Question
I was honestly amazed by how wrong the last guy got this. Reposting.
Thanks!
You are interested in how cells regulate their size and discover that signaling through a G-protein coupled receptor (GPCR) is important for controlling cell size in the mouse pancreas. The G protein downstream of this receptor activates adenylyl cyclase, which activates PKA. Activated PKA phosphorylates a gene regulatory factor, SZE3, on serine 24 (S24). SZE3 can only enter the nucleus when phosphorylated. SZE3 activates the expression of several genes, including SZT8. Production of SZT8 mRNA requires SZE3 binding at the promoter to activate SZT8 transcription. A portion of this pathway is diagrammed in the Figure below. Cells that lack the GPCR are 20% bigger than normal cells, whereas cells that express a constitutively activated version of adenylyl cyclase are 20% smaller than normal cells. Given this information, what do you predict will happen to cell size (bigger, smaller, or no change) compared to normal cells under the following situations: You add a drug that activates PKA. You add non-hydrolysable form of GTP. You replace the normal SZE3 in cells with SZE3 that has changes to its amino acids so that it no longer binds to DNA. You add a drug that inhibits phosphodiesterase. For the three items on the Figure above labeled A, B, and C, write the word from the choices below that best corresponds to what these items represent. calmodulin beta-tubulin ligand cadherin dehydrogenase receptor phosphodiesterase nuclear pore cytoskeleton G beta G gamma G alpha
Explanation / Answer
Since given in the question that, Phosphorylation is important, as well as location is specific Serine 24, any changes in this will leads to inactivation of the pathway. Leading to 20% smaller size.
II) a) Ligand
b) Receptor
c) G
