Final answer:
Microtubules attach to kinetochores through a dynamic process where microtubule-organizing centers (MTOCs) extend microtubules that eventually come into contact with and bind to kinetochores. This process ensures proper alignment and separation of chromosomes during cell division.
Step-by-step explanation:
Duplicated chromosomes undergo condensation during prophase in mitosis and meiosis. This condensation results in visible paired sister chromatids attached at their centromeres. At this stage, specific proteins associate with these centromeres to form a structure known as the kinetochore. As the mitotic spindle forms, some of the spindle fibers, which are essentially microtubules, attach to the kinetochore. These kinetochore microtubules play a crucial role in moving chromosomes during cell division.
Kinetochore microtubules emerge from centrosomes or microtubule-organizing centers (MTOCs) and grow in length by adding tubulin subunits to their plus ends, which extend toward the kinetochores. When these microtubules come into contact with kinetochores—which is facilitated by the natural dynamic instability of microtubules—they form stable attachments. These attachments are essential for the correct alignment and subsequent separation of sister chromatids during anaphase. Microtubules do not directly attach to kinetochores without this process, as the controlled capture of kinetochore microtubules by kinetochore proteins ensures proper chromosome segregation.