What happens to the nucleus and nucleolus during prophase?

Answer 1

During prophase, this is what the nucleus does:

• The chromatin coils into double rod-shaped structures called chromosomes.
• The chromatin becomes visible.

Okay, so now: Since the genetic material has been replicated in the prior interphase of the cell cycle, there are two identical copies of each chromosome in the cell, called homologous chromosomes. Identical chromosomes, called sister chromatids, are attached to each other at a DNA element present on every chromosome called the centromere.

Answer 2

The nucleolus is the ribosome factory and also a multifunctional domain that plays an important role in nuclear organization and function. The nucleolus is assembled at the end of mitosis, is active during interphase, and dis-assembled in prophase. The nucleolar machineries of transcription and processing are inherited from parental to daughter cells through mitosis. The polymerase I transcription machinery is repressed during mitosis although assembled with ribosomal genes (rDNA). The repression of pol I transcription is achieved at the end of prophase and is maintained during mitosis through phosphorylation of transcription factors by cyclin-dependent kinase (CDK) 1. The nucleolar processing machineries relocalize from the nucleolus towards the periphery of all chromosomes in early prophase. The processing complexes remain associated with chromosomes until telophase and this chromosome association depends on CDK1 activity. In telophase, as a consequence of natural inhibition of CDK1 activity, pol I transcription is restored. The processing machineries are recruited to the sites of rDNA transcription after a temporary transit in foci assembled on the chromosome surface. These immobile foci called prenucleolar bodies (PNBs) could correspond to an assembly platform of processing complexes prior to recruitment to transcription sites. The contents of the PNBs are delivered to nucleoli with different kinetics and consequently PNBs have different life-times depending on their contents. Partly processed pre-rRNAs generated during prophase are inherited during mitosis and are found in PNBs. The possibility that the processing complexes forming PNBs can be nucleated by some pre-rRNAs passing through mitosis is proposed. Thereafter, nucleolar assembly is completed by cooperative interactions between chromosome territories. Thus the behavior of the nucleolus during mitosis illustrates the fact that the dynamics of nuclear organization at the beginning of interphase are integrated in a network of interactions and controls that is largely dependent on the coordination of mitotic events.

Answer 3

During telophase 2 several things happen to a cell. The nuclear membrane reforms, the cytoplasm divides, and finally four daughter cells are formed.