By Claire R. G.

Our bodies, and more generally animals and plants, are constituted of millions and millions of cells, and the growth and maintenance of an organism are achieved through the division (and then the specialization) of these cells. 

One of the strongest challenges of cell division is to maintain the integrity of the DNA molecule, which is a long (up to billions) succession of small “letters” (i.e., nucleic acids), aligned on two strands bound together, which has to be faithfully copied before the cell divide into two, and each copy goes in each new cell. 

To achieve that, a small machinery is installed at thousands of positions along the DNA. The process can then begin: some of these machineries are activated by a specific messenger; they unwind the DNA and recruit another machinery which can copy the letters. While the replication machineries are progressing along the DNA, other complexes check that there are no errors in the copy, and take care of re-wrapping the DNA correctly. In addition, yet another complex signaling system is taking care of collision events, between two replication complexes or with other machineries on the DNA. Finally, other players check that everything is fine, that duplication will not begin again, and tell the cell that the division process can carry on.

Thus, I like to think of this complex organization and cross-talk, necessary just to get two cells out of one, then four, … everyday when my nails are growing, my skin is renewing or a small wound is healing.