Prometafázis

Prometafázis (prometaphase) is a stage of mitosis that follows prophase and precedes metaphase in many eukaryotic cells. During prometafázis, the nuclear envelope breaks down, allowing spindle microtubules to interact with chromosomes. Chromosomes condense further and their kinetochores attach to microtubules emanating from opposite spindle poles. As attachments form, chromosomes begin moving toward the cell center, a process known as congression, and become guided toward the metaphase plate.

The kinetochore–microtubule attachments are refined by motor proteins and microtubule dynamics to ensure proper bi-orientation of sister chromatids. The spindle assembly checkpoint monitors whether all kinetochores are properly attached and under appropriate tension, delaying the onset of metaphase until correct alignment is achieved. Chromosome movement toward the poles can occur through depolymerization of microtubules at the kinetochore end (the pac-man mechanism) or at the microtubule minus ends near the poles, and is aided by motor proteins such as dynein and certain kinesins.

By the end of prometafázis, most chromosomes are bi-oriented and congressed near the equatorial region, ready to proceed to metaphase, where they align more stably along the metaphase plate before separation during anaphase. The phase serves as a transitional checkpoint to ensure accurate chromosome bi-orientation and attachment prior to chromosome segregation.