2 . Some people are early risers while others can’t seem to get to bed until well after midnight. Why is this? A research team has a new finding that shows how a “switch” in the biological clocks of early risers leads them to operate on a daily cycle of about 20 hours instead of a full 24-hour cycle.

This finding from Carrie Partch and her colleagues builds on decades of research into biological clocks, which control sleeping and waking, rest and activity, body temperature, heart rate and so on.

Partch and her colleagues focus on two main clock components: an enzyme (酶) known as casein kinase 1 (CK1) and a protein (蛋白质) called PERIOD. It turns out that the timing of biological clocks is strongly influenced by the rise and fall of the PERIOD protein, and this daily change normally takes place over 24 hours. But CK1 adjusts PERIOD levels by chemically modifying the protein, thereby adjusting its stability.

What they’ve discovered is that a part of CK1 acts as a switch. When this switch functions normally, it generates a near- perfect 24-hour cycle by keeping PERIOD’s stability right. In this case, people easily and correctly match their biological clocks with the daily coming and going of daylight.

If the switch favors a faster breakdown of the protein, the daily cycle grows shorter and less tightly bound to daylight. For these early risers, it’s a constant struggle to adjust to life in a 24-hour world. On the contrary, a switch that favors a slower breakdown will lengthen the clock, causing some people to be night owls (夜猫子).

Partch’s discoveries are sure to offer a new view on how the biological clocks make us tick. She hopes they’ll result in new ways to adjust the clocks in people with sleep disorders and even the means to reset the clocks in people who regularly travel overseas or work the night shift.