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CrateDane t1_j3nay17 wrote

The centrosome in an interphase cell uses its radiating microtubules to sense the peripheries of the cell and place itself roughly in the center. Like pushing rods out in every direction to end up in the middle. During mitosis, the centrosome divides and each new baby centrosome does something similar, except they're also pushing each other away. So they end up towards each side of the cell.

The microtubules projecting from each centrosome each bind a chromatid at the other end, at the kinetochore (a big protein complex that sits on a particular sequence of DNA). Microtubules can bind on each side, so both centrosomes get connected to one side of the pair of sister chromatids. They can then do the same pushing thing, and since they're equally good at pushing, the chromatids all end up roughly at the mid-line of the cell. Then it's just a matter of cell cycle regulation - once everything is ready, the anaphase-promoting complex is activated, and activates separase to cleave the proteins holding the sister chromatids together. Then each centrosome can pull its set of chromosomes to its side of the cell in preparation for cytokinesis.

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ihaveredhaironmyhead OP t1_j3ninx3 wrote

This is a great description of what happens, but where are the instructions for all of this located? It's been explained to me that it's nothing but molecules bumping into each other but it sounds so complex it's hard to understand that.

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CrateDane t1_j3nkpyz wrote

The information is stored in DNA. Proteins are made based on the DNA sequence, and the shape of those proteins dictates their function. Like how tubulin makes microtubules and so on.

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ihaveredhaironmyhead OP t1_j3nle7c wrote

So the shape of the centromeres dictates they behave in this complex manner of arrangement? Is it like a child's toy where squares fit into squares and circles fit into circles? I still struggle to understand how this can happen with zero guidance from a brain. It's just the shape of the molecules? What you described they do is so complicated.

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CrateDane t1_j3np57m wrote

> Is it like a child's toy where squares fit into squares and circles fit into circles?

That's pretty much how it works for putting things together. When the proteins have to do more, they have to change shape. But that still depends on how they're put together, they're like little machines with like springs, levers etc.

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