Question

There are eight members of phosphatidylinositol. Which of the following is the target (or substrate) for PI₃K?

1) PIP3
2) PI(4,5)P2
3) PI(3)P

Answer 1

PI3K targets PI(4,5)P2 to produce PIP3 which plays a crucial role in cell signaling pathways, while phospholipase C converts PIP2 into DAG and IP3, both acting as second messengers.

Step-by-step explanation:

The target substrate for PI3K (phosphoinositide 3-kinase) is PI(4,5)P2 (phosphatidylinositol 4,5-bisphosphate). This kinase functions in various signaling pathways, adding a phosphate group to the 3' position of the inositol ring of PI(4,5)P2, thus producing PIP3 (phosphatidylinositol 3,4,5-trisphosphate).

In contrast to PI3K, the enzyme phospholipase C breaks down PIP2 into diacylglycerol (DAG) and inositol triphosphate (IP3), both of which serve as second messengers. DAG stays in the membrane, aiding the activation of protein kinase C (PKC), while IP3 plays a role in the release of Ca2+ from the endoplasmic reticulum, contributing to the signaling cascade.