G protein-coupled receptors (GPCRs) transform external stimuli to intracellular signals. The G protein associated with the receptor is activated by ligand binding, regulating an enzyme that produces a second messenger. The second messenger, in turn, brings about changes within the cell. Components of two common second messenger pathways are given below. Identify the next component of each signaling pathway. Each compound or ion may be used once or more than once. One target requires two answers.

The given abbreviations are used: cAMP, cyclic AMP; DAG, diacylglycerol; IP3, inositol triphosphate; PIP2, phosphatidylinositol 4,5‑bisphosphate; PKA, protein kinase A (cAMP‑dependent protein kinase); PKC, protein kinase C; PLC, phospholipase C.

signaling pathway:

a. IP3:
b. PIP2 and PLC:
c. cAMP:
d. Ca2+:
e. ATP and adenylyl cyclase:
f. DAG:

Compounds:

1. PKC
2. cAMP
3. Ca2+
4. IP3
5. DAG
6. PKA