What are circadian rhythms?

They are the daily rhythms that our body goes through, such as sleeping and waking up. 

But cells making up all the tissues and organs inside our bodies also have circadian rhythms, and they need to communicate their rhythms to other tissues.

Until now it was not known how they could do this!

Where does the hydrogen peroxide in cells come from?

Hydrogen peroxide is produced when mitochondria inside cells break down sugars in the presence of oxygen to make ATP, the energy molecule used to power many chemical reactions inside cells.

Since all cells need ATP to stay alive, hydrogen peroxide is produced continuously, but at certain times of the day more may be produced.

Since too much hydrogen peroxide would poison the cell, cells cycle between burning sugars using oxygen to make ATP, and breaking down the waste products of this process, such as hydrogen peroxide.

Finding that hydrogen peroxide itself is the link between these cycles of metabolism is exciting!

How were the experiments done?

Feeding hydrogen peroxide to fruitflies increased their activity!

Also, certain kinds of mutant fruitflies that had more hydrogen peroxide in their cells (because they had on over-active form of the enzyme that makes hydrogen peroxide in their mitochondria) were more active.