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Figure 1. An interphase nucleus (left) and a set of mitotic chromosomes (right) from human tissue culture cells. Bar, 10 μm. Condensins are large protein complexes that play a central role in chromosome assembly and segregation during mitosis and meiosis (Figure 1).
During mitosis, the chromosomes, which have already duplicated during interphase, condense and attach to spindle fibers that pull one copy of each chromosome to opposite sides of the cell. [4] The result is two genetically identical daughter nuclei. The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells. [5]
The appearance of a prematurely condensed chromosome depends on the stage that the interphase cell was in. [1] Chromosomes that are condensed during the G 1 phase are usually long and have a single strand, while chromosomes condensed during the S phase appear crushed. Condensation during the G 2 phase yields long chromosomes with two chromatids.
Micrograph showing condensed chromosomes in blue, kinetochores in pink, and microtubules in green during metaphase of mitosis. In cell biology, the spindle apparatus is the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells.
Metaphase (from Ancient Greek μετα- beyond, above, transcending and from Ancient Greek φάσις (phásis) 'appearance') is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase). [1]
Condensation and resolution of human sister chromatids in early mitosis. Interphase: The structure of chromatin during interphase of mitosis is optimized to allow simple access of transcription and DNA repair factors to the DNA while compacting the DNA into the nucleus. The structure varies depending on the access required to the DNA.
The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.
Chromosome decondensation (also known as relaxation or decompaction) into expanded chromatin is necessary for the cell's resumption of interphase processes, and occurs in parallel to nuclear envelope assembly during telophase in many eukaryotes. [2] MEN-mediated Cdk dephosphorylation is necessary for chromosome decondensation. [2] [5]