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Biological Clocks: Who, What, Where, How, and Why?

Biological Clocks: Who, What, Where, How, and Why?

Author: Emily Manoogian, PhD

I have studied circadian clocks for the past 8 years; in that time, I realized that many people didn’t know what exactly circadian clocks are. The same was true if I said I study chronobiology, circadian rhythms, biological rhythms, or body clocks. This blog provides me with an opportunity to give a little more clarity into this fascinating field.

As a chronobiologist, I study how organisms control the timing of various biological events, and how they coordinate that timing with the environment. It is a large field with research at every level, including behavioral, cellular, molecular, and genetic analyses in a wide variety of organisms. For my first blog post, I will cover the who, what, where, and how of biological clocks/rhythms, and why they are so important.


All life on earth evolved on a rotating planet in which access to light, food, and safety occurred at a specific time of the day or night. As a result, almost all living organisms have biological clocks including single celled bacteria, fungi, plants, and animals. In nature, biological rhythms produce timely prompts for animals and humans to forage for food, avoid predators, mate, etc.

What and Where

Biological clocks are produced by molecular feedback loops in almost every cell of your body. Biological rhythms are also called circadian (cira = about; dian=day) rhythms because most biological rhythms oscillate with approximately a 24-hour period.

Biological clocks coordinate the timing of behavior (sleep-wake cycles, eating, activity, etc.) and physiology (metabolism, hormone release, blood pressure, body temperature, etc.) to allow for the body to function properly. Put simply, biological clocks make sure that everything in the body is happening at the right time.


Almost every cell in the body has its own molecular clock. In mammals, a region of the brain, known as the suprachiasmatic nucleus (SCN) coordinates all of the clocks in your body.

The SCN is able to produce and maintain circadian rhythms absent of any cues but also coordinates these internal rhythms with the environment. The SCN does this by indirectly responding to external cues such as light, calorie intake, and activity.

The SCN also receives feedback signals from clocks throughout the body. In this way, the SCN in an integration center for both internal and external time. The SCN then interprets those signals, and can reset the timing of the body.

Why does it matter

When biological rhythms are disrupted due to erratic lifestyle (shift work, jet lag, late night eating, high variability in schedule or sleep timing, etc.) the amplitude of biological rhythms is decreased and incompatible behavioral and physiological events can coincide. Repeated disruption of biological rhythms has been shown to lead to an increased risk for a wide variety of diseases including cardiovascular disease, diabetes, cancer, obesity, depression and bipolar disorder, and sleep disorders.

In modern society, we are exposed to many artificial cues (such as artificial light, 24-hour access to food, and late-night activity) that can be hazardous for healthy biological rhythms.


Biological Rhythms: rhythms in behavior or physiology such as sleep-wake cycles, metabolism, and body temperature.

Circadian Rhythms: (Circa = Approximately; Dian = Day). Biological rhythms are often also referred to as circadian rhythms because many biological rhythms have about a 24-hour period (~one day). However, there are also biological rhythms that are shorter or longer than 24 hours such as ultradian rhythms (shorter than a day), circalunar rhythms (~a month), and circannual rhythms (about 1 year).

Body Clocks: Another term to refer to biological clocks, usually in reference to circadian rhythms.

I hope this post has shed some light on the world of biological rhythms. To learn more, see our science section and check back weekly for new posts!

© Copyright by Emily Manoogian.