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1115-1128 Apoptosis - A poptosis Programmed cell death...

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Apoptosis Programmed cell death eliminates unwanted cells o During apoptosis, cells shrink and condense, the cytoskeleton collapses, the nuclear envelope disassembles, and the nuclear chromatin condenses and breaks up into fragments o Cells are eaten o Animal cells that die accidentally do so by cell necrosis, and they swell and burst and spill shit over neighbors o In vertebrate immune system, apoptosis eliminates developing T and B lymphocytes that either fail to produce potentially useful antigen-specific receptors or produce self-reactive receptors that make the cells potentially dangerous o Cell death helps form fingers, helps cut off tadpole tails for frogs o Cell death and cell division have to be tightly regulated to ensure they are exactly in balance Apoptotic cells are biochemically recognizable o During apoptosis, endonuclease cleaves the chromosomal DNA into fragments of distinctive sizes o Cleavages occur in the linker regions between nucleosomes, the fragments separate into a characteristic ladder pattern when analyzed by gel electrophoresis o Cleavage of DNA generates many new DNA ends which can be marked in apoptotic nuclei by using a labeled nucleotide in the TUNEL technique o There is a negatively charged phospholipid PHOSPHATIDYLSERINE that is normally only located in the inner leaflet of the lipid bilayer of the plasma membrane o It flips to the outer leaflet in apoptotic cells, where it can serve as a marker of these cells.
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o Cell-surface helps signal to neighboring cells and macrophages to phagocytose the dying cell. o It serves as an “eat me” signal, and also blocks the inflammation often associated with phagocytosis o The phosphatidylserine dependent engulfment of apoptotic cells inhibits
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