Describe the sequence of events leading to the activation of PI 3-kinase and its role in insulin signaling.

• A. PI 3-kinase is activated by insulin directly, converting PIP2 to PIP3.
• B. PI 3-kinase is activated by glucose binding, converting PIP3 to PIP2.
• C. PI 3-kinase is activated by binding to phosphorylated tyrosine residues on IRS, converting PIP2 to PIP3.
• D. PI 3-kinase is activated by binding to phosphorylated serine residues on IRS, converting PIP3 to PIP2.

Answer: (C)