A FRAP (fluorescence recovery after photobleaching) study shows complete recovery of a GFP-tagged membrane protein in 15 s at 37 °C and 45 s at 10 °C. What is the most likely reason for the slower recovery at the low temperature?

Correct answer: (d) Reduced lateral membrane fluidity

Explanation

In FRAP (fluorescence recovery after photobleaching), a laser bleaches the fluorescent (GFP-tagged) proteins in a small patch of membrane. Fluorescence returns to the patch as unbleached proteins move in sideways from the rest of the membrane, so the speed of recovery measures how freely the proteins move.

By the fluid mosaic model, the membrane's fluidity depends on temperature. At 10 °C the lipid bilayer is more viscous and ordered, so the proteins diffuse sideways more slowly and the recovery takes longer (45 s instead of 15 s). The other options do not explain sideways movement within the membrane.