Balls of String

Inside each of our cells roughly two metres of DNA is packed into a nucleus a thousand times smaller than this full stop. There’s even room to spare – so how does it all fit in? This image from a computer simulation shows how it’s done – special proteins intertwine with the DNA forming a compact structure called chromatin. Over time (moving from left to right in this picture), different proteins (shown here in red and green) pinch together specific areas of DNA (shown in grey), creating loops. These loops are wound tighter as more and more proteins attach, resulting in the neat, compact balls of chromatin on the right. But this isn’t long-term storage – some chromatin loops unravel every few seconds to allow genes on our DNA to be read or repaired before winding up again.

Written by John Ankers

John Ankers

Writer

A former researcher in systems biology, John is now an online biology tutor and professional coach supporting the wellbeing of scientists and NHS professionals. He's writing, too, of course.

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• Mariano Barbieri, Mita Chotalia, James Fraser, Liron-Mark Lavitas, Josée Dostie, Ana Pombo, and Mario Nicodemi
• Published in PNAS 109(40): 16173-16178