Can Cells Tell Time?

Summary:

My previous article ("Can Cells Sense Gravity?") suggested that the orthogonal centrioles in animal cells might be capable of sensing the direction of the local gravity vector. Since the direction of the gravity vector depends on the changing positions of the Sun and Moon, its components change periodically throughout the day, month and year. The cell's proposed ability to detect those periodic changes may therefore enable it to tell the time of day, month and year. This article suggests that such periodic changes may be recognized by comparing the changing horizontal and vertical components of the gravity vector, thereby providing information for controlling the Circadian (daily), Ultradian (weekly, biweekly and monthly), and Seasonal (annual) biological behaviors of animals.

Sunrise, Sunset

The easiest way to visualize the changing magnitudes of the gravity vector components, is to imagine yourself pointing to the Sun as it moves across the sky from sunrise to sunset. (Actually, from 6 a.m. to 6 p.m., since the time of sunrise and sunset varies with the seasons and the latitude of the observer.)

As you point to the Sun your arm represents the direction of the gravity vector between the Sun and the Earth. Start by visualizing yourself standing outside at dawn, facing south (if you are in the northern hemisphere), and pointing to the Sun.

As the Sun comes up on the horizon, your arm would be pointing to your left, and a little forward (toward the south), depending on your latitude and the time of year. If you are at higher latitudes (or during winter months) you would have to point further south, since that's where the Sun would be coming up over the horizon as seen from that latitude (or time of year).

Continue to imagine your arm pointing to the Sun at sunrise. Remember that your arm represents the Sun-Earth gravity vector. Notice that, since your arm is pointing at the horizon, there is no vertical (Up-Down) component of the gravity vector at sunrise.

Now notice that there are two horizontal components of gravity vector. The first is its projection on an East-West axis (the directions to your right and left), and the second is its projection on a North-South axis (the directions directly behind and in front of you).

Now let's see how these Up-Down, East-West and North-South components of the gravity vector change during the day, as the Sun passes across the sky from 6 a.m. to 6 p.m.. Remember that the question is "Can we tell the time of day from a comparison of the changing magnitudes of these orthogonal components of the gravity vector?"

Consider mid-morning when the Sun has moved toward the West and is higher in the sky, say at about 9 AM. Your arm has moved to the right (the West) and is pointing higher (Up).

Notice that the Up component on the Up-Down axis has gone from zero (when it was on the horizon at sunrise) to some higher value. At the same time, since your arm moved west, the East component on the East-West axis has decreased from its maximum value at sunrise, to some lower value. And the South component on the North-South axis (your back to front) has grown from its minimum value at sunrise to a larger value.

Now let's consider Noon. The Sun is halfway across the sky, and at its highest point. Your arm is now pointed due south and as high as it will be that day. So the Up component will be maximum, the South component will be a maximum, while the East-West component will be zero (your arm will not be pointing toward either East or West).

Later that day, say at 3 PM, the Sun has moved further West and fallen from its highest point at noon. You arm is pointing to the south and west, and is lower than it was at noon. Therefore, during the afternoon, the Up component is decreasing, the South component is decreasing, and the West component is increasing.

And now for sunset. Again the Sun is on the horizon. Your arm will be pointing to the south and west, but again is pointing at the horizon, so that the Up component will be zero. The West component will be a maximum, while the South component will again be a minimum.

After sunset the Sun sinks below the horizon, and its gravity vector continues to follow the same pattern from 6 p.m. to 6 a.m., as it did from 6 a.m. to 6 p.m. . The only difference is that you are facing it in opposite directions at night than during the daytime hours (i.e., pointing at the Sun through the Earth). The full cycle of daily changes in the components of the Sun's gravity vector are summarized in the table below.

 

The important point to notice from this table is that for each time of day, from sunrise to sunset, and back to sunrise, there is a unique combination of values of the Sun-Earth gravity vector components. This means that if the cells can determine the status of each of the components (i.e., increasing, decreasing, maximum, minimum, or zero) it will "know" the corresponding time of day!

