Our chromosomes, these microscopic X-shaped elements, carry our genes (containing genetic information). They are passed from mother cells to daughter cells during cell division. For the first time, biophysicists have succeeded in measuring, with great precision, the mass of human chromosomes: the set of chromosomes in each of our cells weighs 242 picograms (trillionths of a gram), according to the study.
To do this, they used a powerful x-ray source from the UK’s national synchrotron science facility, the Diamond Light Source. They were thus able to determine the individual masses of the 46 chromosomes present in human cells. Best of all, the results indicate unexplained excess mass in human chromosomes.
The masses turned out to be significantly higher than expected – about 20 times the DNA they contain – likely reflecting the additional mass of other unknown elements inside the chromosomes, which we have yet to discover, suggest the researchers. Details of the study are available in the journal Chromosome Research.
” We know the mass of DNA thanks to the Human Genome Project, but this is the first time that we have been able to precisely measure the masses of the chromosomes that include this DNA. Said biophysicist Ian Robinson of University College London. ” Our measurement suggests that the 46 chromosomes in each of our cells weigh 242 picograms (trillionths of a gram). It’s heavier than we expected, and, if these results are reproduced, it indicates unexplained excess mass in the chromosomes “.
Chromosomes: they help to preserve the DNA contained
Chromosomes are small, filament-like bundles of DNA found in the cell nuclei of living organisms. Each chromosome contains a DNA molecule, which in turn contains the genetic instructions for the development and survival of that organism.
Each human cell, in metaphase, normally contains 23 pairs of chromosomes – 22 pairs of numbered chromosomes (autosomes) and one pair of sex chromosomes. These contain four copies of 3.5 billion base pairs of DNA. And it’s the chromosomes that keep the DNA they contain from unraveling, helping to maintain its structure during the process of cell replication.
Chromosomes were first discovered in the 19th century and since then scientists have learned a lot about their role in the functioning of living organisms. However, there is still a lot to understand. In this case, the scientists used a technique called hard x-ray ptychography to probe their interior.
This technique involves using a type of particle accelerator, called a synchrotron, to produce a powerful beam of x-rays. When these rays pass through the synchrotron, they turn into x-rays. When these x-rays pass through chromosomes, their diffraction creates an interference pattern that scientists can use to create a high-resolution 3D reconstruction of these.
Significant benefits for medicine and biology
The researchers captured images of human white blood cells in metaphase (a phase of the cell cycle during which chromosomes condense) and just before cell division, when each cell’s 46 chromosomes tightly wrapped DNA.
Using this technique, they were able to determine the number of electrons, or electron density, in chromosomes. The mass of electrons is well known – the resting mass of an electron being one of the fundamental physical constants (9.109 × 10−31 kg). They were thus able to deduce the mass of the chromosome by calculation.
The unexpected mass discovered by the researchers is still a mystery, but the results obtained could already have important consequences for medicine, in particular helping us to better understand the functioning of the human body as a whole. ” Better understanding of chromosomes could have important implications for human health Said bioscientist Archana Bhartiya from University College London. ” Much of the study of chromosomes is undertaken in medical laboratories to diagnose cancer from patient samples. Any improvement in our ability to image chromosomes would therefore be very valuable. “.