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Mitosis160-page12 - 1 G 2 and mid-mitosis where the cell...

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Cell Reproduction: Mitosis - 12 Controlling the Cell Cycle The control of cell division is one of the most active areas of biological research, in part because cancers are diseases that involve cells that have lost their cell division controls. Some cells divide frequently throughout the lifespan of a multicellular organism, and some rarely, or not at all. Others divide only when damage occurs to the tissue. Cell division is regulated by a series of chemical signals that are an important part of current molecular biology research. In the 1970's, researchers learned that there are definite cell-cycle controls that direct and coordinate the events of the cell cycle. These controls are known as checkpoints. The animal cell cycle has at least three "checkpoints" (in G
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Unformatted text preview: 1 , G 2 and mid-mitosis) where the cell cycle remains in that stage until over-ridden by chemical signals. • The first checkpoint, called the G 1 /S checkpoint, is in G 1 and determines whether DNA replication should proceed. Cells that never leave G 1 are said to be in a non-dividing cycle called G . Cells will stay in G 1 until they receive a signal to proceed with DNA duplication. • The second checkpoint, G 2 /M, is in G 2 just prior to mitosis and determines if mitosis will begin by ensuring that DNA duplication has been correctly done. • The third checkpoint, the spindle or APC (anaphase-promoting complex) checkpoint, occurs in metaphase and ensures that chromosomes are properly aligned on the cell's equator....
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