Final answer:
During prophase, the kinetochore on the outer surface of each centromere becomes attached to spindle fibers, which is critical for chromosome alignment and separation during mitosis.
Step-by-step explanation:
During prophase, the kinetochore, on the outer surface of each centromere, becomes directly attached to spindle fibers. The kinetochore is a protein complex that binds the centromeres of a chromosome to the microtubules of the mitotic spindle. Spindle fibers are formed from microtubules that extend from the centrosomes, positioned at opposite poles of the cell, and they play a crucial role in the segregation of sister chromatids during cell division.
As the nuclear membrane disintegrates, the spindle fibers reach the center of the cell and attach to the kinetochores. This attachment ensures that each sister chromatid will be oriented correctly for separation and will be divided evenly between the two emerging daughter cells.
During the transition from prophase to metaphase, also known as prometaphase, this attachment is crucial for the alignment of chromosomes at the metaphase plate and for the accurate distribution of genetic material during the subsequent phases of mitosis.