Phases of Cell Cycle

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2.1 Phases of The Cell Cycle
2.1.1 Interphase Originally this phase of the cell cycle was called the "resting stage", since light microscopy could not detect any activities taking place within the cells. Today, however, it is known as a stage of considerable activity at the molecular and sub-cellular level and is usually subdivided into: * G1 - ("Gap One") - this is a period of molecular synthesis where a newly formed cell turns on a variety of genes on its DNA to make proteins, which in turn churn the metabolism of the cell, produce and breakdown carbohydrates, lipids, etc., and transform energy from food into ATP. The cell grows and enlarges. * S - ("synthesis") - during this phase the chromatin (DNA and proteins) becomes synthetically active. Using elaborate teams of enzymes, the DNA molecules of each chromosome are copied by semiconservative DNA synthesis. This phase cannot be clearly seen or distinguished under the light microscope, even with DNA stains, as the material is too diffuse. However, the making of new DNA molecules can be monitored by following the incorporation of radioactive isotopes into the newly forming DNA molecules. * G2 - ("Gap Two") - another period, of variable length, in which cells prepare for division. Many different proteins are synthesized, especially those that will act as spindle fibers (protein "ropes"). Stocks of energy are accumulated and many organelles, such as mitochondria, also grow and divide, increasing in number.• Interphase is a busy time in the life of a dividing cell. Towards the end of G2, however, things slow down and the cell gets ready for the next major phase in the cycle. |

2.1.2 Mitotic Phase Mitosis
Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same genetic component as the parent cell. Chromosomes replicated during the S phase are divided in such a…...

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