You are interested in how cyclic-AMP-dependent protein kinase A (PKA) affects learning and memory and decide to study its function in the brain. It is known that, in the brain cells you are studying, PKA works via a signal transduction pathway like the one depicted below. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator Nerd that then activates transcription of the gene Brainy. What effect will each of the following situations have on Brainy transcription
a. a mutation in the Nerdgene that produces a protein that cannot be phosphorylatedby PKA
b. a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive
c. a nonhydrolyzable form of GTP
d. a and b
e. b and c