• Apoptosis
      • programmed cell death. (MCQ)
      • involutional process is similar to the physiologic loss of leaves from a tree; apoptosis is a Greek term for "falling away from."
      • Examples of apoptotic removal of cells
        • irreparable DNA damage (from free radicals, viruses, cytotoxic immune mechanisms),
        • protection against neoplastic transformation. (MCQ)
        • It is an important mechanism for
        • physiologic cell removal during embryogenesis (MCQ)
        • programmed cell cycling (e.g., endometrial cells during menstruation). (MCQ)
      • Morphologic features
        • A tendency to involve single isolated cells or small clusters of cells within a tissue
        • Progression through a series of changes marked by a lack of inflammatory response
          • Blebbing of plasma membrane(MCQ)
          • cytoplasmic shrinkage
          • chromatin condensation
          • Budding of cell
          • separation of apoptotic bodies (membrane-bound segments) (MCQ)
          • Phagocytosis of apoptotic bodies
        • Councilman bodies in viral hepatitis(MCQ)
          • Involution and shrinkage of affected cells and cell fragments, results in small round eosinophilic masses often containing chromatin remnants,
        • Necrosis vs Apoptosis in Morphologic features
          • Gross irreversible cellular injury
          • Involves many contiguous cells
          • Increased cytoplasmic eosinophilia due to denaturation of proteins
          • Progressive nuclear condensation and fragmentation with eventual disappearance of nuclei
          •  Preservation of tissue architecture in early stages of coagulative necrosis
      • Biochemical events
        • injurious stimuli (e.g., free radicals, radiation, toxic substances, withdrawal of growth factors or hormones) trigger a variety of stimuli, including
          • cell surface receptors such as FAS (MCQ)
          • mitochondrial response to stress,
          • cytotoxic T cells.
        • The extrinsic pathway of initiation
          • mediated by cell surface receptors exemplified by FAS, a member of the tumor necrosis factor receptor family of proteins. (MCQ)
          • This pathway is initiated by signaling by molecules such as the FAS ligand which in turn signals a series of events that involve activation of caspases
          • Caspases
            • aspartate-specific cysteine proteases (MCQ)
            • referred to as "major executioners" or "molecular guillotines." (MCQ)
          • The death signals are conveyed in a proteolytic cascade, through activation of a chain of caspases and other targets.
          • The initial activating caspases are caspase-8 and caspase-9, (MCQ)
          • terminal caspases (executioners) include caspase-3 and caspase-6 (MCQ)
        • The intrinsic, or mitochondrial, pathway
          • is initiated by the loss of stimulation by growth factors
          • results in the inactivation and loss of bcl-2 and other antiapoptotic proteins from the inner mitochondrial membrane(MCQ)
            • This loss results in
              • increased mitochondrial permeability
              • release of cytochrome c(MCQ)
              • stimulation of proapoptotic proteins such as bax and bak(MCQ)
          • Cytochrome c interacts with Apaf-1 causing self-cleavage and activation of caspase-9(MCQ)
          • Downstream caspases are activated by upstream proteases and act themselves to cleave cellular targets.
        • Cytotoxic T-cell activation
          • characterized by direct activation of caspases by granzyme B
          • granzyme B (MCQ)
            • is a cytotoxic T-cell protease
            • it directly activates the caspase cascade.
          • The entry of granzyme B into target cells is mediated by perforin, a cytotoxic T-cell protein.
        • typical "laddering" appearance of DNA on electrophoresis(MCQ)
          • Degradation of DNA by endonucleases into nucleosomal chromatin fragments that are multiples of 180–200 base pairs results in the typical "laddering" appearance of DNA on electrophoresis.
          • This phenomenon is characteristic of, but not entirely specific for, apoptosis.
          • Activation of transglutaminases crosslinks apoptotic cytoplasmic proteins.
      • TUNEL assay (MCQ)
        • Terminal Transferase dUTP Nick End Labeling (MCQ)
        • A way to quantitate cleaving of nucleosomes and, thus, apoptosis.
      • Caspase assays are used as apoptotic markers(MCQ)
      • Genes that regulate apoptosis
        • bcl-2 (MCQ)
          • gene product inhibits apoptosis
        • bax (MCQ)
          • gene product facilitates apoptosis
        • p53 gene product(MCQ)
          • decreases transcription of bcl-2
          • increases transcription of bax
          • facilitates apoptosis
      • Necrosis vs Apoptosis in Biochemical features
        • Passive form of cell death
        • does not require gene involvement or new protein synthesis
        • DNA fragmentation is haphazard rather than regular, resulting in an electrophoretic smudge pattern
        • Marked inflammatory reaction
        • There is liberation of lysosomal enzymes digestion of cell membranes
        • disruption of cells I
        • nflux of macrophages due to release of chemotactic factors
        • Removal of debris by phagocytic macrophages


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    Apoptotic Pathways
    Genentech BioOncology is currently conducting research on how Apoptosis plays a central role in normal development and tissue homeostasis. Learn more about how this vital cellular process is regulated through cell intrinsic and cell extrinsic pathways.
    What basically happens is that the killer t cell communicates with the diseased cell by adhering to it by binding its death ligand to the death receptor on the diseased cell. This causes adapter proteins to attach to the cytosolic side of the receptor. This leads to a signal cascade which involves the recruitment of various other proteins and ultimately results in the death of the cell.
    Apoptosis Animation: Intrinsic Pathway
    Apoptosis is a cell suicide mechanism that enables metazoans to control cell number in tissues and to eliminate individual cells that threaten the animal’s survival. Certain cells have unique sensors, termed Death Receptors, on their surface, which detect the presence of extracellular death signals and, in response, rapidly ignite the cell’s intrinsic apoptosis machinery.
    Apoptosis is a programmed cell death naturally occuring in cells. in this video real time demonstration of apoptosis mechanism has been seen…