Hi everyone. I did this little research of mine on FRAP. I have no idea what type of question they ask on the exam, nor am I interested in knowing in advance, but Ive gathered this report since for me, finding relevant information on this technique is cumbersome. As far as I know, you get one or two questions dealing with this technique (or none at all), and is it worth it to know? That is up to you. Id like to thank TheWiredNerve and all the students who contributed to the thread: http://forums.studentdoctor.net/showthread.php?t=442518, Ive gathered their data and a number of information from other sources. Lets get started. FRAP, which stands for fluorescent recovery after photobleaching, is a technique that monitors movement within say a cell membrane. The area of interest is tagged with fluorescent markers, and bleached afterwards. What this means is that within a given area, the fluorescent markers are removed. Lets take a look: http://www.olympusfluoview.com/applications/flipandfrap.html In A, the area in pink is used to represent the fluorescent markers. The square is B represents the bleached area, meaning that the fluorescent markers that were present in A were removed. After some time, the fluorescent markers from the surrounding areas moved within the bleached area. What does it show? It means that the membrane, or what is shown above (maybe a protein) has fluidity of some sort and allows for the movement of fluorescent markers into the bleached area. Experimental Setup First thing that is done in FRAP is to tag the specific protein you are examining with a fluorescent compound, usually green fluorescent proteins (GFP) or an antibody of some sort. These fluorescent groups are attached to the proteins using various genetic recombinant techniques such as DNA cloning. A portion of the membrane is then exposed to a very strong laser beam. This laser essentially bleaches the proteins of the fluorescent tags so that the area of the membrane treated with the laser is no longer viewed as green under a confocal microscope. The rate at which tagged proteins move into the now bleached area is called the "fluorescence recovery." 8/31/07 thanks to TheWiredNerve Lets take a look at this very helpful animation: (if you get an ad, press skid this ad): http://www.dnatube.com/view_video2.php?viewkey=125ed6c3f678819b6e05 So the gist of it is that if the membrane has a fluid quality to it, the fluorescence will recover, if not, then you will see this black patch of area indicating that no movement is taking place. Ok seems nothing complicated. Im thinking that its like a mini-GPS system, where it tracks and monitors movements within the cell membrane. Besides using this technique on lipid composition, it is also used to tag proteins. Since proteins can be both integral and peripheral (in regards to cell membrane), it can be used to again measure their movement. The TheWiredNerve brought up a good point lipid rafts. http://www.bms.ed.ac.uk/research/others/smaciver/Cyto-Topics/lipid_rafts_and_the_cytoskeleton.htm As shown above (link), rafts are regions where the phospholipids fatty acid tails are straight, meaning that the bonds are saturated. Remember that unsaturated (presence of double bonds) leads to cis conformation, and hence bending of the tails. Saturaded (single carbon to hydrogen) bonds all for close packing of the area. If a protein is present in such an area, then it will not be able to move. Imagine taking a button and sewing in a tight network of threads onto a shirt its movement in any aspect is impossible. (I think of these analogies to help us understand, they should not be taken word for word, but to develop the underlying concept) Lets make this a bit complicated: Graphs http://www.bio.davidson.edu/Courses/Molbio/FRAPx/FRAP.html A graphical analyses is possible of the technique. This is my understanding: 1) Point 1 represents the initial area that is fluorescencing (I doubt such a word exists, lol). It basically represents the initial area that is lighting up. 2) Point 2 represents the drop is fluorescence due to photobleaching. A bunch of fancy words meaning the area that was cleared up. Imagine you get a stain on your shirt after grabbing a snack at 2AM. You grab one of those Clorox bleach pens (the ones you see on commercials), and clear the area. That clear area is point 2. Why doesnt it reach zero? This is probably due to the technique in which the laser beam cannot bleach the entire area so you are still left with some fluorescent markers (this is why in the animation, there were some fluorescent markers left). 3) If the area is fluid, then the neighboring fluorescent markers start to diffuse into the area 4) This is used to represent equilibrium. It never reached point 1 because you have a lesser amount of fluorescence markers. The notes Ive gathered are my understanding of the technique. I neither have a Ph.D. or am a professor of this stuff, and if some concepts are not addressed or clearly represented, it would be great to add more.