The second law of thermodynamics states that all closed systems tend towards disorder over time and maintain order through the expenditure of energy.

In most developing organisms, scientists assumed that most of the energy was expended on the replication of DNA or the division of cells. Yale researchers decided to test this idea and developed a method to probe the energy utilized by living systems. What they found surprised them.

Researchers Jonathan Rodenfels, Karla Neugebauer and Joe Howard measured the heat flows associated with rapidly dividing cells by placing a developing zebrafish embryo into a calorimeter, a heat sensing device popular for studying chemical reactions.

They recorded an oscillatory energetic flow that correlated with the phases of the cell replication cycle. To investigate the root cause of these oscillations, they used chemical agents to block individual processes within the cell cycle.

Surprisingly, when DNA replication and segregation were blocked these same heat fluctuations persisted. Instead, the bulk of thermodynamic burden seems to be on the signaling system that the cell uses for coordination and information transfer, the authors say.

“Why and how it spends this energy remains an open question. Some theorize that the more the energy a signaling system used, the more robust the signaling becomes, and the less likely it becomes to make an error” said Rodenfels.

The new approach will allow deeper understanding of biological signaling systems and shed light on diseases such as cancer which are marked by the failure of cellular coordination and signaling.

This work appears in Developmental Cell and can be found here.