Mitoz ve Sitokinez

Mitosis consists of prophase, metaphase, anaphase, and telophase. During prophase, chromosomes condense and the mitotic spindle forms. Metaphase aligns chromosomes at the cell's equator. Anaphase separates sister chromatids to opposite poles. Telophase reverses prophase changes as the nuclear envelope reforms around each set of chromosomes.

Sister chromatids are held together by protein complexes called cohesins that hold the sister chromatids together until anaphase. These ring-shaped proteins encircle both chromatids, maintaining their connection through metaphase. When the anaphase-promoting complex signals their removal, cohesins are cleaved, allowing chromatids to separate and move to opposite poles.

The mitotic spindle is a dynamic structure composed of microtubules that organizes and moves chromosomes. Spindle fibers attach to kinetochores on chromosomes and generate forces that pull sister chromatids apart. The spindle also elongates the cell, positioning chromosomes for proper distribution to daughter cells during cell division.

Animal cells undergo cytokinesis through cytokinesis rhoa and contractile ring formation, where a protein ring pinches the cell membrane inward to divide the cytoplasm. Plant cells form a phragmoplast, a structure that guides cell wall deposition between daughter cells. This difference reflects the presence of a rigid cell wall in plants versus the flexible membrane in animals.

The spindle assembly checkpoint is a quality control mechanism that prevents anaphase until all chromosomes are properly attached to spindle fibers. This checkpoint ensures that kinetochores cohesin rings and spindle attachment are correct before sister chromatids separate. It prevents errors that would result in unequal chromosome distribution to daughter cells.

The plane of cell division is determined by the position of the mitotic spindle, which is guided by the centrosome and astral microtubules. The spindle orients perpendicular to the cell's longest axis, and the contractile ring forms at the cell's equator. This ensures determining the plane of cell division results in roughly equal distribution of cytoplasm and organelles to daughter cells.

During prophase, chromosomes condense through the action of condensins and condensation of chromosomes, making them visible under a microscope. Simultaneously, the centrosome duplicates and the two copies move to opposite poles, organizing the mitotic spindle. This condensation compacts DNA and ensures chromosomes are properly structured for attachment to spindle fibers.