Question

3. Rapid cell responses are often generated by positive feedback actinomcin D loops. An experiment was done to test if the rapid release ofUV light cytochrome c from mitochondria in response to cell damage results from this type of feedback loop (ex: caspases activated bv released cvtochrome c ca act on mitochondria to release more cytochrome c). Cells expressing a GFP-tagged cytochrome c were incubated in the presence or absence of a caspase inhibitor called yZAD and then exposed to different apoptosis-inducing agents. The time it took for cytochrome c to be released during each treatment was measured and the results are shown in the figure. 10 ZVAD Figure 18-5 Duration of cytochrome c- GFP release from mitochondria in cells What would you have expected the results to look like if a treated with various apoptosis-inducing positive feedback loop between caspase and cytochrome c agents in the presence and absence ofa release was involved? Do the actual results match this caspase inhibitor (Problem 18-21). Bars expectation? represent the average of measurements on multiple individual cells

Answer 1

Apoptosis is an energy dependent biochemical mechanism of programmed cell death also called clean cell death,Two types of pathways activates apoptosis mechanism in cancerous cells

1. extrinsic pathway

2. ​intrinsic pathway

According to the above information cytochrome c is activated in Intrinsic pathway of Apoptosis.

Intrinsic pathway is activated when there is DNA damage ,mutation,or hypoxia condition. Mutation activates pro-apoptotic cell BCL2 which inturn activates Bad/Bax (Proapoptotic cells)

Bad/Bax have receptors on Mitochondria. when Bad/Bax binds to receptors on mitochondria ,Cytochrome will release from mitochondria and binds on cytosolic end of adoptar protein. APAF 1(Apoptotic Proteases Activating Factor) . The basic role of cytochrome is to trigger the activation of caspase -9 cytochrome interacts with Apaf 1 ATP and procaspase 9 to form a complex called apoptosome .Apoptosome activates caspase 9 which activates two other caspases caspase 7 and caspase 3 then cell death takes place.

Caspase inhibitor vZAD....its a cell permeant Pan caspase inhibitor( Pan caspase inhibitir act on one or more known caspases) of apoptosis. it irreversibly binds to catalytic site of caspase proteases and can inhibit induction of apoptosis.

According to fig 18-5 the bars in presence and absence of vZAD Showing that duration of cytochrome c GFP release per min is 4.5 in absence then in presence of inhibitor its 5/min. it means duration of Cytochrome release from mitochondria is increasing. The vZAD is the only significant inhibitor that significantly inhibited Cytochrome release from mitochondria . so when Cytochrome is not released from mitochondria intrinsic pathway of apoptosis is not activated and cell became cancerous.

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