prometaasi

Prometaasi is the Finnish term for the stage of mitosis known in English as prometaphase. It follows prophase and precedes metaphase, marking a transitional phase in which the cell prepares for chromosome congression and alignment at the metaphase plate.

During prometaasi, the nuclear envelope breaks down, allowing spindle microtubules to interact with chromosomes. Chromosomes condense further and become accessible to spindle fibers. Kinetochores on sister chromatids attach dynamically to the growing microtubules, initially in lateral contacts that mature into end-on attachments. Microtubule dynamics drive chromosome movements toward the cell center, while motor proteins such as dynein and various kinesins help position chromosomes and organize the spindle. The spindle apparatus itself forms between the two centrosomes and organizes microtubule tracks for subsequent alignment.

Cell-cycle checkpoints remain active during prometaasi to ensure that kinetochores achieve proper attachments before the onset of anaphase. The stage is characterized by rapid reorganization of the spindle, continuous attachment and detachment of microtubules at kinetochores, and gradual alignment of chromosomes along the metaphase plate.

Prometaasi is used primarily in Finnish-language biology and medical literature as the direct translation of prometaphase. In international contexts it is typically equated with prometaphase, though some texts may describe regional or species-specific variations in the timing and duration of this phase. Related terms include prophase, metaphase, anaphase, and telophase, which together constitute the core stages of mitosis.