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
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.