At the telophase of meiotic and mitotic cell divisions, the chromosomes of daughter cells uncoil back to chromatin, but after interphase, it coils up again to form visible chromosomes. Why do this happen? Isn't it simpler and more convenient for the chromosomes of the cells coil up in 1 cell cycle?
The condensed form of DNA that exists during cell division is tightly wound and therefore unavailable to the enzymes and transcription factors that interact with and read DNA. So, if chromosomes are constitutively condensed, the cell will not be able to transcribe RNA, and thus will not be able to make new proteins, and thus will not be able to grow and divide. The process of selectively condensing certain regions of DNA to prevent binding of transcription factors and RNA polymerase is actually a conserved method of epigenetic transcriptional regulation in eukaryotes.
You may be thinking Then why condense DNA at all?
Uncondensed chromosomes are difficult to separate, and failure to properly segregate homologous chromosomes during mitosis (a phenomenon called nondisjunction) can lead to aneuploidy. Aneuploidy in germ cells is often lethal, and aneuploidy in somatic cells is a characteristic of cancer.
It’s happening because genetic information from DNA can be read only if it’s in the chromatin form, it can’t be read from chromosomes and so the cell can’t fulfill its functions. But if it’s need to take apart cell’s genetic material, the form of chromosomes makes it easier