Your friend is studying mouse fur color and has isolated the GPCR responsible fo

Question

Your friend is studying mouse fur color and has isolated the GPCR responsible for determining its color, as well as the extracellular signal that activates the receptor. She finds that, on addition of the signal to pigment cells (cells that produce the pigment determining fur color), cAMP levels rise in the cell. She starts a biotech company, and the company isolates more components of the signaling pathway responsible for fur color. Using transgenic mouse technology, the company genetically engineers mice that are defective in various proteins involved in determining fur color. The company obtains the following results. Normal mice have beige (very light brown) fur color. Mice lacking the extracellular signal have white fur. Mice lacking the GPCR have white fur. Mice lacking cAMP phosphodiesterase have dark brown fur. Your friend has also made mice that are defective in the ? subunit of the G protein in this signaling pathway. The defective ? subunit works normally except that, once it binds GTP, it cannot hydrolyze GTP to GDP. What color do you predict that the fur of these mice will be? Why? PLEASE EXPLAIN

Explanation / Answer

The mice with defective alpha subunit should have white fur. We can see that any block in signal due to absence of extracellular signal or defective GPCR lead to mice with white fur. Thus, with defective G-protein the signal will be blocked (since it attaches to GTP but cannot hydrolyze it) . If the signal is not regulated (as in absence of phosphodiesterase) the synthesis of the some pigment protein becomes constitutive (Non stop gene expression) and that results in dark brown fur.

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