Chronotypes Your Internal Biological Clock

The ‘CLOCK’ cell keeping time from within

Our biological clock is responsible for regulating our sleep-wake cycle, as well as other physiological processes such as metabolism, hormone production, and even our mood and cognitive performance. At the heart of this clock are specialized cells known as “clock cells,” which work together to keep our body in sync with the daily rhythms of the environment.

Clock cells are found in many different organs and tissues throughout the body, but they are most abundant in a small region of the brain called the suprachiasmatic nucleus (SCN), located in the hypothalamus, there are only around 20,000 of this cells present in this area of the brain. The SCN is often referred to as the “master clock” because it serves as the central pacemaker for the body’s circadian rhythm.

So what exactly do clock cells do, and how do they work at the cellular level? Let’s dive into the fascinating world of chronobiology to find out, there’s no way around using some technical terms once we get inside the cells but I’ll do my best to explain as I go.

Clock cells are a type of neuron that exhibit a unique property known as “circadian rhythmicity” – in other words, they have an inherent 24-hour cycle of activity that is driven by a set of internal genes and proteins. These genes and proteins interact in a complex feedback loop that helps to keep the clock ticking in a precise and predictable manner. The actual timing of this cell is more like 24 hours 13 minutes to be precise but we maintain 24 hours using other timing cues such as light and temperature to make fine adjustments.

At the heart of this feedback loop are two key proteins known as “CLOCK” and “BMAL1.” These proteins form a heterodimer, which means they bind together to form a single complex. Once formed, the CLOCK/BMAL1 complex binds to specific regions of DNA called “E-boxes,” (nothing to do with your E-mail) which are found in the promoter regions of many clock genes.

When the CLOCK/BMAL1 complex binds to these E-boxes, it activates the transcription of a series of “clock genes,” including Period (Per) and Cryptochrome (Cry). The Per and Cry proteins then accumulate in the cytoplasm of the cell (fluid inside the cell but outside the nucleus of the cell) and eventually form their own complex, which can bind to the CLOCK/BMAL1 complex and inhibit its activity. This feedback loop results in a 24-hour oscillation of gene expression, with the CLOCK/BMAL1 complex driving the upregulation of clock genes during the day and the Per/Cry complex inhibiting their expression at night.

This oscillation of gene expression (information that’s turned into a function) is what gives rise to our circadian rhythm – the natural ebb and flow of physiological processes throughout the day and night. But how do clock cells use this rhythm to regulate our sleep-wake cycle and other functions?

One key mechanism is through the release of hormones such as melatonin, which is synthesized and secreted by the pineal gland in response to signals from the SCN. Melatonin is often referred to as the “sleep hormone” because it helps to promote drowsiness and prepare the body for sleep. Its release is tightly regulated by the circadian rhythm, with levels increasing at night and decreasing during the day.

Clock cells also communicate with other neurons and cells throughout the body, helping to synchronize their activities and maintain a cohesive circadian rhythm. For example, the SCN sends signals to the pineal gland to regulate melatonin release, as well as to the adrenal glands to control the secretion of cortisol, a hormone that helps to regulate metabolism and stress response.

However, disruptions to our circadian rhythm can have negative effects on our health and well-being. For example, shift workers who frequently work overnight or rotating schedules are at increased risk of developing sleep disorders, metabolic problems, and even certain types of cancer. Jet lag, which occurs when we travel across time zones and disrupt our internal clock, can also lead to temporary sleep disturbances and other symptoms.