team of scientists used coherent X-rays, available on the latest synchrotron sources, to determine the mass of all 46 human chromosomes. Their weight was more than expected.

Scientists from the Center for Nanotechnology at University College London (UK) and the State University of New Mexico (USA) for the first time measured the mass of chromosomes in the human body using X-rays. As described in the study, this was done at the expense of the Diamond Light Source-an accelerator complex, a third-generation synchrotron radiation source located in the county of Oxfordshire.

To begin with, the scientists determined the number of electrons in all 46 human chromosomes (23 pairs) — the main structural and functional elements of the cell nucleus, which carry genes arranged in a linear order, and are responsible for storing and reproducing genetic information. As it turned out, these structures are about 20 times heavier than the four copies of 3.5 billion base pairs of DNA contained in them: the fact is that in addition to them, chromosomes consist of proteins that perform many functions — from reading DNA to regulating the processes of cell division and tightly "packing" two-meter strands of this macromolecule in them.

"Scientists have been studying chromosomes for 130 years, but parts of these complex structures are still poorly understood. For the first time, we were able to accurately determine their mass. So, the measurements showed that the 46 chromosomes in each of our cells weigh 242 picograms (trillionths of a gram). This is heavier than we expected and probably indicates an unexplained excess chromosome mass, " said senior study author Professor Ian Robinson.

The method used by the scientists is called X-ray echography — a scanning technique for obtaining images of objects whose dimensions are significantly larger than the transverse dimensions of the focal spot (electrons, X-rays) on the sample. It involves cross-linking the diffraction patterns that occur when an X-ray beam passes through the chromosomes to create a highly sensitive three-dimensional reconstruction.

The high resolution was achieved due to the fact that the Diamond Light Source beam was billions of times brighter than the Sun: a very large number of photons passed through it at a particular time. The chromosomes were depicted in metaphase — before they were about to split into two daughter cells.

The article is published in the journal Chromosome Research
Image - Human chromosomes taken by X-ray echography © Archana Bhartiya et al.

Source: naked-science.ru, sci-dig.ru