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Our genome captured in numbers

‘It's where disciplines intersect that the most exciting scientific questions arise.' This was the message given by John van Noort, Professor of Biophysics, in his inaugural lecture. His own research is at the interface between biology and physics. Inaugural lecture 23 April.

Van Noort is often asked whether he is a biologist or a physicist. 'It really doesn't matter,' he replies, 'just as long as my research is exciting. When disciplines work together, you get innovation and that's when the most interesting research questions come to the fore.' 

What is so fascinating about research at the interface between biology and physics? 

‘Physics can help us quantify biological issues, letting us capture biological processes in numbers. And once we've measured all these numbers, we can see whether we really do understand the complexities of the biology. It goes back to what famous Leiden physicist Heike Kamerlingh Onnes once said: "Measuring is knowing." ’

The title of your inaugural lecture is ‘Our genome in numbers’. What numbers about our DNA and our genes should everyone know about?

‘I ask every new group of students how big our DNA is. DNA is our body's information carrier: in long-chain DNA that is found in every cell of our body are the genes that code for all the proteins that make the biological processes in our bodies possible. This DNA chain is cleverly rolled up into a kind of knot so that it fits into the cell. If you unravel the knot from a single cell, you get a strand around 2 metres long! Not that you could actually see it because the chain is just 2 nanometres thick. These two numbers show you  how amazing that enormous DNA molecule is.' 

‘I'm conducting research on how DNA is folded, how that two-metre strand is organised into a knot. This is where a third number comes into the picture: the persistence length, which is an indication of the maximum length at which the DNA chain is still straight, and at what point it becomes a folded structure. You can compare it with a garden hose. A short piece of hose is straight, but when it's ten metres long, it becomes a complex reel.  You could say that the persistence length of a garden hose is 25 centimetres,  and that of DNA is 50 nanometres.'

What number are you hoping to discover?

‘It will be a combination of numbers. This knot of DNA isn't just random; it's folded in an ingenious way. Each gene takes up around 25 folds, called nucleosomes. I want to understand how the way the thread is folded and unfolded influences gene expression: how often does a cell produce the protein for which it is coded? It won't be possible to capture the answer in a single number.' 


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