 

Let's not forget the Moon!

The previous discussion was simplified by considering on the Sun-Earth gravity vector by itself. However, biological cells are also strongly influenced by the Moon-Earth gravity vector which produce the monthly and diurnal (twice-daily) variations that add to the annual and daily variations caused by the Sun-Earth motions.

The consequence of these combined Sun-Earth-Moon motions is that the gravity vector represents the resultant pattern of cycles of different periodicities and amplitudes. My premise is that, regardless of the complexity of the changing gravity vector, the cell is able to respond appropriately to the components of the Sun's position and the Moon's position, thereby indicating the time of day, month, and year.

What cells must do to sense changing gravity patterns

Any effort to determine how cells may sense "time," must first identify the functions that have to be performed by the cell's structures. For example, the cell must be able to:

1. Sense a gravity vector from any direction,
2. Resolve the vector into its orthogonal components,
3. Relate these directions to an inertial reference direction,
4. Determine the magnitudes and rates of change of the orthogonal components,
5. Store short term and long term information about the component's changing values.

 

How cell structures might do it

In my previous article ("Can Cells Sense Gravity?") I argue that the centriole-pairs within each cell may be able to sense a gravity vector from any direction, and resolve it into three orthogonal spatial components. I suggested that the centriole's array of nine microtubule-triplets appear to be geometrically well suited for supporting these sensing functions.

Here, I further suggest that other structural features of the cell may provide an inertial system that can serve as a reference for establishing the direction of the orthogonal components of the gravity vector. In a September 1996 correspondence from Stuart R. Hameroff, he noted that "Michel Borens in Paris…suggested that centrioles oscillated along their axis, and thus behaved as gyroscopes…". Hameroff has presented an extensive summary of his, and other studies on information processing in microtubules and other cell structures, in his book "Ultimate Computing: Biomolecular Consciousness and Nano Technology," Stuart R. Hameroff, 1987, ISBN 0 444 70283 0. He recommended the book in his September 1996 correspondence. (Hameroff is at http://www.consciousness.arizona.edu/hameroff/ :

His email address is hameroff@u.arizona.edu).

I also suggest that there are yet other cellular structures that can perform the "computations" for recognizing the magnitudes and rates of change of the orthogonal components of the gravity vector. Not that these structures actually perform a Fourier analyses of the time function of the changing gravity vector. Instead, the mechanisms could merely produce an "information-rich" configuration of the cytoplasm, as controlled by its cytoskeleton which is itself influenced by signals from the centriole's array of nine triplets of microtubule gravity sensors. These signals would represent the magnitudes of the orthogonal gravity vector components, as they change relative to each other from sunrise to sunset.

The cytoskeleton is the protein-based skeleton of the cell which transports biomolecules around inside the cell, and which helps to maintain the structure and shape of the cell. The cytoskeleton is made up of other microtubules and smaller microfilaments, held together in a flexible network by an array of Microtubule Associated Proteins (MAP). This network is an excellent conductor of physical vibrations which can act to modify the cell's configuration so as to represent recent, and longer term, past histories of the changing gravity vectors.

Those cellular configurations in turn may then be responsible for generating electrical, chemical and mechanical signals which then trigger the production of molecules that initiate appropriate biological behavior suited to the environmental conditions associated with the sensed gravity conditions. Cells may also fall into configurational alignments in different tissues (much like magnetic domains fall into alignments), providing for larger, more coherent signals to control biological behaviors associated with those tissues.

Conclusion

The preceding remarks were only intended to suggest what to search for when studying cells for their ability to tell time. They provide a starting point for designing experiments that might reveal the cell's proposed gravity sensing and computational behaviors. The experiments themselves will require considerable ingenuity to conduct the detailed examinations of cell structures, which are often transparent, and which are probably engaged in multiple roles for cell management and replication. Clearly this is an exercise that I will leave to the student.

 

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