Vital Question: Energy, Evolution, and the Origins of Complex Life

by Nick Lane

Now cells had evolved active ion pumps and modern membranes, and were finally free to leave the vents, escaping into the open oceans. From a common ancestor that lived from proton gradients in vents, the first free-living cells, bacteria and archaea, emerged independently. It’s not surprising that bacteria and archaea should have come up with distinct cell walls to protect them against these new shocks, nor indeed that they should have ‘invented’ DNA replication independently. Bacteria attach their DNA to the cell membrane during cell division, at a site called the replicon; the attachment enables each daughter cell to receive a copy of the genome. The molecular machinery required to attach DNA to the membrane, and many details of DNA replication, must depend at least partly on the mechanics of that attachment. The fact that cell membranes evolved independently begins to explain why DNA replication should be so different in bacteria and archaea. Much the same applies to cell walls, all the components of which must be exported from inside the cell through specific membrane pores – hence the synthesis of the cell wall depends on the properties of the membrane, and should differ in bacteria and archaea.