Mass Appeal
Chromosomes are a feat of tidy packaging, ensuring all our DNA fits inside a cell nucleus, while keeping it accessible for duplication or transcription as needed. Our 23 pairs of chromosomes contain over 6.4 billion base pairs (the G-C and A-T ‘building blocks’) of DNA in total, representing approximately 2 metres of DNA per chromosome. Interactions with proteins package this into chromatin: DNA is first wrapped around histone proteins, forming nucleosomes, then condensed further, into higher-order structures that are less well understood. To start unravelling their mysteries, we need to know how much protein is involved, so scientists used a powerful X-ray to measure the number of electrons in a set of human chromosomes (pictured), and from that calculated their mass. Weighing in at 242 picograms (or a trillionth of a gram) in total, they may seem diminutive, but are actually far heavier than expected, suggesting there is still much to learn about the structure of chromosomes.
Written by Emmanuelle Briolat
Image from work by Archana Bhartiya and colleagues
London Centre for Nanotechnology, University College, London, UK
Image copyright held by the original authors
Research published in Chromosome Research, March 2021
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