Facts about human DNA are among the most amazing in biology. In each human cell โ and our bodies contain approximately 37 trillion cells โ there is DNA that, if fully stretched, would be about 2 meters long. This means that if we combine the DNA from all the cells in a single human body and stretch it out, it would form a rope over 70 billion kilometers long โ a distance sufficient to go to Pluto and back 17 times.
However, how does a 2-meter-long DNA fit into a cell nucleus that is only 6 micrometers in diameter โ smaller than a drop of ink? The answer lies in highly sophisticated folding engineering. DNA is not just wound like thread in a spool โ it is folded, coiled, and compressed into a highly organized hierarchical structure.
DNA first coils around proteins called histones to form nucleosomes โ structures that resemble beads on a string. These nucleosomes are then folded and condensed further through various stages to form compact chromosomes. This level of condensation is extraordinary โ human DNA is compressed more than 10,000 times its original length to fit inside the cell nucleus.
Even more astonishing, despite being condensed, the cellular machinery is able to read and copy the information from DNA with remarkable accuracy. Every time a cell divides, the entire 6 billion base pairs of DNA must be copied, and this process occurs at an extremely low error rate โ only about one error for every billion base pairs copied.