BIS104 Note14

BIS104 Note14 - Lecture 14 Bio Sci 104 Control of Cell...

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Lecture 14 1 Bio Sci 104 Winter 2010 Control of Cell Growth: Apoptosis and Cancer-I I. Apoptosis A. Some cells are “programmed” to death: 1. During development: specific cells are destined to die at a specific time after they have fulfilled their function. Lack of proper cell death can be detrimental to the organism. Important to help shape the ultimate morphology of the organism, or to get rid of potentially dangerous cells: a. hands begin in fetus as flippers, specific cells then die and are eliminated to form individual fingers b. immune cells that would react to self-antigens are also programmed to die during fetal development. c. Almost all cells appear to have suicide triggers designed to kill the cell if it begins to display signs of uncontrolled/unbalanced growth and differentiation- i.e. CANCER 2. This programmed (suicidal) cell death is called APOPTOSIS , versus non-programmed (accidental) cell death, called NECROSIS. 3. Apoptosis is characterized by specific changes in cell- vacuoles form, cells swell, nuclei condense, DNA genome is chopped up into small pieces to ensure cell death and to help with future recycling B. Mechanism of apoptosis 1. When cells are stressed and damaged, they can kill themselves by producing two main types of cell death signals ; a ) extrinsic/external death signal: express the death receptor Fas on the cell surface. Fas is then recognized a killer lymphocyte expressing a Fas ligand and the target cell is subsequently killed. Fas triggers activation of Caspase 8 or 10 to mediate cell death. See below for Caspase activation) b) intrinsic/internal death signal: release cytochrome C from the mitochondria . 2. Many death signals induce release of cytochrome C from mitochondria into cytoplasm. This is perceived as a very bad sign by the cell, and cytoplasmic cytochrome C can trigger the remaining steps in apoptosis, which involved a cascade of special death-dealing proteases called Caspases ( named after Casper the friendly ghost ). 3. cytoplasmic cytochrome C binds to an adaptor protein called Apaf1 , which then binds and activates caspase 9. 4. Activated caspase 9 protease then can clip, and activate, downstream pro-caspases, turning them into active caspases too.
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Lecture 14 2 5. These activated caspases ultimately mediate the degradation and destruction that represent the actual events of apoptosis. e.g. DNase is activated by caspase to chop up the DNA. 6. Additional regulatory proteins control these processes. For example, proteins in the Bax family enhance apoptosis ( pro-apoptopic proteins ) by enhancing the release of cyt C in to the cytoplasm, whereas proteins in the Bcl-2 family inhibit apoptosis ( anti-apoptopic proteins ) by inhibiting the release of cyt C. 7.
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This note was uploaded on 03/02/2010 for the course ECL 242 taught by Professor Holly during the Winter '10 term at UC Davis.

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BIS104 Note14 - Lecture 14 Bio Sci 104 Control of Cell...

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