Spindle apparatus

The spindle apparatus of mitotic spindle is a cellular structure consisting of many spindle fibers. It is formed from during mitosis and meiosis. The spindle fibers are in turn made ​​up of tiny tubes, the so-called microtubules.

Microtubules are structures made from the tubulin protein, and for the formation of the spindle apparatus is important. You can stochastically between phases of growth and decay back and forth, the cell uses this property, for example in formation of the mitotic spindle. The spindle apparatus forms two poles of a cell, arise from the star-shaped microtubules. The microtubule binding to kinetochores of the two chromatids chromosomes of the cell and play an important role in the separation of chromatids to daughter chromosomes, which are divided equally between the two newly formed cells. There are three types of organizations to which unite microtubules: microtubules, starting far can extend beyond the equatorial plane of the poles are called polar microtubules. They overlap each other ( overlap- microtubules ), so that it looks light microscopy, as if they ranged from pole to pole. Other microtubules sit at the kinetochores ( = protein structures, which sit the centromeres ) chromosome and extend into the vicinity of the poles or are associated with the polar microtubules. They are called kinetochore microtubules. The astral microtubules form a star around the poles and take the cytoskeleton contact. The temporal sequence of mitosis by a control mechanism - the mitotic checkpoint - regulated. This delays the initiation of anaphase, as long as there kinetochores that are not attached yet from both sides of the mitotic spindle (bipolar).

Most animal cells organize the spindle apparatus using centrosomes, each consisting of a pair of centrioles. The centrosome divides into the S phase of the cell cycle. At the beginning of prophase microtubules are formed, which push the Zentriolenpaare in opposite areas of the cell - the poles. Each Zentriolenpaar = centrosome is surrounded by a matrix from which emanate the microtubules. The plants lack centrosomes. There is a specific binding site for microtubules in the chromosome ( it may include the entire chromosome surface in chromosomes with " diffuse " centromere ). The walk to the poles is based on an interaction between the kinetochore microtubules, the polar and astral microtubules. The latter can contact the cell cortex. According to present knowledge, the chromosomes are pulled and pushed. The movement is by motor proteins (eg kinesin 4, 5, 10, 14) that are located at the kinetochores or hike to the microtubules, mediated and not due to a simple sliding mechanism. During telophase, the spindle core dissolves, the microtubules in plant cells accumulate in the region of phragmoplast, from which starts the organization of the interphase cytoskeleton and the new cell wall. The microtubules are the Phragmoplastenebene in closest proximity to the microfilaments.