One simple factor could have made all the difference to cells on the ancient Earth: temperature.
A new computational model from French researchers suggests that the reproduction of very early protocells may have been primarily driven by a temperature difference occurring between the inside and outside of the cell.
“The initial motivation of our study was to identify the main forces driving cell division,” explains Romain Attal of Universcience in France, lead author of the paper published in the Biophysical Journal.
“This is important because cancer is characterised by uncontrolled cell division. This is also important to understand the origin of life.”
Splitting one cell into two daughter cells requires a bunch of different biochemical and mechanical processes to synchronise. In modern cells, these processes involve complex structures within the cells – like genes, RNA, enzymes and organelles – but these structures must have evolved later than the far more basic ability to split.
So how did ancient cells replicate?
In this new study, Attal and colleagues come up with a model based on the idea that early cells were simple vesicles – fluid sacs – containing a network of chemical reactions (that later evolved into modern cellular metabolism).
They hypothesise that the molecules that make up the outside of the cell (the membrane bilayer) are first synthesised inside an oval-shaped cell, via heat-releasing (exothermic) chemical reactions.
As temperature slowly increases inside the cell, the hottest molecules move slowly to the outside of the cell; this asymmetric movement makes the outer parts grow faster than the inner parts.
Then, the cut – where the cell splits in two – occurs in the hottest zone around the middle of the oval.
“The scenario described can be viewed as the ancestor of mitosis,” Attal says. “Having no biological archives as old as 4 billion years, we don’t know exactly what the first unicellular common ancestor (FUCA) contained, but it was probably a vesicle bounded by a lipid bilayer encapsulating some exothermic chemical reactions.”
The authors note that although it’s a theoretical model, it can be tested experimentally – for example, by using fluorescent molecules to measure temperature changes inside modern eukaryotic cells, where mitochondria provide the heat.
“An important message is that the forces driving the development of life are fundamentally simple,” Attal says. “A second lesson is that temperature gradients matter in biochemical processes and cells can function like thermal machines.”