​A transmembrane receptor protein (X) and a transmembrane protein bound to the actin cytoskeleton (Y) with fluorescent tags were expressed in a cell. A fluorescence recovery after photobleaching (FRAP) experiment was performed on these proteins. Which one of the following options represents the most likely outcome of this experiment?​

Correct option is C

Explanation:

• (1): Incorrect. The fluorescence recovery of X and Y will not be the same. X is a transmembrane receptor, while Y is bound to the actin cytoskeleton, which will likely restrict its movement. Therefore, X will recover fluorescence more quickly than Y.

• (2): Incorrect. X (the transmembrane receptor protein) is expected to have more freedom of movement within the membrane compared to Y, which is bound to the actin cytoskeleton, so X will recover fluorescence faster than Y.

• (3): Correct. Y is bound to the actin cytoskeleton, restricting its ability to move, which means that its fluorescence recovery will be slower than X, which is free to diffuse in the membrane.

• (4): Incorrect. Although both X and Y are membrane proteins, they will still exhibit fluorescence recovery after photobleaching, but at different rates. The restriction of Y's movement due to its binding to the cytoskeleton will cause slower recovery compared to X.

Information Booster:

1. FRAP (Fluorescence Recovery After Photobleaching) is a technique used to measure the mobility and dynamics of fluorescently labeled molecules, such as proteins, within living cells.

2. X, being a transmembrane receptor protein, will have a higher mobility in the lipid bilayer and is expected to recover fluorescence faster than Y.

3. Y, which is bound to the actin cytoskeleton, will experience restricted movement, and its fluorescence recovery will be slower.

4. Actin cytoskeleton anchors certain membrane proteins, preventing them from diffusing freely in the membrane, which is why Y's fluorescence recovery will be delayed.