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 activated 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 signmaling pathway responsible fo 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 alpha subunit of the G protein in this signaling pathway. The defective alpha 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?

Answer 1

In GPCR signalling adenylate cyclase is the enzyme which is activated when alpha subunit of G protein is in GTP bound form. So in case of out mutant, the mice will make functional adenylate cyclase which in turn produce cAMP. this cAMP will activate protein kinase and which in turn activate the transcription factor to produce the beige colour producing gene. Since all the genes are functional so the colour of the mutant mice will be beige (very light brown) fur color