Question 1

Which of the following best describes the role of a G-protein coupled receptor (GPCR) in phosphoinositide signaling?

Accepted Answer

It transmits a signal from a ligand to intracellular G-proteins.

Question 2

What is the primary function of phospholipase C in the GPCR signaling pathway?

Accepted Answer

It hydrolyzes PIP2 to generate IP3 and DAG.

Question 3

Which molecule acts as a secondary messenger to release Ca²⁺ from the endoplasmic reticulum?

Accepted Answer

Inositol trisphosphate (IP3)

Question 4

Upon activation by a ligand, the GPCR undergoes a conformational change. What is the immediate consequence of this change?

Accepted Answer

Binding and activation of the G-protein

Question 5

Which enzyme is responsible for generating the secondary messengers DAG and IP3?

Accepted Answer

Phospholipase C

Question 6

What is the role of diacylglycerol (DAG) in the phosphoinositide signaling pathway?

Accepted Answer

It acts as a secondary messenger to activate protein kinase C.

Question 7

Which of the following correctly describes the sequence of events in GPCR-mediated phosphoinositide signaling?

Accepted Answer

Ligand binds GPCR → G-protein activation → Phospholipase C activation → PIP2 hydrolysis → IP3 and DAG formation

Question 8

Which of the following is a direct effect of IP3 in the cell?

Accepted Answer

Opening of Ca²⁺ channels in the endoplasmic reticulum

Question 9

A mutation prevents the hydrolysis of GTP to GDP in the Gα subunit. What is the most likely cellular consequence?

Accepted Answer

Continuous activation of phospholipase C and persistent signaling

Question 10

Which of the following equations represents the hydrolysis of PIP2 by phospholipase C?

Accepted Answer

$$\mathrm{$$PIP_2$$ \xrightarrow{PLC} IP_3$ + DAG}$$

Question 11

Which protein is activated by DAG and Ca²⁺ in the phosphoinositide pathway?

Accepted Answer

Protein kinase C

Question 12

In a cell signaling experiment, blocking IP3 receptors on the ER would most likely result in which outcome?

Accepted Answer

Reduced activation of protein kinase C

Question 13

Which of the following is NOT a function of G-proteins in the phosphoinositide signaling pathway?

Accepted Answer

Hydrolyzing PIP2 to generate IP3 and DAG

Question 14

A patient has a genetic defect in phospholipase C. Which cellular process would be most directly affected?

Accepted Answer

Release of Ca²⁺ from the endoplasmic reticulum

Question 15

Which of the following best explains why DAG remains in the membrane while IP3 diffuses into the cytosol?

Accepted Answer

DAG is hydrophobic, while IP3 is hydrophilic.

Phosphoinositide GPCR Signaling Pathway: Mechanisms and Key Components

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