Inositol-Phospholipid signaling Pathway

Question 1

What second messengers are produced

Answer 1

Diacyglycerol and IP3 which is 1,4,5-triphosphate

Question 2

Where are these second messengers derived from

Answer 2

DAG and IP3 are derived from a plasma membrane phospholipid called phosphatidylinositol 4,5-bisphosphate (PIP2)

Question 3

Pathway Step 1

Answer 3

Following binding of a ligand to a specific receptor, the signal is transduced through the G protein Gq.

Question 4

Pathway Step 2

Answer 4

The active GTP-bound form of Gq activates the effector enzyme phospholipase C that is bound to the cytoplasmic face of the plasma membrane.

Question 5

Pathway Step 3

Answer 5

Phospholipase C catalyzes the hydrolysis of PIP2 to IP3 and diacylglycerol.

Both 2nd messengers transmit the original signal to the interior of the cell.

Question 6

Inositol 1,4,5 triphosphate

Answer 6

Diffuses through the cytosol and binds to a calcium channel in the membrane of the ER. This causes the calcium channel to open for a short time, releasing Ca 2+ from the lumen of the ER into the cytosol.

Question 7

Diacylglycerol

Answer 7

Remains in the plasma membrane. Protein Kinase C, which exists in equilibrium between a soluble cytosolic form and a peripheral membrane form, moves to the inner face of the plasma membrane where it binds transiently and is activated by DAG and Ca 2+.

Question 8

Protein Kinase C

Answer 8

Protein Kinase C catalyzes phophorylation of many target proteins altering their catalytic activity.