DNA Supercoiling

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•  Chromosomes condense by supercoiling during mitosis

Chromatin versus Chromosome


  • DNA is usually loosely packed within the nucleus as unravelled chromatin
  • In this unravelled form, the DNA is accessible to transcriptional machinery and so genetic information can be translated
  • DNA is organised as chromatin in all non-dividing cells and throughout the process of interphase


  • DNA is temporarily packaged into a tightly wound and condensed chromosome prior to division (via supercoiling)
  • In this condensed form, the DNA is able to be easily segregated however is inaccessible to transcriptional machinery
  • DNA is organised as chromosomes during the process of mitosis (condense in prophase, decondense in telophase)

Organisation of DNA into a Mitotic Chromosome

mitotic chromosome

Chromosome versus Chromatid

A chromosome is the condensed form of DNA which is visible during mitosis (via microscopy)

As the DNA is replicated during the S phase of interphase, the chromosome will initially contain two identical DNA strands

These genetically identical strands are called sister chromatids and are held together by a central region called the centromere

When these chromatids separate during mitosis, they become independent chromosomes, each made of a single DNA strand

Single Chromatid versus Sister Chromatid Chromosome

chromatid vs chromosome