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updated 1/26/2011 2:15:37 PM ET 2011-01-26T19:15:37

What makes people tick? Anybody who's ever suffered jet lag knows all about the body's internal clock, which is driven by a cluster of brain cells.

But even the cells throughout our body have their own 24-hour clocks to coordinate activities at the cellular level. Now new research suggests that these internal timepieces may be more complicated than scientists thought.

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For years, scientists have said this clock is basically the activity of certain genes. But in a new study, scientists looked at human cells that don't even have genes. And in these red blood cells, they found an enzyme flip-flopping between two forms on a regular 24-hour cycle.

Is that a clock? Or is it just responding to some clock? Nobody knows yet, says Akhilesh Reddy of Cambridge University. But it seems to be connected in some way to the genetic mechanism found in other cells, he said. Reddy co-authored two studies on the subject in Thursday's issue of the journal Nature.

Joseph Bass of Northwestern University, who co-wrote a Nature commentary on the work, said in an interview that the new findings don't overturn the standard notion of a gene-based clock. Still, he said, "our understanding of the clock is expanding with this work and other work."

Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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