Researchers from the University College London have determined the mass of human chromosomes for the first time, using X-ray beams at Diamond Light Source, the United Kingdom’s national synchrotron facility. The study determined the number of electrons within a spread of 46 human chromosomes, then used that number to calculate the mass of the chromosomes altogether. The study was published in the journal Chromosome Research.
Using a process called X-ray ptychography, a method where the diffraction patterns produced by X-rays passing through a specimen are systematically reconstructed to create a 3D image. The images were produced at a high resolution due to the large number of photons produced by the beam deployed at Diamond Light Source, and the chromosomes were imaged during the cell’s metaphase, or at the moment just before they divide into two daughter cells. The chromosomes were images at this time because it is at this point where packaging proteins wind up DNA into small, precise structures. During metaphase, each human cell contains 23 pairs of chromosomes, for a total of 46, within which are four copies of 3.5 billion DNA base pairs.
Measurements suggest that the chromosomes were about 20 times heavier than the DNA they contained; the 46 chromosomes themselves weigh 242 picograms (trillionths of a gram). DNA, having been weighed before during the span of the Human Genome Project, was already accounted for in this total weight. With the chromosomes measured as having a much larger mass than previously expected, the researchers say this suggests that there may be more components in chromosomes that are yet to be discovered.
According to Archana Bhartiya, lead author and a PhD student at the London Centre for Nanotechnology, University College London, further studying our chromosomes have important implications for human health. “A vast amount of study of chromosomes is undertaken in medical labs to diagnose cancer from patient samples. Any improvements in our abilities to image chromosomes would therefore be highly valuable.”
Bibliography
- University College London. (2021, June 1). Mass of human chromosomes measured. ScienceDaily. Retrieved August 23, 2021, from https://www.sciencedaily.com/releases/2021/06/210601135744.htm
- Bhartiya, A., Batey, D., Cipiccia, S. et al. X-ray Ptychography Imaging of Human Chromosomes After Low-dose Irradiation. Chromosome Res 29, 107–126 (2021). https://doi.org/10.1007/s10577-021-09660-7
