The Detachment of the Kinetochore Microtubule

 

Verily, it is the rapid evolutionary change in the Chromosome’s-to-be form and position, and the Microtubule’s-to-be characteristics themselves that cause the Microtubule-to-be to detach itself from its bond with the Kinetochore-to-be. The word “detach” as used here conveys two meanings. In the first sense, it denotes the process by which all molecules that form the Microtubule free themselves of the bonds they have with the Kinetochore. In the second, it refers to the process by which all those molecules of the Microtubule-to-be that are bonded to the Kinetochore and are close to it detach themselves and merge into the body of the Cell-to-be such that there is a space between the Chromosome-to-be and the Microtubule-to-be. (See Illustration 1d). To put it another way, they (Microtubules-to-be) become shorter. It is possible that at first the space between them is only a few Angstrom; however, as their life demands that they go through a series of phases, the way their “mother” did, these Microtubules-to-be will re-attach themselves to the Kinetochore in the next phase.

 

In Illustration 1a it can be seen that the Microtubule-to-be attaches itself to the Chromosome-to-be. After passing through a long period, and due to the change in and the position of the Chromosome-to-be itself, the Microtubule puts itself at a distance (illustration 1b). Later, however, in the course of undergoing the next phase, it re-attaches itself to the Chromosome-to-be.

In illustration 1c the space is seen to become wider, but the Microtubule-to-be will still re-attach itself later as it did earlier (see illustration 1c, downwards). Although in illustration 1d the space is seen to be very wide, it will still reattach itself in the next phase, out of its desire to follow the footsteps of its “mother”. That is why even until today the Microtubule continues to re-attach itself during the Metaphase.

It is these movements—alternately attaching and detaching (distancing) itself—plus its particular characteristics that accounts for the Microtubule’s-to-be having peculiar features. This explains why today, at a time when it is in the Metaphase, the Microtubule looks as if it were alive and moving, constantly searching for the Kinetochore of the Chromosome to which it will attach itself.

 

It is quite likely that the labile and dynamic nature (or the Dynamic instability) of the Microtubule occurring currently is to a larger extent caused by such movement as is shown in illustration 1—the sort of movement it made some time after it emerged for the first time.

 

Additional Notes:

In the polar Microtubule, the molecules that serve as its building block have been active since the time when it undergoes its natural division; whereas in the Kinetochore Microtubule-to-be, the molecules just appeared after the Chromosome-to-be detaches itself from the Centrosome-to-be. Nevertheless, prior to their division, both types of Microtubules are unable to hold their molecules, consequently causing them to be detached and burst inside the body of the Cell-to-be. That is why in certain phases these molecules are seen to appear, while in other they are seen to disappear.

In Illustration 2 the Centrosome-to-be is seen to divide itself naturally, thus resulting in the dismantling of the compounds. Apart from its being divided, the Centrosome-to-be also twists to the extent that the “slime” blanketing it is also led to elongate and twist as is shown in illustration 2a.

The sight of the Microtubule-to-be being so short (see illustration 2 and 3) should not surprise one. This is a natural phenomenon: things usually start small.

The twists may seem to be very insignificant though; however, as far as evolution is concerned, a twist even as minute as 1/1.000.000 degree may, millions of years later, lead to far-reaching consequences (relate this with the text under the heading “Quotations on the Evolutionary Development of Living Creatures” in the pages that follow).

In illustration 2b the slime is seen to break up and curl back, which to some extent affects the growth of the Centrosome-to-be. However, due to its elasticity, the Centrosome-to-be regains its original form as shown in illustration 2d.

In illustration 3a the Centrosome-to-be is seen to develop chemically and doubles itself.

In illustration 3b the Microtubule-to-be is formed from the slime-like molecules existing around it. The process of the formation of the Microtubule-to-be may at the initial stage look as if some chemical event were taking place, though in the later stages it may look as if it were but a repetition of the initial division by natural force.

What follows next is an event as shown in 3c, where the elongated Microtubule-to-be is seen to be at the Prophase when it emerged from both Centrosomes-to-be. The Kinetochore Microtubule emerges during the Metaphase and the Anaphase of the present time. Even at the Telophase, one can still see the Polar Microtubule.

In illustration 3d the Kinetochore-Microtubule–to-be begins to free its bonds of its molecules such that it no longer appears as it was in the Telophase. On the contrary, the Polar Microtubule-to-be continues to preserve its form until the Cytokinesis event.

 

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