Biology and Physical Factors #2: On and Off
DNA strands are long (several meters long). How on earth do they then fit inside the nucleus of a cell? By bending and folding themselves. But not in any random way. They wrap themselves around proteins 10 nanometers in size called histones . But it would require a lot of force to compress them like this. What is the source of that much force? The answer is electrostatic force, between the negatively charged DNA and the positively charged histone. This isn’t just “intellectual curiosity”. Which parts of the DNA are “expressed” as proteins depends on the packaging and wrapping of the DNA. How? Remember DNA strands are read by a transcription molecule called RNA. Parts of the DNA that are inaccessible (due to the way they are wrapped) won’t be expressed. It has thus been turned “off”! Accessible = On; inaccessible = Off. “The physical arrangement of DNA is a powerful tool for regulating the activities of the cell.” writes Raghuveer Parthasarathy in So Simple a Beginning . ...