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The Cell Cycle
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G1 Phase: Also known as the first gap phase, G1 is the period after cell division (mitosis) when the cell grows and carries out its normal functions. During this phase, the cell synthesizes proteins and organelles, and prepares for DNA replication. G1 is followed by a checkpoint called the G1/S checkpoint, which ensures that the conditions are favorable for DNA synthesis.
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S Phase: In the S phase, DNA replication takes place. Each chromosome is duplicated, resulting in the formation of sister chromatids, which are held together by a structure called the centromere. By the end of the S phase, the cell’s DNA content has doubled. DNA replication is tightly regulated to ensure accurate and complete duplication of the genetic material.
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G2 Phase: G2, the second gap phase, follows DNA synthesis. During this phase, the cell continues to grow and prepare for cell division. The cell synthesizes proteins and checks for DNA damage or errors. The G2/M checkpoint occurs at the end of G2 and ensures that the cell’s DNA is intact and properly replicated before entering the mitotic phase.
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M Phase (Mitosis): The M phase is the phase of cell division itself. It consists of several stages, including prophase, metaphase, anaphase, and telophase, which were briefly described in the “Cell Division” response. During mitosis, the duplicated chromosomes are segregated into two daughter cells. Cytokinesis, the division of the cytoplasm, typically follows mitosis, resulting in the formation of two genetically identical daughter cells.
The cell cycle is regulated by a complex network of regulatory proteins and checkpoints that monitor the progression of the cell through each phase. These checkpoints ensure that the cell’s DNA is intact, the replication process is completed accurately, and the cell is ready for division. If abnormalities or errors are detected, the cell cycle may be halted, allowing for DNA repair or triggering programmed cell death (apoptosis).
The control of the cell cycle is crucial for maintaining the integrity and proper functioning of cells. Dysregulation of the cell cycle can lead to uncontrolled cell division and the development of diseases such as cancer.