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The cell cycle is a series of complex, ordered, sequential events that control how a single cell divides into two cells, and involves several different phases. The phases include the G1 and G2 phases, DNA replication or S phase, and the actual process of cell division, mitosis or M phase. [ 1 ]
The G2 to M transition is dramatic; there is an all-or-nothing effect, and the transition is irreversible. This is advantageous to the cell because entering mitosis is a critical step in the life cycle of a cell. If it does not fully commit, the cell would run into many issues with partially dividing, ultimately likely leading to the cell's death.
In any case, the temporal order of replication along the length of each chromosome can be plotted in graphical form to produce a "replication timing profile". Figure 4 shows an example of such a profile across 70,000,000 base pairs of human Chromosome 2.
Furthermore, the composition and properties of chromatin vary from one cell type to another, during the development of a specific cell type, and at different stages in the cell cycle. The DNA + histone = chromatin definition: The DNA double helix in the cell nucleus is packaged by special proteins termed histones. The formed protein/DNA complex ...
Schematic karyogram of the human chromosomes, showing their usual state in the G 0 and G 1 phase of the cell cycle. At top center it also shows the chromosome 3 pair in metaphase (annotated as "Meta."), which takes place after having undergone DNA synthesis which occurs in the S phase (annotated as S) of the cell cycle.
Three types of cell division: binary fission (taking place in prokaryotes), mitosis and meiosis (taking place in eukaryotes).. When cells are ready to divide, because cell size is big enough or because they receive the appropriate stimulus, [20] they activate the mechanism to enter into the cell cycle, and they duplicate most organelles during S (synthesis) phase, including their centrosome.
Once the paired sister chromatids have separated from one another (in the anaphase of mitosis) each is known as a daughter chromosome. The short arm of the right chromatid (3), and the long arm of the right chromatid (4), are also marked. Schematic karyogram of the human chromosomes, showing their usual state in the G 0 and G 1 phase of the ...
Second, individual chromosome preference is variable among different cell types. For example, the X-chromosome has shown to localize to the periphery more often in liver cells than in kidney cells. [45] Another conserved property of chromosome territories is that homologous chromosomes tend to be far apart from one another during cell interphase.