The Cell Cycle Essay

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The cell cycle is the process that regulates the duplication and division of cells. It is tightly controlled by a series of checkpoints. The cycle begins when a cell receives an external signal to divide. The first stage of the cell cycle is G1, where cells commit to enter the cycle and prepare to duplicate their DNA.. The cell is now committed to progress from G1 to S phase, where the DNA is duplicated. After S phase comes G2. If the intracellular envronment is favourable, and the DNA has been deuplicated corerectly, the cell progress to the M phase. Here, the chromosomes condense and the nuclear envelope breaks down. The mitotic spindle forms, in preparation for chrmatid separation. At this stage, key roles are played by the Aurora kinases. Aurora A is thought to act at the spindle poles. Aurora B acts at the kinetechores, ensuring the chromsoomes are correctly aligned to the mitotic spindle. It also has functions in cell division. If everything is in order, the sister chromatids separate to opposite poles of the cell. The nuclear envelope reforms, and the cell divides into two identical daughter cells. Chromosome abnormalities are a hallmark of cancer, and their occurrence may be due to the deregulation of checkpoints during mitosis. Aurora kinases are involved in this checkpoint function. These kinases are only expressed during mitosis and overexpressed in a wide range of tumours. Aurora A is thought to play a role in regulating centrosome function. At the spindle checkpoint, Aurora B plays an essential role in recruiting proteins such as baba1 to the kinetechores. This promotes chromosome alignemtne, and ensures each daughter cell receives the correct number of chromosomes, The eukaryotic cell cycle is divided into several phases - G1, S, G2 and M. Chromosomal DNA replication takes place during S phase, whereas cell division (mitosis and cytokinesis) occurs

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