Mitosis: Prophase Overview

Mitosis Overview

• Mitosis is the process of nuclear division, resulting in two daughter cells with identical chromosome sets.
• Chromosome duplication is essential for mitosis to occur.

Prophase

• Prophase accounts for about 80% of the time taken for cell division, making it the longest phase.
• The cytoskeleton is dismantled to reform a new structure, increasing cytoplasm viscosity.
• Chromosomes condense into visible filaments as nucleolus material disperses within the nucleus.
• The nuclear envelope breaks down, producing membranes similar to the endoplasmic reticulum, allowing chromosomes to interact with the cytoplasm.
• Each sister chromatid possesses a kinetochore, a protein ring that connects to the microtubules of the mitotic spindle.
• Sister chromatids originate from the same chromosome and are held together by the centromere during early mitosis.

Metaphase

• Centrioles separate and migrate to opposite poles, facilitating the formation of spindle fibers.
• Kinetochore fibers attach spindle microtubules to the kinetochores on chromosomes.
• Polar fibers extend from centriole to centriole, not attaching to kinetochores.
• Astral fibers are positioned outward, supporting spindle structure.
• Chromosomes align at the cell's equator on the metaphase plate, held in place by spindle fibers connected to their centromeres.
• In plant cells, spindle fiber orientation is guided by the plasma membrane and cell poles, as they lack centrioles.