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Unformatted text preview: 552 Chapter 17 Genetic Regulation of Cell Number: Normal and Cancer Cells 17.3 The machinery of programmed cell death In multicellular organisms, systems have evolved to eliminate damaged (and hence potentially harmful) cells by a self-destruct and disposal mechanism called pro- grammed cell death or apoptosis. This self-destruct mechanism can be activated under many different cir- cumstances, such as cells that are no longer needed for development. In all cases, however, the events in apopto- sis seem to be the same (Figure 17-6). First, the DNA of the chromosomes is fragmented, organelle structure is disrupted, and the cell loses its normal shape and be- comes spherical. Then, the cell breaks up into small frag- ments called apoptotic bodies, which are phagocytosed (literally, eaten up) by motile scavenger cells. The engines of self-destruction are a series of enzymes called caspases, which is short for c ysteine- containing as partate-specific p rote ases (see the Model Organism box,...
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- Spring '08