Prophase:
* Chromatin Condensation: The loose, thread-like chromatin fibers within the nucleus begin to coil and condense into visible, thick, rod-like structures called chromosomes. Each chromosome consists of two identical copies called sister chromatids, joined at a centromere.
* Nuclear Envelope Breakdown: The nuclear envelope, which encloses the nucleus, starts to fragment and disintegrate. This allows the chromosomes to move freely within the cytoplasm.
* Nucleolus Disappears: The nucleolus, a dense region within the nucleus involved in ribosome synthesis, gradually disappears.
* Centrioles Migrate: In animal cells (and some plant cells), centrioles, which are small, cylindrical structures, move to opposite poles of the cell. These will eventually become the poles of the spindle fibers.
* Spindle Fiber Formation: Microtubules, protein fibers that make up the cytoskeleton, start to assemble into a spindle apparatus, which extends between the poles of the cell.
Prophase Plus
Prophase plus, also called prometaphase, is actually a distinct stage that comes *after* prophase. It represents a crucial transition period where the chromosomes attach to the spindle fibers and begin moving toward the center of the cell.
Prometaphase:
* Chromosomes Attach to Spindle Fibers: The kinetochores (specialized structures on the centromere of each chromosome) attach to spindle fibers extending from the poles of the cell.
* Chromosome Movement: As the spindle fibers shorten, the chromosomes start moving toward the center of the cell, aligning along the metaphase plate (an imaginary plane in the middle of the cell).
In Summary:
* Prophase: The nucleus prepares for division by condensing chromosomes, breaking down the nuclear envelope, and setting up the spindle fibers.
* Prometaphase: The chromosomes attach to the spindle fibers and begin moving towards the center of the cell, marking the transition to the next stage of mitosis.
Remember that this is a simplified overview, and the details of each stage can vary depending on the specific cell type.
