AP BIOLOGY

Detailed explanation-1: -When prophase is complete, the cell enters prometaphase-the second stage of mitosis. During prometaphase, phosphorylation of nuclear lamins by M-CDK causes the nuclear membrane to break down into numerous small vesicles. As a result, the spindle microtubules now have direct access to the genetic material of the cell.

Detailed explanation-2: -The nuclear envelope, including nuclear pore complexes, breaks down at the beginning of mitosis to accommodate the capture of massively condensed chromosomes by the spindle apparatus.

Detailed explanation-3: -NE disassembly is facilitated by two mechanisms: breakdown of the nuclear lamina and physical tearing of the membrane by the microtubule cytoskeleton [66]. Although centrosomes are not inserted in the NE, centrosomes are tethered to the nucleus by multiple mechanisms.

Detailed explanation-4: -At the end of prophase I, the nuclear membrane breaks down, the centrosomes have migrated to the opposite ends of the cell, and the spindle apparatus is being formed. This is followed by metaphase I. During this stage, the spindle fibers, or microtubules, attach to the centromere of each chromosome.

Detailed explanation-5: -Prophase I Events that occur during prophase of mitosis also occur during prophase I of meiosis. The chromosomes coil up, the nuclear membrane begins to disintegrate, and the centrosomes begin moving apart.