Chapter_18_Solutions - Chapter 18 Apoptosis DEFINITIONS 181...

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DEFINITIONS 18–1 Caspase 18–2 Apoptosome 18–3 Apoptosis 18–4 Death-inducing signaling complex (DISC) 18–5 Extrinsic pathway 18–6 Survival factor 18–7 Intrinsic pathway 18–8 Programmed cell death 18–9 Death receptor 18–10 Initiator procaspase TRUE/FALSE 18–11 True. Adult tissues are maintained at a constant size, so that there must be a balance between cell death and cell division. If this were not so, the tissue would grow or shrink. 18–12 True. Cytochrome c mediates apoptosis from signals within a mammalian cell—the intrinsic pathway of apoptosis. This has been confirmed directly by generating cytochrome c -deficient mouse embryo fibroblasts (MEFs) by reverse genetics. Although mice with knockouts of their cytochrome c genes die about midway through gestation, fibroblasts from such embryos can be cultured under special conditions and tested for sensitivity to various apop- totic signals. They are resistant to a variety of agents that induce the intrin- sic pathway of apoptosis. Reference: Li K, Li Y, Shelton JM, Richardson JA, Spencer E, Chen ZJ, Wang X & Williams RS (2000) Cytochrome c deficiency causes embryonic lethality and attenuates stress-induced apoptosis. Cell 101, 389–399. THOUGHT PROBLEMS 18–13 Because programmed cell death occurs on a large scale in both developing and adult tissues, it is important that it does not trigger the alarm reactions normally associated with cell injury. In tissue injury, for example, signals are released that can cause a destructive inflammatory reaction. Moreover, the release of intracellular contents could elicit an immune response against molecules that are normally not encountered by the immune system. In normal development, such reactions would be self-defeating, even danger- ous, if they occurred in response to programmed cell death. A431 Chapter 18 18 Apoptosis
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18–14 Cells in an animal must behave for the good of the organism as a whole—to a much greater extent than people generally act for the good of society as a whole. In the context of an organism, unsocial behavior would lead to loss of organization and to cancer. Many of the rules that cells have to obey would be unacceptable in a human society. Most people, for example, would be reluc- tant to kill themselves for the good of society, yet our cells do it all the time. 18–15 The plasma membrane of the cell that died by necrosis (see Figure 18–1A) is ruptured; several clear breaks are visible, for example, at 8, 9, and 12 o’clock. The cell’s contents, mostly membranous and cytoskeletal debris, are seen spilling into the surroundings. The cytosol stains lightly, as most soluble components had been lost before the cell was fixed. By contrast, an intact membrane surrounds the cell that underwent apoptosis (see Figure 18–1B), and its cytosol is densely stained, indicating a normal concentration of cel- lular components. The cell’s interior is remarkably different from a normal cell, however. Particularly characteristic are the large blobs that extrude
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Chapter_18_Solutions - Chapter 18 Apoptosis DEFINITIONS 181...

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