Final answer:
The main microtubule organizing center in animal cells is the centrosome, containing a pair of centrioles, which is essential for spindle fiber formation during mitosis. Spindle fibers, including kinetochore and polar microtubules, grow from the centrosomes, attach to chromosomes, and facilitate their separation into daughter cells. In plant cells, an analogous structure called the Microtubule Organizing Center (MTOC) serves the same function.
Step-by-step explanation:
Main Microtubule Organizing Center
The primary microtubule organizing center in animal cells is the centrosome, which contains a pair of centrioles. During mitosis, the centrosomes serve as pivotal points from which the spindle fibers grow. The spindle fibers are essential in the process of chromosome separation. There are two types of microtubules in spindle fibers: kinetochore microtubules and polar microtubules. The kinetochore microtubules attach to a protein complex known as the kinetochore, which is located at the centromere of each chromosome. The polar microtubules, on the other hand, assist in cell elongation.
Role of the Spindle Apparatus During Mitosis
During mitosis, specifically in the prometaphase, the centrosomes move apart to opposite ends of the cell, and the spindle apparatus assembles. Chromosomes become more condensed, and the kinetochores bind to the mitotic spindle microtubules. This connection is crucial as it helps to orient the chromosomes so that the sister chromatids can face the opposite poles of the cell. Subsequently, in anaphase, the kinetochore microtubules shorten, pulling the separated sister chromatids toward the opposing poles, ensuring that each new cell receives an equal complement of chromosomes. In plant cells, which typically do not have centrioles, the spindle apparatus forms from a structure functionally equivalent to the centrosome called the Microtubule Organizing Center (MTOC).