1. You have constructed a cell strain whose actin is fused with a photo-activate

Question

1. You have constructed a cell strain whose actin is fused with a photo-activated greern fluorescent protein, PA-GFP. When PA-GFP is first expressed, it starts as non-fluorescent lt is activated by a brief laser pulse, after which it fluoresces similarly to regular GFP. Suppose you activate the actin-PA-GFP in a small spot close to the leading edge of a crawling cell. A. (2pts) Would you expect the fluorescent spot to move towards the leading edge, towards the trailing edge, or stay stationary with respect to the cell? Why? B. (2pts) Eventually, you observe that the fluorescent spot disappears. How can you explain this result? (You can assume that once activated, the PA-GFP will not photobleach or turn off.)

Explanation / Answer

Ans a) In this strain initially the PA-GFP is not expressed as fluorescence but only on exposure of brief laser it fluorescence. The laser travels faster than the speed of light and hence when it is activated or fluorescence using laser impulse, the spot moves towards the leading edge towards the trailing edge. It moves faster than light causing it to crawl to the edge.

Ans b) The fluorescence spot disappears gradually as the laser impulse effect is removed. It leads to removal of the fluorescence as the laser starts the travel and reaches the edge of the trail.

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