At a guess, ninety-nine percent of biologists’ attention to DNA and gene expression is based on biochemistry. That’s good, since the biochemistry is obviously important and difficult enough to analyze. However, there is something else – it’s called physics. Cells, cell components, and DNA all exist in the physical world and therefore are also affected by the laws of physics. A new, first of its kind, study on the mechanics (physics) of gene expression reveals that genes can (also) be turned on or off because of tension and other mechanical means.
The research, conducted at the University of Michigan (USA), used ‘optical tweezers’ – specially constructed lasers to ‘pinch’ or ‘pull’ on the ends of DNA strands. It’s a very small pull – about 200 femtonewtons, or roughly equivalent to one-billionth of the weight of a grain of rice. The resulting tension on the strands caused the DNA to ‘tighten the loops.’ If you recall the classic picture of DNA as a ‘spiral staircase’, pulling on the ends causes the spiral to tighten. It’s known that this position with tighter loops prevents expression (creation of proteins) for many of the genes within the loops. Of course, this can have an effect on the condition of the cell.
While this experiment was performed on free DNA, the scientists say forces as much as 100 times stronger are regularly created inside cells as contents shift and buffet each other.
“If we can basically shut this process down with the tiniest force, how could all these larger forces not have an impact on gene expression?” Milstein said [University of Michigan, Department of Physics].
This exercise in biophysics shows that genetics isn’t all chemistry. There are situations where mechanical stresses and other physical forces may also have a role to play in mutations, diseases, and other changes in cell biology.