Indian-American scientist, colleagues, at UChicago find body clocks differ between humans and other organisms

Arvind Murugan, assistant professor of physics, University of Chicago, Illinois. (Photo:

An Indian-American scientist at the University of Chicago, Illinois, along with his colleagues, found out why some internal clocks are like wristwatches and some like hourglasses.

In experimental and theoretical papers published in Nature Communications and eLife, Arvind Murugan, assistant professor of physics, et al, studied the mechanisms of two kinds of circadian “clocks” that nearly all living organisms use to keep track of time.

Their results showed that if chemical fluctuations going on inside a cell are higher, then the body prefers a simpler type of clock.

Murugan, whose runs the Murugan Lab, works on problems in quantitative biology, non-equilibrium dynamics, and theoretical computer science, his website says.

All species have evolved with some type of body clock after thousands of years living on a planet with a 24-hour cycle, and scientists theorize that it’s because living beings find it useful to know when the next meal is coming or when to get back to your burrow after sunrise. The result is two broad types of clocks, one, a “true” clock like a wristwatch, with its own internal mechanisms to keep it going, which humans have; and the other is more like an hourglass which needs resetting on a daily basis, an Aug. 3, press release from the University said.

“Even if you didn’t see the sun rise and set, you still wake up and go to sleep on your cycle—it’s why you have to get over jet lag,” Murugan explains in the press release referring to the human wristwatch body clock.

The hourglass body clock is more common in bacteria or other small organisms.

The researchers wanted to know why an organism would gravitate toward one or the other. The question they asked was: What are the disadvantages to each kind of clock?

“The answer is that if your internal biochemistry is noisy or fluctuating, which may be especially true in small cells, those are conditions where it’s worse to build a wristwatch-type clock,” said coauthor Michael Rust, an associate professor of molecular genetics and cell biology.

All cells use a complicated set of chemical reactions to carry out their tasks. Everything from digestion to sensing to keeping track of time is accomplished by a flood of biochemical reactions. Through both theory and experiments with cyanobacteria, the team found that the noisier this internal chemical dance, the simpler the cell tends to make its clock.

Wristwatch-type clocks have more moving parts, so they can break down more easily. But simpler clocks can be fooled by cloudy weather. Basically, if your outside environment is more likely to fluctuate, you want a wristwatch clock. But if conditions inside the cell are more likely to fluctuate, you want an hourglass clock, the researchers concluded.

“This was a bit of a surprise because people have been looking at biological fluctuations for a long time, but only from one angle. Here we have these sharp examples of two different kinds of fluctuations, and they cannot be solved at the same time,” Murugan said. “It doesn’t matter how the specific biological clock works—if it’s many cells, like in humans, or within one cell like a bacterium—it’s just intrinsic to the physics of oscillation and the geometry of the underlying dynamical system,” Murugan added.




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