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Apoptosis DNA ladder | |
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Introduction Cell death can occur by two distinct mechanisms, necrosis or apoptosis. Necrosis occurs when cells are exposed to serious physical or chemical stress. Apoptosis ("programmed cell death") is a physiological process by which cells are eliminated during the development of the organism and other normal biological processes. Important examples from the field of immunology are the positive and negative selection during the maturation of T-lymphocytes. Cell-mediated cytotoxicity caused by either cytotoxic T lymphocytes (CTL) or natural killer (NK) cells combines some aspects of both necrosis and apoptosis. With increased understanding of the physiological events that occur during apoptosis, a number of assay methods have been developed for its detection. These assays are based on different events which characterize the apoptotic process. Apoptosis and cell mediated cytotoxicity are characterized by a fragmentation of the genomic DNA. These DNA fragments have a length of about 180 base pairs or multiples thereof (360, 540, 720, ...), the characteristic DNA-length of a nucleosome (DNA-histone-complex). Endonucleases selectively cleave DNA at sites located between nucleosomal units (linker DNA). In agarose gel electrophoresis these DNA fragments are resolved to a distinctive ladder pattern. The method  Related topic  Apoptosis TUNEL reaction |
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