A set of human chromosomes has a greater mass than expected – there's more to learn about their structure
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.
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