Apply your understanding of PI 3-kinase activation to explain its role in insulin signaling.

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

Answer: (B)