Question

What are centromeres composed of?

Answer 1

The chromosome structure is similar in most cases to an X, but the location of the point where the two arms of the X touch may vary. This contact point has a name, of course (a biologist never misses a chance to name something): the centromere.

Without centromeres, cells cannot divide properly and mitosis fails.
Centromeres are actually defined by specific regions of DNA called alpha satellite, which specifically bind centromere proteins.
Scientists have identified over 20 that contribute to forming the centromere complex.

Without them, kinetochores do not have a place to attach to pull the sister chromatids apart.