The survival of many other types of cells in animals

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Unformatted text preview: program. The survival of many other types of cells in animals is similarly dependent on growth factors or contacts with neighboring cells or the extracellular matrix, so programmed cell death is thought to play an important role in regulating the associations between cells in tissues. The Events of Apoptosis In contrast to the accidental death of cells that results from an acute injury (necrosis), programmed cell death is an active process, which usually proceeds by a distinct series of cellular changes known as a poptosis , first described in 1972 (Figure 17.1). During apoptosis, chromosomal DNA is (A) (B) (C) Hours after induction of apoptosis 0 1 2 3 DNA fragmentation Chromatin condensation Normal Fragmentation of nucleus Fragmentation of the cell Apoptotic FIGURE 17.1 Apoptosis (A) Diagrammatic representation of the events of apoptosis. (B) Light micrographs of normal and apoptotic human leukemia cells illustrating chromatin condensation and nuclear fragmentation. (C) Gel electrophoresis of DNA from apoptotic cells, showing its degradation to fragments corresponding to multiples of 200 base pairs (the size of nucleosomes) at 1–4 hours following induction of apopto...
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