D2.1.7
Cards (6)
- During interphase the chromosomes are dispersed through the nucleus so they are not individually visible. To prepare for mitosis all of the DNA is replicated and each chromosome then consists of two very elongated chromatids containing identical DNA.
- During prophase the chromosomes condense by packing the DNA tightly into thicker, shorter structures. Towards the end of prophase, microtubules grow from structures at the poles of the cell called microtubule organising centres to form a spindle-shaped array linking the poles of the cell. At the end of prophase the nuclear membrane breaks down.
- In Metaphase, microtubules growing from the poles attach to the centromere of each chromatid. Sister chromatids within each chromosome become attached to opposite poles. The spindle microtubules are put under tension to test whether the attachment is correct. If the attachment is correct, the chromosomes cannot yet be pulled to either pole due to cohesin loops. At the end of metaphase, the chromosomes are aligned on the equator of the cell.
- In Anaphase, the cohesin loops that have held the sister chromatids together are now cut, so the chromatids become separate chromosomes. Microtubules link each chromosome to one of the poles and then the kinetochore shorten the microtubules, pulling the chromosome to the pole. At the end of anaphase all the chromosomes have reached the poles but have not started to decondense.
- In Telophase each the chromosomes are pulled into a tight group near the MTOC at each pole, and a nuclear membrane forms around them. The chromosomes decondense and spread out to form dispersed chromatin inside the nucleus. By this stage the cell is usually already dividing its cytoplasm (cytokinesis) and the two daughter cells produced enter interphase again.
- In Interphase following mitosis, the genes in the decondensed chromosomes can be transcribed and the mRNA translated to synthesise proteins that the cell needs. The cell grows usually doubling in size before the next mitosis.