In the beginning … but how do you begin? That question has long perplexed scientists in fields from cosmology to anthropology. Fortunately, researchers at the Office of Science’s Brookhaven National Lab (Brookhaven Lab) are beginning to get at the answer on a small but important scale — in biology.
Specifically, the researchers looked at how cells begin to duplicate their DNA, so they can then begin to replicate themselves. DNA is the essential stuff of beginnings. Its double strands — which consist of chemical ‘letters’ or base pairs — tell cells how to remake themselves; how to build the protein machines that keep them alive and make them distinct. So before they divide, cells have to duplicate their DNA.
This is a relatively straightforward affair for bacteria (and other simple cells, also called prokaryotes) since they typically only have a single loop of DNA, even though it can be millions of base pairs long. As a consequence, they have just a single point along the strand where the copying starts, called an origin of replication.