Problem 1 (10 points) Two different fluorescent dyes are attached one to the N-

Question

Problem 1 (10 points) Two different fluorescent dyes are attached one to the N- and the other to the C-terminus of a helical protein consisting of 30 amino acid residues. The dyes are small and form a donor-acceptor pair for a FRET experiment, with a Forster radius Ro = 5.3 nm. The protein undergoes a structural transition from a -helix (rise 0.15 nm/residue) to a 310 helix (rise = 0.20 nm/residue). What is the FRET efficiency measured for the two conformations? Assuming that the fluorescence lifetime of the donor in the absence of the acceptor is D = 4.1 ns, what is the difference between the donor lifetimes measured for the two helical conformations?

Explanation / Answer

FRET efficiency=1/[1 + (r/R0)6]=1/[1+(0.2/5.3)6]=0.99=1(Nearly/approx.)

The fluorescence lifetime of the donor in the absence of the acceptor is D = 4.1 ns

So, there is a little difference between the donor lifetimes measured for the two helical conformations i.e a reduction of the fluorescence lifetime causes increase in  acceptor fluorescence emission.

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